In the present work, an approach of freeze-dry pulsated orifice ejection method (FD-POEM) was utilized to fabricate monodispersed MoSiBTiC-La2O3 composite powders for laser powder bed fusion (L-PBF). The FD-POEM powders were spherically shaped, possessing a narrow size range and uniform element distribution. As revealed by the single-track and single-layer experiments, the porous FD-POEM particles were sufficiently fused under laser irradiation, leading to the generation of continuous laser tracks and low surface roughness layers, which proved a feasible L-PBF processability of MoSiBTiC-La2O3 powders. Careful microstructural observations confirmed that the microstructure of the molten pools was primarily composed of Mo solid solution dendrites reinforced with La2O3 nanoparticles. Consequently, the single MoSiBTiC-La2O3 track had a high Martens hardness of 3955 HM. The result of this work reveals that the combination of FD-POEM and L-PBF has a great potential of developing advanced heat-resistant Mo-based alloys with tailored structures for ultrahigh-temperature applications.

Poor understanding of composite powder properties is a bottleneck in the design of high-performance metallic components via laser powder bed fusion (L-PBF). Traditional particle- or fiber-like fillers are known to result in reduced powder flowability and the uncontrollable morphology of composite powders. In this work, we demonstrate a first example of improving the powder properties and L-PBF manufacturability of metallic powders decorated by two-dimensional (2D) nanofillers. 0.5 wt% graphene oxide (GO) sheets were uniformly adhered onto the surface of Ti–6Al–4V (Ti64) powders via an electrostatic self-assembly, with their spherical morphology and particle size uncompromised. The notably enhanced quality of the GO-decorated Ti64 (GO@Ti64) powder bed, indicated by the results of a novel centrifugal separation testing and a recoating experiment, was attributed to the significant reduction in powder/powder and powder/substrate adhesive forces. Moreover, while the thermal conductivity of the GO@Ti64 powders was found to decrease, the laser absorptivity increased as a result of multiple local absorptions of wrinkled GO. The optimal process zone of GO@Ti64 powders was therefore shown to have been extended and to have become wider, enhancing L-PBF printability. High-resolution transmission electron microscopy inspections revealed that the GO/Ti64 build fully consisted of ultrafine α’ martensite structures with a lath width of ∼91 nm. This novel structure was attributed to the high-temperature, nonequilibrium densification of L-PBF; the complete dissolution of the 2D GO nanosheets into the Ti64 matrix generated a novel carbon-supersaturated, precipitation-free structure. The grain refinement and solid-solution strengthening behaviors led to an increase in the yield strength of the GO/Ti64 build from 1375 MPa to 1793 MPa, and also an increase in its compressive strength, from 1796 MPa to 2032 MPa. The results of this investigation contribute to a better understanding of composite powder properties and can be seen as a significant step toward the preparation of high-performance metallic components via L-PBF.

In this work, commercial 316L stainless steel (SS) powder was used to experimentally determine the impacts of severe oxidation on the powder characteristics and laser powder bed fusion (L-PBF) melting behaviors. The morphology, surface state, and laser absorptivity of both virgin and oxidized powders were systematically characterized. Their impacts on the flowability and powder bed quality were monitored by custom-designed recoating experiments and powder shear tests. The results of an in situ wetting analysis and microstructure evaluation were compared to establish a correlation between the powder characteristics and laser fusion. The powder oxidation enhanced L-PBF processability by improving the homogeneity of powder spreading and the formation of stable, consecutive laser beads. A thin ceramic layer-coated SS alloy reinforced with uniform (Si, Mn)-based oxides was synthesized by the L-PBF processing of severely oxidized powders. The mechanical strength of this alloy was found to be similar to that processed using the virgin powders, whereas the elongation was slightly decreased, likely due to the amorphous oxide feature and the mechanical oxide-Fe interface. This study provides a systematic understanding of powder reuse and new insight into the potential for economically developing high-performance parts by the positive utilization of powder oxidation and the L-PBF process.

The densification process plays a critical role in determining the microstructure and performance of Ti matrix composites (TMCs). Herein, a comparative study was performed on a graphene oxide (GO)/Ti-6Al-4V composite fabricated by laser powder bed fusion (L-PBF) and spark plasma sintering (SPS). The flexible GO sheets were homogeneously decorated onto the Ti-6Al-4V powders via an electrostatic self-assembly without significantly changing the particle size or sphericity. Under high-energy laser irradiation, the GO sheets were completely dissolved into the matrix. The L-PBF-produced composite was composed of fine α’ martensite structures due to the rapid solidification and the solute carbon atoms. In contrast, the GO was reacted with Ti matrix and completely transformed into sub-micron TiC particles during SPS; the composite consisted of α ＋ β phases with randomly dispersed TiC. Moreover, the L-PBF-produced composite exhibited a higher hardness of 481 HV as compared with the SPS-produced one of 367 HV, attributing to the fine α’ microstructures and high residual stresses. The present work offers deep understanding on the structural evolution of GO during high-temperature densifications, and shows new insights for fabrication of high-performance TMCs with tailored microstructures.

Zirconium (Zr) alloys are conventionally used for protective tubes of nuclear fuel rods. On the other hand, a Zr-Nb alloy is used for artificial joints with an oxidized zirconium surface. For the last two decades, Zr alloys have been researched and developed for medical implants, because Zr belongs to the 4th group in the periodic table, the same as titanium (Ti), indicating that Zr shows a similar property of Ti. In addition, there is no evidence that Zr shows toxicity. In this review, first, the history and properties of Zr and Zr alloys are summarized. Then, Zr elements in the human body, roles of Zr as alloying elements to form Ti alloys, cobalt- chromium alloys and zinc are overviewed. On the other hand, Zr-base bulk metallic glasses are one candidate of corrosion resistant and nontoxic implant materials. Thereafter, magnetic resonance image (MRI) compatible Zr-based alloys, Zr-metallic glass, and surface treatments of Zr and Zr alloys, are explained. Zr-based crystalline alloys as well as metallic glass are predominant candidates to decease MRI artifact volume. Development of surface modification techniques must be studied to improve tissue compatibility and adding biofunction may be necessary. Zr and Zr alloys will be researched and developed continuously in the future.

To obtain an optimal powder bed condition for laser powder bed fusion (L-PBF), it is essential to clarify powder flow behaviors during the recoating process. In this work, the flow behaviors of Ti-6Al-4V powders were experimentally analyzed using a simple slope model by Particle image velocimetry (PIV) and were subsequently compared with the behaviors simulated using the similar model by discrete element method (DEM). The velocity of particles and the distribution were able to be obtained experimentally using PIV. In the DEM simulation, when the coefficient of restitution was increased, the angle between restituted particles and the slope and the average particle velocity were increased. Comparing those obtained by the DEM simulation, it was found that the velocity and distribution obtained by PIV analyses were close to those obtained by the DEM simulation at the coefficient of restitution of 0.3. These results suggest that the powder flow velocity analysis on the slope using PIV analyses is an effective method to validate the parameter of powder properties in DEM simulations.

It is very challenging to fabricate spherical refractory material powders for additive manufacturing (AM) because of their high melting points and complex compositions. In this study, a novel technique, freeze-dry pulsated orifice ejection method (FD-POEM), was developed to fabricate spherical MoSiBTiC particles without a melting process. Elemental nanopowders were dispersed in water to prepare a high-concentration slurry, which was subsequently extruded from an orifice by diaphragm vibration and frozen instantly in liquid nitrogen. After a freeze-drying process, spherical composite particles with arbitrary composition ratios were obtained. The FD-POEM particles had a narrow size range and uniform elemental distribution. Mesh structures were formed within the FD-POEM particles, which was attributed to the sublimation of ice crystals. Furthermore, owing to their spherical morphology, the FD-POEM particles had a low avalanche angle of 42.6 degrees, exhibiting good flowability. Consequently, the combination of FD-POEM and additive manufacturing has great potential for developing complex refractory components used in industrial applications.

Generally, high strength and high ductility are two mutually exclusive properties of engineering materials. Nacre exhibits high strength and toughness owing to the presence of intelligent brick-and-mortar architectures. The present study demonstrates the design of a bioinspired nacre-like Zr-1Mo alloy via an appropriate thermomechanical treatment. The α-Zr phases and the elongated β-Zr nanoparticles in the alloy functioned as the hard bricks and soft mortar, respectively. Consequently, the nacre-like Zr-1Mo alloy possesses a high potential for biomaterial applications owing to its unique combination of high tensile strength (~812–968 MPa), high ductility (~10.3–12.6%), and low magnetic susceptibility (~1.2–1.4 × 10 cm g ). This work provides new insights into the fabrication of bioinspired metallic materials with exceptionally high strength and ductility. −6 3 −1

Raw powders are processed in water during the freeze-dry pulsated orifice ejection method (FD-POEM), leading to the inclusion of oxygen impurities. This study proposes a strategy for removing the oxygen content and enhancing the mechanical performance of laser powder bed fusion (L-PBF) builds from powders using carbon nanotubes (CNTs) and H2 reduction. Spherical 1.5 wt.% CNT/Mo composite powders with uniform dispersion were fabricated via FD-POEM. The quantity of MoO2 decreased significantly, and a hexagonally structured Mo2C phase was simultaneously formed in the L-PBF build. The Mo2C with network structure was distributed along the boundaries of equiaxed Mo grains, leading to an increased Vickers hardness of the matrix. This study demonstrates the feasibility of fabricating oxygen-free and high-strength refractory parts during L-PBF for ultrahigh-temperature applications.

Novel TiC-reinforced titanium matrix composites (TMCs) were in situ synthesized by laser powder bed fusion (L-PBF) of unique carbon nanotube (CNT)-decorated Ti-6Al-4V powders. Acid-treated CNTs were coated on the surface of Ti-6Al-4V particles by electrostatic self-assembly without varying the powder sphericity, leading to improved printability, as proved by laser-absorption and single-track experiments. During L-PBF, the CNTs were completely transformed into monocrystalline TiC dispersed in the α’-Ti matrix via a dissolution/precipitation mechanism. As illustrated by high-resolution transmission electron microscopy, the in situ-synthesized TiC crystals were closely bonded to the matrix, exhibiting typical TiC [001]//Ti [00−1] and TiC (220)//Ti (−100) orientation relationships. Significantly, the morphology of TiC underwent an interesting evolution from nanorods to micro-spheres, and to dendrites with an increase in the CNT content, causing a gradual increase in hardness of TMCs. This study may provide insights into the design of high-performance TMCs with unique microstructures, excellent properties, and tailored architectures.

Hot isostatic pressing and subsequent heat treatment were performed to achieve defect-free and high-mechanical-performance Zr-1Mo components manufactured by laser powder bed fusion. The strong but brittle acicular α’ martensite phase was observed in the as-fabricated Zr-1Mo components, which transformed into a basketweave α + β microstructure after the HIP process and then transformed into a stress-relieved α phase after subsequent HT. Optical microscopy images and fracture observations revealed that the defects in the as-fabricated components were eliminated after the HIP process and did not regrow during subsequent HT. An ultimate tensile strength of 990 MPa, yield strength of 831 MPa, and elongation of 9.1% were achieved in the heat-treated Zr-1Mo components. The combination of HIP and subsequent HT could be a promising post-processing treatment for L-PBF-fabricated Zr-1Mo components.

In recent years, a low magnetic and fully dense Zr–1Mo (wt%) part was successfully manufactured via the laser powder bed fusion (L-PBF) process, which shows the great potential as metallic biomaterials under the magnetic resonance imaging (MRI) environment. However, due to the high cooling rate after laser incident during the L-PBF process, the as-fabricated Zr–1Mo part consists of a non-equilibrium α′ phase, which contributed to high strength (UTS: 1107 MPa) but insufficient ductility (elongation: 4.3%) for biomedical applications. In order to enhance the mechanical performance of as-fabricated Zr–1Mo parts, various annealing processes that have been recognized as an efficient post-treatment to adjust the mechanical performance of additive manufactured products were executed. After the annealing process, acicular martensite α’ microstructure in as-fabricated Zr–1Mo parts changed to stress relieved/partial relieved acicular α microstructure, basketweave α + β microstructure, lamellar α + β microstructure or retain α+ lamellar α + β microstructure depending on different annealing conditions. In the meantime, elongation increased with increasing holding temperature and residence time, but the tensile strength exhibits a converse trend. The specimens annealed at 873 K, 803 K for 2 h and at 773 K for 8 h possessed UTS of 779 MPa, 964 MPa and 981 MPa as well as elongation of 14.3%, 11.0% and 9.6%, respectively. These annealing conditions could contributed to adequate strength and sufficient ductility, and should be the appropriate annealing conditions for Zr–1Mo parts produced by the L-PBF technology. By comparison with other conventional metallic biomaterials, annealed Zr–1Mo alloy could be applied for the medical devices under MRI environments.

Simultaneously achieving homogeneous dispersion and appropriate interfacial adhesion is the foremost concern for designing high-performance carbon nanotube (CNT)/Al matrix composites. Herein, a strategy for surface modification was developed to fabricate uniform CNT/Al composites with enhanced interfacial strength. Small quantities of Al O nanoparticles were locally adhered to the surface of functionalized CNTs by electrostatic self-assembly, thereby promoting the adsorption of high concentrations of CNTs onto Al powders and hindering the agglomeration of CNTs. After densification, the CNTs retained their structural integrity and exhibited both individual distribution and unidirectional alignment in the matrix. As revealed by high-resolution transmission electron microscopy, the Al O nanoparticles promoted a large elastic buckling of the nanotube inner wall and formed a curved, stable contact with the CNTs, producing strong anchors at the CNT-Al interface. Consequently, the CNT-Al O /Al composites exhibited enhanced mechanical properties compared with the CNT/Al composites, while maintaining superior electrical conductivity. This work demonstrates the great potential of surface decoration in producing advanced CNT/metal composites in electrical applications. 2 3 2 3 2 3

In this study, Al matrix composites (AMCs) reinforced with few-layered MXene (FLM) were fabricated for the first time using self-assembly protocol and powder metallurgy. Individual FLM platelets, which decorated the grain boundaries without structural degradation, were singly incorporated into the Al matrix. The interfacial load transfer was considerably increased due to the generation of strong anchors at the FLM–Al interface via Al phase infiltration under densification. Consequently, the addition of 0.26 vol.% FLM considerably increased the composite strength by approximately 66%. This work demonstrated the effective application of MXene as a 2D reinforcement for AMCs towards high-specific-strength materials.

