The relaxation state and partial crystallization are crucial factors that affect the material properties of metallic glasses. Rejuvenation induces a less relaxed glass state and hence facilitates the control of the relaxation state. The rejuvenation and crystallization during thermal processing are associated closely with the phase changes of metallic glasses upon heating. Most nanocrystalline metallic glasses formed via conventional thermal annealing have a relaxed glassy matrix. In this molecular dynamics study, we investigate the feasibility of thermal processing to simultaneously realise both partial crystallization and rejuvenation using model alloy system. Dynamic mechanical analyses reveal relaxation behaviours and local deformation features of metallic glasses composed of a crystalline phase and a rejuvenated glass matrix. The crystalline phase increases the macroscopic shear stiffness of the composite model over a wide temperature range, whereas it does not significantly affect the internal friction of the rejuvenated glass matrix. In addition, dispersed nanocrystals suppress the development of sharp and concentrated shear localisation in the rejuvenated glass matrix. The simultaneous adjustment of the relaxation state and crystalline phase in the glass matrix is discussed from a viewpoint of the microstructure design of metallic glasses.

<title>Abstract</title>Pressure-induced structural changes in metallic glasses have been of great interest as they are expected to open new ways to synthesize novel materials with unexpected properties. Here, we investigated the effect of simultaneous high-pressure and high-temperature treatment on the structure and properties of a Zr₅₀Cu₄₀Al₁₀ metallic glass by in situ X-ray structure measurement and property analysis of the final material. We found the unusual formation of Cu-rich nanocrystals at high pressure and temperature, accompanied by significant strength and hardness enhancement. Based on reverse Monte Carlo modeling and molecular dynamics simulations, the structure of the metallic glass changed to a densely packed, chemically uniform configuration with high short-range and medium-range ordering at high pressure and temperature. These results show that high-pressure annealing processes provide a new way to improve and control properties without changing their composition.

The uniformity of the glassy state of [(Fe Co ) Si B ] Nb metallic glassy particles prepared using our own developed technique, called the pulsated orifice ejection method (POEM), was investigated. Differential scanning calorimetry (DSC) results revealed that the thermal histories of the particles prepared from the same batch were almost identical. This suggested that the particles with the same size/volume possessed almost the same glassy state and had advantages as raw materials for microparts. The fabricated final product using our proposed process, termed as micro viscous flow processing, where a single particle is compressed with a precise jig under strictly controlled processing conditions, was confirmed to maintain a fully amorphous structure. DSC scans of each micropart traced nearly the same path, which indicated that their glassy states were still almost identical after processing. The precise control of the temperature and applied load enable the final products to achieve almost the same thermal histories and also geometric shapes. This is the first report that proves the high reproducibility of fabricating Fe-based metallic glassy microparts with high quality. Our proposed sequential process may shed light on a new fabrication technique of microparts using metallic glasses. 0.5 0.5 0.75 0.05 0.2 96 4

A relaxed heterogeneous metallic glass is successfully rejuvenated by using a recovery-annealing technique. It is found that the rejuvenation state is related to the final cooling rate and more nano-clusters are formed in the less rejuvenated heterogeneous metallic glass with a slower final cooling rate. Interestingly, the less rejuvenated heterogeneous metallic glass shows better plasticity than the more rejuvenated glass, which may result from the stress-induced crystallization (SIC) during deformation. The reasons for the SIC in the less rejuvenated sample are considered to be the evolution of nano-clusters, a more unstable glassy phase (easier to crystallize), and the high temperature rise in each shear band. These results suggest that not only the relaxation state of the amorphous phase, but also the heterogeneous microstructures, including nano-clusters, should be considered to improve the mechanical properties of metallic glasses.

A Zr-based metallic glass is treated by a cryogenic- to room-temperature cycling treatment with 30 cycles. Though the structure after treatment maintains its monolithic amorphous structure, the treated sample exhibits a rejuvenation behavior contrasting with that of an untreated as-cast sample, including a higher relaxation enthalpy and a lower density. The atomic level core-shell heterogeneous microstructure is considered to contribute to the rejuvenation because of the internal stress generated during cycling. The microscopic deformation of the core region by the internal stress may be equivalent to the macroscopic shear band deformation by the external stress, which induces the evolution of the core region and an increased amount of excess free volume. The treated sample also exhibits lower hardness and better plasticity than the untreated sample. A lower shear plane formation energy and larger shear transformation zone volume and size are considered to promote shear band formation and to generate more multiple shear bands to accommodate the plastic deformation. The deep cryogenic cycling treatment is believed to be a feasible and non-destructive way to rejuvenate metallic glass and improve the mechanical properties.

Periodic lines with intervals ranging from ∼220 μm down to ∼27 μm were fabricated on the surface of Zr55Cu30Al10Ni5 metallic glass ribbon and disk samples by laser irradiation. The X-ray diffraction results indicated that both oxides (monoclinic ZrO2, tetragonal ZrO2) and crystallites (Cu10Zr7, NiZr2) existed together with the amorphous phase on the surface of the laser-patterned metallic glass samples. The energy-dispersive X-ray spectroscopy of a cross section of a disk sample clearly showed that high amounts of aluminum (292% of the nominal composition) and oxygen were present in the laser-irradiated area, suggesting that Al2O3 formed on the surface of the laser-irradiated region. Reflective diffraction spots were observed from the fine grids with a grating period of ∼27 μm, indicating the excellent periodicity and accuracy of the pattern in two dimensions on the surface of the metallic glass substrates. Calculation of the grating period using Bragg's law confirmed that the spots originated from the periodic patterns of the laser-irradiated lines. Along the lines, pairs of ridges and hollows with a height/depth of ∼0.5 μm were observed such specific morphology generated the diffraction spots as a reflective grating. We observed structural color gradation from the periodic fine grids under a fluorescent light. The present study showed that it is possible to prepare optical gratings on the surface of metallic glasses by laser irradiation more cheaply and easily than by conventional imprinting.

Pulsed neutron diffraction and synchrotron X-ray diffraction measurements were performed on a melt-quenching Ni67Zr33 amorphous alloy sample. The Ni-Ni, Ni-Zr and Zr-Zr nearest neighbour distributions were obtained from differences in the scattering intensities between the two probes in conjunction with the Gaussian fitting. The results demonstrate that the Ni-Zr and Zr-Zr nearest neighbour distributions are respectively represented by single Gaussian peaks but the Ni-Ni one is an asymmetric shape. Three-dimensional structure models were constructed by using reverse Monte Carlo (RMC) modelling method with fitting to the neutron and X-ray diffraction data sets. The Voronoi-Delaunay method was used on the RMC configurations to investigate the local packing properties of each coordination cluster. With reference to the macroscopic packing fraction, inhomogeneous structural feature arising from dense and loose packing domains is observed in the structure of Ni67Zr33 amorphous alloy. (C) 2017 Elsevier B.V. All rights reserved.

Periodic lines, approximately 15-mm-wide and separated by several hundred micrometers, were prepared on the surface of Zr55Cu30Al10Ni5 metallic glass by scanning a focused laser beam across the samples in air. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) suggested that the lines produced by the focused laser beam consisted of localized metal oxides (tetragonal ZrO2, monoclinic ZrO2) and crystallites (Cu10Zr7), which was in contrast to the amorphous substrate. The electron backscatter diffraction (EBSD) also confirmed the successful patterning of the lines which was mainly composed of the fine ZrO2 grains. The energy dispersive X-ray spectroscopy (EDS) mapping clearly exhibits that high amounts of zirconium (161% of the nominal composition) as well as oxygen (58.9%) and a certain amount of aluminum (80% of the nominal composition) were presented in the beam-scanned area. The Auger electron spectroscopy (AES) was also conducted to see the atomic percentage from the top surface to the depth direction and showed that the created oxides were thermally stable and therefore oxidization cannot proceed with increasing the number of laser scan. We confirmed that the laser irradiation method has a large degree of freedom for designing patterns, such as interdigital, dots, and letters because of the precise control over the scanning stage. (C) 2017 Elsevier B.V. All rights reserved.

The effect of a noble metal (Pd) on the local atomic structure of the glassy state and the transformation behavior of quasicrystal (QC) precipitation in Zr-70(Cu and Ni)(30-x)Pd-x (x = 0, 5, 10, 20) alloys were investigated. A QC phase precipitates in Zr-Cu glassy alloys at Pd concentrations of 5-20 at.% and in Zr-Ni glassy alloys at Pd concentrations of 10-20 at.%. The radial distribution function (RDF) indicates a change in the local atomic structure upon the addition of Pd. The QC phase is abruptly formed from the glassy structure above a certain temperature. The activation energy for nucleation is much larger than that for the precipitation of conventional intermetallic compounds. The QC growth is suddenly suppressed when their diameter reaches approximately 20 nm. The cooperative motion of icosahedral clusters as the precipitation mechanism was discussed. It was assumed that QC nucleus has a Zr-centered icosahedral medium-range order (MRO) as its core, and it grows by the aggregation of surrounding small icosahedral clusters. Noble metals might play a role of stabilizing the individual Zr-centered icosahedral MROs. (C) 2016 Elsevier B.V. All rights reserved.

In-situ Ti-reinforced Mg-based (MT-D) and in-situ Ta-reinforced Zr-based (ZT-D) bulk metallic glass matrix composites (BMGMCs) were prepared by a novel dealloying method, which contains an element-selective leaching process in a metallic melt. The BMGMCs exhibit better mechanical properties, including higher fracture strength and larger plastic strain, than their monolithic glassy counterparts or similar BMGMCs by ex-situ dispersing or conventional arc-melting methods. The differences of Young's modulus between the dispersoids and the glassy matrix for these BMGMCs generate stress concentration at the interface, which is considered to suppress the propagation of the single main shear band and initiate multiple shear bands to accommodate the plastic deformation. Furthermore, the fine size of dispersoids for these BMGMCs, caused by low reaction temperature during dealloying in the metallic melt, results in more interfaces with the matrix for further improvement of mechanical properties. In addition, the low reaction temperature can also contribute to less composition fluctuation of the matrix to maintain the glass-forming ability of itself, which can introduce no undesired phases to degrade the mechanical properties. This novel in-situ dealloying method is believed to make a breakthrough in designing ductile BMGMCs with fine-sized secondary particles. (C) 2016 Elsevier B.V. All rights reserved.

Multiphase (Ta-rich phase, B2 and B19′-CuZr) reinforced bulk metallic glass matrix composites (BMGMCs) were successfully developed. The Ta-rich phase appeared not only to hinder the propagation of shear bands, but also to act as a nucleant for the B2 and B19′ phases to homogenize their distribution. The composites showed superior tensile plasticity, work-hardening, and a unique triple yielding behavior. The martensitic transformation of B2-CuZr, the deformation of the Ta-rich phase, and the twinning and detwinning of B19′-CuZr all contributed to these mechanical properties. The present novel BMGMC is expected to lead to a breakthrough in designing work-hardenable and ductile BMGMCs.

The recovery annealing technique was used to clarify the crystallization behavior of a rejuvenated Zr50Cu40Al10 metallic glass. Specific heat and thermal expansion measurements showed that the glassy states of fast cooled and recovery annealed samples are almost identical from the energetic and volumetric points of view. Dynamic mechanical analysis also suggested that their internal microstructures resemble each other. These results indicate that the glassy state and the structure can be controlled according to the final cooling conditions from the supercooled liquid region. However, a clear difference of the incubation time for crystallization was observed between the fast cooled and recovery annealed samples, implying that thermal accumulation seems to mostly correlate to the crystallization rather than to atomic diffusion through the newly created excess free volume in the rejuvenated sample. In addition, a transmission electron microscopy image of the sample, performed on double sets of the recovery annealing process, shows a precipitation of the crystalline phase with approximately 50 nm in diameter in the amorphous matrix. These results suggest that the recovery annealing independently leads to two different thermal paths, one towards structural rejuvenation and the other towards crystallization. The high-resolution transmission electron microscopy result of the recovery annealed sample indicates that these two regions co-exist in the amorphous matrix.

Structural rejuvenation in metallic glasses by a thermal process (i.e. through recovery annealing) was investigated experimentally and theoretically for various alloy compositions. An increase in the potential energy, a decrease in the density, and a change in the local structure as well as mechanical softening were observed after thermal rejuvenation. Two parameters, one related to the annealing temperature, T-a/T-g, and the other related to the cooling rate during the recovery annealing process, V-c/V-i, were proposed to evaluate the rejuvenation phenomena. A rejuvenation map was constructed using these two parameters. Since the thermal history of metallic glasses is reset above 1.2T(g), accompanied by a change in the local structure, it is essential that the condition of T-a/T-g &gt;= 1.2 is satisfied during annealing. The glassy structure transforms into a more disordered state with the decomposition of icosahedral short-range order within this temperature range. Therefore, a new glassy structure (rejuvenation) depending on the subsequent quenching rate is generated. Partial rejuvenation also occurs in a Zr55Al10Ni5Cu30 bulk metallic glass when annealing is performed at a low temperature (T-a/T-g similar to 1.07) followed by rapid cooling. This behavior probably originates from disordering in the weakly bonded (loosely packed) region. This study provides a novel approach to improving the mechanical properties of metallic glasses by controlling their glassy structure. [GRAPHICS]

Elastic deformation behaviors of as-cast and annealed eutectic and hypoeutectic Zr-Cu-Al bulk metallic glasses (BMG) were investigated on a basis of different strain-scales, determined by X-ray scattering and the strain gauge. The microscopic strains determined by Direct-space method and Reciprocal-space method were compared with the macroscopic strain measured by the strain gauge, and the difference in the deformation mechanism between eutectic and hypoeutectic Zr-Cu-Al BMGs was investigated by their correlation. The eutectic Zr50Cu40Al10 BMG obtains more homogeneous microstructure by free-volume annihilation after annealing, improving a resistance to deformation but degrading ductility because of a decrease in the volume fraction of weakly-bonded regions with relatively high mobility. On the other hand, the as-cast hypoeutectic Zr60Cu30Al10 BMG originally has homogeneous microstructure but loses its structural and elastic homogeneities because of nanocluster formation after annealing. Such structural changes by annealing might develop unique mechanical properties showing no degradations of ductility and toughness for the structural-relaxed hypoeutectic Zr60Cu30Al10 BMGs.

Rejuvenation is the configurational excitation of amorphous materials and is one of the more promising approaches for improving the deformability of amorphous metals that usually exhibit macroscopic brittle fracture modes. Here, we propose a method to control the level of rejuvenation through systematic thermal processing and clarify the crucial feasibility conditions by means of molecular dynamics simulations of annealing and quenching. We also experimentally demonstrate rejuvenation level control in Zr55Al10Ni5Cu30 bulk metallic glass. Our local heat-treatment recipe (rising temperature above 1.1T(g), followed by a temperature quench rate exceeding the previous) opens avenue to modifying the glass properties after it has been cast and processed into near component shape, where a higher local cooling rate may be afforded by for example transient laser heating, adding spatial control and great flexibility to the processing.

The relaxation state of metallic glass is determined by the cooling rate at low temperatures in a supercooled liquid. Based on this result, we can control the relaxation state of Zr55Al10Ni5Cu30 bulk metallic glass by recovery annealing just above the glass transition temperature (T-g). We rejuvenate the relaxation state for approximately 50% in the enthalpy of relaxation at a cooling rate of 4.4K/s after annealing, as compared with that of the as-cast state. Mechanical softening also occurred upon the rejuvenation. The results suggest another method of controlling the structure of metallic glasses to improve their properties. (C) 2013 AIP Publishing LLC.

The primary transformation kinetics of nanoicosahedral quasicrystalline (QC) phase formation were investigated in Zr65Al7.5Ni 10Cu12.5Pd5 bulk metallic glass (BMG) in various relaxation states. A less relaxed (unrelaxed) BMG exhibited higher activation energy for atomic diffusion in the glassy structure than that of a relaxed one, which represents a change in the nucleation and grain growth kinetics of the primary phase with the relaxation state. Actually, the grain growth rate of a QC particle near the crystallization temperature was approximately 1 × 10-9 m/s in the less relaxed BMGs, which was less than half of that in the relaxed BMGs. In contrast, the calculated homogeneous nucleation rate significantly increased in the less relaxed samples. It increased with the volume fraction transformed in the early stage. It is concluded that the relaxation state of glassy alloys markedly affects the primary transformation kinetics. The current study also indicates a necessity of development of the relaxation state for structure controlling in industrial applications of BMGs. © 2012 The Minerals, Metals &amp Materials Society and ASM International.

The compressive deformation mechanism of a Zr55Al10Ni5Cu30 bulk metallic glass containing 10 vol.% ZrC (ZrC-BMG) has been clarified based on the residual stresses in the compressed specimens. The deformation behavior can be classified into four stages through local plastic deformation around ZrC particles until macroscopic fracture when the ZrC particles break. It was suggested that the plasticity and strength of the ZrC-BMG depend on the compressive strength of the ZrC particles and the stress partitioning into both phases. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Zr(65)Al(7.5)Ni(10)Cu(12.5)Pd(5) bulk metallic glasses (BMGs) in various relaxation states were prepared under different cooling rates. The grain growth rate of the primary quasicrystal was examined near the crystallization temperature. It was approximately 1 x 10(-9) m/s in less relaxed BMGs and approximately twice as large in relaxed BMGs. In contrast, the calculated homogeneous nucleation rate of the less relaxed samples was five to ten times higher (5 x 10(19)-1 x 10(20)/m(3)s) than those in the relaxed BMGs. The results indicate that the relaxation state of glassy alloys has a marked effect on nucleation and grain growth behaviors. (C) 2011 American Institute of Physics. [doi:10.1063/1.3622117]

Cooling process in the production of Zr65Al7.5Ni10Cu17.5-based bulk metallic glasses (BMGs) was investigated in various chamber atmospheres in Cu mold casting. Two different cooling modes, consisting of the direct heat transfer between the melt and Cu mold in the high temperature and indirect transfer via cavity in the low-temperature regions, are suggested. In the later case, the cooling effect should depend on the chamber atmosphere, which results in the formation of glassy structure with large relaxation enthalpy casting under the ambient Ar and He atmospheres due to a good thermal conductivity. The less relaxed BMGs produced by an improved cooling effect are also expected to contain a large amount of free volume for significant deformability. Actually, it is clarified that the compressive plastic deformation is improved with an increase of the relaxation enthalpy. The present study indicates a necessity of development of the glassy structure, i.e., relaxation state, and provides a new technique of the formation of less relaxed glassy structure for the improvement of plasticity in BMGs.