The low laser absorptivity and high thermal conductivity of Al are the foremost concerns when developing Al matrix composites (AMCs) through laser powder bed fusion (L-PBF) process. In this study, we demonstrated an example of improving the 3D-printability of AMCs by means of powder surface modification. Flexible graphene oxide (GO) sheets were carefully coated onto the surface of AlSi10Mg powders under electrostatic self-assembly via a hetero-agglomeration process. In addition to maintaining a shape and particle size similar to the initial metallic powders, the GO-coated AlSi10Mg powders exhibited enhanced laser absorptivity and decreased thermal conductivity, beneficial to their fusion. Under high-energy irradiation, the GO sheets were partially transformed to Al C nanorods individually distributed in the matrix, while the un-reacted parts floated within molten pools under buoyancy, forming an in-situ carbon layer tightly deposited on the surface of the composite build. This work may provide significant guidance for the design and production of high-performance AMCs with advanced architectures for practical applications. 4 3

Increased strength of Al matrix composites (AMCs) with a high electrical conductivity are in demand to replace copper conductors. In this study, a high-performance Al C /Al composite was synthesized in situ via the high-energy densification of uniform graphene oxide (GO)/Al powder combination; GO was completely transformed to monocrystalline Al C nanorod structures, robustly bridging across the Al grain boundary. The formation mechanism of interfacial Al C was illustrated by high-resolution transmission electron microscope observations. The Al C nanorods were homogeneously dispersed and possessed an intimate and faceted interface with the matrix, resulting in the enhanced tensile strength of Al. Moreover, the Al C /Al composite retained the required electrical conductivity similar to that of pure Al, in addition to the stable interface at elevated temperatures and long-term service reliability in moist environment. The findings of this study will be significant in providing the basis of designing novel heat-resistant AMCs in electrical applications. 4 3 4 3 4 3 4 3 4 3

To avoid the “susceptibility artifacts” in magnetic resonance imaging (MRI) and realize patient-specific medical devices with complicated shapes, a novel MRI compatible Zr-1Mo alloy with low porosity (c.a. 0.4%) were manufactured by laser powder bed fusion process(L-PBF) using gas-atomized Zr-1Mo(wt%) alloy powder. However, as-built Zr-1Mo(wt%) components using optimized process parameters show relatively high mechanical performance(elongation of 6.4%, UTS of 1175 MPa), but contain 0.4 vol% defects which show a spherical morphology and distribute in the builds randomly. These defects definitely deteriorate the mechanical performance(especially ductility, fatigue behavior) of Zr-1Mo components manufactured by L-PBF. In order to eliminate defects in as-built Zr-1Mo components, hot isostatic pressing(HIP), which has been known as an effective process to decrease the porosity of additive manufactured products, was executed. Due to the elevated temperature and high pressure during HIP treatment, the randomly distributed defects were eliminated after the HIP process. Moreover, the α-martensite structure in the as-built alloy was transformed into a basketweave α + β structure at low HIP temperature(1023 K and 1073 K) or lamellar α + β structure at relatively high HIP temperature(1173 K and 1273 K). In the meantime, the elongation of HIP-treated Zr-1Mo components significantly increased, but the strength shows the opposite trend. From the viewpoint of mechanical property, Zr-1Mo components HIP-treated at 1023 K possessed elongation of 19.9%, and UTS of 628 MPa should be optimized in this study. More importantly, porosity regrowth behavior was investigated to evaluate subsequent heat treatment feasibility for further improvement of mechanical performance. Due to intact raw material power as well as vacuum/low pressure inside the original defect caused by evaporation of metals, porosity regrowth can not be confirmed in HIP-treated Zr-1Mo components after subsequent heat treatment(holding temperature higher than the β transus of Zr-1Mo alloy). Therefore, further improvement of mechanical performance by subsequent heat treatment for HIP-treated Zr-1Mo components is very promising and should conduct further research in the future

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

© 2020 Elsevier Ltd In order to solve the artifact problem in magnetic resonance images, a low magnetic Zr–1Mo(wt%) alloy with high mechanical performance was successfully fabricated by laser powder bed fusion (L-PBF) using gas-atomized Zr–1Mo alloy powder. The as-built Zr–1Mo alloy showed superior strength and elongation compared to the as-cast Zr–1Mo alloy due to grain refinement and the inexistence of large casting defects. The microstructure of L-PBF-processed Zr–1Mo alloy builds was not sensitive to process parameters. On the other hand, morphology and distribution of defects, interstitials concentration, and crystallographic orientation comprehensively influenced the mechanical properties of the builds. Increasing interstitials concentration caused by increasing energy density render to increasing strength. Large pores caused by balling effect lead to a severe decrease of both strength and ductility of builds using high energy density (over 70.3 J·mm−3) and high scanning speed (1050/1200 mm·s−1). On the contrary, spherical pores possessing several microns in size has much less effect on mechanical properties than the large-size pores. There are two kinds of texture({1 1 0}α texture and {1 1 0}α+{1 0 2}α bi-texture) were confirmed in this study. {1 1 0}α texture contributed to the slight increase of elongation with increasing energy density in low scanning speed case (600/750 mm·s−1) and the superior elongation of low scanning speed specimens compare to that of high scanning speed specimens in medium energy density range (about 48 J·mm−3). From the viewpoints of the ultimate tensile strength(UTS) and elongation, it was found that an energy density of 84.4 mm·s−1 with a scanning speed of 600 mm·s−1 is preferable for the L-PBF-processed Zr–1Mo alloy in this study. These experimental results may provide direct guidelines regarding the applicability of Zr–1Mo alloy fabricated by L-PBF for biomedical applications.

A novel Mo-based composite with simultaneously improved mechanical and oxidation properties was fabricated by laser powder bed fusion (L-PBF), using uniform Al2O3 -nanoparticle-decorated MoTiAl powders bridged by functionalized carbon nanotubes. A tight ceramic coating similar to 2.57 mu m in thickness consisting of an alpha-Al2O3 matrix with dispersed TiC particles was formed on the surface of the Al2O3-CNT/MoTiAl composite, which has been proved to effectively increase resistance to oxidation at 1173 K. Meanwhile, the nanoparticles were homogenously dispersed and tightly contacted with the matrix, giving rise to an enhanced Vickers hardness. This work shed light on designing and producing high-performance Mo-based composites for application to ultrahigh-temperature materials. (C) 2019 Elsevier B.V. All rights reserved.

© 2018 The Authors In order to depress the “susceptibility artifacts” in magnetic resonance imaging (MRI), improve the mechanical reliability for biomedical structural applications and realize tailor-made medical devices with complex shape, low magnetic Zr-1Mo(wt%) alloy builds with high relative density (c.a. 99.9%) fabricated by laser powder bed fusion process(L-PBF) were subjected to various heat treatment conditions followed by water quenching. After quenching process acicular α′ microsturcture in as-build Zr-1Mo(wt%) alloy builds changed to basket weave α + β structure, unique retained α + ultra fine (α′ + α″) martensite structure or retained α + acicular α′ microsturcture depending on quenching conditions. X-ray diffraction (XRD) and high resolution-transmission electron microscope(HR-TEM) revealed a unique retained α + ultra fine (α′ + α″) martensite microstructure in 1123 K specimens. The stress-induced competition between β to α′ transformation and β to α″ transformation contributed to this unique microstructure. This unique microstructure contributed to a good balance between strength (UTS:822 MPa) and ductility (Elongation:11.7%). The volume magnetic susceptibility of quenched Zr-1Mo(wt%) alloy builds maintained low(about 1.01 × 10−4) indicating good MRI compatibility. The magnetic susceptibility of each phase was modified to be χα″ > χβ > χα > χα′ > χω. Zr-1Mo(wt%) alloy quenched from 1123 K will be an promising candidates for tailor made devices under MRI environments.

© 2019 The crystalline integrity of multi-walled carbon nanotubes (MWCNTs) plays a critical role in determining the performance of MWCNT/Al composites. In this work, the structural evolution of MWCNTs during composite consolidation was studied via high-resolution transmission electron microscopy and Raman spectroscopy. The MWCNTs were not structurally damaged during the spark plasma sintering of MWCNT/Al mixed powders. However, two kinds of fractures, i.e., clear break and sword-in-sheath failure, were generated under severe plastic deformation of Al during hot extrusion. We concluded that the MWCNT failure, seen on the fractured composites, was caused by the consolidation process rather than the tensile tests. This work provides a better understanding of the strengthening behavior of MWCNTs, and the design of high-performance MWCNT/Al composites using suitable consolidation techniques.

Nanoporous metals represent a class of functional materials with unique bicontinuous open porous structural properties, making them ideal candidates for various catalyst applications. However, the pursuit of nanoporous properties, extremely small pores, and high surface area, results in the restriction of mass transport. Herein, a free-standing hierarchical nanoporous Cu material, prepared by a selective laser melting 3D printing technique and a one-step dealloying process, is presented as a highly efficient electrocatalyst for methanol oxidation. It is demonstrated that the digitally controlled hierarchical structure with macro-and nano-scaled pores can be utilized for promoting and directing mass transport as well as for the enhancement of catalytic properties. This work highlights a facile, low-cost, and alternative strategy for hierarchical nanoporous structure design that can be applied to binary, ternary, and quaternary metal alloys for various functional applications.

3D-networks of few-layer graphene (FLG) platelets at grain boundaries, sandwiched between thin amorphous Al2O3 layers, were fabricated by spark plasma sintering (SPS) of graphene oxide (GO)/Al mixed powders. The GO was prepared by a modified Hummers’ method, and was thermally reduced to FLG simultaneously during SPS densification. Subsequent plastic flow of the Al matrix during the hot extrusion process caused the destruction of this structure, rearranged the FLG platelets individually into the uniaxial direction, and made them incorporate in the Al matrix. Observations by high-resolution transmission electron microscopy proved the existence of a direct-contact interface between the FLG and the Al matrix without any interfacial compounds, and revealed that the Al matrix featured a fairly low dislocation density. Consequently, the mechanical strength of Al matrix was noticeably enhanced by FLG incorporation, agreeing with the potential strengthening effect predicted by the load transfer mechanism.

Zr alloy is expected to decrease the artifact volume of magnetic resonance imaging (MRI) due to its relatively small magnetic susceptibility. To improve the mechanical properties of a Zr– 1mass%Mo alloy that yielded a reduced artifact volume during MRI, the alloy was melted, hot-forged, and cold-swaged with area reduction ratios of 30%, 50%, 60%, 70%, and 84%. The effects of cold swaging on the microstructure, mechanical properties, and magnetic susceptibility of the alloy were investigated. Before cold swaging, the microstructure consisted of laminated and layered α-and β-phases however, after cold swaging, the α-and β-phases were bent and distorted, and the α-phase became oriented along the {1010} plane. The ultimate tensile strength and elongation to fracture of the Zr–1Mo alloy after cold swaging with an 84% area reduction were 1001 MPa and 10.7%, respectively. The alloy only experienced work-hardening when subjected to large deformations. On the other hand, the change in magnetic susceptibility with cold-swaging was small, from 13.85 × 10−9 to 14.87 × 10−9 m3·kg−1. Thus, a good balance of mechanical properties and low magnetic susceptibility in the Zr–1Mo alloy was obtained by cold swaging. Therefore, this alloy is suitable for utilization in medical devices and is expected to decrease the artifact volume.

Selective laser melting (SLM) technology was recently introduced to fabricate dental prostheses. However, the fatigue strength of clasps in removable partial dentures prepared by SLM still requires improvement. In this study, we attempted to improve the fatigue strength of clasps by adding support structures for overhanging parts, which can generally be manufactured at an angle to be self-supporting. The results show that the fatigue strength of the supported specimens was more than twice that of unsupported specimens. Electron back-scattered diffraction analysis revealed that the supported specimens exhibited lower kernel average misorientation values than the unsupported specimens, which suggested that the support structure reduced the residual strain during the SLM process and helped to prevent micro-cracks led by thermal distortion. In addition, the supported specimens cooled more rapidly, thereby forming a finer grain size compared to that of the unsupported specimens, which contributed to improving the fatigue strength. The results of this study suggest that the fatigue strength of overhanging parts can be improved by intentionally adding support structures.

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.

Amorphous Fe76Si9B10P5 particles were fabricated by a container-free solidification process and subsequent annealing, and their structural and magnetic properties were investigated by X-ray diffraction analysis, transmission electronic microscopy, and vibrating sample magnetometry. The annealing induced the nanocrystallisation of alpha-Fe and Fe-B compounds. The proportions of the different crystalline phases formed were dependent on the annealing temperature. The saturation magnetisation of the single particles was higher than that of the samples prepared by a conventional quenching process; this was attributable to the higher homogeneity of the nanocrystalline grains of the former as well as their higher alpha-Fe to Fe-B compound ratio.[GRAPHICS].

Laser powder bed fusion (PBF) offers many technological opportunities for producing high-performance composite parts with tailored structures. However, fabrication of suitable composite powders possessing homogenous dispersion, good flowability, suitable particle size and distribution is a prerequisite and main challenge currently faced. In this study, a novel strategy was developed to prepare nanoceramic/metal powders by using acid-treated carbon nanotubes (ATCNTs) as an agent. In detail, a 3 wt% ATCNT/Al2O3 colloid, in which the negatively-charged ATCNTs were partially covered with positively-charged Al2O3 nanoparticles under electrostatic attraction, was obtained by heteroagglomeration; subsequently, the uncovered surface areas of ATCNTs were intimately bonded to the positively-charged MoTiAl powders during their mixing. This ATCNT bridging made individual Al2O3 uniformly wrap on the surface of MoTiAl without aggregation. The Al2O3-coated MoTiAl powders remained similar in shape, particle size, and distribution to uncoated ones, simultaneously showing higher laser absorptivity due to an increased surface roughness. The PBF-processed Al2O3-ATCNT/MoTiAl composite was dense, in which Al2O3 nanoparticles were homogenously dispersed and intimately contacted with MoTiAl, giving rise to an increase in the hardness of the matrix. (C) 2017 Elsevier Ltd. 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.

A low magnetic Zr-1Mo alloy was fabricated by a powder bed fusion (PBF) process using a fiber laser. The microstructure, surface morphology, and pore distribution of the as-built Zr-1Mo alloy were observed. Its magnetic susceptibility and Vickers hardness were evaluated by magnetic susceptibility balance and a microindentation tester, respectively. The as-built Zr-1Mo alloy mainly consisted of an phase with an acicular structure. From the processing maps of the surface morphology and pore distribution, open pores on the top surface due to the lack of fusion corresponded to grid-like distributed pores, and large pores corresponded to balling particles on the top surface. The Vickers hardness was influenced by the oxygen and nitrogen contents rather than the porosity. The magnetic susceptibilities of the as-built Zr-1Mo alloy still were one-third those of Ti-6Al-4V and Ti-6Al-7Nb, thus PBF can be applicable to the fabrication process for the low magnetic Zr-1Mo alloy.

Magnesium silicide (Mg2Si)/carbon nanotube (CNT) thermoelectric nanofibers for use as a flexible thermoelectric material were successfully synthesized through the combined processes of the sol-gel method, magnesiothermic reduction, and liquid-solid phase reaction. In the resulting product, each CNT was coated with Mg2Si which was an approximately 60-nm-thick single crystal. The synthesized Mg2Si-coated CNTs exhibited n-type thermoelectric behavior confirming that n-type thermoelectric composite nanofibers were successfully obtained.

Oxygen vacancy plays an important role in optimizing the thermoelectric properties for achieving high figure of merit in perovskite oxides. However, it remains very challenging to find a facile and effective method for creating oxygen vacancy in bulk perovskite material. Using undoped strontium titanate (STO) as a model for perovskite, it is demonstrated here that incorporating graphene into STO can promote the formation of oxygen vacancy in perovskite far more effectively than the time and energy consuming hydrogen reduction method. With only 0.64 vol% of graphene content, reduced graphene oxide (RGO)/STO composite shows highly increased electrical conductivity and power factor compared to hydrogen reduced STO. Electron energy loss spectrum confirms the high concentration of oxygen vacancy in the area close to RGO in RGO/STO composite, which suggests a mild reaction between RGO and STO during sintering. In addition, the thermal conductivity is also depressed due to greatly restricted grain growth via adding RGO. Therefore, this study provides a fast, green and effective way of preparing oxygen deficient perovskite towards improved thermoelectric properties. (C) 2016 Elsevier Ltd. All rights reserved.

The thermal expansion response of multi-walled carbon nanotube (MWCNT) reinforced Al matrix composites was employed to discuss the improvement of the load transfer at the interface between the MWCNTs and the Al matrix. An aluminum carbide (AI(4)C(3)) nanostructure at the end of the MWCNTs, incorporated in the Al matrix, was produced by appropriate heat-treatment. The stress contrast around the Al4C3 observed in the high-resolution transmission electron microscopy (HRTEM) image revealed the evidence of a trace of friction, which would lead to the enhancement of the anchor effect from the Al matrix. This anchor effect of Al4C3 may hinder the local interfacial slippage and constrain the deformation of the Al matrix. As a result, the thermal expansion behavior became linear and reversible under cyclic thermal load. It is concluded that the formation of Al4C3 could effectively enhance the load transfer in MWCNT/Al composites. The yield strength of MWCNT/Al composites was substantially increased under the appropriate quantity of Al4C3 produced at the MWCNT-Al interface by precisely controlled heat-treatment. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Zr-Ag composites were fabricated to decrease the magnetic susceptibility by compensating for the magnetic susceptibility of their components. The Zr-Ag composites with a different Zr-Ag ratio were swaged, and their magnetic susceptibility, artifact volume, and mechanical properties were evaluated by magnetic balance, three-dimensional (3-D) artifact rendering, and a tensile test, respectively. These properties were correlated with the volume fraction of Ag using the linear rule of mixture. We successfully obtained the swaged Zr-Ag composites up to the reduction ratio of 96% for Zr-4, 16, 36, 64Ag and 86% for Zr-81Ag. However, the volume fraction of Ag after swaging tended to be lower than that before swaging, especially for Ag-rich Zr-Ag composites. The magnetic susceptibility of the composites linearly decreased with the increasing volume fraction of Ag. No artifact could be estimated with the Ag volume fraction in the range from 93.7% to 95.4% in three conditions. Young's modulus, ultimate tensile strength (UTS), and 0.2% yield strength of Zr-Ag composites showed slightly lower values compared to the estimated values using a linear rule of mixture. The decrease in magnetic susceptibility of Zr and Ag by alloying or combining would contribute to the decrease of the Ag fraction, leading to the improvement of mechanical properties.

World PM2016 Congress and Exhibition, 9-13 October 2016, Hamburg, Germany<br /> ISBN: 978-1-899072-48-4

To evaluate the mechanical properties and biologic response of single-phase Ti-Zr alloys cast in higher-purity casting conditions, with comprehensive compositions (from 10 to 90 mol% of Zr).<br /> The mechanical properties and in vitro biologic response with proportional increase of Zr to Ti-Zr alloy composition were assessed. Tensile strength, surface hardness, and Young&#039;s modulus were examined. The in vitro cell response of the alloys was also tested with mouse osteoblast cells.<br /> Analyses of mechanical tests demonstrated improved strength and reduced Young&#039;s modulus on this binary alloy system. In vitro cell culture studies with osteogenic MCT3T-E1 cells exhibited the highest attachment rate with the largest and more mature cells on Ti10Zr, instead of commercially pure Ti, whereas a significantly lower cell attachment rate and delayed alkaline phosphatase-specific activity (ALP) differentiation were detected on Ti50Zr.<br /> The results revealed that the composition did have an impact on the in vitro biologic response. Ti-Zr alloys with 50-50 mol% composition had a decreased biologic response, although the mechanical properties improved. The overall highest strength was Ti with 30 mol% Zr wit

We aimed to investigate the fatigue strength of Co-Cr-Mo clasps for removable partial dentures prepared by selective laser melting (SLM). The Co-Cr-Mo alloy specimens for tensile tests (dumbbell specimens) and fatigue tests (clasp specimens) were prepared by SLM with varying angles between the building and longitudinal directions (i.e., 0 degrees (TLO, FLO), 45 degrees (TL45, FL45), and 90 degrees (TL90, FL90)). The clasp specimens were subjected to cyclic deformations of 0.25 mm and 0.50 mm for 10(6) cycles. The SLM specimens showed no obvious mechanical anisotropy in tensile tests and exhibited significantly higher yield strength and ultimate tensile strength than the cast specimens under all conditions. In contrast, a high degree of anisotropy in fatigue performance associated with the build orientation was found. For specimens under the 0.50 mm deflection, FL90 exhibited significantly longer fatigue life (205,418 cycles) than the cast specimens (112,770 cycles). In contrast, the fatigue lives of FLO (28,484 cycles) and FL45 (43,465 cycles) were significantly shorter. The surface roughnesses of FLO and FL45 were considerably higher than those of the cast specimens, whereas there were no significant differences between FL90 and the cast specimens. Electron backscatter diffraction (EBSD) analysis indicated the grains of FLO showed preferential close to &lt; 001 &gt; orientation of the gamma phase along the normal direction to the fracture surface. In contrast, the FL45 and FL90 grains showed no significant preferential orientation. Fatigue strength may therefore be affected by a number of factors, including surface roughness and crystal orientation. The SLM process is a promising candidate for preparing tough removable partial denture frameworks, as long as the appropriate build direction is adopted. (C) 2016 Elsevier Ltd. All rights reserved.

Purpose: To evaluate the mechanical properties and biologic response of single-phase Ti-Zr alloys cast in higher-purity casting conditions, with comprehensive compositions (from 10 to 90 mol% of Zr). Materials and Methods: The mechanical properties and in vitro biologic response with proportional increase of Zr to Ti-Zr alloy composition were assessed. Tensile strength, surface hardness, and Young's modulus were examined. The in vitro cell response of the alloys was also tested with mouse osteoblast cells. Results: Analyses of mechanical tests demonstrated improved strength and reduced Young's modulus on this binary alloy system. In vitro cell culture studies with osteogenic MCT3T-E1 cells exhibited the highest attachment rate with the largest and more mature cells on Ti10Zr, instead of commercially pure Ti, whereas a significantly lower cell attachment rate and delayed alkaline phosphatase-specific activity (ALP) differentiation were detected on Ti50Zr. Conclusion: The results revealed that the composition did have an impact on the in vitro biologic response. Ti-Zr alloys with 50-50 mol% composition had a decreased biologic response, although the mechanical properties improved. The overall highest strength was Ti with 30 mol% Zr without significant decrease of biologic response.

<p>Co-Cr-Mo合金は，強度および耐食性に優れていることから，生体用金属材料として広く応用されている．また，歯科用合金として古くから使用されており，特に歯科鋳造用合金として様々な種類のコバルトクロム合金が実用化されている．この合金のN濃度を増加させることにより，機械的性質が向上することが著者らの研究によりわかった．さらに，Crの濃度を増加させた時の諸性質についても詳細な検討が必要と考えられる．そこで，Co-Cr-Mo合金のN濃度とCr濃度を変化させた時の機械的性質と耐食性について，引張試験と1％乳酸中での溶出試験により検討した．その結果，N濃度が0.2〜0.4 mass％の合金において延性が向上することがわかった．また，Cr濃度は32 mass％から増加するに従って強度が増加するが，36％より多くなると脆くなることがわかった．耐食性に関しては，N，Cr濃度を変化させても影響がないことがわかった．</p>

The microstructure and mechanical properties of thermomechanically processed Zr-14Nb alloy with low magnetic susceptibility were investigated in this study. The stress-strain curves of Zr-14Nb alloy were classified as higher or lower work-hardening types depending on the thermomechanical process. Serration was observed in curves of the higher work-hardening type. SEM-EBSD analysis indicated that {332}&lt;113&gt; twinning should form at the hands that appear after tensile testing. On the other hand, no serration appeared in the lower hardening rate curves. The mechanical properties of centrifugally cast Zr-14Nb alloy with a lower work-hardening rate possessed moderate tensile strength and high elongation because of the formation of the isothermal re phase during cooling after centrifugal casting, although the tensile strength was increased and the elongation was decreased with increase of the isothermal w phase formed after aging. The magnetic susceptibilities of thermomechanically processed Zr-14Nb alloys were still one-third lower than those of Ti-6A1-7Nb. Accordingly, the mechanical properties of Zr-14Nb can be controlled by thermomechanical processing while keeping low magnetic susceptibility.

Air-formed surface oxide films on four types of Co-Cr-alloys were characterized using X-ray photoelectron spectroscopy (XPS) and five types of Co-Cr alloys were anodically polarized, to identify the effects of the addition of N, Mo, and W to Co-Cr alloys containing high Cr on the surface composition and corrosion resistance. Co-20Cr-15W-10Ni (ASTM P90), Co-30Cr-6Mo, Co-33Cr-5Mo-0.3N, and Co-33Cr-9W0.3N were employed for XPS and the above four alloys and another Co-30Cr-6Mo (ASTM F75) were employed for anodic polarization. The surface oxide film on the Co-Cr alloys consisted of oxide species of Co, Cr, Mo, W and/or Ni contains a large amount of OH-with a thickness of 2.6-3.2 nm. Cations existed in the oxide as Co2+, Cr3+, Mo4+, Mo6+, W6+ and Ni2+. Cr and Mo are enriched and Co and Ni are depleted in the surface oxide film. W was enriched in the case of Co-20Cr-15W-10Ni but depleted in the case of Co-33Cr-9W-0.3N. On the other hand, Cr, Mo, W and Ni were enriched and Co was depleted in the substrate alloy just under the surface oxide film in the polished alloy. During rapid formation of the surface oxide film, Cr was preferentially oxidized and the oxidation of Co and Ni delayed, according to the oxidation and reduction potentials of these elements, The Co-Cr alloys essentially have high localized corrosion resistance that is not easily affected by a small change of composition. Co-33Cr5Mo-0.3N shows higher corrosion resistance compare than conventional Co-Cr alloys.

A large-scale ingot of Zr-1Mo alloy was produced for industrial manufacturing to investigate whether it is possible to produce an ingot with homogeneity. The homogeneous ingot with a chemical composition of Zr-1 mass%Mo was prepared successfully. The microstructure, mechanical properties, and magnetic susceptibility were evaluated. The microstructure showed a coarse colony structure of a plate-like a phase and a thin beta phase. An omega phase precipitation was observed in the phase. Elongation of 23% and magnetic susceptibility of 12.4 x 10(-9) m(3) kg(-1) (0.98 x 10(-6) cm(3) g(-1)) were achieved. We found that it is possible to produce a homogeneous large-scale ingot of Zr-1Mo with high elongation and low magnetic susceptibility.

Statement of problem. Casting difficulties have led to the limited use of titanium in dental prostheses. The selective laser melting system was recently developed to fabricate biomedical components from titanium alloys. However, the fabrication of a titanium alloy framework for a maxillary complete denture by selective laser melting has not yet been investigated. Purpose. The purpose of the study was to fabricate thin titanium alloy frameworks for a maxillary complete denture with a selective laser melting system and to evaluate their hardness and microstructure. Material and methods. A cast of an edentulous maxilla was scanned with a dental 3-dimensional cone-beam computed tomography system, and standard triangulation language data were produced with the DICOM Viewer (Digital Imaging and Communications in Medicine). Two types of metal frameworks for complete dentures were designed with 3-dimensional computer-aided design software. Two titanium alloy frameworks, SLM-1 and SLM-2, were fabricated from these designs with the selective laser melting system. Plate-shaped specimens were cut from the central flat region of SLM-1, SLM-2, and as-cast Ti-6Al-4V (As-cast). Vickers hardness testing, optical microscopy, and x-ray diffraction measurements were performed. Results. Thin titanium alloy frameworks for maxillary complete dentures could be fabricated by selective laser melting. The hardness values for SLM-1 and SLM-2 were higher than that for the as-cast specimen. Optical microscopy images of the SLM-1 and SLM-2 microstructure showed that the specimens did not exhibit pores, indicating that dense frameworks were successfully obtained with the selective laser melting process. In the x-ray diffraction patterns, only peaks associated with the a phase were observed for SLM-1 and SLM-2. In addition, the lattice parameters for SLM-1 and SLM-2 were slightly larger than those for the as-cast specimen. Conclusions. The mechanical properties and microstructure of the denture frameworks prepared by selective laser melting indicate that these dentures are appropriate for clinical use.

The effects of cyclic fatigue on bending properties of NiTi endodontic instruments were investigated. Sixteen Profiles (R) were divided into two groups (A, and B). The sequence of cantilever bending test and cyclic fatigue test was alternated repeatedly until file separation occurred. In the cyclic fatigue test, the instrument curvature was 19 degrees in group A and 38 degrees in group B. Fractographic examination was performed to determine fracture patterns. In group A, there were significant differences between the bending load values measured before the cyclic fatigue test and the last cantilever bending test before instrument fracture at each deflection (p&lt;0.05). Fractographic examination showed the specific patterns of cyclic fatigue fracture. The stress required to induce martensitic transformation might be reduced due to the softening behavior caused by the cyclic fatigue under the relaxation condition of the superelasticity range (group A). The SEM images were able to display specific patterns indicating cyclic fatigue fracture.