We report the results of the local structural evaluation and mechanism of QC formation in the Zr(70)Pd(30) and Zr(80)Pt(20) glassy alloys. Voronoi analysis indicates the difference of local environment between two alloys. The perfect icosahedron frequently exists around Zr atom and major polyhedra have prism-like structure around Pd in Zr(70)Pd(30). In contrast, icosahedral-like distorted polyhedra formation is favorable around Pt as well as Zr in Zr(80)Pt(20). It is therefore, concluded that the quasicrystallization originates from the medium-range order based on the Zr-centered perfect icosahedron and the Pd-centered prism-like ones remain during the QC phase formation in Zr(70)Pd(30). Icosahedral-like local structure around Zr and Pt might contribute together to the nucleation of QC phase in Zr(80)Pt(20). This feature with a different mechanism of QC formation in the two alloys may correlate to the difference of solute concentration and the structure of stable crystalline phase after the decomposition of QC phase. (C) 2010 Elsevier B.V. All rights reserved.

The effects of Pd and Pt, which are known quasicrystal (QC)-forming elements, on the local atomic structure in Zr70Cu30 glassy alloys are investigated. A QC phase precipitates from a glassy phase above a certain temperature by a cooperative-like motion of icosahedral clusters. Quasicrystallization is accompanied by a significant change in the local environment around the Zr atoms and a slight change around the noble metal. However, the local environment around the Cu atoms remains almost the same during QC formation. It is suggested that two types of icosahedral polyhedra exist in the glassy state: one has a relatively perfect icosahedral structure formed around the Zr atoms. The other is in a distorted state around the Cu atoms. We speculate that the medium-range order (i.e. QC nucleus) has a Zr-centered icosahedral cluster as its core, and the QC grows via aggregation of possible clusters in the initial stage. Pd or Pt atoms stabilize and/or connect individual Zr-centered icosahedral clusters, facilitating the formation of the nucleus and growth of the QC phase.

The origin of Zr(65)Al(7.5)Ni(10)Cu(12.5)Pd(5) and Zr(65)Al(7.5)Ni(10)Cu(12.5)Nb(5) glassy alloys exhibiting a remarkable plastic strain of about 6% and over 10%, respectively, under compressive deformation is compared. Observation by transmission electron microscopic (TEM) indicates that the deformation-induced structural transformation from monolithic glassy phase is responsible for the large plasticity. The degree of structural change, however, is different between both alloys: the fcc-Zr(2)Ni crystals emerged within glassy phase for the former, while only ordered clusters were observed for the latter. The difference is suggested to correlate to the slower grain-growth of the primary crystallization phase in the Zr(65)Al(7.5) Ni(10)Cu(12.5)Nb(5) compared to those in the Zr(65)Al(7.5)Ni(10)Cu(12.5)Pd(5) alloy. (C) 2010 Elsevier Ltd. All rights reserved.

This paper reports on the unusual solidification behavior of Zr55Cu30Al10Ni5 bulk glassy alloy produced using low-purity Zr in which both primary and eutectic-type structural constituents were formed simultaneously during solidification of the melt. Additionally, two different types of primary crystalline phases were observed. One of them was cF96 and contained all the four constituent elements. Reasons for these observations have been related to the presence of impurities in the alloy leading to inhomogeneous nucleation and consequent modification of the crystallization behavior. The structure and thermal stability of the samples were studied using X-ray diffraction, scanning and transmission electron microscopy, as well as differential scanning calorimetry methods. Although the cast alloys made with low-purity Zr showed somewhat decreased glass-forming ability, their mechanical strength was still high. (C) 2010 Elsevier Ltd. All rights reserved.

Zr(65)Al(7.5)Ni(10)Cu(17.5-x)Pd(x) (x = 0-17.5) bulk metallic glasses (BMGs) were produced in various chamber atmospheres in Cu mold casting. The glassy structure with a larger amount of relaxation enthalpy can be obtained casting under the ambient Ar and He atmospheres, which originates from enhanced cooling effect. These unrelaxed BMGs exhibit an improvement of ductility in the compressive deformation. Especially, Pd-containing BMGs have a significant plasticity of approximately 6%, in which deformation-induced inhomogeneous nanocrystallization also occurs. The synergistic effect of unrelaxed glassy structure and deformation-induced nanostructure change is regarded as a new technique for the improvement of ductility in the BMGs. (C) 2010 Elsevier B.V. All rights reserved.

In-situ observation of elastic deformation behaviors of Zr55Al10Ni5Cu30 bulk metallic glass under tensile stress was carried out using the high-energy X-ray scattering method. Two analytical procedures the reciprocal-space method and direct-space method were applied. The reciprocal-space method, used for the estimation of an apparent atomic spacing, can evaluate the strain in the range of several nanometers. We found that this method yields a large Young's modulus (115 GPa) and a small Poisson's ratio (0.32), as compared to the macroscopic values of 101 GPa and 0.38, respectively. Thus, the macroscopic deformation is larger than the microscopic deformation characterized by the X-ray scattering method. This feature indicates the possibility of inhomogeneous regions with weakly bonded structures existing locally in the glassy structure and acting as significant deformation sites in the elastic stage. The direct-space method suggests that the Zr-Zr nearest pair has a higher sensitivity to an applied stress than the Zr-Cu pair. Moreover, both the nearest pairs in the first shell (r &lt; 0.4 nm) exhibit a slight distortion, as compared with the deformation observed in the second or higher coordination shell (r &gt; 0.4 nm). We explain this deformability gap with the hypothesis that the free volume in the first coordination shell assists the glide of atoms. This results in a larger strain in the second or higher coordination shell than in the first shell. [doi: 10.2320/matertrans.M2010052]

The effect of Nb addition on the nucleation and grain growth behaviors has been investigated in the monolithic Zr65Al7.5Ni10Cu12.5Nb5 metallic glass. Nb has been well-known as an element for icosahedral quasicrystalline (QC) phase formation in the primary crystallization stage as well as for improving mechanical properties and corrosion resistance. The grain growth rate of the QC phase at near the crystallization temperature is 1.2 x 10(-9) m/s, which is approximately 10 times smaller than that of the primary fcc Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 metallic glass. In contrast, nucleation rate increases drastically by Nb addition. It can be calculated as 1.2 x 10(21)/m(3) s, which is approximately 105 times larger than that of the Zr65Al7.5Ni10Cu17.5 alloy. The results indicate that Nb is a very effective element for controlling grain growth and nucleation rates. Good plasticity is exhibited in the as-cast alloy, however, it is lost drastically even after the structural relaxation as well as the QC precipitation. Such significant change may be attributed to the local ordering and/or phase separating tendencies by a positive chemical affinity of the Zr-Nb pair. [doi:10.2320/matertrans.M2010054]

Zr65Al7.5Ni10Cu12.5Nb5 glass was found to exhibit a large plastic compressive strain of over 10% and the property was suggested to be due to deformation-induced nanocrystallization. A transmission electron microscopic observation, however, only revealed obscure ordered clusters with a size of similar to 2 nm in the fracture surface of a deformed sample, instead of well-identified crystals as previously reported for the Zr-Al-Ni-Cu-Pd system. This phenomenon is suggested to correlate with the higher viscosity of supercooled liquid and the slower grain growth of icosahedral phase during primary crystallization in the Zr65Al7.5Ni10Cu12.5Nb5 compared to those in the Zr65Al7.5Ni10Cu12.5Pd5 alloy. The role of the deformation-induced nanoclusters on the enhanced compressive plasticity was discussed.

We have investigated acoustic-phonon behavior of Pd-, Pt-, and Zr-based metallic glasses with the combination of inelastic x-ray scattering and ultrasonic (US) measurements. In the dispersion of the longitudinal acoustic modes at small wave number Q, the phase velocity of phonon tends to exceed the US velocity with a wavelength of macroscopic scale for Pd-and Pt-based glasses, whereas the former goes close to the latter for Zr-based glasses. Furthermore, in all the cases, the mean free path L of phonon apparently increases steeply at a certain Q value. These phenomena on the acoustic phonon behavior can be qualitatively explained by the elastic-wave-scattering theory with a simple two-phase model.

Microstructure evolutions of nano-quasicrystals precipitated in ZrCuPt metallic glass ribbons during annealing has been examined by in-situ small-angle scattering and wide angle diffraction (SWAXS). The time-resolved measurements were made at a photon energy close to the Zr K absorption edge to obtain reasonable balance between transmission and resolution. During annealing the sample in vacuum, increase in SAXS intensity and diffraction peak at medium angle region was observed. The size obtained from SAXS and diffraction almost agreed, suggesting that the precipitation process in the glass ribbon is described by a growth process of single-crystalline nano-quasicrystals. Development of precipitated microstructure was further discussed by comparing SAXS profiles and diffraction profiles.

This paper presents a study of the deformation behaviour of a glassy phase in two Zr-based alloys, Zr(65)Ni(10)Cu(5)Al(7.5)Pd(12.5) and Zr(65)Al(7.5)Ni(10)Pd(17.5), performed in situ in a transmission electron microscope. In contrast to the case of shear localisation and formation of 10-20 nm thick shear bands in deformed bulk glassy samples studied earlier, it is found that in thin (electron-transparent) samples the glassy phase in front of a crack deforms more homogeneously and no nanocrystallisation takes place. The reasons for such behaviour are discussed. According to the observed results, one can conclude that the studied metallic glasses can be intrinsically ductile in submicrometre-sized volumes.

The local atomic structure of nano-quasicrystal-forming Zr80Pt20 binary glassy alloy was investigated by reverse Monte Carlo modeling based on the results of x-ray diffraction. A prepeak at Q similar to 17 nm(-1) originating from the unique bonding between the Pt-Pt pair is observed in the structure factor. Voronoi analysis indicates that an icosahedral-like polyhedron is formed around Pt. It is also found that icosahedral-like polyhedra exist around Zr; however, the fraction of perfect icosahedra is considerably lower than that in the nano-quasicrystal-forming Zr70Pd30 glassy alloy. A difference in the local environment between the two binary quasicrystal-forming glassy alloys is suggested.

Viscoelastic behaviour of a metallic glass Zr(55)Al(10)Ni(5)CU(30) has been studied by measuring the dynamic shear modulus G under forced vibration at low frequencies below 1 Hz. In measurements with increasing temperature, the shear modulus falls markedly at temperatures around the glass transition but at different rates under different vibration frequencies. The dynamic viscosity eta has been evaluated using the relation eta = G/(i omega), where omega is the angular frequency. The curves of vertical bar eta vertical bar vs temperature of different frequencies converge to a single curve in the glass transition region, and the converged curve is in fair agreement with the data reported in the literature. The dynamic glass transition point, defined as the vibration frequency and temperature at which the curves of the storage modulus G(1) and the loss modulus G(2) cross each other, obeys the Arrhenius law. The pre-exponential factor and the activation energy of the transition frequency are unusually large, suggesting that collective movements of atoms control the transition. (C) 2009 Elsevier B.V. All rights reserved.

Heating rate dependence of glass transition and crystallization temperatures is applicable for evaluation of glass structural stability and also for discussion on the apparent activation energies for glass transition and crystallization. The glass-structure stabilities of the Zr-based BMGs (Zr50Cu40Al10, Zr70Cu20Al10 and Zr70Ni20Al10) and the conventional amorphous alloys (Zr70Cu30 and Zr70Ni30) are assessed by the densely packed glass structure as well as the complicated crystallization process. By the reverse Monte Carlo (RMC) simulation with X-ray and neutron diffraction data, it is shown that the densely packed structure is built by icosahedron-like clusters. In Zr65Al7.5Ni10Pd17.5 and Zr65Al7.5Ni10Cu17.5, the effect of Pd atoms on the glass structure is also described. (C) 2008 Elsevier B.V. All rights reserved.

Glass-nano(quasi)crystal composite materials based on Zr-Al-Ni-Cu metallic glasses have been synthesized by controlling the nucleation and growth rates of the precipitated phase correlated with a unique icosahedral local structure. It is well known that the Zr(65)Al(7.5)Ni(10)Cu(17.5) metallic glass has a high glass-forming ability (GFA), which enables us to produce the glassy sample with a bulky shape. Controlling a substitution of QC-forming elements such as noble metals with Cu and annealing condition, the nanoscale icosahedral quasicrystalline phase (I-phase) with various grain sizes and nucleus densities can be formed. Moreover, we have succeeded to control the nano-QC phase nucleation by changing the atmosphere pressure during casting, which results in the formation of new bulk metallic glasses (BMGs). These nanoscale structure and nucleation controlling techniques in BMGs bring a significant improvement of mechanical properties such as high strength and good ductility. (C) 2008 Elsevier B.V. All rights reserved.

The material design tailoring of a synergistic effect of an in-situ nano secondary phase formation and defomation-induced nanocrystallization for improving the mechanical strength and ductility, has been investigated in Zr65Al7.5Ni10Cu17.5-xPdx bulk metallic glasses (BMGs). As-cast Zr65Al7.5Ni10Cu17.5-xPdx (x = 5-17.5) BMGs have significant ductility in compressive deformation, which is attributed to deformation-induced dynamic nanocrystallization. The 10at% Pd-containing BMG with a low volume fraction of the quasicrystalline (QC) phase of less than 6% exhibits increases in strength and Young's modulus, in addition to a remaining plasticity of similar to 5%, compared with the monolithic glassy alloy. Such improvements in the mechanical properties originate from the combination of two effects of in-situ homogenous nano-QC formation and deformation-induced inhomogeneous nanocrystallization. The present method should be regarded as a new technique for the production of BMGs with high strength and good ductility. [doi:10.2320/matertrans.M2009135]

The residual stress and deformation behavior of a Zr55Al10Ni5Cu30 bulk metallic glass containing 10 vol.% ZrC particles were measured using neutron diffraction. Elastic deformation behavior under uniaxial tensile loading can be predicted by the self-consistent model. The higher strength in compressive deformation in this sample originates from the thermal tensile residual stresses, and from the phase stresses transferred to the metallic glass matrix, which are 5% less than the applied stresses under uniaxial loading. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

We have prepared Zr-Al-Ni-Cu-Pd bulk metallic glasses (BMGs) cast in an ambient Ar atmosphere, in which the cooling effect is enhanced. The Zr65Al7.5Ni10Cu17.5-xPdx(x = 1-5) BMGs exhibit a good plasticity during the compressive deformation process. A significant plasticity of 6% plastic strain is obtained in the Zr65Al7.5Ni10Cu12.5Pd5 BMG, where the deformation mode with multi shearbands appears near the fracture Surface. Nanocrystalline particles are arranged in it band-like formation in the glassy matrix around the multi shear bands, indicating the restraint of shear band propagation owing to the dynamic precipitation of the nanocrystals. The unrelaxed structure owing to the higher cooling rate in the present condition may also contribute to the good plasticity. [doi: 10.2320/matertrans.MER2008162]

Anomalous small-angle X-ray scattering (ASAXS) profiles of Zr(80)Pt(20) ribbons have been measured at the Zr K absorption edge. By annealing the melt-spun ribbons at 800 K, well defined SAXS patterns from nanoquasicrystals were observed, although the compositions of the quasicrystals (QC) and the amorphous matrix have previously been reported to be the same. The SAXS intensities were found to show a small anomalous effect at the Zr K edge. Contrast analysis suggested that the origin of the small-angle scattering is a small compositional fluctuation coupled with a small density difference, which enhances SAXS intensity but reduces the anomalous effect. A constant ASAXS intensity ratio for QC microstructure suggests that the ratio of the composition difference to the density difference between QC and the amorphous matrix is almost constant for the ZrPt ribbons examined here.

In this work, we study the cooling behavior of several typical bulk glassy alloys on casing and present the relationship between the thermal conductivity of a glassy alloy and the cooling rate upon mold casting. The cooling rates obtained for Ti-, Zr-, Pd-, and Cu-based bulk glass forming alloys are found to scale with the thermal conductivities of the studied glassy alloys.

The limited plasticity of bulk metallic glasses (BMGs) is commonly circumvented by introducing micrometer- or nanometer-sized heterogeneities (crystallites and/or phase separation) into the BMGs. In this work, we report the improvement of plasticity in a ternary monolithic BMG caused by a large amount of randomly distributed free volume induced during solidification using a high cooling rate. This indicates that introducing large amounts of free volume into BMGs might be another promising way of improving the plasticity of these materials. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The influence of the cooling rate on the structure, microhardness, relaxation, and devitrification behavior of Cu44Ag15Zr36Ti5 glassy alloy on heating is studied in the present work. According to transmission electron microscopy investigations, the structures of Cu44Ag15Zr36Ti5 glassy ribbon and bulk samples are somewhat different. The structure of the ribbon samples is amorphous while, the nanoscale clusters of the crystalline phase (highly ordered regions) are formed in the bulk samples. It is reflected in the shift of the x-ray diffraction peak, in the magnitude of the heat of structure relaxation and crystallization, as well as in the change in the Vickers microhardness. An analysis of the cooling curve is also performed.