This study aimed to evaluate effects of torsional loading on the mechanical properties of endodontic instruments using the nanoindentation technique. ProFile (PF; size 30, taper 04; Dentsply Maillefer, Switzerland) and stainless steel (SS; size 30, taper 02; Mani, Japan) instruments were subjected to torsional test. Nanoindentation was then performed adjacent to the edge of fracture (edge) and at the cutting part beside the shank (shank). Hardness and elastic modulus were measured under 100-mN force on 100 locations at each region, and compared to those obtained from the same regions on new instruments. It showed that PF and SS instruments failed at 559 +/- 67 and 596 +/- 73 rotation degrees and mean maximum torque of 0.90 +/- 0.07 and 0.99 +/- 0.05 N-cm, respectively. Hardness and elastic modulus ranged 4.8-6.7 and 118-339 GPa in SS, and 2.7-3.2 and 52-81 GPa in PF. Significant differences between torsion-fractured and new instruments in hardness and elastic modulus were detected in the SS system used. While in PF system, the edge region after torsional fracture had significantly lower hardness and elastic modulus compared to new instruments. The local hardness and modulus of elasticity of endodontic instruments adjacent to the fracture edge are significantly reduced by torsional loading. (C) 2014 Wiley Periodicals, Inc.

Susceptibility artifacts generated in magnetic resonance (MR) images were quantitatively evaluated for various metals using a three-dimensional (3-D) artifact rendering to demonstrate the correlation between magnetic susceptibility and artifact volume. Ten metals (stainless steel, Co-Cr alloy, Nb, Ti, Zr, Mo, Al, Sn, Cu and Ag) were prepared, and their magnetic susceptibilities measured using a magnetic balance. Each metal was embedded in a Ni-doped agarose gel phantom and the MR images of the metal-containing phantoms were taken using 1.5 and 3.0 T MR scanners under both fast spin echo and gradient echo conditions. 3-D renderings of the artifacts were constructed from the images and the artifact volumes were calculated for each metal. The artifact volumes of metals decreased with decreasing magnetic susceptibility, with the exception of Ag. Although Sn possesses the lowest absolute magnetic susceptibility (1.8 x 10(-6)), the artifact volume from Cu (-7.8 x 10(-6)) was smaller than that of Sn. This is because the magnetic susceptibility of Cu was close to that of the agarose gel phantom (-7.3 x 10(-6)). Since the difference in magnetic susceptibility between the agarose and Sn is close to that between the agarose and Ag (-17.5 x 10(-6)), their artifact volumes were almost the same, although they formed artifacts that were reversed in all three dimensions. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The selective laser melting (SLM) process was applied to a Co-29Cr-6Mo alloy, and its microstructure, mechanical properties, and metal elution were investigated to determine whether the fabrication process is suitable for dental applications. The microstructure was evaluated using scanning electron microscopy with energy-dispersed X-ray spectroscopy (SEM-EDS), X-ray diffractometry (XRD), and electron back-scattered diffraction pattern analysis. The mechanical properties were evaluated using a tensile test. Dense builds were obtained when the input energy of the laser scan was higher than 400 J mm(-3), whereas porous builds were formed when the input energy was lower than 150 J mm(-3). The microstructure obtained was unique with fine cellular dendrites in the elongated grains parallel to the building direction. The gamma phase was dominant in the build and its preferential &lt;0 0 1&gt; orientation was confirmed along the building direction, which was clearly observed for the builds fabricated at lower input energy. Although the mechanical anisotropy was confirmed in the SLM builds due to the unique microstructure, the yield strength, UTS, and elongation were higher than those of the as-cast alloy and satisfied the type 5 criteria in ISO22764. Metal elution from the SLM build was smaller than that of the as-cast alloy, and thus, the SLM process for the Co-29Cr-6Mo alloy is a promising candidate for fabricating dental devices. (C) 2013 Elsevier Ltd. All rights reserved.

The magnetic susceptibility of cold-rolled Zr-14Nb was evaluated to apply a new metallic medical device used for magnetic resonance imaging (MRI). The magnetic susceptibility of cold-rolled Zr-14Nb decreased up to the reduction ratio of 30%, then gradually decreased up to the ratio of 90%. Transmission electron microscopic observation revealed the strain-induced formation of omega phase after cold rolling at the reduction ratio of 5%, indicating that the initial decrease in magnetic susceptibility was caused by the formation of the omega phase. The omega phase was saturated at the reduction ratio of 30%. The formation of the omega phase could be explained on the basis of the increase in the Young's modulus and Vickers hardness of cold-rolled Zr-14Nb. The effect of texture formation on these properties was not obvious in the cold-rolled Zr-14Nb. Because of the strain-induced formation of the omega phase, the magnetic susceptibility of Zr-14Nb can be reduced by cold rolling to as low as that of as-cast Zr-9Nb, which is one-third that of Ti and Ti alloys. Therefore, cold-workable Zr-14Nb with low magnetic susceptibility could be a promising alloy for medical devices under MRI. 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

To enhance hard-tissue compatibility of Ti, galvanic current between titanium ( Ti) and gold ( Au) may be available. Prior to the design of medical devices with the capability to generate a galvanic current, it is necessary to understand the control mechanism. In this study, we first measured galvanic current between Ti and Au with various surface areas in Hanks' solution. The galvanic current increased immediately after connection of two electrodes, followed by an abrupt decrease and a steady state. The galvanic current varied with the combinations of Ti and Au areas. We, thereafter, evaluated the formation of calcium phosphate on Ti under a condition of applying simulated galvanic current. Surface characterization was revealed in which the calcium phosphate formation was enhanced accompanied by growth of Ti oxide layer under the galvanic current application. A similar result was observed on Ti with patterned Au coating without outer electric power. Therefore, galvanic current is useful to enhance hard-tissue compatibility, and this technique has potential for applications to metallic biomaterials.

Cooling rate and composition dependences of the magnetic susceptibility for Zr54-xCu30+xAl8Ag8 glassy alloys which are candidate materials for magnetic resonance imaging (MRI) were investigated. Lower magnetic susceptibility was achieved by reducing Zr content in the present series of the alloys, and also by higher cooling rate during the preparing glassy alloys. The magnetic susceptibility values were hard to be explained by the simple free-electron model. It is suggesting that the effects of the enhancement of the density of states by 4d-conduction band should be taken into the consideration. The results obtained by utilizing the pair correlation functions suggested that the different magnetic susceptibilities between the ribbon and bulk glassy alloys were originated from the structural difference in the middle range order caused by the different cooling rates. © 2013 The Japan Institute of Metals and Materials.

Micro-arc oxidation (MAO) was performed on a beta-type Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) in this study to improve its bioactivity in a body fluid and its hard-tissue compatibility. The surface oxide layer formed on TNTZ by MAO treatment in a mixture of calcium glycerophosphate and magnesium acetate was characterized using various surface analyses. The oxide layer was mainly composed of two types of TiO2 (rutile and anatase), and it also contained Ca, P, and Mg, which were incorporated from the electrolyte during the treatment. The calcium phosphate formation on the surface of the specimens after immersion in Hanks' solution was evaluated to determine the bioactivity of TNTZ with and without MAO treatment. As a result, thick calcium phosphate layers formed on the TNTZ specimen that underwent MAO treatment, whereas only a small amount of precipitate was observed on TNTZ without treatment. Thus, the MAO treatment is a promising method to improve the bioactivity and hard-tissue compatibility of TNTZ. (c) 2012 Elsevier B.V. All rights reserved.

The microstructure and mechanical properties of as-cast Co-(20-33)Cr-5Mo-N alloys were investigated to develop ductile Co-Cr-Mo alloys without Ni addition for dental applications that satisfy the requirements of the type 5 criteria in ISO 22674. The effects of the Cr and N contents on the microstructure and mechanical properties are discussed. The microstructures were evaluated using scanning electron microscopy with energy-dispersive X-ray spectroscopy (EDS), X-ray diffractometry (XRD), and electron back-scattered diffraction pattern analysis. The mechanical properties were evaluated using tensile testing. The proof strength and elongation of N-containing 33Cr satisfied the type 5 criteria in ISO 22674. epsilon-phase with striations was formed in the N-free (20-29)Cr alloys, while there was slight formation of epsilon-phase in the N-containing (20-29)Cr alloys, which disappeared in N-containing 33Cr. The lattice parameter of the gamma-phase increased with increasing Cr content (i.e. N content) in the N-containing alloys, although the lattice parameter remained almost the same in the N-free alloys because of the small atomic radius difference between Co and Cr. Compositional analyses by EDS and XRD revealed that in the N-containing alloys Cr and Mo were concentrated in the cell boundary, which became enriched in N, stabilizing the gamma-phase. The mechanical properties of the N-free alloys were independent of the Cr content and showed low strength and limited elongation. Strain-induced martensite was formed in all the N-free alloys after tensile testing. On the other hand, the proof strength, ultimate tensile strength, and elongation of the N-containing alloys increased with increasing Cr content (i.e. N content). Since formation of epsilon-phase after tensile testing was confirmed in the N-containing alloys the deformation mechanism may change from strain-induced martensite transformation to another form, such as twinning or dislocation slip, as the N content increases. Thus the N-containing 33Cr alloy with large elongation is promising for use in dentures with adjustable clasps through one piece casting. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Aim To investigate the effect of cyclic fatigue on nickel-titanium (NiTi) endodontic instruments using a nano-indentation test. Methodology Eight ProFile NiTi rotary instruments (size 30, taper 0.06; Dentsply Maillefer, Ballaigues, Switzerland) were tested using a cyclic fatigue set-up until fracture. The fractured instruments and eight new NiTi instruments of the same size and taper were used for a nano-indentation test on the internal surfaces of a NiTi instruments in the region just adjacent to their fractured edge (group I) and in the same region of the new group (group II), and the cutting part beside the shaft for both instruments [group III (fractured) and group IV (new)]. Data were statistically analyzed using one-way analysis of variance and GamesHowell post hoc test. The alpha-type error was set at 0.05. Results Significant differences in terms of hardness and elastic modulus for each group (P &lt; 0.05) were found, with group I having the lowest mean values followed by group III. Additionally, standard deviations increased remarkably after failure, as represented by groups I and III. Conclusion The nano-indentation technique can be applied to determine the performance and the failure mechanism of NiTi instruments. The fatigue process revealed a significant decrease in the hardness and elastic modulus of the NiTi instrument. As indicated by the low hardness, the fatigue process did not result in work hardening but rather work softening.

The corrosion behavior of the Ti-33.5Nb-5.7Ta alloy (Ti-Nb-Ta) as a biocompatible beta-type Ti alloy during long-term immersion in simulated body fluid was investigated. Like pure Ti, pitting corrosion did not occur on Ti-Nb-Ta during anodic polarization. Thus, alloying of Ti with Nb and Ta did not change the chloride-ion sensitivity. Metal ion release of Ti, Nb, and Ta was detected after 7-d immersion in the solution; however, the amounts of ions were much smaller than those from Type316L stainless steel. X-ray photoelectron spectroscopy revealed that the fractions of Nb and Ta in the passive layer increased during the immersion while that of Ti decreased. The corrosion rate of Ti-Nb-Ta determined by electrochemical impedance spectroscopy kept decreasing over a period of 15 d while the thickness of the passive layer did not change after 1 d. Thus, the reconstruction of the passive layer of the alloy was proven to be important for metal ion release during long-term implantation in a living body. Thus, Ti-Nb-Ta has sufficient corrosion resistance as a biocompatible beta-type Ti alloy. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.045210jes] All rights reserved.

The effects of the microstructures and phases of Zr-rich Mo alloys on their magnetic susceptibilities and mechanical properties were investigated in order to develop a Zr alloy with low magnetic susceptibility for use in magnetic resonance imaging (MRI). The magnetic susceptibility was measured with a magnetic susceptibility balance, while mechanical properties were evaluated by a tensile test. The microstructure was evaluated with an X-ray diffractometer, an optical microscope, and a transmission electron microscope. Evaluation of the microstructures revealed that the alpha&apos; phase was the dominant form at less than 2% Mo content in the as-cast alloy. The omega phase was formed in as-cast Zr-3Mo but disappeared with aging at 973 K. Magnetic susceptibility was reflected in the phase constitution: the susceptibility showed a local minimum at Zr-(0.5-1)Mo with mostly alpha&apos; phase and a minimum at Zr-3Mo with mostly beta and omega phases. The magnetic susceptibility of as-cast Zr-3Mo increased at 973 K due to disappearance of the omega phase. However, the susceptibility was still as low as that of as-cast Zr-1Mo. The ultimate tensile strength of alpha&apos;-based Zr-Mo alloys was tailored from 674 to 970 MPa, and the corresponding elongation varied from 11.1% to 2.9%. Because Zr-Mo alloys containing omega phase were found, through tensile tests, to be brittle this phase should be avoided, irrespective of the low magnetic susceptibility, in order to maintain mechanical reliability. Elongation of the Zr-3Mo alloy was dramatically improved when the phase constitution was changed to alpha and beta phases by aging at 973 K for 86.4 ks. The magnetic susceptibilities of the alpha&apos;-based Zr-Mo alloys are one-third those of Ti-6Al-4V and Ti-6Al-7Nb, and thus these Zr alloys are useful for medical devices under MRI. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

On the basis of the microstructures and mechanical properties of as-cast Zr-(0-24)Nb alloys the effects of phase constitution on the mechanical properties and magnetic susceptibility are discussed in order to develop Zr alloys for use in magnetic resonance imaging (MRI). The microstructures were evaluated using an X-ray diffractometer, an optical microscope, and a transmission electron microscope; the mechanical properties were evaluated by a tensile test. The alpha&apos; phase was dominantly formed with less than 6 mass% Nb content. The omega phase was formed in Zr-(6-20)Nb alloys, but disappeared from Zr-22Nb. The beta phase dominantly existed in Zr-(9-24)Nb alloys. The mechanical properties as well as the magnetic susceptibility of the Zr-Nb alloys varied depending on the phase constitution. The Zr-Nb alloys consisting of mainly alpha&apos; phase showed high strength, moderate ductility, and a high Young&apos;s modulus, retaining low magnetic susceptibility. Zr-Nb alloys containing a larger volume of omega phase were found to be brittle and, thus, should be avoided, despite their low magnetic susceptibility. When the Zr-Nb alloys consisted primarily of beta phase the effect of omega phase weakened the mechanical properties, thereby leading to an increase in ductility, even with an increase in magnetic susceptibility. The minimum value of Young&apos;s modulus was obtained for Zr-20Nb, because this composition was the phase boundary between the beta and omega phases. However, the magnetic susceptibility of the alloy was half that of Ti-6Al-4V alloys. Zr-Nb alloys consisting of alpha&apos; or beta phase have excellent mechanical properties with low magnetic susceptibility and, thus, these alloys could be useful for medical devices used in MRI. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A novel coating technique of thin ceramic layer resembling teeth color on titanium (Ti) surface was developed by combination of sputter deposition of metal zirconium (Zr) and subsequent micro-arc oxidation (MAO) treatment. The oxide layer grown by MAO treatment had a porous structure with a thickness of approximately 6 micrometers and was mainly composed of zirconium dioxide (ZrO(2)) with both tetragonal and monoclinic crystal structures. The surface of the specimen was hardened by this technique, and the hardness of the specimen was significantly larger than that of untreated Ti and MAO-treated Ti without Zr layer. The bonding strength test revealed that fracture occurred inside the oxide layer, indicating that adhesion between the oxide layer and the Ti substrate was sufficiently strong. From these results, this technique has an advantage for the development of novel dental materials with excellent mechanical and aesthetic properties.

Immobilization of RGD peptides on titanium (Ti) surfaces enhances implant bone healing by promoting early osteoblastic cell attachment and subsequent differentiation by facilitating integrin binding. Our previous studies have demonstrated the efficacy of RGD peptide immobilization on Ti surfaces through the electrodeposition of poly(ethylene glycol) (PEG) (RGD/PEG/Ti), which exhibited good chemical stability and bonding. The RGD/PEG/Ti surface promoted differentiation and mineralization of pre-osteoblasts. This study investigated the in vivo bone healing capacity of the RGD/PEG/Ti surface for biomedical application as a more osteoconductive implant surface in dentistry. The RGD/PEG/Ti surface was produced on an osteoconductive implant surface, i.e. the grit blasted micro-rough surface of a commercial oral implant. The osteoconductivity of the RGD/PEG/Ti surface was compared by histomorphometric evaluation with an RGD peptide-coated surface obtained by simple adsorption in rabbit cancellous bone after 2 and 4 weeks healing. The RGD/PEG/Ti implants displayed a high degree of direct bone apposition in cancellous bone and achieved greater active bone apposition, even in areas of poor surrounding bone. Significant increases in the bone to implant contact percentage were observed for RGD/PEG/Ti implants compared with RGD-coated Ti implants obtained by simple adsorption both after 2 and 4 weeks healing (P &lt; 0.05). These results demonstrate that RGD peptide immobilization on a Ti surface through electrodeposited PEG may be an effective method for enhancing bone healing with commercial micro-rough surface oral implants in cancellous bone by achieving rapid bone apposition on the implant surface. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Surface treatments with various combinations of micro-arc oxidation (MAO) and chemical treatments were performed on zirconium (Zr) disks in this study to enhance the bioactivity of Zr. The surface oxide layers formed with MAO and chemical treatments on Zr disks were characterized using surface analyses; the calcium phosphate formation on the specimens after immersion in Hanks&apos; solution was evaluated. As a result, thick calcium phosphate layers formed on Zr specimens that underwent MAO treatment with a mixture of calcium glycerophosphate and magnesium acetate and subsequent chemical treatment with sulfuric acid or sodium hydroxide solutions, while no precipitate was observed without treatment. The surface analyses revealed that the porous oxide layer formed by MAO treatment contained Ca, P, and Mg, which were incorporated from the electrolytes during the treatments. In addition, both the composition and crystal structure of the oxide layers uniquely changed as a result of the various chemical treatments. (C) 2011 Elsevier B.V. All rights reserved.

The effects of Pt and Pd addition to a Zr-20Nb alloy on its microstructure and mechanical property, as well as the elution of metals from the alloys in lactic acid solution, were investigated. The microstructure was characterized with an X-ray diffractometer (XRD), an optical microscope (OM), and a transmission electron microscope (TEM). The mechanical properties were evaluated by a tensile test. The beta phase is dominantly observed in the Zr-20Nb as well as in the Pt-added and Pd-added Zr-20Nb alloys. Needle-like microstructures are observed in equiaxed grains in all alloys. Pd addition to the Zr-20Nb alloy suppresses omega phase formation more than Pt addition does. The 0.2% offset yield strength and the ultimate tensile strength of the Pt-added and Pd-added Zr-20Nb alloys increase with the Pt and Pd concentrations. XRD analysis revealed that the lattice parameter of beta-Zr in the Pt-added and Pd-added Zr-20Nb alloys decreases with the Pt and Pd concentrations. Pt and Pd solute in beta-Zr as a substitutional element and contribute to the increase in the strength by solid solution hardening. The addition of 2Pt and 2Pd to the Zr-20Nb alloy also improves metal elution from the alloys in lactic acid solution. (C) 2011 Elsevier B.V. All rights reserved.

This study investigated the surface characteristics and in vitro biocompatibility of a titanium (Ti) oxide layer incorporating calcium ions (Ca) obtained by hydrothermal treatment with or without post heat-treatment in the Ti-13Nb-13Zr alloy. The surface characteristics were evaluated by scanning electron microscopy, thin-film X-ray diffractometry, X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurements. In vitro biocompatibility of the Ca-containing surfaces was assessed in comparison with untreated surfaces using a pre-osteoblast cell line. Hydrothermal treatment produced a crystalline CaTiO3 layer. Post heat-treatment at 400 degrees C for 2 h in air significantly decreased water contact angles in the CaTiO3 layer (p &lt; 0.001). The Ca-incorporated alloy surfaces displayed markedly increased cell viability and ALP activity compared with untreated surfaces (p &lt; 0.001), and also an upregulated expression of various integrin genes (alpha 1, alpha 2, alpha 5, alpha v, beta 1 and beta 3) at an early incubation time-point. Post heat-treatment further increased attachment and ALP activity in cells grown on Ca-incorporated Ti-13Nb-13Zr alloy surfaces. The results indicate that the Ca-incorporated oxide layer produced by hydrothermal treatment and a simple post heat-treatment may be effective in improving bone healing in Ti-13Nb-13Zr alloy implants by enhancing the viability and differentiation of osteoblastic cells. (C) 2011 Elsevier B. V. All rights reserved.

Collagen is expected to work as a bonding agent of soft and hard tissues to solid materials. In this study, the electrodeposition of collagen to a titanium (Ti) surface under various conditions, i.e., the pH of the collagen solution, potential, and electrodeposition time, was performed to understand the optimal electrodeposition conditions for the immobilization of collagen to Ti. The effects of these conditions on the thickness and residual ratio of the collagen layer after shaking in water were evaluated by ellipsometry, scanning probe microscopy, and X-ray photoelectron spectroscopy. Collagen molecules were attracted to Ti cathode and immobilized with high durability by combining electrodeposition conditions, pH 5, alternating potential between -1 V and +1 V vs. SCE with 1 Hz, and 1800s. The surface of this electrodeposited collagen layer was smooth and uniform maintaining the collagen fibril and natural structure. On the other hand, the collagen layer immobilized by immersion technique in a collagen solution, was rough and irregular. Electrodeposition with alternating potential at pH 5 for 1800s is a much more appropriate technique to immobilize collagen to Ti than the conventional immersion technique. [doi:10.2320/matertrans.M2010311]

Protein-resistant coatings have been studied for inhibiting biofilm formation on implant devices. In this study, titanium (Ti) surfaces were biofunctionalized with poly(ethylene glycol) (PEG) by electrodeposition and were evaluated as biofilm substrates under an oral simulated environment. Streptococcus gordonii, an early colonizer of oral biofilms, was inoculated on Ti and PEG-electrodeposited Ti (PEG-Ti) surfaces and was analyzed quantitatively and topographically. Streptococcus mutans supplemented with sucrose, a late colonizer mainly found in dental plaque, was also used to form biofilms on the surfaces of Ti and PEG-Ti for 20 h followed by sonication as a means of detaching the biofilms. The results indicated that the attachment of S. gordonii on PEG-Ti surfaces was inhibited compared with Ti, and the S. mutans biofilm was easier to be detached from the surface of PEG-Ti than that of Ti. Moreover, the presence of PEG electrodeposited on Ti surface inhibited salivary protein adsorption. The degree of detachment of biofilms from PEG-Ti was associated with the inhibition of the salivary protein adsorption, suggesting weak basal attachment of the biofilms to the electrodeposited surfaces. Therefore, controlling protein adsorption at the initial stage of biofilm formation may be an effective strategy to protect metal surfaces from bacterial contamination not only in dental manipulations but also in orthopedic applications. (C) 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 95A: 1105-1113,2010.

The static frictional coefficients (SFC) of a Co-Cr and a gold alloys were evaluated for the application of a cone crown telescope system in removable prosthesis. The SFCs of the Co-Cr alloy were lower than those of the gold alloy. The SFC of the gold alloy decreased by annealing at 85 degrees C in air and was restored by re-polishing, although that of the Co-Cr alloy was stable irrespective of the annealing. The XPS analysis revealed the formation of a surface oxide layer on the gold alloy after annealing. The decrease in the SFC of the gold alloy may have been caused by the formation of an oxide layer on the surface due to annealing. The relationships among such factors as the retentive force, SFC and cone crown angle indicate that the angle of the Co-Cr alloy should be lower than that of the gold alloy based on the Korber's model.

The cathodic polarization technique to form an alkaline environment on a zirconium (Zr) surface, discussed in the present study, is unique, and gives the ability to form calcium phosphate in a simulated body fluid to Zr, on the other hand, many previous studies have been conducted using immersion in alkaline solutions. In this study, two discrete techniques were investigated Zr was cathodically polarized in an electrolyte without calcium and phosphate ions, and Zr was cathodically polarized in another electrolyte containing calcium and phosphate ions, Hanks&apos; solution, to directly form a calcium phosphate layer The surface was characterized using X-ray photoelectron spectroscopy, and the performance of the material was evaluated by immersion in Hanks&apos; solution As a result, the ability to form calcium phosphate in Hanks&apos; solution was given by cathodic polarization in the Na(2)SO(4) solution containing H(2)O(2). In addition, a cathodic potential under -1.5 V(SCE) is required to form hydroxyapatite directly in Hanks&apos; solution. This research clearly reveals useful surface modification techniques giving the ability to form calcium phosphate in a simulated body fluid by cathodic polarization (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd All rights reserved

The roughness and cleanness of a titanium surface must be controlled in order to investigate the expression mechanism of hard tissue compatibility on titanium. In this study, osteogenic MC3T3-E1 cells were cultured and differentiation-induced on bulk and sputter-deposited titanium specimens, and the osteogenesis were investigated. For the preparation of bulk specimens, titanium discs were mirror-polished. On the other hand, titanium was sputter-deposited on smooth and clean cover glasses as sputter-deposited specimens. As a result, no significant difference was observed in the cell morphology and attached number. On the other hand, the time showing maximum activity in the alkaline phosphatase and gene expressions, which are related to bone differentiation on the bulk titanium, were superior to those on the sputter-deposited titanium. From the surface observation of the specimens with a scanning electron microscope and a scanning probe microscope, the surface on the sputter-deposited titanium was more uniform and cleaner than that on the bulk titanium. According to Xray photoelectron spectroscopy, the thickness of surface oxide film on the sputter-deposited titanium was smaller than that on the bulk titanium. In addition, the proportions of TiO and Ti(2)O(3) in the surface oxide film on the sputter-deposited titanium were larger than those on the bulk titanium. These differences might influence the differentiation of osteoblastic cells. (C) 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 94A: 611-618, 2010

Porous Ti (pTi)/hydroxylapatite (HA) composites were fabricated by an infiltration method in a vacuum and sintering. The Young's modulus of the composites was evaluated before and after the immersion in Hanks' solution. The strength of the composites was also evaluated by four-point bending test. The Young's modulus of the compacts was governed by the porosity and was comparable to the human bone in the porosity range from 24 to 34%. The Young's modulus of sintered pTi/HA composites was larger than that of pTi. The Young's modulus of the sintered pTi/HA composites decreased after immersion in Hanks' solution. The proof and bending strengths of the sintered pTi/HA composites were larger than those of pTi. Solid solution hardening of Ti by oxygen contributed the increase of the proof strength. [doi:10.2320/matertrans.M2010092]

The microstructures of Zr-added Co-29Cr-6Mo alloy compacts fabricated with a metal injection molding (MIM) process and their metal release from the compacts immersed in 1% lactic acid were investigated for medical applications. The relationship between the microstructure and amount of Co released from the compacts is discussed phenomenologically. The relative density of the Co-29Cr-6Mo compacts increased when Zr was added to the powder with amounts of 0.03 and 0.1 mass% and sintered in Ar or N-2. The amounts of Co released from the compacts containing 0.03 and 0.1 mass% Zr sintered in Ar N-2 were smaller than those from the other compacts. Therefore, the addition of Zr to the Co-29Cr-6Mo powders enhanced the sintering of the compacts and decreased the porosity in the resultant products, leading to the suppression of the Co release from the compacts. When the Zr-added Co-29Cr-6Mo alloy powders were sintered in N-2, the relative density of the compacts was smaller than that of those sintered in Ar. The powders were nitrided during sintering in N-2, and the nitrides disturbed the densification during sintering. In addition, a lamellar structure was formed in the Co-29Cr-6Mo and Co-29Cr-6Mo-0.5Zr compacts. The amount of Co released from these compacts was larger than that released from the other compacts because local corrosion occurred at the interface between the different phases in these compacts during immersion in 1% lactic acid. In the MIM process, a small addition of Zr (less than 0.1 mass%) to the Co-29Cr-6Mo alloy is effective for densification during sintering and suppression of the Co release from the compacts. [doi:10.2320/matertrans.M2010040]