Formation of the nanoscale icosahedral quasicrystalline phase (I-phase) in the melt-spun Zr(70)Pd(30) and Zr(80)Pt(20) binary metallic glasses were reported. Local atomic structure in the glassy and quasicrystal (QC)-formed states were also analyzed by XRD and EXAFS measurements in order to investigate the formation mechanism of QC phase. The distorted icosahedral-like local structure can be identified around Zr atom in the Zr(70)Pd(30) metallic glass. In the QC formation process, a change of local environment around Zr is detected, in which the approximately one Zr atom substitutes for one Pd atom. In contrast, since the local environment around Pt atom is remaining during the QC precipitation, it is suggested that the stable icosahedral local structure is mainly formed around a center Pt atom in the glassy state in Zr(80)Pt(20). We also found that the local environment around Zr atom significantly changes during the quasicrystallization in the alloy. These results differ from those in the Zr(70)Pd(30) metallic glass.

The local structure of melt-spun Zr80Pt20 alloy was investigated in the amorphous and icosahedral quasicrystal (QC)-formed states by x-ray diffraction and extended x-ray absorption fine structure measurements. While the local environment around the Zr atom in the amorphous state is considerably different from that in the QC-formed state, it remains during the quasicrystallization around the Pt atom. It is suggested that the stable icosahedral local structure is mainly formed in the center of the Pt atom in the amorphous state.

Low-temperature elastic constant C-ij(T) measurements for Cu60Zr30Ti10 and Cu60Hf25Ti15 bulk metallic glasses (BMGs) have been carried out to clarify their acoustic properties including a nonlinear interaction term. The BMGs show remarkably low shear to bulk modulus ratio C-44/B or equivalently high Poisson's ratio nu compared with the corresponding crystalline states. The C-ij(T) behaviors are well described by Varshni's formula [Phys. Rev. B 2, 3952 (1970)] and estimated Einstein temperatures suggested significant softening in the transverse-mode acoustic phonon. Mean Gruneisen parameters gamma derived from dB/dT slopes become almost identical with those of crystalline Cu. Our theoretical analysis based on inhomogeneous microstructure model successively explains the elastic constants and characteristic features of the BMGs within a framework of quasiharmonic thermodynamics, suggesting that microstructural inhomogeneity plays a dominant role in the BMGs.

The local structure in the glassy state is investigated in the Zr80Pt20 and Zr70Cu30 binary and Zr70Al10Ni20 ternary alloys in correlation with the quasicrystalline (QC) phase forniation. The Zr80Pt20 alloy has a high QC-forming ability. It is easily formed in the as-quenched state with a considerably low cooling rate or by annealing the glassy alloy. The radial distribution function (RDF) and extended X-ray absorption fine structure (EXAFS) analysis clearly indicate the existence of icosahedral local structure around Pt atom. The Zr70Cu30 binary and Zr70Al10Ni20 ternary metallic glasses have a QC-forming ability by the addition of a very small amount of noble metals such as Pd. We can also investigate the icosahedral local structure in these alloys. These results are realized that the icosahedral local structure can be applied as a dominant local atomic configuration in the supercooled liquid and/or glassy states in the QC-forming metallic glasses.

Temperature dependent elastic constants Cij(T) of Cu60Zr30Ti10() bulk metallic glass (BMG) have been studied using MHz frequency range electromagnetic acoustic resonance (EMAR) from 4.5 to 300K. At ambient temperature, the BMG shows low shear/bulk modulus ratio (or equivalently high Poisson ratio) compared with that of corresponding crystalline state dues to the dense random packed glassy structure. Analysis of Cii(T) based on the Einstein type lattice vibration model revealed the notable softening in transverse mode acoustic phonons. This unusual vibrational property suggests the existence of liquid like weakly bonded region in the BMG.

We provide a quantitative analysis of the importance of the gas species and pressure during mold-casting process on the apparent glass-forming ability (GFA) of Zr65Al7.5Ni10Pd17.5 alloy, recently reported by Kato et al. (e.g. Scripta Mater. 51 (2004) 13). The cooling characteristics are found to depend in remarkable detail on the g-as species and the pressure existing in the cavity between the melt and the mold presumably formed during the cooling process. This understanding has been successfully applied to significantly improve the critical diameter of the glassy rods to 7 mm in an atmosphere of helium environment from 5 mm in that of argon.

Nanoscale dynamic transformations during tensile and compressive deformation of Zr65Al7.5Ni10Cu17.5 and Zr65Al7.5Ni10Pd17.5 bulk metallic glasses have been investigated. Although no apparent differences are observed in the stress-strain curves in the tensile deformation between the two alloys, fine striations and depression zones with viscous flow appear at the fracture surface near the edge in the Zr65Al7.5Ni10Pd17.5 alloy. Unlike the Zr65Al7.5Ni10Cu17.5 alloy and other bulk metallic glasses, the Zr65Al7.5Ni10Pd17.5 bulk metallic glass exhibits a large plastic strain of approximately 7% during compressive deformation. By detailed examination of the inicrostructure, we provide direct evidence for nanoscale multistep shear band formation in the Zr65Al7.5Ni10Pd17.5 metallic glass. A novel nanoscale structure where fcc Zr2Ni nanocrystalline particles are arranged in "bandlike" areas in the glassy matrix is observed near the compressive fracture tip. The suppression of the propagation of the shear bands due to dynamic nanocrystallization causes this structure. Furthermore, the results are recognized as a novel phenomenon, a nanoscale dynamic structural change by shear band propagation. and provide a new method for improving the mechanical properties of bulk metallic glasses.

The effect of At addition on the local structure and the thermal stability in the Zr-Ni-based metallic glass is investigated. It is well known that At is a very effective element on the enhancement of glass-forming ability (GFA), i.e., stability of supercooled liquid state in the alloy system. We have found that the dominant local structure is icosahedral-like in the Zr(70)AI(10)Ni(20) metallic glass and the tetragonal Zr2Ni-like local in the Zr70Ni30 amorphous alloy. It is concluded that the change in the dominant local structure contributes to the enhancement of the stability of supercooled liquid state in the alloy. (C) 2006 Elsevier B.V. All rights reserved.

Structures of Zr70Ni20Al10, Zr70Cu20Al10, Zr70CU30 and Zr70Ni30 amorphous alloys were analyzed by high-energy X-ray diffraction. The relatively stable Zr2Cu amorphous alloy shows a local atom arrangement different from the Zr2Cu crystalline phase. By contrast, the less stable Zr70Ni30 amorphous alloy has a structure similar to Zr2Ni. In the Zr70CU20Al10 metallic glass, Zr-Al nearest neighbor pairs are introduced in the amorphous structure. In the Zr70Ni20Al10 metallic glass, the strong correlation between Zr-Ni pairs is drastically modified by the formation of Zr-Al pairs. The presence of Zr-Al pairs in the ternary alloys suppresses the crystallization and stabilizes the glassy state. (C) 2006 Elsevier B.V. All rights reserved.

Anomalous small-angle X-ray scattering measurements of Zr-Cu-Al-Ni quaternary alloys have been made at the Zr K absorption edge. In melt-quenched samples, small cluster components without crystallization were found. The contrast change at the edge suggested that compositional fluctuation of Al is incorporated.

Thermal diffusivity of three alloys of Zr55Al10Ni5Cu30, Zr60Al15Ni25 and Zr65Al7.5Cu27.5 has been measured in the liquid state with a laser flash technique. The thermal diffusivity values of three Zr-based alloys in the liquid state are summarized in the linear equations with positive temperature dependency. The lower the thermal diffusivity values of Zr-based alloys at liquidus temperature, the lower the critical cooling rate to produce metallic glass phase becomes. The measured thermal diffusivity was compared with the value for Pd-based metallic glass. The results indicate that critical cooling rate to obtain metallic glass phase could be an increasing function of thermal diffusivity for each alloy system.

This article presents a comparative study of the deformation-induced structural changes observed within a glassy phase in two different Zr- and Ni-based alloys. Ductile Zr65Al7.5Ni10Pd17.5 bulk glassy alloy, which exhibits dynamic nanocrystallization forming a crystalline cubic phase within shear bands on plastic deformation, is presumed to contain pre-existing nuclei. On the contrary, no obvious dynamic nanocrystallization is observed within the shear bands in the glassy phase of the Ni50Pd30P20 bulk alloy, which, however, contains clear medium-range order zones on the order of 1 nm in size in an as-solidified state. This alloy exhibits nucleation and growth-transformation behavior on heating. At the same time, clear nucleation and growth of the cubic Ni-based phase are observed near the microcrack area in the deformed sample. High energy released at the time of the microcrack propagation caused nanocrystallization and blockage of the crack-tip propagation.

Temperature dependent elastic constants Cij(T) of Cu60Hf30Ti10 bulk metallic glass (BMG) have been investigated in a MHz frequency range using electromagnetic acoustic resonance (EMAR) up to 823 K. At room temperature, the BMG showed high Poisson's ratio v arising from low shear modulus G compared with that of constitutive crystalline elements. With increasing temperature, G showed usual linear temperature dependence while it suddenly drops around glass transition temperature, T-g. Within a framework of quasiharmonic approximation, Gruneisen parameter gamma around T-g is estimated to be 10. This extremely large gamma indicates the high anhramonicity of long wavelength limit acoustic mode phonon in the supercooled liquid state. The unusual elastic behavior can be interpreted on the basis of heterogeneous microstructure.

Monolithic Zr65Al7.5Ni10Pd17.5 and Zr65Al7.5Ni10Cu17.5 hardly had plastic deformability in tension at room temperature, although Zr65Al7.5Ni10Pd17.5 showed a large plastic strain in compression. A depressed zone that is the evidence of viscous flow deformation (so-called viscous flow depression zone; VFD-zone) was observed for Zr65Al7.5Ni10Pd17.5 around the edge at the point of failure on its specimen surfaces. However, no VFD-zone was seen for Zr65Al7.5Ni10Cu17.5. Thus, a clear difference in tensile plastic behavior was found between Zr65Al7.5Ni10Pd17.5 and Zr65Al7.5Ni10Cu17.5. A structural change in the vicinity of the fracture surface of Zr65Al7.5Ni10Pd17.5 was measured by micro-beam X-ray diffiractometry (MB-XRD). We may be able to discuss the room temperature plasticity of Zr65Al7.5Ni10Cu17.5-xPdx bulk metallic glasses correlating with the phase stability of the amorphous and icosahedral quasi-crystalline phases.

A Zr65Al7.5Ni10Cu17.5-xPdx (x=0-17.5 at. %) alloy system is found to exhibit a different dependence of glass-forming ability (GFA) on atmosphere-pressure during mold casting process. High-Pd alloys (x=7.5-17.5) show a remarkable increase of critical size for glass formation (d(c)) as casting-atmosphere (Ar) pressure varies from vacuum to ambient. No significant change of d(c), however, is observed in low-Pd alloys (x=0-5) despite the variation in atmosphere pressure. The origin of the phenomenon is unveiled by correlating the cooling characteristic during mold casting and on-cooling phase transformation characteristic of the alloy system.

Anomalous small-angle scattering (ASAXS) measurements at Zr-K absorption edge were carried out to examine precursory structural and/or chemical fluctuation of quenched quaternary ZrCuNiAl bulk metallic glasses and their welds. The measurements were carried out at BL-40B2 of SPring8, Japan. The incident photon energies were about 30 and 100 eV lower than the K-absorption edge. The intensity profiles for the ZrCuNiAl alloys exhibited two characteristic scattering components. One is a monotonically decreasing component at low q, and the other is a shoulder component observed at higher q, suggesting a cluster-like fluctuation with a size of about a nanometer in radius. From the difference of the scattering intensity between the two energies, it is concluded that the scattering contrast between the clusters and the matrix is very low, with less than about one electron/atom, and chemical fluctuations is involved. (c) 2006 Elsevier Ltd. All rights reserved.

The fragility parameter m of (Pt or Pd)-(Ni, Cu)-P bulk metallic glasses (BMGs) was characterized and compared to other systems. The results indicate that the Pt65Ni15P25 alloy is the most fragile and thermally stable at the supercooled liquid state, thus is the most workable among the presently developed BMGs. To express the degree of workability, a deformability d* = log[eta(T-g(*))/eta(T-x)] is introduced then correlated with in and the reduced thermal stability Delta T-rx(*) = (T-x - T-g(*))/T-g(*). A master curve in term of eta(T-g(*))/eta(T) and m (.) [(T - T-g(*))/T-g(*)] has been established for various BMGs, d(*) thus can be uniquely related to m (.) Delta T-rx(*). (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

By utilizing ultrasonic annealing at a temperature below (or near) the glass transition temperature T-g, we revealed a microstructural pattern of a partially crystallized Pd-based metallic glass with a high-resolution electron microscopy. On the basis of the observed microstructure, we inferred a plausible microstructural model of fragile metallic glasses composed of strongly bonded regions surrounded by weakly bonded regions (WBRs). The crystallization in WBRs at such a low temperature under the ultrasonic vibrations is caused by accumulation of atomic jumps associated with the beta relaxation being resonant with the ultrasonic strains. This microstructural model successfully illustrates a marked increase of elasticity after crystallization with a small density change and a correlation between the fragility of the liquid and the Poisson ratio of the solid.

In order to investigate the role of Al on the thermal stability of supercooled liquid state, the local structures of Zr70M30 and Zr70M20Al10 (M = Ni, Cu) metallic glasses have been studied by the X-ray diffraction and EXAFS measurements. It is found that the different effect of Al substitution on the local structures around Cu and Ni elements is exhibited. No characteristic change is observed in the local structure in the Zr-Cu metallic glass by Al substitution, whereas a drastic change in the environment around Ni atom can be confirmed in the Zr-Ni metallic glass. That is, the coordination number of Zr around Ni decreases significantly by substitution of Al in the Zr-Ni metallic glass. This would be caused by the preferential correlation between Al and Zr. This result suggests that Al plays a dominant role on the formation of novel local structure with a decomposition of the tetragonal Zr, Ni-like local environment in the Zr-Ni binary alloy. We conclude that the novel local structure contributes to the stability of the supercooled liquid state in the Zr-Al-Ni metallic glass.

In this work, the characteristics of shear bands and fracture surfaces of Zr65Al7.5Ni10Pd17.5 bulk metallic glass fractured by a tensile test was investigated. Zr65Al7.5Ni10Pd17.5 bulk metallic glass shows a yield stress of approximately 1.3 GPa, a fracture stress of approximately 1.5 GPa and a tensile plastic strain of 0.1-0.2% irrespective of the applied strain. Wavy, meandering shear bands were observed in the relatively wide area of specimen surfaces around the point of failure, and typical vein patterns were observed on the fracture surfaces. Shear bands and fracture surfaces were further examined by confocal microscopy to obtain more precise information on their roughness. On the other hand, evidence of viscous flow due to crack propagation was also obtained around the edge at the point of failure on specimen surfaces by confocal microscopy. The defomiability of Zr65Al7.5Ni10Pd17.5 bulk metallic glass is discussed on the basis of the obtained results.

The physical significance of the glass transition observed by differential scanning calorimetry (DSC) in the metallic glasses was considered through the measurements of the heating-rate, 0, dependence of the glass transition temperature. T-g. and the crystallization temperature, T,. in the Zr70Cu30 and Zr70Ni30 amorphous alloys and X-ray study of their structures in as-quenched and crystallized states. Zr70Cu30 exhibits the glass transition before crystallization, but Zr70Ni30 is immediately crystallized at heating rates of conventional time scale in the DSC measurement. The heating rate 0, at the intersection of the two linear curves of Tg and T, against log provides us with a significant measure to determine the glass-forming ability or thermal stability of the metallic glasses. By heating at beta larger than beta(c), the crystallization is suppressed and the glass transition is clearly observed even in Zr70Ni30.. The thermal stability of the Zr70Cu30 amorphous alloy is caused by retardation of crystallization due to the amorphous structure that is different from the Zr2Cu crystalline phase, In contrast, the thermal instability of Zr70Ni30 is attributed to the structural similarity to the Zr2Ni crystalline phase. Thus, suppressing the crystallization is shown to be a key to enhance the thermal stability of the present amorphous alloys.

A single Zr65Al7.5Ni10Pd17.5 bulk metallic glass exhibits a large plastic strain of 6.6% during the compressive deformation process, which is attributed to the deformation mode with nanoscale multistep shear bands. We have observed that nanocrystals with a metastable fcc Zr2Ni structure containing several distorted icosahedral clusters are arranged in a "bandlike" formation in the glassy matrix around the multistep shear bands. This is recognized as direct evidence of the novel phenomenon of the restraint of shear band propagation owing to the dynamic precipitation of the nanocrystals. (C) 2005 American Institute of Physics.

The devitrification of Ni60Nb25Ti15 glassy alloy has been investigated by X-ray diffraction (XRD), differential scanning and isothermal calorimetry and transmission electron microscopy (TEM). The primarily crystallized phase was a cubic Ni(Ti,Nb) phase with a lattice parameter of 0.293 nm. A Ni3Nb phase follows precipitation of the Ni(Ti,Nb) phase. The cubic Ni(Ti,Nb) phase undergoes partial transformation to Ni4Ti3 phase. These cubic Ni(Ti,Nb) phases disappear at the equilibrium conditions. The supercooled liquid region (Delta T-x) of the Ni60Nb25Ti15 glassy alloy was extended to 64 K with the addition of Pt. The Ni55Nb25Ti15Pt5 glassy alloy rods with diameters up to 2 mm were formed by mold casting. Pt and the other noble metals additions do not alter devitrification of Ni60Nb25Ti15 glassy alloy.

The local structure of Zr70Al9Ni20Pd1 metallic glass, in which a nano-icosahedral quasi-crystalline phase (I-phase) is formed in the primary stage of crystallization, has been examined and compared with that of Zr70Al10Ni20, the supercooled liquid state of which has a high stability. Since the local environments around the Zr and Ni atoms do not change drastically by the addition of 1 at.% Pd to Zr70Al10Ni20, as evidenced by radial distribution function (RDF) and extended x-ray absorption. ne structure (EXAFS) studies, we deduce that the icosahedral phase formed in the Zr70Al9Ni20Pd1 metallic glass has a local structure similar to that in Zr70Al10Ni20. Although a very slight rearrangement of Zr-Zr atomic pairs occurs during quasi-crystallization, the I-phase formation is achieved without disturbing the dominant local structure in the glassy state of the Zr70Al9Ni20Pd1. An icosahedral local structure is proposed for Zr-Al-Ni metallic glass system as well as for primary quasi-crystal (QC)-forming Zr-based metallic glasses.

The primary transformation reaction of the Zr65Al7.5Cu27.5 ternary glassy alloy with a low oxygen impurity of approximately 100 mass ppm was investigated. We have discovered the precipitation of the metastable icosahedral phase with a fine grain size of 50-100 nm in diameter accompanying with the formation of stable Zr2CU phase at the annealing temperatures ranging from 715 to 730 K. The lattice spacing of Zr2CU phase decreases at higher temperatures, which is attributed to the rearrangement of Zr and Cu in the decomposition of the icosahedral phase. It is suggested that the formation of the icosahedral phase in the primary stage originates from the existence of the quenched-in icosahedral local atomic configuration in the glassy state.

Nanoquasicrystallization and local structure of Zr-based metallic glasses were investigated. The nano icosahedral. quasicrystalline phase (QC) is formed in the Zr70Al10Ni20 ternary and Zr70Cu30 binary metallic glasses with a high stability of supercooled liquid state by addition of a small amount of noble metal. The QC formation proceeds without the significant change of local structure. We can propose the icosahedral local structure in these QC-forming metallic glasses. We also investigate the correlation between the QC formation and stability of supercooled liquid state.

It is found that an increase in the hydrostatic chamber pressure (P) during the casting process suppresses the glass forming ability (GFA) of the Zr65Al7.5Ni10Cu17.5 alloy, on the contrary, it enhances the GFA of the Zr65Al7.5Ni10Pd17.5 alloy. This opposite dependence of the GFA on P in these alloys may be because the volume increases or decreases by the primary crystallization. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The tensile fracture structure in the as-quenched Zr80Pt 20 alloy hardened by the homogeneously precipitation of nanoicosahedral phase is investigated by high-resolution transmission electron microscopic observation. The evidence which indicates that the tensile fracture occurs in the residual amorphous phase in the intergranular region, is obtained in the nanocomposite alloy consisting of icosahedral and amorphous phases. © 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The pressure effect on amorphous-to-quasicrystalline-to-intermetallic phase transformations in a Zr70Pd30 metallic glass has been investigated by in situ x-ray diffraction measurements using synchrotron radiation. It is found that the glass crystallizes in two steps: (1) amorphous-to-icosahedral quasicrystalline and (2) icosahedral quasicrystalline-to-intermetallic Zr2+xPd alloy. The intermetallic alloy has a tetragonal structure with lattice parameters, a=3.310(1) Angstrom and c=10.974(1) Angstrom, and a space group of I4/mmm. External pressure enhances the onset temperatures for the formation of quasicrystalline phase and intermetallic compound with rates of 11+/-3 and 9+/-4 K/GPa, respectively, while the temperature interval for the stability of quasicrystals remains almost unchanged in the pressure range of 0-3 GPa. External pressure does not affect the phase-selection sequence. The enhancement of the onset temperature for the formation of quasicrystals has been further discussed with the nucleation theory. (C) 2004 American Institute of Physics.

A glassy phase containing cubic phase particles with a size of 3-5 am was formed in Cast Cu60Zr30Ti10 and Cu60Hf60Ti10 bulk alloys. The cubic phase is in a metastable state and its lattice parameter (a(0)) is 0.45 nm for the former alloy and 0.51 nm for the latter. These bulk alloys exhibit good mechanical properties of 2000-2130 MPa for tensile strength (sigma(t.f)), 2060-216OMPa for compressive strength (sigma(c.f)) and 0.008-0.017 for compressive plastic strain (epsilon(c.p)). The temperature interval of the supercooled liquid (SL) region prior to crystallization is 37 K for Cu60Zr30Ti10 and 67 K for Cu60Hf30Ti10. The primary crystallization occurred by precipitation of cubic CuZr (a(0) = 0.35 nm) in a diffusion-controlled growth mode of nuclei and an orthorhornbic Cu8Hf3 phase in an interface diffusion-control led growth of nuclei with decreasing nucleation rate. The difference in the precipitation modes is interpreted to be the origin of the difference in the SL region. Furthermore. the addition of Al to Cu-Zr and Cu-Hf alloys caused the formation of a glassy single phase in the rod form with diameters up to at least 3 mm, though bulk glassy alloy rods with critical diameters up to 1.5 mm and sigma(c.f) of 1920-2260 MPa were formed in Cu-Zr and Cu-Hf binary systems. The ternary bulk glassy alloys exhibited high sigma(c.f) of 2100-2370 MPa with epsilon(c.f) of 0.002-0.006. The addition of Pd, Pt, Ag or Au increased DeltaT(x) and a large DeltaT(x) of 102-110 K was obtained for the Cu-Hf-Al-M (M = Pd or Ag) glassy alloys. The synthesis of Cu-based bulk glassy alloys with good mechanical properties and large AT. in glassy single, and mixed glassy and cubic phase states, is important for future applications of bulk glassy alloys.

The glassy structure and the primary precipitation phase from supercooled liquid were examined in metal-metal type Zr-, Hf- and Cu-based alloy systems by various advanced analytical techniques. The icosahedral phase precipitates as the primary phase from supercooled liquid for all the metal-metal type glassy alloys examined in the, present study. The icosahedral phase has a rhombic triacontahedra type for the Zr-Al-Ni-Cu-NM (NM=Ag, Pd, Au, Pt), Zr-Cu-NM, Hf-Al-Ni-Cu-NM, Cu-Zr-Ti-Pd and Cu-Hf-Ti alloys. In addition, the short-range atomic configurations in their glassy alloys have the features of highly dense packed atomic configuration, new local atomic configurations and long-range homogeneity with attractive interaction. It is therefore concluded that the high glass-forming ability of the metal-metal type alloys is due to the self-formation of the unique glassy structure with the above-described three features which are consistent with the formation of short-range icosahedral atomic configuration.

Bulk glassy alloys containing cubic phase particles with a size of 3 to 5 nm were formed in Cu60Zr30Ti10 and Cu 60Hf30Ti10 ternary systems by copper mold casting. The cubic phase had a lattice parameter of 0.45 nm for the former alloy and 0.51 nm for the latter alloy and was analyzed to have Cu-rich compositions as compared with their nominal compositions. The mixed phase bulk alloys exhibit good mechanical properties of 2000 to 2130 MPa for tensile fracture strength, 2060 to 2160 MPa for compressive fracture strength and 0.008 to 0.017 for compressive plastic strain. The temperature interval of the supercooled liquid region prior to crystallization is 37 K for the Cu 60Zr30Ti10 alloy and 67 K for the Cu 60Hf30Ti10 alloy. The primary crystallization occurred by the precipitation of a cubic CuZr phase with a lattice parameter of 0.35 nm in a diffusion-controlled growth mode of nuclei and an orthorhombic Cu8Hf3 phase in an interface diffusion-controlled growth mode of nuclei with decreasing nucleation rate, respectively. The difference in the precipitation modes is interpreted to be the origin for the difference in the supercooled liquid region. The formation of Cu-based alloys with high strength in the nanoscale mixed phase state is encouraging for future development as a new type of structural materials.

Change in local atomic environment during crystallization of Zr-based glassy alloys was studied by extended x-ray absorption fine structure (EXAFS) spectroscopy. The formation of icosahedral quasicrystalline phase followed by crystallization of tetragonal CuZr2 has been observed in the Zr70Cu29Pd1 glassy alloy during annealing up to 850 K. On the other hand, the binary Zr70Cu30 alloy shows a single glassy to crystalline CuZr2 phase transformation. The local atomic environment of as-quenched Zr70Cu30 alloy is matched to an icosahedral local atomic configuration, which is similar to that of the as-quenched Zr70Cu29Pd1 alloy and the alloy annealed at 593 K containing icosahedral phase. Considering that the supercooled liquid region appears prior to crystallization in the Zr70Cu30 glassy alloy, the observed results support the theory claiming a strong correlation between the existence of local icosahedral short-range order and stability of the supercooled liquid state. (C) 2003 American Institute of Physics.

Microscopic structures of Cu60Ti10+xZr30-x (x=0 and 10) alloys have been investigated by transmission electron microscopy, x-ray diffraction (XRD) and differential scanning calorimeter (DSC). In the Cu60Ti10Zr30 samples annealed at 708 K for times ranging from 0 to 130 min, where the enthalpy of the first exothermic peak decreases by 80%, the corresponding XRD patterns still look similar to that for the as-prepared sample. However, the simulated XRD patterns for the pure Cu51Zr14 phase, which is the crystalline phase formed during the first exothermic reaction, with small grain sizes and defects clearly show a broadened amorphous-like feature. This might be the reason that no diffraction peaks from the nanocrystalline component were detected in the XRD patterns recorded for the as-cast or as-spun Cu60Ti10+xZr30-x (x=0 and 10) alloys and for the alloys annealed at lower temperatures, in which the enthalpy of the first exothermic peak has a significant reduction. The second exothermic peak found in DSC curves is due to the formation of another hexagonal phase, spacing group P6(3)/mmc (194) and lattice parameters a=5.105 A and c=8.231 Angstrom. (C) 2003 American Institute of Physics.

The microstructure of the melt-spun CU60Hf30Ti10 and Cu50Hf40Ti10 alloys was investigated. The high-resolution transmission electron microscopy (HRTEM) image in the Cu60Hf30Ti10 alloy reveals the existence of nanoscale inhomogeneity, which appears to originate from nanocrystalline particles. The compositional segregation with a diameter of approximately 5 nm was detected, and its size agrees with the scale of nanocrystalline particle. Small-angle x-ray scattering measurement of the melt-spun Cu60Hf30Ti10 alloy also indicates the development of nanoscale inhomogeneity with the same size as that of nanocrystalline particles. It is found that the Cu element is enriched in and Hf element is rejected from the nanocrystalline particles. Since the melt-spun CU50Hf40Ti10 alloy, which has a similar alloy composition to that of the glassy region of melt-spun Cu60Hf30Ti10 alloy, has a homogeneous glassy structure without fringe contrast in the HRTEM image, it is suggested that the excess of Cu causes the nanoscale inhomogeneity with crystalline structure in the rapidly quenched Cu-Hf-Ti alloys.

The structure and primary devitrification process of the melt-spun Cu-60(Zr or Hf)(30)Ti-10 alloys were investigated. It was confirmed that the compositional segregation in the diameter range of 5-10 nm exists in the as-quenched state. The nanocrystalline particles with cubic structure are observed in the glassy matrix in the high-resolution transmission electron microscopy images, of which size is corresponding to the scale of compositional segregation. Small-angle X-ray scattering measurement also indicates the development of nanoscale inhomogeneity with the same size as that of nanocrystalline particles. The nanocrystalline region has high Cu content. In contrast, Zr or Hf and Ti elements are enriched in the glassy region. These results are recognized as the formation of novel structure consisting of the glassy and nanocrystalline phases. It is suggested that the precipitation of bcc CuZr phase as a primary crystallization phase proceeds in the glassy phase remaining the nanocrystalline phase in the Cu-Zr-Ti alloy. Meanwhile, the glassy and nanocrystalline phases are transformed to an orthorhombic Cu8Hf3 phase at the initial crystallization stage in the Cu-Hf-Ti alloy. These differences of crystallization process are consistent with the results of thermodynamic and kinetic analyses of the transformation mode. (C) 2003 Elsevier Ltd. All rights reserved.

The microstructures of Cu60Ti10Zr30 alloys fabricated by using two different methods, (rods of 2.5 mm in diameter prepared by a copper-mold casting method, and ribbons of about 0.03 mm in thickness prepared by the melt-spinning method), have been investigated by transmission electron microscopy and high-resolution transmission electron microscopy. Surprisingly, we found that the alloy in both geometries contains cubic nanometer-sized crystals of about 5-7 nm in diameter with a lattice parameter of 0.45 nm for ribbons and 7-15 nm in diameter with a lattice parameter of 0.42 nm for rods. Nanocrystals with a significant volume fraction are randomly distributed in the amorphous matrix. The copper element is enriched in nanocrystals while a slightly high zirconium content is found in the matrix. We classify that the Cu60Ti10Zr30 alloy prepared by both of the aforementioned methods is a nanocomposite: Nanocrystals embedded in an amorphous matrix. (C) 2003 American Institute of Physics.

Change in the primary crystallization from a single icosahedral quasicrystalline phase into the fcc Zr2Ni phase by mechanical disordering was investigated in a melt-spun Zr65Al7.5Ni10Cu12.5Pd5 glassy alloy. The transition of the primary phase is attributed to the mechanical strain induced in the icosahedral local structure in the glassy state. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

A single glassy phase of Zr70Pd20Ni10 alloy powder was synthesized by mechanical alloying the elemental powders for 48 hours, using a high-energy ball-milling technique. The obtained glassy phase transformed into a metastable big-cube phase upon increasing the ball-milling time (100 hours). After 150 hours of milling, a complete glass-metastable-phase transformation was achieved, and the end product was nanocrystalline big-cube powder, which has a lattice constant of 1.23 nm. As the ball-milling time was further increased the big-cube phase could no longer withstand the mechanical deformation that was generated by the milling media and transformed into a new metastable phase of nanocrystalline fcc Zr70Pd20Ni10. The lattice constant of this metastable phase was calculated to be 0.455 nm. The reported metastable phases here are new and have never been, so far as we know, reported for the ternary Zr-Pd-Ni system, or its binary-phase relations.

It was found that the nano-icosahedral phase was formed in the devitrification stage of Zr- and Hf-based glassy alloys. The primary phases are metastable fcc Zr2Ni and fcc Hf2Ni phases in the Zr65Al7.5Ni10Cu17.5 and Hf65Al7.5Ni10Cu17.5 glassy alloys, respectively. By substitution of 5 at.% Pd for Cu, the primary phase changes to an icosahedral quasicrystalline phase in both alloys. The addition of elements, that have a positive or weak chemical affinity with one of the constitutional elements in the Zr-Al-Ni-Cu and Hf-Al-Ni-Cu glassy alloys is effective for the precipitation of the icosahedral phase. The icosahedral phase also precipitated with a slight deviation from the composition with a high glass-forming ability. Since an icosahedron is contained as a structure unit in the icosahedral, fcc Zr2Ni and fcc Hf2Ni phases, it is concluded that these phases are correlated with the local icosahedral order of the-glass. The high-resolution transmission electron microscopy images of the as-spun Zr65Al7.5Ni10Cu7.5Pd10, Zr70Al7.5Ni10Cu12.5 and Hf65Al7.5Ni10Cu12.5Pd5 alloys reveal a possibility of the existence of the icosahedral ordered regions. It is, therefore, concluded that the existence of icosahedral short- or medium-range order stabilizes the glassy state in the Zr- and Hf-based multicomponent alloys. (C) 2003 Elsevier Science B.V. All rights reserved.

A single phase of glassy Zr60Ni25Al15 alloy powder was synthesized by mechanically induced solid-state reaction (MISSR) technique. The MISSR was performed in a room-temperature high-energy ball mill, using a mechanical alloying method. Whereas the glass transition temperature of the obtained glassy alloy is 681 K, the melting and liquidus temperatures are 1179 K and 1256 K, respectively. The mechanically alloyed Zr60Ni25Al15 glassy powders maintain its unique disordered structure through a large supercooled liquid region (99 K). It, however, transforms into a mixture of Zr5Ni4Al and Zr6NiAl2 crystalline phases at 780 K with a large enthalpy change of crystallization of -81.8 J/g. The possibility of devitrification of the synthetic glassy phase upon increasing the ball milling time was investigated. The results have shown that the glassy powder obtained after 173 ks of milling is subject to heavy lattice imperfections and tends to transform into a metastable-big cube phase after further ball milling times (216-259 ks). After 446 ks of milling, a complete glassy-metastable phase transformation is achieved and the end-product of this stage of milling is nanocrystalline big-cube powders which have a lattice constant of 1.2282 nm. The big-cube Zr(60)Ni(25)A(15) phase transforms into the same crystalline mixture of Zr5Ni4Al and Zr6NiAl2 phases at 799 K with an enthalpy change of transformation of -73.7 J/g. As the milling time increases (720 ks), the obtained big-cube phase can no longer withstand against the shear and impact stresses that are generated by the milling media and surprisingly transformed into a new metastable phase of nanocrystalline fcc- Zr60Ni25Al15. The lattice constant of this metastable phase was calculated and found to be 0.45449 nm. The fcc-metastable phase transforms into a mixture of Zr5Ni4Al and Zr6NiAl2 crystalline phases at rather a high temperature, as high as 901 K with a heat change of transformation of -24.4 J/g. The reported metastable phase here is new and has never been, so far as we know, reported for ternary Zr-Ni-Al system, or its binary phase relations. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Mechanical alloying using a high-energy ball milling technique was used to fabricate a single glassy phase of Zr70Pd20Ni10 alloy powders after 100 h milling time. Annealing the glassy powders at a temperature just below the crystallization onset temperature led to thermally enhanced devitrification and the formation of a metastable big-cube phase with a lattice constant of 1.2289 nm. The same metastable phase was obtained upon subjecting the end product of the glassy powders to further ball milling time (150 h). This metastable big-cube phase could no longer withstand the shear and impact stresses generated by the milling media and transformed into a new metastable phase of face-centered cubic Zr70Pd20Ni10. The lattice constant of this metastable phase was calculated to be 0.56838 nm. These metastable phases are new and have never been, so far as we know, reported for the ternary Zr-Pd-Ni system or its binary phase,relations.