The microstructures and magnetic susceptibilities of Zr-Mo alloys were investigated to develop a Zr alloy with a low magnetic susceptibility for magnetic resonance imaging (MRI) The microstructure was evaluated with an X-ray diffractometer (XRD), an optical microscope (OM) and a transmission electron microscope (TEM), and the magnetic susceptibility was measured with a magnetic Susceptibility balance. The alpha' phase with acicular structure was dominant in Zr-1Mo alloys. while the omega and beta phases with the equiaxed and relatively flat (no acicular) microstructure was dominant in Zr-3Mo. The mixed microstructural features of Zr-1Mo and Zr-3Mo were observed in Zr-2Mo, which consists of the alpha', omega and beta phases. The beta phase is stabilized when the Mo content exceeds over 3 mass% Mo As-cast Zr-Mo alloys showed a minimum Value of magnetic susceptibility at 3 mass% Mo. and the value abruptly increased up to 10% Mo before remaining stable up to 15 mass% Mo XRD, OM and TEM revealed that the minimum value of the susceptibility was closely related to the appearance of the athermal omega phase in the beta phase As the Mo content decreases from 3 mass%, the alpha' phase appears with the omega and beta phases Oil the other hand, as the Mo content increases from 3 mass%, the beta phase increases and the omega phase decreases Thus the appearance of the alpha and beta phase leads to an increase in magnetic Susceptibility The magnetic susceptibility of as-cast Zr-3Mo alloy was almost one-third that of Ti-6AI-4V, which is commonly used for medical implant devices. Zr-Mo alloys are useful for medical devices used under MRI (C) 2009 Acta Materialia Inc Published by Elsevier Ltd. All rights reserved

Changes in Young's modulus of the Co-31 mass%Ni-19 mass%Cr-10 mass%Mo alloy (Co-Ni based alloy) with cold-swaging. combined with heat-treatment at temperatures from 673 to 1323 K, was investigated to enhance the Young's modulus of Co-Ni based alloy. After cold-swaging, the Co-Ni based alloy, forming &lt; 111 &gt; fiber deformation texture, shows the Young's modulus of 220 GPa. Furthermore, after ageing the cold-swaged alloy at temperatures from 673 to 1323K. the Young's modulus increased to 230 GPa, accompanied by a decrease in the internal fiction and an increase in the tensile strength. This suggests that the increment in Young's modulus is caused by a moving of the vacancies to the dislocation cores and a continuous locking of the dislocations along their entire length with solute atoms (trough model). By annealing at 1323 K after cold swaging, Young's modulus slightly increased to 236 GPa. On the other hand, the tensile strength decreases to almost the same value as that before cold swaging due to recrystallization. These results suggest that the Young's modulus and the strength in the present alloy are simultaneously enhanced by the continuous dislocation locking during aging as well as the formation of &lt; 111 &gt; fiber deformation texture. [doi: 10.2320/matertrans.M2009327]

The magnetic susceptibilities and microstructures of Zr-Nb binary alloys were investigated to develop a new metallic biomaterial with a low magnetic susceptibility for magnetic resonance imaging (MRI). The magnetic susceptibility was measured with a magnetic susceptibility balance, and the microstructure was evaluated with an X-ray diffractometer (XRD), an optical microscope (OM), and a transmission electron microscope (TEM). Zr-Nb alloys as-cast showed a minimum value of magnetic susceptibility between 3 and 9 mass% Nb, and the value abruptly increased up to 20 mass% Nb, followed by a gradual increase with the increase of the Nb content. XRD, OM, and TEM revealed that the minimum value of the susceptibility was closely related to the appearance of the athermal omega phase in the beta phase. Since the magnetic susceptibility of Zr-3Nb alloy consisting of an alpha' phase was as low as that of Zr-9Nb alloy consisting of the beta and omega phases, that of the omega phase was lower than that of the alpha' and beta phases. When Zr-16Nb alloy was heat-treated, the isothermal omega phase appeared, and, simultaneously, the magnetic susceptibility decreased. Therefore, the omega phase contributes to the decrease of the magnetic susceptibility, independently of the formation process of the omega phase. The magnetic susceptibility of the Zr-3Nb alloy as-cast was almost one-third that of Ti-6Al-4V alloy, which is commonly used for medical implant devices. Zr-Nb alloys are useful for medical devices used under MRI. [doi:10.2320/matertrans.M2009187]

Titanium and zirconium were immersed in Hanks&apos; solution with and without calcium and phosphate ions, and the surfaces were characterized with X-ray photoelectron spectroscopy (XPS) to determine the mechanism of calcium phosphate formation on titanium in simulated body fluids and in a living body. In addition, they were cathodically polarized in the above solutions. XPS characterization and cathodic polarization revealed differences in the surface properties in the ability of calcium phosphate formation between titanium and zirconium. The surface oxide film on titanium is not completely oxidized and is relatively reactive; that on zirconium is more passive and protective than that on titanium. Neither calcium nor phosphate stably exists alone on titanium, and calcium phosphate is naturally formed on it; calcium phosphate formed on titanium is stable and protective. On the other hand, calcium is never incorporated on zirconium, while zirconium phosphate, which is easily formed on zirconium, is highly stable and protective. Our study presents new information regarding the surface property of titanium and demonstrates that the characteristics of titanium and zirconium may be applied to various medical devices and new surface modification techniques. (C) 2009 Elsevier B.V. All rights reserved.

The effect of a cell-adhesive peptide containing Arg-Gly-Asp (RGD) immobilized through poly(ethylene glycol) (PEG) on titanium (Ti) on calcification by MC3T3-E1 cells was investigated to develop a new surface mollification technique using biofunctional molecules. RGD was immobilized on Ti through PEG, both terminals of which were terminated with -NH(2) and -COOH to combine with the Ti surface and RGD. PEG was immobilized on Ti with electrodeposition, and RGD, with immersion. For comparison, glycine was employed because it is the simplest molecule containing both -NH(2) and -COOH at its terminals. MC3T3-E1 cells were cultured and differentiation-induced on each specimen, and the cell calcification properties were investigated. As a result, there was no significant difference in the morphology and extension of MC3T3-E1 cells cultured on each specimen, while the number of cells cultured on RGD/PEG/Ti was the largest. After differentiation-induction, there was no significant difference in the ALP activity among all specimens. On the other hand, the level of cell calcification on RGD/PEG/Ti was the highest. Therefore, the hard tissue compatibility of Ti is improved by immobilizing RGD through functional molecules which have a long molecular chain. (c) 2008 Elsevier Ltd. All rights reserved.

A trial on an artificial hip joint stem made of Ni-free Co-29Cr-6Mo alloy was conducted by an isothermal hot semiclosed die forging method. The hot forging conditions (i.e., sample dimensions, forging temperature and stroke-speed) were determined by process simulation using &ldquo;DEFORM-3D&rdquo; based on FEM. A prototype stem with a shape designed using a FEM simulator was successfully obtained without surface defects or flaws under the predetermined forging conditions. The microstructure of the obtained stem consisted of mainly the &epsilon; (H.C.P.) phase as well as the minor &gamma; (F.C.C.) and &sigma;(CoCr:<i>P42/mnm</i>) phases. In addition, inhomogeneous distributions of the &sigma; phase and grain size could be observed in the microstructure of the stem, resulting from the inhomogeneous distributions of effective strain rate, effective strain and effective stress induced in the stem during the forging process. Thus, Vickers hardness exhibited marked scattering, depending on the position of the stem.

The isoelectric points (IEPs) of two zwitterions, glycine and both-terminals-terminated poly(ethylene glycol) (NH(2)-PEG-COOH), were determined from the titration curves, and the thicknesses of zwitterion layers immobilized on titanium (Ti) with immersion and electrodeposition at various pH based on IEPs were evaluated with ellipsometry to investigate the effect of pH and the immobilization technique on the interactions between the zwitterions and the Ti surface. From the titration curves, pK(1), pK(2), and the IEP of glycine were determined as 2.8, 8.9, and 5.9, respectively, and pK(1), pK(2), and the IEP of NH(2)-PEG-COOH were determined as 2.1, 11.7, and 6.9, respectively. At a certain specific pH, (+)H(3)N-CH(2)-COO(-) or (+)H(3)N-PEG-COO(-) was formed by hydrolysis of glycine or NH(2)-PEG-COOH. In addition, the Ti surface was negatively charged at this pH. As a result, for immersion, the electrostatic reactivity between terminal groups of zwitterions and hydroxyl groups on the Ti surface was the highest and the thickness of the immobilized layer was significantly the largest at pH 12. For electrodeposition, glycine, with its lower molecular weight, was more easily attracted to the Ti surface than NH(2)-PEG-COOH, which has a higher molecular weight, while the thickness of the immobilized layer was the greatest at pH 12 in both zwitterions. (C) 2008 Elsevier Inc. All rights reserved.

The in vitro short-term platelet adhesion oil various metals, as accelerated by the addition of Ca(2+), was evaluated in this study. Metals used for medical devices [ail austenitic stainless steel, a cobalt (Co)-chromium (Cr)-molybdenum (Mo) alloy, a titanium (Ti)-6 aluminum (Al)-4 vanadium (V) alloy, a Ti-6Al-7 niobium (Nb) alloy, a Ti-nickel (Ni) alloy, and commercially pure Ti] were immersed into a platelet-rich plasma Solution for 5 or 20 min, and platelet adhesion and aggregation on the Surfaces were observed using a scanning electron microscope. The platelet adhesion level oil each metal after 5 min of immersion in it platelet-rich plasma solution was the smallest in this order: stainless steel &lt;= Co-Cr-Mo alloy &lt; Ti-6Al-4V alloy &lt; Ti-6Al-7Nb alloy &lt; Ti-Ni alloy = Ti. The levels after 5 min of immersion were almost the same as those after 20 min of immersion. Platelet adhesion was minimal oil stainless steel and Co-Cr-Mo alloy, which have it Cr(2)O(3)-containing passive surface oxide film, but was accelerated oil Ti and Ti alloys having a TiO(2)-contanining film. A Cr(2)O(3)-containing oxide film has a lower relative permittivity than a TiO(2)-contanining film, it thus supports a larger electrostatic force than the latter, adsorbs more albumins, which work as inhibitory proteins, and inhibits platelet aggregation. Therefore, platelet adhesion and aggregation are controlled by the composition of the surface oxide film oil a metal due to the relative permittivity of the metal, which influences the amount of adsorbed proteins.

An improvement in the mechanical properties of a biomedical Ni-free Co-Cr-Mo alloy under as-cast condition has been examined by means of tensile tests and microstructure observations. The solubility of N in Co-Cr-Mo alloys increases with increasing Cr content from 29 to 34 mass%. This results in a significant improvement in mechanical properties such as yield stress, tensile strength, and fracture elongation. The improvement in the mechanical properties results from the gamma phase stabilization and inhibition of the a phase formation due to N addition. Increasing the Cr content also has contributed to the improved mechanical properties.

A series of Co-Cr-Mo alloys with Fe contents ranging from 5 to 20 mass% were prepared in order to study the effect of Fe addition on the microstructures and mechanical properties (tensile strength, yield strength, elongation, and Rockwell C scale hardness) of Ni- and C-free Co-Cr-Mo alloys. Fe was added with the composition of Co-29Cr-6Mo-xFe (where x = 0, 5, 10, and 20). Alloys were heat-treated at 1230 degrees C for 3 h and 1250 degrees C for 5 h. These heat treatment conditions were decided as considering pre-heat treatment followed by hot-forging process. An optical microscope and an XRD were used to determine the microstructure and identify the crystal structure. The volume ratio of gamma phase to epsilon phase increases not only with heat treatment temperature and time but also with Fe content. The tensile strength, yield strength, and elongation are significantly improved by Fe addition. However, the tendency toward a phase formation becomes higher as the Fe content increases, causing a deterioration of mechanical properties. From the viewpoint of mechanical properties, the amount of Fe addition should be less than 10 mass% in pre-heated condition of Co-29Cr-6Mo alloys.

The wear behavior of a forged Co-29Cr-6Mo alloy without any Ni and C added has been investigated by using a tribosystem consisting of a pin-on-disc type wear testing machine in distilled water containing different dissolved oxygen content. Dissolved oxygen content in the distilled water was controlled by aerating with oxygen or by deaerating with argon. Wear volume in the distilled water containing high oxygen content is approximately two times larger than in that containing low oxygen content. Accordingly, it is deduced that the overall wear volume is significantly affected by the dissolved oxygen content in the distilled water surrounding the tribosystem. Although abrasive wear, caused by wear debris, is operative as a wear mechanism in the present tribosystem irrespective of oxygen content, the transfer of the wear debris to sliding surfaces, as well its the aggregation of the wear debris on the sliding Surfaces, is more prone to occur during the wear process with the lower oxygen content. Therefore, in the present tribosystem with the lower oxygen content, since the transfer of the wear debris to the disc or the pin readily occurs, the generation of the wear debris does not directly contribute to the wear volume, leading to the apparently lower wear volume in the tribosystem with lower oxygen content than in that with higher oxygen content; the transfer of the wear debris is not counted as wear loss because the wear volume is estimated based on the loss in disc and pin weight that occurs during the wear test.

Mechanical properties of Co-29Cr-6Mo alloys consisting of epsilon phase and sigma phase were examined at room temperature. Solution treatment at 1523 K for 7.2 ks was carried out for cast Co-29Cr-6Mo alloy, followed by various aging treatments at 1023 K for up to 21.6 ks. The area fraction of the sigma phase in the aged alloys increases with the aging time at 1023 K and reaches 0.6% after aging at 1023 K for 21.6 ks. However, mechanical properties such as 0.2% proof strength, ultimate tensile strength and plastic elongation of the aged alloys do not depend on the aging time. It is found that the or phase less than 0.6% does not cause the deterioration of mechanical properties of the aged Co-29Cr-6Mo alloy.

Co-29Cr-6Mo alloys consisting of 0 similar to 1.76% Zr were prepared and heat-treated at 1210 degrees C for 2 h or 1230 degrees C for 3 h. Three types of precipitates were identified. With more than 0.37% Zr content, precipitates are mixtures of or phase and (Zr, Mo)-rich phase. The sigma phase dissolves into a matrix and the (Zr, Mo)-rich phases change its composition into a Zr-rich phase with heat treatment. An alloy with a solid solution containing 0.01% Zr exhibits improved mechanical properties.