Nanoquasicrystallization in Zr-based glassy alloys was investigated. It is found that the nano scale icosahedral quasicrystalline phase (I-phase) is formed by addition of the elements, which obstruct the glass-forming ability (GFA) in the glassy alloy. The primary phase of fee Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 glassy alloy with high GFA changes to the fcc Zr2Ni plus I-phases by substitution of noble metals or Zr for only 1 at% Cu. Since each phase is precipitated independently and the icosahedral local atomic configuration exits in the fee Zr2Ni and I-phases, they are originated from the same local structure in the Zr-based glassy alloy with high GFA. We found that the icosahedral local structure is strongly correlated with the stability of the supercooled liquid state. The origin of the icosahedral local structure is combination of Zr + Cu and Zr + Al + Ni elements. In these alloy systems, the I-phase is easy to precipitate as a primary phase by addition of a very small amount of appropriate element. From the present results, it is concluded that the icosahedral local structure stabilizes the supercooled liquid state. We suggest that the high GFA for the preparation of bulk glassy alloy is attributed to the stability of icosahedral local structure.

The structure and primary crystallization process of the melt-spun Cu-60 (Zr or Hf)(30)Ti-10 alloys were investigated. Compositional segregation in the diameter range of 5-10 nm was observed in the as-quenched state. In the high-resolution transmission electron microscopy images, nanocrystalline particles are observed in the glassy matrix, the size of which corresponds to the scale of compositional segregation. The glassy region has comparatively high Zr or Hf and Ti contents. In contrast, the Cu element is enriched in the nanocrystalline phases. The nanocrystalline phases are identified as the cubic structure with a lattice constant of approximately 0.5 nm. These results are recognized as the formation of novel structure consisting of the glassy and nanocrystalline phases. It is suggested that the precipitation of body-centred-cubic CuZr phase as a primary crystallization phase proceeds in the glassy phase, the nanocrystalline phase remaining in the Cu-Zr-Ti alloy. Meanwhile, the glassy and nanocrystalline phases are transformed to an orthorhombic Cu8Hf3 phase in the initial crystallization stage in the Cu-Hf-Ti alloy.

A nanoscale icosahedral quasicrystalline phase formation was found by the slight deviation from the three-component rule for high glass-forming ability in a Zr65Al7.5Ni10Cu17.5 glassy alloy. Since the primary phase consists of fcc Zr2Ni and I-phases in the Zr65Al7.5Ni10Cu16.5(Ag, Pd, Au or Pt)1 glassy alloys, where an icosahedron is contained in both the phases, it is suggested that the local icosahedral atomic configuration exists in the glassy state and it stabilizes the supercooled liquid state. We also clarified that an I-phase precipitates in the Zr70Cu29Pd1 and Zr70Ni20Al9Pd1 glassy alloys and no I-phase formation is observed in the Zr70Ni29Pd1 amorphous alloy. Since the supercooled liquid region is confirmed in the Zr70Cu30 and Zr70Ni20Al10 glassy alloys and is not observed in the Zr70Ni30 amorphous alloy, it is concluded that the stability of the supercooled liquid state is strongly correlated with the existence of the local icosahedral order. © 2002 Elsevier Science Ltd. All rights reserved.

It was found that a nano icosahedral phase with a diameter less than 20 nm is formed as a primary crystalline phase in the melt-spun Zr70Pd30 and Zr80Pt20 binary amorphous alloys. The nano icosahedral phase is also formed in the as-quenched state in the Zr80Pt20 binary alloy by controlling the quenching rate. A slight redistribution of approximately 3 at% is observed during the quasicrystallization in the Zr70Pd30 alloy. In contrast, no significant compositional change between the nano icosahedral and residual amorphous phases is observed in the Zr80Pt20 alloy. The icosahedral medium-range order in the diameter range less than approximately 3 nm is observed in the high-resolution electron micrograph of the Zr70Pd30 amorphous alloy. It is suggested that the icosahedral quasicrystalline phase grows with assimilating the icosahedral medium-range order due to a slight redistribution of constitutional elements during quasicrystallization. The formation of the nano icosahedral phase in the Zr70Pd30 and Zr80Pt20 binary alloys seems to be attributed to the existence of the icosahedral medium-range order in the amorphous and/or liquid states. © 2002 Elsevier Science B.V.

We investigated the stability of the supercooled liquid in Zr-based glassy alloys by examination of their transformation behavior. The primary phase is an fee Zr2Ni phase in a Zr65Al7.5Ni10Cu17.5 glassy alloy with high glass-forming ability (GFA). By substitution of Ag, Pd, Au or Pt for only 1 at%Cu, an icosahedral quasicrystalline phase (I-phase) precipitates with the fee Zr2Ni phase. The primary phase changes to the single I-phase at higher noble metal contents. It is further found that the I-phase precipitates by a small amount of substitution for Cu with other elements as well as the noble metals, which have a weak or positive chemical affinity with one of the constitutional elements in the Zr-Al-Ni-Cu glassy alloy. Thus, the slight deviation from the three component rules for high GFA is effective for the I-phase formation. The I-phase is also formed as a primary phase in the Zr65+yAl7.5Ni10Cu17.5-y (y = 1-7) glassy alloys. A slight change in the composition has the similar effect as the addition of element such as noble metals and so on. An icosahedron is contained as a structure unit in the fee Zr2Ni and I-phases and hence the glassy structure is correlated with the local icosahedral atomic configuration. The high-resolution transmission electron microscopy image of the Zr70Al7.5Ni10Cu12.5 glassy alloy reveals a possibility of the existence of the icosahedral ordered regions. It is therefore, concluded that the icosahedral short- or medium-range order exists in the supercooled liquid as well as in the glassy phase and it stabilizes the supercooled liquid state in the Zr-based alloys. An I-phase also precipitates as a primary phase by substituting Pd, Au or Pt for only 1 at%Cu in the Zr70Cu30 glassy alloy. From these results, the appearance of the supercooled liquid region is attributed to the existence of the icosahedral atomic configuration consisting of Zr and Cu.

The alloy Zr65Al7.5Ni10Cu7.3Fe0.2Ag 10 in the amorphous and icosahedral states, and the bulk amorphous alloy Zr65Al7.5Ni10Cu7.5Ag10, have been studied with 57Fe Mössbauer spectroscopy, electrical resistance and magnetoresistance, techniques. The average quadrupole splitting in both alloys decreases with temperature as T3/2. The average quadrupole splitting in the icosahedral alloy is the largest ever reported for a metallic system. The lattice vibrations of the Fe atoms in the amorphous and icosahedral alloys are well described by a simple Debye model, with the characteristic Mössbauer temperatures of 379(29) and 439(28) K, respectively. Amorphous alloys Zr65Al7.5Ni10Cu7.5Ag10 and Zr65Al7.5Ni10Cu7.3Fe0.2Ag 10 have been found to be superconducting with the transition temperature, Tc, of about 1.7 K. The magnitude of Tc and the critical field slope at Tc are in agreement with previous work on Zr-based amorphous superconductors, while the low-temperature normal state resistivity is larger than typical results for binary and ternary Zr-based alloys. The resistivity of icosahedral Zr65Al7.5Ni10Cu7.3Fe0.2Ag 10 is larger than that for the amorphous ribbon of the same composition, as inferred both from direct measurements on the ribbons and from the observed magnetoresistance. However the icosahedral sample is non-superconducting in the measurement range down to 1.5 K. The results for the resistivity and the superconducting Tc both suggest a stronger electronic disorder in the icosahedral phase than in the amorphous phase.

A single phase of glassy Zr 70Pd 30 binary alloy has been synthesized by solid-state reaction (SSR) and rapid-solidification (RS) techniques. The SSR was performed in a room temperature high-energy ball mill, employing mechanical alloying (MA) and mechanical disordering (MD) methods. A single roller melt-spinning method was performed for the RS. The results show that the mode of amorphization and subsequent crystallization of the obtained glassy materials strongly depends on the employed way of fabrication. In the MA method, post-annealing the mechanically deformed Zr/Pd multilayered composite powders at 723 K leads to the formation of a heterogeneous glassy phase (thermally enhanced glass formation reaction), which its heat formation was measured directly and found to be -2.16 kJ/mol. Further MA time (259 ks) was necessary to obtain a homogeneous glassy phase (mechanically induced glass formation reaction). In the MD method, however, the crystalline-glassy phase transformation is taking place through a single stage by introducing numerous lattice imperfections to the stable crystalline powders and this leads to raising of the free energy from the most stable phase (tetragonal-Zr 2Pd) to a less stable phase (glassy) that is obtained after 216-259 ks of MD time. The similarity in the crystallization behavior between the two classes of MA and MD glassy powders, implying the formation of the same glassy phase. In melt-spinning method, the solidification of the molten state occurs so rapidly that a small volume fraction of nano-icosahedral potential clusters are precipitated when the atoms are frozen in their liquid configuration. In contrast to the SSR glassy material powders, the crystallization of the RS-Zr 70Pd 30 ribbon proceeds through two separate exothermic reactions. The first reaction is owing to the short-or medium-range order transformation and the formation of metastable i-phase however, the second crystallization step refers to metastable-ordered phase transformation and formation of single tetragonal-Zr 2Pd material. We assume that if such clusters are formed during the MA and/or MD procedures, increasing the milling time can homogenize them. © 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

The quasicrystallization at the initial stage under viscous flow at 673 K (20 K above the glass transition temperature) was investigated in a Zr65Al7.5Ni10Cu12.5Pd5 bulk glassy alloy. The compressive deformation at strain rates of 2x10(-3) s(-1) and 1x10(-2) s(-1) was subjected to the bulk glassy alloy for 60 s followed by the preannealing for 120 s for thermal equilibration in an Ar atmosphere. The glass undergoes Newtonian and non-Newtonian flow at the strain rates of 2x10(-3) s(-1) and 1x10(-2) s(-1), respectively. The linear viscous flow brings a significant decrease in the first exothermic peak in the differential scanning calorimetry (DSC) curve corresponding to the transformation from glassy to icosahedral phase, but is identical to that in the reference sample annealed for 180 s at 673 K without deformation. However, the number of icosahedral particles in the transmission electron microscopy image as well as the decrease of the first exothermic peak in the DSC curve in the nonlinear viscous flow is much less as compared with those in the linearly deformed and reference samples. These results indicate the suppression of the transformation from the glassy to icosahedral phase by the nonlinear viscous flow. The suppression of the transformation is suggested to be originated from the retardation of the growth by the stress-induced disordered atomic configuration in the glassy state during the nonlinear viscous flow. (C) 2002 American Institute of Physics.

The evolution of specific heat of a Pd40Ni40P20 glassy alloy subjected to different degrees of non-Newtonian flow condition near the glass transition temperature, T-g, was investigated by a differential scanning calorimetry (DSC) method. Three exothermic relaxation spectrums were observed in temperature dependence of the specific heat. One of the relaxations in T &gt; 490 K (= T-g - 95 K) strongly depended on the flow condition, on the other hand, the others did weakly. This relaxation has previously been reported and is due to the long-range disordering between metal and metalloid constituents. Thus, appearance of the non-Newtonian viscous flow in this glassy alloy is associated with the disordering of the glass skeleton framed with Pd-P and Ni-P coupling by the strong shear action.

The amorphous-to-quasicrystalline phase transformation and the pressure effect on the transformation in a Zr66.7Pd33.3 metallic glass have been investigated by in situ x-ray diffraction measurements using synchrotron radiation. It is found that the transformation is a polymorphous reaction and external pressure enhances the onset temperature for the formation of quasicrystals with a rate of 22 K/GPa while the temperature interval for the stability of quasicrystals remains almost unchanged in the pressure range of 0-4 GPa. The enhancement of the onset temperature for the formation of quasicrystals has been further discussed with the nucleation theory. (C) 2002 American Institute of Physics.

The formation of an icosahedral quasicrystalline phase as a primary phase was found in Zr(65)Al(7.5)Ni(10)Cu(12.5)X(5) (X = V, Nb or Ta) glassy alloys. The icosahedral phase was precipitated during the first exothermic reaction in a two-stage crystallization process after a distinct glass transition. The diameters of the icosahedral particles are as small as 10-50 nm, similar to those found in Zr-based glassy alloys made with the addition of noble metals. Based on a Johnson-Mehl-Avrami analysis, we suggest that nano-quasicrystallization proceeds by a diffusion-controlled growth mode. The icosahedral phase in the Zr(65)Al(7.5)Ni(10)Cu(17.5-x)Ta(x) (x = 0-4) glassy alloys was formed at a Ta concentration of as little as 1 at.%, the primary crystallization phases were the fcc Zr(2)Ni and icosahedral phases. For Ta concentrations above 3 at.%, a nearly single icosahedral phase was formed as the primary phase. The formation of a nano-scale icosahedral phase in Zr-Al-Ni-Cu glassy alloys with the addition of V, Nb or Ta, as well as noble metals, indicates that an increasing nucleation rate contributes to the precipitation of the icosahedral phase, leading to the concept that icosahedral short- or medium-range order exists in the glassy state of the Zr-Al-Ni-Cu alloy. (C) 2002 Elsevier Science B.V. All rights reserved.

We investigated the transformation behavior of glassy phase in the Zr(65+x)Al(7.5)Ni(10)Cu(17.5-x) (x = 0-9) alloys with low oxygen concentrations below 500 mass ppm. In the initial crystallization stage, metastable fcc Zr(2)Ni, Zr(2)Cu and Zr(6)NiAl(2) phases are precipitated in the alloy where x = 0. A weak diffraction peak corresponding to an icosahedral phase is found in addition to the mixture phases of fcc Zr(2)Ni, Zr(2)Cu and Zr(6)NiAl(2) in alloys with x = 1 and 2. The primary phase changes to the single icosahedral phase in the range of x = 3-6 and a bcc Zr phase is precipitated above x = 7. The icosahedral particles have a dendritic morphology with a grain diameter ranging from 500 to 2000 nm for the Zr(70)Al(7.5)Ni(10)Cu(12.5) glassy alloy. A slight concentration redistribution leading to the enrichment of Zr and the rejection of Ni in the icosahedral phase is confirmed. The nucleation rate of the icosahedral phase at the crystallization temperature is calculated to be 1.5 x 10(14) m(-3) s(-1), which is 10(2) times lower than that of the fcc Zr,Ni phase. It is suggested that the formation of the icosahedral phase with such a low nucleation rate is attributed to the existence of icosahedral clusters in the glassy state, and the high grain growth rate of the icosahedral phase is due to the slight redistribution of constituent elements during quasicrystallization. (C) 2002 Elsevier Science B.V. All rights reserved.

Glassy Zr(70)Pd(30) and Zr(80)Pt(20) alloys were prepared by melt spinning. Icosahedral-like local atomic configurations were identified in these alloys by ordinary and anomalous X-ray scattering measurements. In the case of Zr(70)Pd(30) alloy, the total coordination numbers (N) around Zr and Pd in the nearest neighboring region were 11.3 and 8.9, respectively, which implies the existence of an icosahedral-like local atomic structure around Zr. On the other hand, the glassy Zr(80)Pt(20) alloy shows a pronounced pre-peak in its X-ray scattering intensity profile, indicating strong chemical short-range-ordered clusters. The N values around Zr and Pt are both 11.1, and close to 12.0. Furthermore, the atomic distances of Zr-Zr and Pt-Pt are almost the same. Thus, icosahedral-like local atomic structures with strong correlations are already formed both around Zr and Pt. The stronger chemical affinity of the Zr-Pt pair over the Zr-Pd pair seems to contribute to the stabilization of the quasicrystalline phase through the rigid icosahedral clusters. (C) 2002 Elsevier Science B.V. All rights reserved.

We investigated the stability of the glassy state by examination of transformation behaviour and structural analysis in Zr-based binary and ternary glassy alloys. It is well known that the melt-spun Zr-Cu binary alloys have a distinct glass transition prior to crystallization in a wide composition region of 20 to 70 at% Cu, while no supercooled liquid state appears in the melt-spun Zr-Ni binary alloys. It is expected that the local structure of the disordered state in the two alloy systems is different. The icosahedral quasicrystalline phase (I-phase) is formed as a primary phase in the Zr70Cu30 binary glassy alloy by substitution of Pd for Cu. The minimum Pd concentration for I-phase formation is 0.5 at%. In contrast, the primary phase is a tetragonal Zr2Ni phase in a Zr70Ni30 amorphous alloy by substitution of Pd by less than 10 at% for the Ni element. The radial distribution function (RDF) of the Zr70Cu30 glassy alloy is different from that of the Zr70Ni30 amorphous alloy. The coordination numbers around Zr in the melt-spun Zr70(Cu or Ni)30 binary alloys are 12.4 and 10.7, respectively, indicating the possibility of existence of the icosahedral local atomic configuration in the Zr70Cu30 glassy alloy. It is also realized that a tetragonal Zr2Ni-like local atomic configuration is formed in the Zr70Ni30 amorphous alloy. Considering that the I-phase is also formed in the Zr60Ni25Al15 glassy alloy by addition of 3 at% Pd, where the distinct glass transition is observed, the appearance of the supercooled liquid region is attributed to the existence of the icosahedral local atomic configurations consisting of Zr-Cu or Zr-Ni-Al. These results show that the icosahedral short- and medium-range orders exist in the supercooled liquid as well as in the glassy phase and they stabilize the glassy state in the Zr-based alloys.