A modified in-rotating-water spinning process has been applied for producing the alloy wire of Ni-free Co-29Cr-8Mo suitable for biomedical use. The microstructure and tensile properties of the as-spun and heat-treated wires were investigated using backscattered electron microscopy, X-ray diffraction analyses and tensile tests. The microstructure of the as-spun wire exhibits a cellular structure and evolves into an equiaxed and fine-grained structure with an average grain size of several micrometers, containing sigma-phase precipitates after heat treatment at 1373 K. Grains increase in size and reach an average diameter ranging from 10 to 20 mu m at 1473 K. The crystal structure of the as-spun wire changes from face-centered cubic to strain-induced hexagonal close-packed martensite through wire-drawing. The wiredrawing, combined with heat treatments, improves the mechanical properties of the as-spun wire. The present modified melt-spinning process is an effective method to produce Ni-free Co-Cr-Mo alloy wire for biomedical applications. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In order to examine the effects of carbides and microstructures on the wear behavior of a biomedical Co-Cr-Mo alloy in Hanks solution, the wear behavior of a forged Co-Cr-Mo alloy without addition of Ni and C (hereafter designated the forged CoCr alloy) and a high carbon cast CoCr alloy (hereafter designated the cast CoCr alloy) sliding against themselves have been investigated using a pin-on-disk type wear testing machine. The wear loss of the forged CoCr alloy was found to be much smaller than that of the cast CoCr alloy. Carbide precipitation in the coarse-grained structure of the cast CoCr alloy would account for the higher abrasive wear loss. The forged CoCr alloy, with no carbide and a refined grain size, which is more prone to strain-induced martensitic transformation, would exhibit excellent like-on-like wear resistance, mostly against surface fatigue wear, compared to the carbide-hardened cast CoCr alloy. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Porous Ti compacts reinforced by ultra-high molecular weight polyethylene (UHMWPE) were fabricated and their mechanical properties were evaluated. Ti powder atomized by plasma rotating electrode process (PREP) was sintered at temperatures ranging from 1473 K to 1673 K for 7.2 ks in a vacuum. The porous Ti compacts contain the porosity of about 40%, irrespective of the sintering temperature. Porous Ti/UHMWPE composites were successfully fabricated by compressing UHMWPE powder into the porous Ti compacts. The compacts exhibit open pore structure and enables the penetration of UHMWPE into pores in the compacts. Young's modulus of the composites is higher than that of the porous Ti compacts. The increment in Young's modulus is not simply explained by the rule of mixture because Young's modulus of the UHMWPE is approximately 1.3 GPa. Three-point bending strength of the composites is improved, presumably due to the local stress relief by UHMWPE in the vicinity of neck in the composites.

The present study was designed to investigate whether porous titanium (Ti) having Young's modulus similar to bone has osteoconductive characteristics in rat critical-sized calvarial bone defect. The effect of coating by octacalcium phosphate (OCP) was also examined. OCP is known as a precursor of initial mineral crystals of biological apatite in bones and teeth. Ti powder was prepared by plasma rotating electrode process in an Ar atmosphere. Then, porous Ti disks, 8 mm in diameter with 1 mm thick, were obtained using the particles ranging from 300 to 500 μm, by sintering at 1573 K without applied pressure. The disks had about 35 vol% in porosity and about 10 GPa in Young's modulus which corresponds to that of human cortical bone. Newly formed bone was observed so as to fill the pore up at 12 weeks, confirming the ability to conduct the ingrowths of the bone tissue. Although in vitro study showed that proliferation of mouse bone marrow stromal ST-2 cells was inhibited on the dishes coated by OCP rather than the control dish, OCP coating on porous Ti seemed to stimulate the bone formation in vivo. Taken together, it seems likely that porous Ti having Young's modulus similar to bone shows osteoconductive characteristics to conduct bone ingrowths. OCP could be a potential coating agent to assist bone regeneration on porous Ti.

Effect of the sigma (a) phase in Co-29Cr-6Mo alloy on corrosion and mechanical behavior has been investigated. The area fraction of the a phase varies depending on the aging time at 1023 K. The area fraction of the sigma phase increases with increasing aging time and reaches 0.6 % after aging at 1023 K for 21.6 ks. Inductively coupled plasma atomic emission spectrometer (ICP-AES) analysis revealed the quantity of released Co ion shows almost the same values regardless of different area fraction of the a phase. In addition, plastic elongation and 0.2% proof strength exhibit almost the same values, although the alloys have different area fraction of the a phase. These results suggest that a small amount of the a phase (<0.6%) hardly affect the corrosion and mechanical properties in the Co-29Cr-6Mo alloy.

The microstructure and mechanical properties of compacts produced from hot-pressing the Co-29Cr-6Mo alloy powder, fabricated by gas atomization, were investigated in this study. The average diameter of the alloy powder is 41 μm. Electron probe micro analysis revealed that the concentration scattering of chromium and molybdenum is relatively small between the powders. The compact hot-pressed at 1273 K in Ar with an applied pressure of 80 MPa possesses the relative density of 97% and the fine grain (2.7 μm). The ultimate tensile strength of the compact is 1240 MPa, which is comparable to that of the forged Co-29Cr-6Mo alloy.

Porous Co-29Cr-6Mo alloy compacts were fabricated and their microstructures were examined. The Co-29Cr-6Mo alloy powders were atomized by using Plasma Rotating Electrode Process (PREP) in an Ar atmosphere. These powders were hot-pressed at 1223 K in Ar or nitrogen and annealed at 1473 K in vacuum or nitrogen. X-ray analysis revealed that the y phase (f.c.c.) mostly exists in the compact hot-pressed in nitrogen although the E phase (h.c.p.) is dominant in the compact hot-pressed in Ar. In addition, precipitates are observed at the interdendritic region in the compact hot-pressed in nitrogen. These results suggest that the Co-29Cr-6Mo alloy powders react with nitrogen to stabilize the y phase. Accordingly, the constituent phase in the Co-29Cr-6Mo alloy is strongly affected by the atmosphere during hot-pressing.

The effects of Fe addition on the mechanical properties, corrosion resistance, and cytotoxicity of Co-29Cr-6Mo alloys were studied for the possibility of new biomaterial applications. The amount of Fe addition was varied from 0 to 20 wt%. Increasing Fe content up to 10 wt% increases tensile strength and ductility of Co-29Cr-6Mo alloy. Anodic polarization test in the saline and the Hank's solution shows that Fe added Co-29Cr-6Mo alloys remains in passive state before breakdown. Moreover, it is found from a cytotoxicity test that Fe added Co-29Cr-6Mo alloys shows a good biocompatibility. These results concluded that Fe added Co-29Cr-6Mo alloys have a reasonable mechanical properties, good corrosion resistance and biocompatibility.

Effect of the sigma (or) phase in Co-29Cr-6Mo alloy on corrosion behavior in saline solution has been investigated. The area fraction of the a phase contained in Co-29Cr-6Mo alloy varies depending on the aging time at 1023 K. The a phase is mainly observed at grain boundaries. The area fraction of the or phase increases with increasing aging time and reaches 0.6% after aging at 1023 K for 21.6 ks. The Co-29Cr-6Mo alloys aged at 1023 K for various aging times were immersed in saline solution at 3 10 K for I week and metal ions released from the alloys were examined by inductively coupled plasma atomic emission spectrometer (ICP-AES). The quantity of a released Co ion does not depend on the aging time and shows almost the same value regardless of the different area fraction of the or phase, while that of released Cr, Mo and Ni ions increases with increasing area fraction of the a phase. Results of polarization test in saline solution at 3 10 K revealed that passive current density and breakdown potential of Co-29Cr-6Mo alloys aged at 1023 K for various aging times exhibit almost the same values, although the alloys have different area fraction of the or phase. These results suggest that a small amount of the a phase (&lt; 0.6%) hardly affect the formation and breakdown of passive film in the Co-29Cr-6Mo alloy aged at 1023 K.

The effect of pre-heat treatments, followed by a hot forging process, on the microstructure and strength of Co-Cr-Mo alloys was investigated. Four pre-heat treatments were conducted at 1443, 1473, 1503 and 1533 K for three different time condition: 7.2 ks, 21.6 ks and 54.0 ks and then water cooled to room temperature. Tensile tests and XRD analyses were carried out on both ascast alloy and heat-treated alloys. The volume fraction of retained gamma phase increases with an increase in temperature of heat treatment, suggesting that the gamma-epsilon martensitic transformation is suppressed after experiencing the heat treatment at higher temperatures. Tensile strength slightly decreases with increasing the temperature and the time of heat treatment, whereas the ductility slightly increases. The sigma phase completely dissolves into matrix when the alloy is heat-treated at temperature of 1533 K longer than 21.6 ks.

A dry wear behavior of a forged Co-Cr-Mo alloy without Ni and C additions have been investigated using a ball-on-disc type wear testing machine with an alumina ball in ambient air. The wear factor of the Co-Cr-Mo forged alloy without Ni and C additions (hereafter, designated the forged alloy) shows negative contact load dependence. The coefficient of friction decreases with increasing contact load. Worn surfaces are hardened during the wear tests, forming oxide films. This results from significantly high work hardening rate of the forged alloy, caused by the strain-induced martensitic transformation from an fcc-gamma phase to an hcp-epsilon phase, which contributes to the improvement in the dry wear resistance. Wear mechanisms of the forged alloy are discussed on the basis of Hertzian contact theory and observations of the wear scars formed on the alloy disc and the alumina ball surfaces. It is considered that the dominant wear mechanism of the forged alloy is the mild adhesive wear, though the extrinsic abrasive wear mediated by the wear debris, i.e., third-body abrasive wear, is exerted as an extrinsic wear mechanism. In addition, it is suggested that a delamination wear resulting from the fatigue fracture likely occurs under the present dry wear condition.

Porous Co-29Cr-6Mo (mass%) compacts without Ni were fabricated by hot pressing and their microstructure and mechanical properties were investigated. PREPed Co-29Mo-6Mo powder with a diameter range (300-500 mu m) was hot-pressed under the Uniaxial pressure of 40 MPa at 1223 K for 7.2 ks. Hot-pressed compacts were annealed at 1473 K for 7.2 ks for further sintering. X-ray diffraction analysis revealed that gamma and epsilon phases appeared dominantly in the PREPed powder, while epsilon and sigma phases coexisted in the compact which was hot-pressed at 1223 K. After annealing at 1473 K, only the E phase was detected although the gamma phase was stable at this temperature. Therefore. the F phase formed during furnace cooling. Tensile behavior of porous Co-29Cr-6Mo compacts was characterized by the stress-strain curves. The as-hot pressed compact showed linear deformation followed by sudden fracture. The annealed compact showed higher ultimate tensile strength (UTS) and lower yield strength than the as-hot pressed compact. Young's modulus of the annealed compact was difficult to determine from the stress-strain curve. However, the annealed compact possessed a tensile strength of 116 MPa, which is comparable to that of human cortical bone.

The wrought Co-Cr-Mo alloys with C contents of 0.02, 0.09 and 0.18% (mass%) were fabricated by hot-forging process to Study the influence of carbon contents on the microstructures and mechanical properties. The microstructures of Co-29Cr-6Mo-0.02C and Co-29Cr-6Mo-0.09C consist of equiaxed uniform grains which contain stacking faults. twins and epsilon martensite hands. No carbide found at inter- and intragranular region. Co-29Cr-Wo-0.18C consists of irregular grain sizes and carbide found at inter- and intra-granular region. The carbide in Co-29Cr-6Mo-0.18C was identified as M23C6 type carbide from the XRD pattern analysis. It is found that the amount of stacking fault and epsilon martensite are strongly dependent upon the C content. The density of stacking faults and epsilon martensites observed in Co-29Cr-6Mo-0.09C decrease as compared with those observed in Co-29Cr-6Mo-0.02C. Moreover. the volume fraction of the gamma phase slightly increased with C content. Within an extent of C addition that no carbide precipitation occurs, the carbon addition reduces the amounts of crystal defects such as stacking faults and twins. and epsilon martensites. In addition, tensile strength slightly increases with C content and ductility reaches a maximum at C content of 0.09%. though 0.2% proof strength shows no noticeable differences.

The effect of pre-heat treatments, followed by a hot forging process, on the microstructure and strength of Co-Cr-Mo alloys was investigated. Four pre-heat treatments were conducted at 1170, 1200, 1230 and 1260 degrees C for three different time condition: 2, 6 and 15 h and then water cooled to room temperature. Tensile tests and XRD analyses were carried out on both as-east alloy and heat-treated alloys. The volume fraction of retained gamma phase increases with increasing the heat treatment temperature, suggesting that the gamma -&gt; epsilon martensitic transformation is suppressed by a higher temperature heat treatment. Tensile strength slightly decreases with increasing the heat treatment temperature and the heat treatment time, whereas the ductility slightly increases. The a phase completely dissolves into matrix when the alloy is heat-treated at 1260 degrees C for longer than 6 h.

Laminates of an iron aluminide intermetallic alloy and a CrMo steel prepared by solid state bonding has been investigated to improve the oxidation resistance of the steel. Microstructural observation reveals that the joint is free of any defects, and columnar grains are evolved towards the steel from the joint interface at high temperatures above A(3). A continuous change of composition is observed between the constituents, without the formation of an intermetallic phase. The formation of the columnar microstructure is explained by a nucleation at the joint interface caused by A1 diffusion to stabilize a, followed by grain growth in the steel. The composite demonstrates high bonding strength due to sufficient interdiffusion between the constituents, and an improvement of the oxidation resistance of the steel due to A1 diffusion from the intermetallic to the steel resulting in alpha-alumina oxide on the surface. The composite prepared by clad-rolling is found to be free of crack and warp, and exhibits outstanding resistance to oxidation. These results suggest that the composite based on iron aluminide intermetallic has a potential for oxidation resistant application. (c) 2005 Elsevier Ltd. All rights reserved.

Hydroxyapatite (HA) coating was carried out by plasma spraying on bulk Ti substrates and porous Ti substrates having a Young's modulus similar to that of human bone. The microstructures and bond strengths of HA coatings were investigated in this study. The HA coatings with thickness of 200-250 mu m were free from cracks at interfaces between the coating and Ti substrates. XRD analysis revealed that the HA powder used for plasma spraying had a highly crystallized apatite structure, while the HA coating contained several phases other than HA. The bond strength between the HA coating and the Ti substrates evaluated by standard bonding test ASTM C633-01) were strongly affected by the failure behavior of the HA coating. A mechanism to explain the failure is discussed in terms of surface roughness of the plasma-sprayed HA coatings on the bulk and porous Ti substrates. (C) 2005 Springer Science + Business Media, Inc.

A dry wear behavior of a forged Co-Cr-Mo alloy without Ni and C additions have been investigated using a ball-on-disc type wear testing machine with an alumina ball in ambient air. The wear factor of the Co-Cr-Mo forged alloy without Ni and C additions (hereafter, designated the forged alloy) shows negative contact load dependence. The coefficient of friction decreases with increasing contact load. Worn surfaces are hardened during the wear tests, forming oxide films. This results from significantly high work hardening rate of the forged alloy, caused by the strain-induced martensitic transformation from an fcc-gamma phase to an hcp-epsilon phase, which contributes to the improvement in the dry wear resistance. Wear mechanisms of the forged alloy are discussed on the basis of Hertzian contact theory and observations of the wear scars formed on the alloy disc and the alumina ball surfaces. It is considered that the dominant wear mechanism of the forged alloy is the mild adhesive wear, though the extrinsic abrasive wear mediated by the wear debris, i.e., third-body abrasive wear, is exerted as an extrinsic wear mechanism. In addition, it is suggested that a delamination wear resulting from the fatigue fracture likely occurs under the present dry wear condition.