The transformation behavior from glassy state was investigated in Zr- and Hf-based glassy alloys. The primary phases are metastable face-centered-cubic (fcc) Zr2Ni and fee Hf2Ni phases in the Zr65Al7.5Ni10Cu17.5 and Hf65Al7.5Ni10Cu17.5 glassy alloys, respectively. By substitution of 5 at.% Pd for Cu, the primary phase changes to an icosahedral quasicrystalline phase in both alloys. It is found that the addition of elements, which have a positive or weak chemical affinity with one of the constitutional elements in the Zr-Al-Ni-Cu and Hf-Al-Ni-Cu glassy alloys, is effective for the precipitation of the icosahedral phase. It is suggested that Pd plays a dominant role in an increase in the number of nucleation sites. Since an icosahedron is contained as a structure unit in the icosahedral, fee Zr2Ni and fee Hf2Ni phases, it is implied that these phases are correlated with the local icosahedral order. The high-resolution transmission electron microscopy images of the as-spun Zr65Al7.5Ni10Cu7.5Pd10 and Hf65Al7.5Ni10Cu12.5Pd5 alloys reveal a possibility of the existence of the icosahedral ordered regions. It is therefore, concluded that the icosahedral short- or medium-range order exists and it stabilizes the glassy state in the Zr- and Hf-based multicomponent alloys.

The local atomic structures in glassy, supercooled liquid and quasicrystalline phases for a Zr70Pd30 binary alloy have been examined by the x-ray diffraction method. It was found that the local atomic structure in the glassy phase can be identified as the distorted icosahedral-like structure around Zr and remains almost unchanged by the phase transformation into the supercooled liquid. In the formation process of the icosahedral phase, approximately one Zr atom substitutes with one Pd atom in this local structure. This kind of atomic rearrangement may improve the perfectibility of the as-quenched icosahedral-like cluster, leading to the phase evolution of the icosahedral phase.

It is found that a nanoicosahedral phase in the diameter less than 20 nm is formed as a primary crystalline phase in the melt-spun Zr70Pd30 and Zr80Pt20 binary amorphous alloys. The nanoicosahedral phase is also formed in the as-quenched state in the Zr80Pt20 binary alloy by controlling the quenching rate. The slight redistribution of approximately 3 at % is observed during the quasicrystallization in the Zr70Pd30 alloy. In contrast, no significant compositional change between the nanoicosahedral and residual amorphous phases is observed in the Zr80Pt20 alloy. It is suggested that the precipitation of nanoicosahedral phase in the Zr70Pd30 alloy takes place by a diffusion-controlled growth mode accompanying an increase in nucleation rate. The activation energy for grain growth is calculated to be 270 kJ mol(-1), which implies the growth of icosahedral phase without a long-range atomic redistribution. The icosahedral medium-range order in the diameter range less than similar to2 nm is observed in the high-resolution electron micrographs of the melt-spun Zr70Pd30 and Zr80Pt20 amorphous alloys. It is realized that the icosahedral quasicrystalline phase can grow easily with assimilating the icosahedral medium-range order due to a slight redistribution of constitutional elements during quasicrystallization. The formation of the nanoicosahedral phase in the Zr70Pd30 and Zr80Pt20 binary alloys appears to be attributed to the existence of the icosahedral medium-range order in the amorphous and/or liquid states. (C) 2001 American Institute of Physics.

A nano icosahedral quasicrystalline phase was confirmed as the primary precipitation phase in the melt-spun Zr65Al7.5Ni10Ag17.5 quaternary glassy alloy with a two-stage crystallization process, The onset temperature of the first exothermic peak is 704 K at a heating rate of 0.67 Ks(-1), Although no significant X-ray diffraction peaks were observed in the sample annealed at 705 K, we confirmed the formation of the icosahedral phase by nano beam electron diffraction using FE-TEM. The icosahedral particles have an extremely fine grain size in the diameter range of 2 to 4 nm. In addition to the icosahedral phase, the nano crystalline particles corresponding to Zr2Ag and/or fcc-Zr2Ni structures are also observed in the annealed sample. The second exothermic peak denotes the transition from the nano icosahedral to the crystalline phase of Zr2Ag, fcc-Zr2Ni and Zr4Al3. The formation of the nano icosahedral phase as the primary phase is due to a high nucleation rate and strongly implies the existence of an icosahedral short-range order in the glassy state.

We investigated the transformation behavior from gassy to icosahedral and/or fcc Zr2Ni phases in the Zr65Al7.5Ni10Cu17.5-xPdx (x = 0 to 4) glassy alloy,, with low oxygen contents of less than 400 ppm mass%. The primary phase is a metastable single fcc Zr2Ni phase in the x = 0 alloy and a single icosahedral quasicrystal line phase in the 2 to 4 at%Pd alloys. The mixture phase of icosahedral and fcc Zr2Ni precipitates at the initial crystallization stage in the x = I alloy. It is therefore confirmed that the icosahedral phase is formed by the addition of 1 at% Pd to the Zr-Al-Ni-Cu glassy alloy. The icosahedral and Zr2Ni particles have grain sizes in the diameter range of 500 to 1000 nm and arc in an isolated state for (lie sample annealed at a temperature near the crystallization temperature. A significant redistribution leading to the enrichment of Zr in the icosahedral phase is confirmed. Moreover, it is recognized that Ni and Cu are rejected from the icosahedral phase. We also observed the enrichment of Zr and Ni and the rejection of Cu in the Zr2Ni phase, No significant difference in Al content is observed among the icosahedral, Zr2Ni and residual glassy phases. The Pd content in the icosahedral phase is the same as that in the Zr2Ni phase. The difference of Zr, Ni and Cu contents among the icosahedral, Zr2Ni and remaining glassy phases is in the range of 2 to 9 at%. No significant difference in the Pd content is observed between the icosahedral and Zr2Ni phases. Considering that the diameter of the primary phase decreases significantly with increasing Pd content, it is suggested that Pd plays a dominant role in the increase in the number of nucleation sites of the icosahedral phase. Moreover, it is strongly suggested that the icosahedral phase originates from the icosahedral short-range order with an increase of nucleation rate as a result of the addition of noble metal.

The glass-to-icosahedral phase transformation in Zr70Pd20Ni10 and Zr65Al7.5Cu7.5Ni10Ag10 glasses was examined by the electrical resistivity measurement performed with a heating rate of 0.67 K/s. The resistivity increased with the promotion of icosahedral precipitation in Zr70Pd20Ni10 glass. On the other hand, Zr65Al7.5Cu7.5Ni10Ag10 glass exhibited the decrement of the resistivity according to the evolution of icosahedral phase. The latter was qualitatively explained by the drop of the resistivity of supercooled liquid phase due to the transfer of oxide atoms into the icosahedral phase. Also, the low temperature resistivity experiment showed that the conductivity of glassy and icosahedral phases might obey the weak localization model of conduction electrons. (C) 2001 American Institute of Physics.

The evolution of specific heat near the glass transition temperature, Tg, of a Zr55Al10Ni5Cu30 glassy alloy subjected to different degrees of non-Newtonian flow conditions was investigated. At conditions in which non-Newtonian flow begins, a gradual exothermic relaxation near Tg was observed. This is attributed to the change in configuration of the long-range liquid structure of the alloy. At conditions in which a high degree of non-Newtonian flow is favored, the alloy exhibits both high-temperature and low-temperature relaxation due to a change in local short-range order. The enthalpy of relaxation is found to scale as the logarithm of the normalized viscosity and is interpreted in terms of the free volume model of viscous flow. The decrease in viscosity in the non-Newtonian flow region is associated with a highly disordered structure and induced free volume. © 2001 American Institute of Physics.

The medium-range order in the Zr70Pd30 binary glassy alloy, where the nanoicosahedral phase precipitates as a primary phase, was examined using the high-resolution electron microscopic technique. The ordered region in the diameter of similar to2 nm was observed in the as-quenched glassy state. This region grows slightly to the diameter of 3-4 nm by annealing for 120 s at 690 K, where the amorphous structure remains. The nanobeam electron diffraction pattern taken from the medium-range order shows the fivefold symmetry, indicating that this region has the icosahedral structure. This result is recognized as a direct evidence for the existence of the icosahedral cluster in the alloy. For further annealing for 600 s at 690 K, the icosahedral quasicrystalline phase in the diameter of 5-8 nm precipitates by assimilating the icosahedral cluster. The formation of the nanoicosahedral phase originates from the existence of the quenched-in icosahedral clusters in the glassy state followed by their easy growth to the icosahedral particle without significant rearrangement of the constitutional elements. (C) 2001 American Institute of Physics.

We investigated the transformation behavior at the initial crystallization stage in the Zr-Al-Ni-Cu-Mo glassy alloy. In the Zr65Al7.5Ni10Cu12.5Mo5 alloy, the crystallization reaction changes to two reactions and the first reaction corresponds to the nanoscale fee Zr2Ni phase formation. The two-stage crystallization reaction is also observed in the Zr65Al7.5Ni5Cu17.5Mo5 alloy, where the primary phase is the nanoscale icosahedral quasicrystalline phase. The difference in the primary phase between the two alloys is attributed to the difference in the chemical affinities of Mo with Cu and Ni. The formation of nanoscale icosahedral and fcc Zr2Ni phases leads to the hypothesis that the icosahedral short-range order exists in the glassy state of the Zr-Al-Ni-Cu alloy as a unit structure in both phases.

Structural change with quenching rate in the Zr80Pt20 alloy was studied by controlling the roll speed in the melt-spinning technique. The as-quenched ribbon had an amorphous structure at a roll speed of 50 ms(-1). An icosahedral quasicrystalline phase was directly formed at a roll speed in the range of 40 to 30 ms(-1). The critical roll speed for the formation of the icosahedral phase was 25 ms(-1), where the volume fraction of the icosahedral phase was very small. Several crystalline phases precipitated in the melt-spun ribbon at roll speeds below 20ms(-1). The DSC curve of the sample prepared at 50 ms(-1) clearly exhibited two exothermic peaks. The first exothermic peak at 717 K, corresponded to the transformation from the amorphous to the icosahedral phase and the second peak was due to the decomposition reaction of the icosahedral phase. The size of the icosahedral phase in the as-quenched and annealed samples lay in the diameter range of 5 to 20 nm and the particles were distributed homogeneously. Thus, it was clarified that the nano icosahedral phase can be formed in the as-quenched state from the melt and in the annealed state from the amorphous phase in the Zr80Pt20 binary alloy. The icosahedral phase transformed to Zr, ZrPt, Zr9Pt11 and Zr5Pt3 phases at a temperature of approximately 900 K. The formation of the nano scale icosahedral phase indicated the possibility that icosahedral short-range order exists in the melted state of the Zr-Pt binary alloy. The strong chemical affinity between Zr and Pt probably contributed to the stabilization of the icosahedral short-range order and restraining the long-range rearrangement of constitutional elements to form a stable crystalline phase, which is an important factor in the formation of an icosahedral phase.

The phase transition by crystallization and a grain growth behavior of a Zr65 Cu27.5Al7.5 metallic glass were examined as a function of isothermal annealing time at various temperatures. At the initial stage of crystallization, a metastable Zr(Al,Cu) phase is observed, in addition to a main phase of Zr2Cu, below the annealing temperature of 730 K. The formation of Zr(Al, Cu) may be attributed to the strong chemical affinity between Al and Zr. The grain growth rate for Zr2 Cu is extremely low comparing with that for a Zr65Cu35 binary metallic glass. Therefore, the strong chemical affinity between Al and Zr seems to contribute to the retardation of nucleation and grain growth of the crystalline phases. The grain growth kinetics can be described by log(dD/dtg) = log(k/3) - 2 log D where D is the measured grain size, tg the grain growth time and k the constant. The activation energy Q for grain growth is calculated to be 165 kJ mol-1. © 2001 Elsevier Science B.V. All rights reserved.

This paper is intended to investigate the effect of additional solute elements on the glass-forming ability by studying the crystallization processes of Cu40Ti30Ni15Zr10Sn5 and Zr60Ni25Al15 amorphous alloys in the supercooled liquid region. The crystallization of Cu40Ti30Ni15Zr10Sn5 amorphous alloy takes place through the reactions of Am → CuTi + Cu10Zr7 → Cu10Zr7 + Cu3Ti + CuTi2 + Cu2Ti. Enrichment of Sn in the Cu10Zr7 phase was revealed by compositional analysis. On the other hand, the crystallization of Zr60Ni25Al15 amorphous alloy takes place through the reaction of Am → Zr5Ni4Al + Zr6NiAl2. The common feature in the crystallization processes of the two alloys is the necessity of significant redistribution of the solute elements (Sn or Al), which is believed to play an important role in the stability of the supercooled liquid against crystallization. © 2001 Elsevier Science B.V. All rights reserved.

The formation of an icosahedral phase is found as a primary phase in the Zr-Ni-M (M = Pd, Au, Pt), Zr-TM-Pd (TM = Fe, Co, Cu), Zr-Pt-Pd and Zr-Au-Pd ternary glassy alloys. The icosahedral particle has a nearly spherical morphology and grain size in the diameter range below 50 nm. The precipitation of the nano icosahedral phase from the glassy phase implies the existence of an icosahedral atomic configuration. The icosahedral atomic configuration is presumably stabilized by the mixed structure with two strong chemical affinities of two Zr-M pairs or Zr-M and Zr-Ni atomic pairs, which contributes to the restraint of long-range atomic rearrangements.

The microstructure and mechanical properties of Zr-based bulk glassy alloys containing nanoscale quasicrystalline particles were analyzed. The bulk glassy alloys were in a cylindrical form with diameters of 3 to 4 mm which were produced using coppler mold casting method. Glassy alloy ribbons were also produced using melt spinning.

The primary precipitation phase for the Hf62Al10Ni8Cu20 metallic glass is face centered cubic (FCC)-Hf2Ni and those for Hf57Al10Ni8Cu20Ti5 are FCC-Hf2Ni and I-phase. Addition of Ti to the Hf62Al10Ni8Cu20 alloy is essential for the formation of I-phase. Retardation of the precipitation of FCC-Hf2Ni in Hf62Al10Ni8Cu20 is considered as one of the reasons for the formation of I-phase caused by the addition of Ti. This effect is explained by considering the size mismatch between the constitute elements.

The local atomic structures around Pt as well as Zr in amorphous and quasicrystalline Zr70Al6Ni10Pt14 are determined anomalous X-ray scattering (AXS) method. Their distinctive structural features are clarified to find a clue to the mechanism of formation of the quasicrystalline phase. A ribbon sample 0.3 nm thick and 1 mm wide is produced by melt-spinning from the alloy which is prepared by arc melting a mixture of pure metals in an argon atmosphere.

The local structures around Pt and Zr atoms have been measured by EXAFS method for amorphous and quasicrystalline Zr70Ni10Al6Pt14, Zr70Ni10Pt20 and Zr80Pt20 alloys. Main coordinate atoms around Pt atom in quasicrystalline ZrPt-based alloys are Zr. Although, Pt-Zr correlation peak of quasicrystal is narrower than amorphous for Zr70Ni10Al6Pt14, while that of quasicrystal is comparable to amorphous for Zr70Ni10Pt20. The Zr-Ni correlations of Zr70Ni10R20 alloy for quasicrystal and amorphous also are similar to each other. Therefore it is expected that the chemical short range order similar to the quasicrystal is formed in the amorphous phase. The local structure around Pt atom for Zr70Ni10Al6Pt14 alloy is similar to that for Zr,A. alloy and different from that for Zr70Ni10Pt20 alloy. In the case of Zr70Ni10Al6Pt14, Ni atoms are expelled from quasicrystalline phase and condense in amorphous phase around quasicrystal with Al atom is also suggested.

We investigated the transformation behavior from glassy to Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5, glassy alloy with a low oxygen content below 400 ppm mass%. The mostly single face centered cubic Zr2Ni phase precipitated as a primary phase at the initial crystallization stage. The Zr2Ni particles had a cubical morphology in the diameter range of 300 to 500 nm and were in an isolated state for the sample annealed at the temperature near crystallization temperature. A significant redistribution leading to the enrichment of Zr and Ni into the Zr2Ni phase is confirmed. Moreover, it is recognized that Cu and Al are rejected from the Zr2Ni phase. The compositional differences of Zr, Al, Ni, and Cu between the Zr2Ni and remaining glassy phases are in the range of 1.5 to 5 at.%. It is strongly suggested that such a significant redistribution of the constitutional elements restrains the nucleation and growth of crystalline phases. It is one of the important factors for the stabilization of the glassy state in Zr-Al-Ni-Cu alloy.

It is found that a single icosahedral quasicrystalline phase is formed as a primary precipitation phase in the melt-spun Zr70Pd30 binary glassy alloy with a two-stage crystallization process. The onset temperature of the transformation from the amorphous to the icosahedral phase is 701 K at the heating rate of 0.67 K s(1). The size of the icosahedral particles lies in the diameter range below 10 nm and the particles are distributed homogeneously. The second-stage crystallization reaction results in the formation of a Zr2Pd phase through a single exothermic reaction. The formation of the nanoscale icosahedral phase indicates the possibility that icosahedral short-range order exists in the Zr-Pd binary glassy state. Comparison with the thermal stability of an icosahedral phase in the Zr-Ni-Pd system shows that the icosahedral phase is stabilized by the addition of Ni. The stabilization is due to the restraint of the long-range rearrangement of the constitutional elements resulting from the strong chemical affinity between Zr and Ni.