Porous Ti alloy compacts were fabricated and their microstructure and mechanical properties were investigated in this study. Ti alloy powders were atomized from Ti-15Mo-5Zr-3Al (wt.%) bar using the plasma rotating electrode process (PREP) in an Ar atmosphere. These alloy powders were sintered under 1-30 MPa at 1223 K for 7.2 ks by hot-pressing (HP). These compacts were solution treated at 1223 K for 1.2 ks, and then quenched into iced water (STQ). X-ray diffraction analysis revealed that a small amount of alpha phase appeared in the beta phase of the HP compacts, while not in the STQ compacts. Young's modulus of STQ compacts is lower than that of HP compacts. It was found that the strength of porous Ti-15Mo-5Zr-3Al is higher than those of porous pure Ti and human cortical bone, as compared in the range from 10 to 30 GPa of Young's modulus for human bone. (c) 2005 Elsevier B.V All rights reserved.

Nitrogen-doped and -undoped Ti powders were obtained by Plasma Rotating Electrode Process (PREP) in an Ar atmosphere using Ar-2 vol.%N2 and pure Ar, respectively, for plasma flame. Auger electron spectroscopy (AES) revealed that nitrogen is enriched at the surface of nitrogen-doped Ti powder and decreases along with the depth direction. Microstructure of a compact prepared by hot pressing the nitrogen-doped Ti powder shows a shell structure. The outer area is considered to form by the diffusion of nitrogen. This microstructure disappears after annealing at 1373 K for 3.6 ks. It is found that the compressive yield strength of porous Ti compacts can be improved by introducing nitrogen in Ti powder and is superior to that of human cortical bone. © 2005 Trans Tech Publications, Switzerland.

In order to examine the influence of variation in grain size and microstructure on mechanical properties of a low Ni and C-containing Co-29Cr-6Mo alloy for biomedical implant materials, the tensile properties and the dry friction wear characteristics of the wrought Co-29Cr-6Mo alloy without addition of Ni and C were investigated. The microstructure of as-forged alloys, consisting of fee phase mixed with athermal hep martensite, is found to become finer as the reduction during forging increases. The hot-forging processes for fabricating the fine microstructure with different grain sizes of 43, 11 and 3 μm has been successfully established under the condition that forging temperature of higher than 1273 K is strictly kept during forging. The tensile properties, such as the yield stress, the tensile stress and the elongation, are improved with decreasing the grain size and thereby increasing the volume fraction of the fee phase in the microstructure. The dry wear resistance against the alumina ball is enhanced by decreasing the grain size. © 2005 Trans Tech Publications, Switzerland.

Porous Ti compacts for biomedical applications are successfully fabricated in the porosity range from 5.0 to 37.1 vol% by controlling sintering conditions and Ti powder sizes. Young's modulus and bending strength at the porosity of around 30 vol% are found to be similar to those of human cortical bone. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Four Mo/Mo5SiB2 in-situ composites with different volume fractions of Mo solid solution, V-f(Mo), were produced by ingot metallurgy and their microstructure, thermal expansion, compressive strength and oxidation behavior were investigated relating to V-f(Mo). Mo-8.5Si-13.2B annealed at 2073 K for 24 h has nearly eutectic microstructure consisting of Mo solid solution and Mo5SiB2. to For higher V-f(Mo), there are micro-cracks in Mo5SiB2, phase probably induced by thermal stress during the cooling process. Mo-8.5Si-13.2B shows the highest yield stress among the four Mo/Mo5SiB2 in-situ composites, and about 1 GPa even at 1773 K. For lower V-f(Mo) than that of Mo-8.5Si-13.2B, the steady state oxidation behavior is observed at temperatures between 1173 and 1473 K, indicating that the oxidation resistance is relatively good, whereas the oxidation resistance is catastrophic for higher V-f(Mo) than that of Mo-8.5Si-13.2B. (C) 2003 Elsevier Ltd. All rights reserved.

A multiphase Mo-Si-B alloy coating can be successfully deposited onto the Mo-ZrC composite using a low pressure plasma spraying method. Microstructure of the plasma sprayed Mo-Si-B coating consists of Mo5Si3, Mo3Si and Mo5SiB2 phases, which are the same constituents as Mo-Si-B alloy powder. Nanostructure is formed in the Mo-Si-B coating with the eutectic composition owing to the rapid quenching effect by plasma spraying. The oxidation behavior of the Mo-Si-B coating shows rapid mass loss followed by slow mass gain at 1673 K in Ar-20%O-2. Dense and adherent borosilicate glass formation passivates the coating against further oxidation at 1673 K. (C) 2003 Elsevier Science Ltd. All rights reserved.

Microstructures and mechanical properties of porosity-graded Ti compacts were investigated in this study. To fabricate the porosity-graded compacts, Ti powders with three different particle sizes, 65, 189 and 374mum were prepared by the plasma rotating electrode process (PREP) and the gas atomization process, and these powders were sintered with and without applied stress. Porosity and pore size of porosity-graded Ti compacts decrease significantly with decreasing initial powder size and by applying stress. The most porous layer (374 mum) is severely deformed in compression tests compared to other layers. The compressive strength of porosity graded-compacts is found to be in fairly good agreement with the strength of most porous layer. Bend strength of compact sintered at 1223 K and I MPa (223.3 MPa) shows a higher value than that of human bone (156.9 MPa).

Joining of oxidation-resistant Mo-Si-B multiphase alloy and to heat-resistant Mo-ZrC in-situ composite was studied through observation of microstructural evolution and measurement of hardness near the joint interface. As jointed at 1773 K for 7.2 ks, Mo3Si is formed in Mo-ZrC because of the non-equilibrium state between Mo and Mo5Si3. As jointed at 1973 K for 5.4 ks, a reactant containing Mo, Zr and Si is formed along the interface between Mo-Si-B and Mo-ZrC. Si is enriched in prior ZrC particles away from the interface in distances of 0 to about 4 mum. The hardness of Mo-ZrC after jointed at 1773 K shows no change near the joint interface in the range beyond 5 mum. On the other hand, the hardness values of Mo-ZrC jointed at 1973 K increases in the range of 0-10 mum. This indicates that Si diffuses at least by 10 mum into Mo in Mo-ZrC during bonding at 1973 K for 5.4 ks. (C) 2003 Elsevier Science Ltd. All rights reserved.

Microstructures and fracture toughness of arc-melted and directionally solidified Mo-ZrC eutectic composites were investigated in this study. Two kinds of directionally solidified composites were prepared by spot-melting and floating zone-melting. Microstructure of the arc melted composite (AMC) consists of equiaxed eutectic colonies, in which ZrC particles are dispersed. The spot-melted composite (SMC) exhibits spheroidal colony structure, which is rather inhomogeneous in size and morphology. ZrC fibers in the eutectic colonies are aligned almost parallel to the growth direction. Well aligned, homogeneous columnar structure with thin ZrC fibers evolves in the floating zone melted composite (FZC). Texture measurement by X-ray diffractometry revealed that the growth direction of Mo solid solution (Mo-SS) in FZC is preferentially &lt; 100 &gt;, while that of SMC is scattered. Fracture toughness K-Q evaluated by three point bending test using the single edge notched beam method is &gt;13 MPa m(1/2) for AMC, 20 MPa m(1/2) for SMC and 9 MPa m(1/2) for FZC. Intergranular fracture along colony boundaries is often observed in AMC. In contrast, transgranular fracture is dominant in SMC and FZC, although significant gaps caused by intergranular fracture are occasionally observed in SEM micrographs of SMC. Fracture surface in FZC is wholly flat. Pull-out of ZrC occurs owing to Mo/ZrC interfacial debonding in intergranularly fractured regions of AMC and SMC. Coarse elongated colonies in SMC and FZC induce transgranular fracture instead of intergranular fracture. Intergranular fracture and interfacial debonding in AMC and SMC causes frequent crack deflection accompanied by ligament formation and crack branching, which is responsible for the high fracture toughness of the composites. Preferred &lt; 100 &gt; growth of Moss phase in FZC leads to brittle {100} cleavage fracture associated with low fracture toughness. (C) 2002 Elsevier Science Ltd. All rights reserved.

Using pure Ti powder with particle sizes from 300 to 500 mum prepared by the plasma rotating electrode process (PREP), porous pure Ticompacts for biomedical applications were synthesized by powder sintering, and microstructures and mechanical proper-ties of the compacts were investigated in this study. Porous compacts having porosity of 19-35 vol% are successfully fabricated by controlling sintering condition, It is found that Young's modulus and compressive yield strength decrease linearly with increasing porosity, and porous Ti compacts having porosity of about 30-35 vol% exhibit identical Young's modulus of human bone.

The introduction of oxygen diffusion barrier such as alumina is one of the promising solutions to use Ni-based superalloys with TBC for longer periods. Three types of TBC systems containing alumina are proposed in this study. Residual thermal stresses at room temperature were calculated for the proposed systems using a linear plate model. In the case of a layered composite system (stabilized zirconia / alumina / bond coat), tensile stresses in the bond coat are shown to be much higher than its yield limit. If a pure bond coat layer was replaced by an alumina / bond coat graded layer was under zirconia layer, the stress distribution significantly depends on the profile of concentration. TBC systems containing metal-rich graded layer were found to have substantially reduced thermal stresses. The system of stepwise FGM is more promising from the standpoint of thermal stress relaxation.

Functionally graded (FG) NiCr/Al2O3 coatings with and without porosity were theoretically designed to alleviate thermal stress between coating and substrate. It is found that the thermal stress increases with increasing volume percent of Al2O3 in the coatings and the increase is more significant in the dense coating than in the porous coating. Introduction of porosity is suggested to decrease elastic modulus of the coating, thereby reducing thermal stress. Referring to the calculated stress distribution, FG coatings were produced by high velocity oxygen fuel spraying (HVOF). FG NiCr/Al2O3 coatings were successfully sprayed onto the carbon steel substrate as designed. That is, the composition of coatings is graded stepwise from NrCr to Al2O3 and porosity is also graded in the FG coatings. Porosity of 14-18% exists in Al2O3 layer, while NiCr layer contains almost no porosity. NiCr powder contributes to the densification of the coatings.

Microstructures and fracture toughness of Mo-ZrC eutectic composites were investigated in this study. Two kinds of composites were prepared with an arc-melting method and a directional solidification method. Each sample was annealed at 1873 K for 252 ks in vacuum for homogenization. Arc-melted and annealed composite (CA16) consists of equiaxed eutectic colonies, where fine ZrC particles are dispersed in Mo-ss grains. Columnar structure containing coarse eutectic colonies of Mo-ss and fibrous ZrC was observed in the directionally solidified composite (DS16). Preferred growth direction of Mo-ss in DS16 was identified almost parallel to &lt;110&gt;, while the orientation of ZrC is accumulated in the zone close to &lt;001&gt;. Fracture toughness measured by 3-point bending test at room temperature was 13 MPa.m(1/2) for CA16 and 20 MPa.m(1/2) for DS16. intergranular fracture was predominantly observed in CA16. On the other hand, DS16 exhibited transgranular fracture in a wide area, which is due to the columnar structure with coarse colonies. It is suggested that the intrinsic fracture resistance derived from the crystallographic orientation of Mo-ss contributes to fracture toughness of DS16. Additionally, it is found that ZrC fiber in DS16 causes crack blunting, more effectively than ZrC particle in CA16.

M-40 mol%TiC and Mo-20 mol%Nb-40 mol%TiC in-situ composites were synthesized by hot-pressing mixed Mo, Nb and TiC powders. Both composites consist of two phases, Mo solid solution (A2) and TiC (B1), after hot-pressing at 2073 K and 70 MPa for 2 h followed by annealing at 2073 K for 24h. Porosity of hot-pressed compacts decreased by Nb addition to Mo-40 mol%TiC. The composites have different microstructural features. Clusters consisting of fine bcc particles are observed in sizes similar to original Nb powder in Mo-20mol%Nb-40 mol%TiC, while there are no clusters in Mo-40 mol%TiC. These composites show excellent strength superior to monolithic TiC at high temperatures. The addition of Nb to M-40 mol%TiC suppresses effectively intergranular fracture above 1473 K. Furthermore. fracture toughness of these composites is higher than that of monolithic TiC. Fracture toughness of Mo-20 mol%rNb-40 mol%TiC is slightly lower than that of Mo-40 mol%TiC. The obtained results are discussed in relation to microstructural characteristics.

Microstructure and creep of are-melted and annealed Mo-40 mol%ZrC in-situ composite were investigated in this study. Microstructure after annealing is found to consist of primary ZrC particles and fine Mo/ZrC eutectic structure, i.e. hyper-eutectic structure. Compressive creep tests in the temperature range from 1673 to 1873 K indicate that the stress exponent, n: is approximately 5 in the stress range from 100 to 500 MPa, and the apparent activation energy for the creep deformation is estimated to be about 500 kJ/mol at 200 MPa and 300 MPa. TEM observation for crept specimens shows that the creep deformation is accompanied with sub-boundary formation in Mo solid solution phase. It is suggested that the creep deformation of the composite in the temperature range examined is interpreted in terms of the dislocation creep of Mo solid solution phase controlled by the lattice diffusion of either Mo or Zr.

In-situ composites of Nb3Al/Nb solid solution (Nb-ss) were produced by hot pressing of prealloyed powder prepared by the rotating electrode process (REP) and by isothermal forging of cast ingots. The microstructure and high temperature creep resistance have been investigated in the present study. Isothermally-forged and annealed Nb-14.1 and 19.5 mol.%Al alloy ingots have homogeneous, equiaxed grain structures, while Nb-16.5mol.%Al alloy made from the REP powder under vacuum hot pressing retains prior powder particle boundaries. Yield stress of the three Nb-Al in-situ composites at 1573 K is remarkably dependent on the volume fraction of a ductile Nb-ss phase; it increases with decreasing the ductile Nb-ss phase. The isothermally-forged and annealed Nb-19.5mol%Al ahoy exhibits good creep resistance at 1573 K. After creep of the isothermally forged specimens, high densities of dislocations were observed within Nb3Al grains, suggesting that Nb3Al deforms by dislocation creep at the present test conditions. Also, micro crack formation was observed at triple junctions of boundaries between Nb3Al grains. This observation indicates that microcracks are produced in Nb3Al grains because of the insufficient slip systems.