It is found that an icosahedral quasicrystalline phase is formed in the Zr-Al-Ni-Cu glassy alloy by addition of Nb, Ta or V elements. The icosahedral phase was confirmed as a primary precipitation phase in the melt-spun Zr65Al7.5Ni10Cu12.5X5 (X=Nb Ta or V) glassy alloys with a two-stage crystallization process after the distinct glass transition. The onset temperature of the transformation from glass to icosahedral phase is 705 K fur Nb, 710 K for Ta and 702 K for V at the heating rate of 0.67 Ks(-1). The size of the icosahedral particles is in the range of 10 to 50 nm. The second crystallization reaction results in the formation of Zr2Cu + Zr2Ni + Zr3Al2 phases through a sharp exothermic reaction. The formation of a nano scale icosahedral phase in the Zr-Al-Ni-Cu glassy alloy by addition of Nb, Ta or V, as well as noble metals, indicates that the increase of the nucleation rate contributes to the precipitation of the icosahedral phase, leading to the concept that the icosahedral short-range order exists in the glassy state in the Zr-Al-Ni-Cu alloy.

An icosahedral phase was found to be formed as a primary precipitation phase in the crystallization process of binary Zr70Pd30, ternary Zr70Ni30-xPdx and Zr70Cu30-xPdx (x = 10 and 20 at.%) and quaternary Zr70Ni10Cu10Pd10 amorphous alloys. The maximum volume fraction of the icosahedral phase was nearly 100% for the 20% Pd alloys and the grain size tended to decrease in the range from 40 to 70 nm with increasing Pd content. No icosahedral phase was formed in the Zr-Ni-Cu alloys without Pd, and hence, the addition of Pd was concluded to be essential for the formation of the icosahedral phase in the Zr-based amorphous alloys. It also was noticed that the icosahedral phase was formed even in the binary Zr70Pd30 amorphous alloy. The icosahedral phase was in a metastable state and changes to equilibrium crystalline phases by annealing in the higher temperature range. The finding of the formation of the icosahedral phase in the binary alloy system allowed us to predict the future appearance of a number of icosahedral base alloys in other alloy systems.

We examined the nucleation and growth behavior of a nano icosahedral phase from a supercooled liquid region in the Zr65Al7.5Ni10Cu7.5M10 (M=Ag or Pd) glassy alloys by differential scanning calorimetry and transmission electron microscopy. It is found that the growth rate of the icosahedral phase is nearly constant at the initial stage and much slower than that of the Zr2Ni phase in the Zr65Al7.5Ni10CU17.5 glassy alloy. The maximum homogeneous nucleation rate of the icosahedral phase in the Zr65Al7.5Ni10CU7.5Ag10 glass is calculated as 4.4x10(20) m(-3)s(-1) at 695 K, which is approximately 10(4) times higher than that of the Zr2Ni phase in the Zr65Al7.5Ni10CU17.5 glass. The nucleation rate of the primary phase increases significantly and the growth rate at the crystallization temperature decreases with increasing Pd content. Thus, the addition of Ag and Pd is effective for the increase of the number of nucleation sites and the suppression of grain growth, which is the main reason for the formation of icosahedral nano particles. It is, therefore strongly suggested that an icosahedral short-range order exists in the glassy stale of the present alloys.

A nano icosahedral quasicrystalline phase was confirmed as a primary precipitation phase in the melt-spun Zr70Ni10M20 (M=Pd, Au and Pt) ternary glassy alloys. It is clarified that the precipitation of the icosahedral phase takes place by a diffusion-controlled growth mode with increasing nucleation rate. The formation of the nano scale icosahedral phase also indicates the existence of short-range order correlated with an icosahedral structure in the glassy state.

The alloys Zr65Al7.5Ni10Cu7.3Fe0.2Ag10 in the amorphous and icosahedral state have been studied with Fe-57 Mossbauer spectroscopy in the temperature range 77-300 K. The average quadrupole splitting decreases with temperature as T-3/2 and is significantly larger for the icosahedral alloy. The quadrupole splitting in the icosahedral alloy is the largest ever reported for a metallic system. The vibrations of the Fe atoms in both alloys are well described by a simple Debye model.

The effect of pressure on the formation of quasicrystals and the amorphous-to-quasicrystalline phase transformation kinetics in the supercooled liquid region for a (formula presented) metallic glass have been investigated by in situ high-pressure and high-temperature nonisothermal and isothermal x-ray powder diffraction measurements using synchrotron radiation, respectively. It is found that with increasing pressure, the onset temperature for the formation of quasicrystals increases with a slope of 9.4 K/GPa while the temperature interval of the stability and the average grain size of quasicrystals decrease. Atomic mobility is important for the formation of quasicrystals from the metallic glass whereas the relationship of the crystallization temperature vs pressure for the transition from the quasicrystalline state to intermetallic compounds may mainly depend on the thermodynamic potential energy barrier. To study the amorphous-to-quasicrystalline phase transformation kinetics in the metallic glass, relative volume fractions of the transferred quasicrystalline phase as a function of annealing time, obtained at 663, 673, 683, and 693 K, have been analyzed in details using 14 nucleation and growth models together with the Johnson-Mehl-Avrami model. The Avrami exponent was found to be near 1 at all four temperatures, also indicating that atomic diffusion might involve in the amorphous-to-quasicrystalline phase transformation for the (formula presented) metallic glass. It is found that the time-dependent transient nucleation is essential for the transformation and different nucleation and growth models have been critically assessed. © 2001 The American Physical Society.

The formation of a nanoicosahedral phase in the diameter range below 20 nm from the melt-spun Zr70Pd70 binary glassy alloy was confirmed, and the kinetics of the precipitation upon isothermal annealing in the supercooled liquid region was examined by differential scanning calorimetry. Based on the kinetic analysis, it is clarified that the precipitation in the supercooled liquid region takes place by a diffusion-controlled growth with increasing nucleation rate. The Arrhenius plot between effective time lag, tau, of nucleation and isothermal annealing temperature yields a single linear relation, in which the activation energy for nucleation is evaluated to be 267 kJ mol(-1). The activation energy in the present alloy is much lower than that of the Zr65Al7.5Ni10Cu7.5Pd10 alloy, which is due to the difference in the magnitude as well as the number of atoms for the rearrangements in the nucleation stage. It is concluded that the formation of a nanoscale icosahedral quasicrystalline phase is attributed to the transformation mode of an increase of nucleation rate, which is different from that of Zr65Al7.5Ni10Cu7.5Ag10 quasicrystal arising from an interfacial controlled growth with a steady-state nucleation rate. The formation of a nanoicosahedral phase in the Zr70Pd30 binary glassy alloy implies the existence of the icosahedral short-range order in the glassy state. (C) 2000 American Institute of Physics. [S0021-8979(00)00624-1].

The nucleation and growth of a nano-icosahedral phase from a supercooled liquid region of Zr65Al7.5Ni10Cu7.5M10 (M = Ag Or Pd) glasses have been examined by differential scanning calorimetry and transmission electron microscopy. The growth rate of the icosahedral phase is nearly constant at the initial stage and much slower than that of the Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 metallic glass. The homogeneous nucleation rate has a maximum value of 4.4 x 10(20) m(-3) s(-1) at 695 K in the Zr65Al7.5Ni10Cu7.5Ag10 glass, which is approximately 10(2) times higher than that for the formation of quasicrystalline phase in the Zr69.5Al7.5Ni11Cu12 glass and 10(4) times higher than that of the Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 glass. With increasing Pd content, the nucleation rate of the primary phase increases significantly and the growth rate decreases at the crystallization temperature. Thus, the addition of Ag and Pd is effective for an increase in the number of nucleation sites and the suppression of grain growth, which is the main reason for the formation of icosahedral nanoparticles. The significant increase in the nucleation rate is due to an increase in the number of nucleation sites resulting from the short-range ordering consisting of Zr-(Ag or Pd) strong pairs. It is implied that the strong pair Zr-(Ag or Pd) also contributes to the restraint of the long-range rearrangements of the constitutional elements. The formation of the nanoicosahedral phase suggests that icosahedral short-range order exists in the glassy state in the present alloys.

The crystallization processes of (Zr0.64Ni0.36)(100-x)Al-x (x = 5, 7.5 and 10) and (Zr0.64Ni0.36-0.0xCu0.0x)(95)Al-5 (x = 0, 6, 10, 13 and 16) metallic glasses were studied by using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). For the (Zr0.64Ni0.36)(100-x)Al-x (x = 5 and 7.5) and (Zr0.64Ni0.36-Cu-0.0x(0.0x))(95)Al-5 (x = 0, 6, 10 and 13) alloys, crystallization proceeds through double-stage exothermic reactions. The first exothermic reaction corresponds to the precipitation of a metastable face-centered cubic Zr2Ni (F-Zr2Ni). For the (Zr0.64Ni0.36)100-Al-x(x) (x = 10) and (Zr0.64Ni0.36-0.0xCu0.0x)(95)Al-5 (x = 16) alloys, crystallization proceeds through a single-stage exothermic reaction, corresponding to the precipitation of stable crystalline phases. Accompanying the above changes in crystallization mode, the supercooled liquid region DeltaT(x), defined as the temperature interval between the glass transition temperature T-g and the crystallization temperature T-x, increases from 39 K for (Zr0.64Ni0.36)(95)Al-5 to 64 K for the (Zr0.64Ni0.36)(90)Al-10 in (Zr0.64Ni0.36)(100-x)Al-x (x = 5, 7.5 and 10) alloy series, and from 39 K for (Zr0.64Ni0.36)(95)Al-5 to 70K for (Zr0.64Ni0.20Cu0.16)(95)Al-5 in the (Zr0.64Ni0.36-0.0xCu0.0x)(95)Al-5 (x = 0, 6, 10, 13 and 16) alloy series. The reason for the stabilization of the supercooled liquid state at higher Al concentrations in the (Zr0.64Ni0.36)(100-x)Al-x (x = 5, 7 5 and 10) alloy series and at higher Cu concentrations in the (Zr0.64Ni0.36-0.0xCu0.0x)(95)Al-5 (x = 0, 6, 10, 13 and 16) alloy series is discussed.

We examined the nucleation and grain growth kinetics of a nano icosahedral phase formed as a primary phase in the Zr65Al7.5Ni10Cu17.5-xPdx (x = 5, 10 and 17.5) glassy alloys by differential scanning calorimetry and transmission electron microscopy. The nano icosahedral grains are distributed homogeneously, indicating the homogeneous nucleation mode. The grain growth rate of the icosahedral phase is nearly constant at the initial stage and much lower than that of the cubic Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 glassy alloy. The growth rate decreases with increasing Pd content. It is (4.5+/-0.4) x 10(-9) m s(-1) at x = 5 and decreases to (8.3+/-0.8) x 10(-10) ms(-1) at x = 17.5. The homogeneous nucleation rate at crystallization temperature, T-x, changes drastically with Pd content, and is (1.1 +/- 0.3) x 10(20) m(-3) s(-1) in the Zr65Al7.5Ni10Cu7.5Pd10 glass, which is approximately 10(2) times higher than that in the Zr(65)A(17.5)Ni(10)Cu(12.5)Pd(5) glass and 10(4) times higher than that of the Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 glass. Thus, it is clarified that with increasing the Pd content, the nucleation rate of the primary phase increases significantly and its growth rate decreases. The addition of Pd is effective for the increase in the number of nucleation sites and the suppression of grain growth. The formation of the nano icosahedral phase by the addition of Pd implies the existence of icosahedral short-range order in the glassy state of the Zr-Al-Ni-Cu alloy.

The crystallization process of a Hf59Ni8Cu20Al10Ti3 metallic glass was studied using differential scanning calorimetry (DSC), X-ray diffraction and transmission electron microscopy. Two exothermic peaks are observed in the DSC curve of the as-quenched sample. It was revealed that the two reactions correspond to the phase transformations amorphous --&gt; icosahedral phase + fee phase and icosahedral phase + fcc phase --&gt; Hf2Cu + Al16Hf6Ni7 + Hf3Al2, where a = 0.254nm for the icosahedral phase and a = 0.53nm for the fee phase. Nanobeam electron diffraction patterns corresponding to the fivefold, threefold and twofold symmetries of a quasicrystal were obtained, revealing that the quasicrystal is an icosahedral phase. It is suggested that the present report on a Hf-based icosahedral phase is helpful for understanding the structural relationship between amorphous and icosahedral phases.

The grain growth kinetics of a Zr2Cu crystalline phase in a supercooled liquid region of Zr65Cu27.5Al7.5 and Zr65Cu35 metallic glasses was examined at different temperatures. For this purpose, the grain size calculated from a half value width of the X-ray diffraction peak by Scherrer's formula was used. Results emphasize the importance of the difference in the grain growth mechanism to stabilize the glassy state.

It is found that an icosahedral quasicrystalline phase is directly formed in a Zr80Pt20 binary alloy during rapid solidification from the melt. The size of the icosahedral particles lies in the diameter range below 10 nm, and the particles are distributed homogeneously. The formation of the nanoscale icosahedral phase indicates that the icosahedral short-range order exists in the melted state of Zr-Pt binary alloy. The strong chemical affinity between Zr and Pt contributes to the restraint of the long-range rearrangement of constitutional elements to form a stable crystalline phase, which is the important factor of the stabilization of an icosahedral phase. (C) 2000 American Institute of Physics. [S0003-6951(00)05027-0].

An icosahedral quasicrystalline phase was found in a Hf65Al7.5Ni10Cu12.5Pd5 metallic glass annealed in the supercooled liquid region. Upon annealing at high temperature, the quasicrystalline phase was found to decompose to regular crystalline phases, indicating that it is a metastable phase. The present alloy was compared with the previously reported Zr- and Ti-based alloys with the formation of icosahedral quasicrystalline phases. Hf, Zr, and Ti belong to the same 4A column in the element periodical table. Based on the above comparison, conditions in terms of atomic radius and alloy composition which favor the formation of icosahedral quasicrystalline phase in 4A element based alloys, were suggested. (C) 2000 American Institute of Physics. [S0003-6951(00)04530-7].

The grain growth behavior of a Zr2Cu crystalline phase from a supercooled liquid region of Zr65Cu27.5Al7.5 and Zr65Cu35 metallic glasses was examined as a function of annealing time, ta at various temperatures. Since no distinct change of constitution and strain in Zr2Cu phase is seen, the grain size calculated from a line-broadening of X-ray diffraction peak by Scherrer's formula can be used. The calculated grain size is in agreement with that obtained by transmission electron microscopy observation. The curve of grain size with ta is parabolic. The grain growth in Zr65Cu35 takes place at lower temperature and its rate is extremely larger as compared with those of Zr65Cu27.5Al7.5. These differences are originated from the suppression of growth of Zr2Cy by Al atom, which retards the diffusion of Cu owing to the primary precipitation of ZrAl in Zr65Cu27.5Al7.5. The formation of ZrAl may be attributed to the strong chemical affinity between Al and Zr. The activation energies for grain growth of 115 kJ mol-1 for Zr65Cu27.5Al7.5 and 363 kJ mol-1 for Zr65Cu35 are obtained by the Arrhenius plot of grain growth rate against a reciprocal of temperature. These activation energies reflect the kind and/or magnitude of diffusion atoms during the grain growth.

An icosahedral quasicrystalline phase was confirmed as a primary precipitation phase in melt-spun Zr70Ni10M20 (M=Pd, Au and Pt) ternary metallic glasses with two-stage crystallization process. The onset temperature of the transformation from amorphous to icosahedral phase are 687 K for Pd, 754 K for Au and 783 K for Pt at a heating rate of 0.67 K s(-1). The size of the icosahedral particles is in the range of 5-20 nm. The second crystallization reaction results in the formation of Zr2Ni+Zr2Pd and Zr2Ni+ZrPt phases in the Zr-Ni-Pd and Zr-Ni-Pt alloys, respectively, and Zr3Au phase in the Zr-Ni-Au alloy through a single exothermic reaction. The formation of nanoscale icosahedral phase indicates the possibility that icosahedral short-range order exists in the glassy state. (C) 2000 American Institute of Physics. [S0003-6951(00)00524-6].

A nanoscale icosahedral quasicrystalline phase was confirmed as a primary precipitation phase in the melt-spun Zr70TM10Pd20 (TM = Fe, Co, or Cu) ternary glassy alloys with a two-stage crystallization process. The onset temperature of the transformation from amorphous to icosahedral phase is 713 K for Fe-, 696 K for Co-, and 680 K for Cu-containing alloys at the heating rate of 0.67 Ks(-1). The size of the icosahedral particles is in the range of 20 to 50 nm for the Zr70Cu10Pd20 glassy alloy annealed for 120 s at 720 K. The icosahedral phase has a very fine particle size in a diameter range below 10 nm for the Zr70Fe10Pd20 and Zr70Co10Pd20 alloys. The crystallization reaction after the first exothermic peak results in the transition from the icosahedral to crystalline phases through a sharp exothermic reaction. Thus, the formation of the nanoscale icosahedral phase indicates the possibility that an icosahedral short-range order exists in the present glassy alloys.

This paper reports the crystallization process of Zr60Ni25Al15 amorphous alloy studied by using differential scanning calorimetry (DSC), analytical transmission electron microscopy (ATEM) and X-ray diffraction (XRD). The crystallization of Zr60Ni25Al15 amorphous alloy proceeds through an eutectic reaction, corresponding to the precipitation of Zr6NiAl2 and Zr5Ni4Al phases. The following reasons are addressed to the large glass-forming ability (GFA) of Zr60Ni25Al15: (a) the significant atomic redistribution of Al and Ni in the dense random packed atomic configuration and (b) the strict elemental limitation for a determined crystal site in the precipitation of Zr6NiAl2 and Zr5Ni4Al. (C) 2000 Elsevier Science B.V. All rights reserved.

It was found that an icosahedral quasicrystalline phase was formed as a primary precipitation phase from the supercooled liquid region of the melt-spun Zr70Fe20Ni10 ternary metallic glass. The precipitation of an icosahedral phase takes place at 673 K at the heating rate of 0.67 K s(-1). The precipitated icosahedral particle has a nearly spherical morphology and a fine grain size in the diameter range of 5-10 nm. The second crystallization reaction proceeds through a broad exothermic peak and results in the formation of Zr2Ni and Zr2Fe phases. The formation of nanoscale icosahedral phase by the addition of Fe as well as noble metals such as Pd, Au, and Pt indicates the possibility of existence of an icosahedral short-range order in the various Zr-based metallic glasses. (C) 2000 American Institute of Physics. [S0003-6951(00)02921-1].

An icosahedral quasicrystalline phase was found to precipitate as primary crystal in the melt-spun Zr70Pd20Ni10 ternary amorphous phase with two-stage crystallization processes. The onset temperature of the transformation from amorphous to icosahedral phase is 687 K, and the decomposition of the icosahedral phase to crystalline phases takes place at 778 K, at a heating rate of 0.67 K/s. The icosahedral phase has a nearly spherical shape with a size of 5 to 20 nm. The second-stage crystallization reaction results in the precipitation of Zr2Pd and Zr2Ni phases.

An icosahedral (I) phase was found to be formed as a metastable phase in the crystallization process of amorphous Zr65Al7.5Ni10M17.5 (M = Pd, An or Pt) alloys. The three amorphous alloys show an endothermic reaction due to the glass transition, followed by two exothermic peaks. The first exothermic peak is due to the precipitation of an I-phase and the second one results from the transition from the I to crystalline mixed phases of Zr4Al3 + Zr2Ni + Zr2Pd (Zr2Au or ZrPt). The I-phase consists of fine grains with a size of about 10 nm and no distinct residual amorphous phase is seen. The formation of the I-phase in the new Zr-based alloy systems with a large supercooled liquid region and high glass-forming ability is important for the future development of bulk quasicrystalline alloys as basic science and engineering materials.

The transformation and grain growth behaviour of an icosahedral phase from the supercooled liquid region of rapidly quenched Zr65Cu7.5Al7.5Ni10Ag10 metallic glass have been examined by transmission electron microscopy. The precipitation of the icosahedral phase proceeds according to a polymorphic reaction without any concentration change. The grain size increases linearly with an increase in annealing time and the growth rate strongly depends on the temperature. An Arrhenius plot of the logarithm of growth rate versus the reciprocal of annealing temperature yields a linear relationship, from which an activation energy for grain growth of 409 kJ mol(-1) is obtained. This activation energy is much higher than those in the AI-Cu-V and Al-Mn-Si systems. This activation energy is attributed to the strong bonding among constitutional elements and the necessity of the rearrangement of atoms on a long length scale for grain growth. The kinetic data suggest that the icosahedral phase is stabilized by the difficulty of rearrangement of atoms.

It was recently found that the addition of special elements leading to the deviation from the three empirical rules for the achievement of high glass-forming ability causes new mixed structures consisting of the amorphous phase containing nanoscale compound or quasicrystal particles in Zr-Al-Ni-Cu-M (M = Ag, Pd, Au, Pt or Nb) bulk alloys prepared by the copper mold casting and squeeze casting methods. In addition, the mechanical strength and ductility of the nonequilibrium phase bulk alloys are significantly improved by the formation of the nanostructures as compared with the corresponding amorphous single phase alloys. The composition ranges, formation factors, preparation processes, unique microstructures and improved mechanical properties of the nanocrystalline and nanoquasicrystalline Zr-based bulk alloys are reviewed on the basis of our recent results reported over the last two years. The success of synthesizing the novel nonequilibrium, high-strength bulk alloys with good mechanical properties is significant for the future progress of basic science and engineering. (C) 2000 Published by Elsevier Science Ltd.

Recently, a new bulk amorphous system Cu40Ti30Ni15Zr10Sn5 has been reported. The glass transition temperature Tg is 735 K and the crystallization temperatures are 780 K (Tx1) and 816 K (Tx2), respectively. The phase transition of the Cu40Ti30Ni15Zr10Sn5 amorphous alloy annealed at 735 (Tg), 758 (Tg+Tx1)/2, 780 (Tx1), 900 and 1000 K, respectively, was studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and high-resolution analytical electron microscopy (HRATEM). The crystallization of the alloy proceeds by the process Am (amorphous state) →CuTi+Cu10Zr7→Cu3Ti+Cu2Ti+CuTi2 +Cu10Zr7. Two exothermic peaks are observed in the DSC curve of the as-quenched sample, corresponding to the reactions of Am→CuTi+Cu10Zr7 and CuTi+Cu10Zr7→Cu3Ti+CuTi2+Cu2 Ti+Cu10Zr7, respectively. During the first-stage of crystallization, a significant redistribution of Zr and Sn was recognized by a composition analysis with energy dispersive X-ray spectroscopy (EDS), implying that the phase transition is controlled mainly by the rearrangement of the solute elements Zr and Sn. The necessity of this long-range rearrangement of Zr and Sn in the first-stage of crystallization seems to be one of the reasons for the high stability of the supercooled liquid in the present alloy system.

Direct real time observation of nucleation and crystallisation in Zr-based bulk metallic glasses using high intensity high energy monochromatic synchrotron beam in transmission has been extended from the initial Zr55Cu30Al10Ni5 to alloys containing either titanium or a higher Zr content. Previously, it was established that crystallisation of the amorphous phase occurs via initial nucleation and growth of metastable phases that transform to equilibrium tetragonal Zr2Cu before melting. However, no trace of nucleation of the metastable phase was obtained during cooling of the liquid alloy from above liquidus temperature T-1 and Zr2Cu forms directly from the liquid. The metastable crystalline nanostructure obtained during rapid heating was found to depend sensitively on the alloy composition. Ti addition suppresses the previously detected metastable state and leads to a new phase with structure close to that of tetragonal Zr2Ni phase but with a highly stressed nanostructure. On the other hand, increasing the Zr content to nealy 70 at.% allows easy preparation of the metastable state during heating.

The formation of an icosahedral phase from the rapidly quenched Zr65Cu7.5Al7.5Ni10Ag10 metallic glass was confirmed and the kinetics of the precipitation upon isothermal annealing in the supercooled liquid region were examined by differential scanning calorimetry. Based on the kinetic analysis, it is clarified that the precipitation in the supercooled liquid region takes place by an interfacial controlled growth with a nearly steady-state nucleation rate. The Arrhenius plot between effective time lag, tau, of nucleation and isothermal annealing temperature yields a single linear relation, in which the activation energy for nucleation is evaluated to be 366 kJ/mol. It is concluded that the transformation of amorphous to quasicrystal proceeds by a homogeneous nucleation mode, which is different from those of Pd-U-Si and Al-Cu-V quasicrystals arising from an inhomogeneous distribution of quenched-in nuclei. (C) 1999 American Institute of Physics. [S0003-6951(99)04948-7].

An icosahedral quasicrystalline phase was found to precipitate as a primary phase from the supercooled liquid in the Zr65Al7.5Ni10Cu17.5-xPdx (x = 5 and 10 at%) amorphous alloys. No icosahedral phase is formed for the present Zr65Al7.5Ni10Cu17.5 alloy and hence the addition of Pd promotes the precipitation of the icosahedral phase. The volume fraction of the icosahedral phase increases with increasing Pd content and exceeds 90% for the 10%Pd alloy. The icosahedral phase changes to Zr2Cu+Zr2Ni+Zr2Al3 phases with further increasing annealing temperature. The icosahedral phase consists of fine grains with a size of about 35 nm and has a disordered (P-type) structure. Bulk amorphous alloys were produced in the diameter range up to 4 mm at 5%Pd and 2 mm at 10%Pd by copper mold casting. The icosahedral base alloys obtained by annealing the bulk amorphous phase exhibit improved mechanical properties. The Young's modulus, compressive yield strength, compressive fracture strength and fracture elongation including elastic elongation of the bulk 10%Pd alloy are 85 GPa, 1510 MPa, 1640 MPa and 2.2%, respectively, in the as-cast amorphous state and increase to 88 GPa, 1780 MPa, 1830 MPa and 3.1%, respectively, for the icosahedral base state obtained by annealing for 60 s at 705 K. The success of synthesizing the high-strength bulk alloys consisting mainly of icosahedral phase is promising for the future development of a new class of high-strength quasicrystalline material.

Icosahedral (I) particles with spherical morphology were found to appear as a primary precipitation phase in amorphous Zr65Al7.5Ni10Cu12.5M5 (M = Ag, Pd, Au or Pt) alloys with two-stage crystallization process. The element M was selected with the aim of deviating the three empirical rules for stabilization of supercooled liquid, i.e., multicomponent of more than three elements, atomic size mismatch over 12%, and negative enthalpy of mixing. The I phase in an amorphous matrix has a small size of 25 to 40 nm. The second crystallization reaction results in the formation of Zr2Cu, Zr2Ni and Zr2Al3 phases for the alloys containing Ag, Pd or Au, and Zr2Cu, Zr2Ni, Zr2Al3 and ZrPt phases for the Pt-containing alloy. The Zr65Al7.5Ni10Cu17.5 amorphous alloy crystallizes directly to a mixed structure of Zr,Ni, Zr2Cu, Zr2Al3 and ZrNi phases through a single exothermic reaction. The addition of the element M is essential for the precipitation of the metastable I phase. The reason is that the structure changes from a long-range homogeneous configuration to an inhomogeneous one by the addition of the element M.

The phase transformation by crystallization of a Zr65Cu27.5Al7.5 metallic glass was examined as a function of annealing temperature, T-a. The crystallization temperature decreases gradually by annealing at the temperature over 20 K than glass transition temperature, T-g. At the initial stage of crystallization, Zr(Al, Cu) phase is observed in addition to a main phase of Zr2Cu. Thus, the Zr65Cu27.5Al7.5 metallic glass crystallizes through a eutectoid-like reaction of the two phases. The Zr(Al, Cu) phase is a metastable phase and disappears in the higher T-a range. The formation of metastable Zr(Al, Cu) may be attributed to the difficulty of diffusion of Al into Zr2Cu and the strong chemical affinity between Al and Zr. The strong chemical affinity between Al and Zr seems to contribute to the retardation of nucleation and grain growth of the crystalline phases. The lattice spacing of Zr2Cu increases with deconvolution of metastable Zr(Al, Cu) and hence Al atom is thought to be substituted with Cu atom in Zr2Cu. The grain size of Zr2Cu increases significantly accompanied by the disappearance of metastable Zr(Al, Cu). After the completion of crystallization, a part of supersaturated Al precipitates as the Zr2Al phase from the Zr-2(Cu, Al) phase at annealing temperatures above approximately 860 K, accompanying a reduction of lattice spacing and a significant grain growth of Zr2Cu. Thus, Al affects significantly the structure change through the crystallization. It is therefore concluded that the necessity of long-range redistribution of Al during the crystallization process plays a dominant role in the stabilization of supercooled liquid and the degradation of grain growth reaction.

Mechanical alloying of elemental niobium and aluminum was carried out in Argon for 180 ks to produce a nanocrystalline intermetallic compound Nb3Al. The detailed analysis of XRD shows that the as-MAed product has the volume distribution of 13% Nb (4 nm), 40% Nb2Al (4 nm) and 47% Nb3Al (3.8 nm). This three-phase mixture was converted into a two-phase mixture of 19 vol.% Nb2Al and 81 vol.% Nb3Al upon heating to 873 K for 3.6 ks, the resultant grain sizes being 4.7 nm. Isochronal annealing from 873 to 1423 K revealed that a significant grain growth occurs above 1173 K to approximately 33 nm at the maximum temperature. At the respective temperatures isothermal annealing was carried out for 3.6, 7.2 and 14.3 ks to deduce the grain growth kinetics that can be described by In (dD/dt)=ln (k/8)-7 In (D) where D is the measured grain size and k a constant, implying that the kinetics is of a high order (D to the 8th). This k is related to temperature T as k=k(0) exp (-Q/RT) where Q is the activation energy for grain growth and R the gas constant. The Arrhenius plots of In [(D-8-D-0(8))/t] versus 1/T yield two distinct slopes, from which the activation energies of 166+/-5.2 and 118+/-3.5 kJ/mol for the grain growth of Nb3Al and Nb2Al are obtained at temperatures higher than 1173 K and below this temperature they are 74.4+/-4.4 and 59.6+/-1 kJ/mol respectively. But the kinetic order remains the same regardless of temperature and phase.

Amorphous (Fe, Co, Ni)-B binary and ternary alloy particles of diameter 20-50 nm can be prepared by chemical reduction using KBH4 as a reduction agent. In the Fe-B binary system, the structure and chemical concentration of particles depend on the mixing molar ratio of KBH4 to Fe2+ ions M(R). The structure is amorphous for M(R) greater-than-or-equal-to 0.0 and with decreasing M(R) a crystalline a-phase is precipitated in an amorphous matrix. The B concentration in the amorphous phase is about 33 at.% for M(R) greater-than-or-equal-to 9.0 and about 25 at.% for M(R) less-than-or-equal-to 8.0. The amorphous alloy particles in (Fe, Ni, Co)-B binary and ternary systems are consolidated to a cylindrical shape at various temperatures. The structure of hot-pressed compacts is amorphous for pressing temperatures below the crystallization temperature T(x). These crystalline phases are confirmed to have a nanometer-scale structure. It is concluded that these particles should form a fully dense amorphous bulk or a crystalline bulk consisting of nanometer-scale mixed phase.

Amorphous ultra-fine particles have been prepared in the systems of Fe-B and Fe-M-B (M: transition metal) by a chemical reduction method using KBH4 in aqueous solution. The chemical composition of the Fe-B particles depends on the molar ratio, M(R), of KBH4 to Fe2+ ions on mixing. X-ray diffraction patterns show that for M(R) &lt; 9.0 the particles contain a crystalline phase that corresponds to a boron concentration of &lt; 30 at.%. The particles have an amorphous structure for values of M(R) &gt; 9.0. The results of Mossbauer measurements show that the particles consist of an amorphous phase, Fe3+ oxide and alpha-Fe for M(R) &lt; 10.0 and of an amorphous phase and Fe3+ oxide for M(R) greater-than-or-equal-to 10.0. It is also confirmed that the distribution of hyperfine magnetic field, P(B(hf)), changes with M(R).

Mossbauer spectroscopy was applied for the structure analysis of chemically synthesized Fe-B and Fe-M-B (M = Co, Ni) particles using KBH4 as a reducing agent. The structure of Fe-B particles depends on the mixing molar ratio of KBH4 to Fe2+ ions, M(R). The particles consist of amorphous Fe-B alloys and Fe3+ oxides for M(R) greater-than-or-equal-to 10.0, while amorphous Fe-B alloys, Fe 3 + oxides and the alpha-phase for M(R) &lt; 10.0. The distribution of magnetic hyperfine field P(B(hf)) also changes with M(R). The average value of B(hf) changes discontinuously around M(R) = 10.0. The substitution of Fe by Ni atoms has a drastic effect on the Mossbauer parameters, indicating the change of the hyperfine field.

Amorphous ultrafine powders in (Fe, Co, Ni)-B binary systems were prepared in different reduction conditions of metal ions in an aqueous solution by use of KBH4, with the aim of clarifying the effect of reaction conditions on the composition, thermal stability, and magnetic properties of the resultant amorphous powders. As the mol ratio of KBH4 to metal ions decreases, the structure of the ultrafine powders changes from amorphous to crystalline phase. The morphology of these powders is in a nearly spherical shape with a particle size of about 20 nm for the amorphous phase and changes to the chain-like or net-like shape for the crystalline phase. The B content in the Fe-B amorphous powder decreases with a decrease of the ratio of KBH4 to metal ions, and the powder size decreases with an increase of the reduction temperature.

Ultra-fine amorphous powders in (Fe, Co, Ni)-B binary and ternary systems were produced by the chemical reduction method. The powders have a spherical shape with diameters ranging from 5 to 50 nm. The reaction consists mainly of the process of producing Me2B and Me(Me = Fe, Co, Ni). Fully dense bulks of the ultra-fine amorphous (Fe, Co, Ni)-B powders were prepared by hot-pressing at temperatures below the crystallization temperature. Their densities are almost equal to those of the corresponding arc-melted powders. The hardness values of the hot-pressed compacts are considerably lower than those of the melt-spun amorphous ribbons with the same compositions.

The chemical composition of ultrafine amorphous Fe-B powders prepared by a chemical reduction depends on the mixed molar ratio of KBH4 to Fe ions. We propose the following reaction processes for the formation of ultrafine Fe-B powders: (1) 4Fe2+ + 2BH4- + 6 OH- --&gt; 2Fe2B+6H2O+H2 and (2) 4Fe2+ + 2BH4- + 7 OH- --&gt; 2Fe3B+Fe+BO2+5H2O+5/2H2.

Ultrafine amorphous (Fe, Co, Ni)-B powders have been prepared by a chemical reduction method. The influence of the Co and Ni atoms on the distribution of internal magnetic fields P(B(hf)) has been investigated. The quadrupole splitting distribution P(QS) of ultrafine amorphous Fe-Ni-B powders has a form similar to that derived for the dense random packing of atoms.