三浦 永理

We found that specific biomedical Ti and its alloys, such as CP Ti, Ti–29Nb–13Ta–4.6Zr, and Ti–36Nb–2Ta–3Zr–0.3O, form a bright white oxide layer after a particular oxidation heat treatment. In this paper, the interfacial microstructure of the oxide layer on Ti–29Nb–13Ta–4.6Zr and the exfoliation resistance of commercially pure (CP) Ti, Ti–29Nb–13Ta–4.6Zr, and Ti–36Nb–2Ta–3Zr– 0.3O were investigated. The alloys investigated were oxidized at 1273 or 1323 K for 0.3–3.6 ks in an air furnace. The exfoliation stress of the oxide layer was high in Ti–29Nb–13Ta–4.6Zr and Ti–36Nb– 2Ta–3Zr–0.3O, and the maximum exfoliation stress was as high as 70 MPa, which is almost the same as the stress exhibited by epoxy adhesives, whereas the exfoliation stress of the oxide layer on CP Ti was less than 7 MPa, regardless of duration time. The nanoindentation hardness and frictional coefficients of the oxide layer on Ti–29Nb–13Ta–4.6Zr suggested that the oxide layer was hard and robust enough for artificial tooth coating. The cross‐sectional transmission electron microscopic observations of the microstructure of oxidized Ti–29Nb–13Ta–4.6Zr revealed that a continuous oxide layer formed on the surface of the alloys. The Au marker method revealed that both in‐ and outdiffusion occur during oxidation in Ti–29Nb–13Ta–4.6Zr and Ti–36Nb–2Ta–3Zr–0.3O, whereas only out‐diffusion governs oxidation in CP Ti. The obtained results indicate that the high exfoliation resistance of the oxide layer on Ti–29Nb–13Ta–4.6Zr and Ti‐36Nb‐2Ta‐3Zr‐0.3O are attributed to their dense microstructures composing of fine particles, and a composition‐graded interfacial microstructure. On the basis of the results of our microstructural observations, the oxide formation mechanism of the Ti–Nb–Ta–Zr alloy is discussed.

Society is demanding clean energy to substitute greatly polluting carbon-based fuels. As an alternative, the use of green hydrogen produced by electrocatalysis constitutes a nice strategy as its products and reactants are not toxic to the environment. However, the use of scarce materials and high overpotentials to accomplish the oxygen evolution reaction (OER) make electrocatalysis an uncompetitive process. To solve these challenges, a low-cost procedure for the preparation of earth-abundant Ni, Fe and NiFe decorated electrodes has been developed. For this purpose, pencil graphite rods have been selected as highly porous substrates. A reasonable performance is achieved when they are employed for the OER. Furthermore, for the first time, a detailed analysis of impedance spectroscopy allows the association of the Ni redox transitions Ni2+/Ni3+and Ni3+/Ni4+(including the identification of the hydrated α-γ and the non-hydrated β phases) with an electrochemical redox capacitance response. Additionally, the Ni3+/Ni4+redox peak capacitance together with a quick decrease in the charge transfer resistance indicates the implication of Ni4+in the OER. These results show the utility of impedance spectroscopy as a non-destructive and non-invasive technique to study these electrochemical systems in detail under operating conditions.

One of the applications of titanium in the dental field is a porcelain-fired-metal crown. It is made by firing porcelain multiple times with different composition of ceramics on a metallic abutment tooth. Regarding firing process to metallic abutment, a primer is generally required to be applied in advance of a porcelain firing and the opaque porcelain is applied to cover the metallic color of the abutment. By the way, our recent research shows that white oxide films formed on the Ti substrate have a color tone similar to opaque porcelain. Therefore, porcelain-fired-Ti samples replacing primer and opaque porcelain firing with the TiO2 oxide layer were fabricated and evaluated in this study. Color tone and peel strength were evaluated, and cross-sectional observation was observed by SEM and EPMA.

Ti-Nb alloys in deionized water and Hanks' balanced salt solution were investigated at 310K using a ball-on-disc type frictional test machine with a ZrO2 ball counterface. In this study, besides the fretting wear behavior of Ti-Nb alloys was investigated, the relationship between the microstructure and mechanical properties of the Nb-added Ti alloy was investigated, and the relationship between the composition and hardness on the fretting wear of the alloy will be clarified from the results of the wear volume and surface analysis of wear track. The results obtained from the frictional test indicate that the dynamic coefficient of friction converged to a constant value with time variation. Also, wear volume in HBSS was smaller than in water, and wear volume of heat-treated became smaller than As-Rolled. Microstructural observations suggest the scars of adhesive wear were observed. Comparing each morphology, the ratio of the peeling part was more significant in Ti-Nb alloys, which have α+β than in Ti-Nb alloys, which have only β. Moreover, the results of Open circuit potentiometry indicate that the corrosion potential difference increased with wear. This is most likely due to the passive film was damaged. Besides, the corrosion potential difference of β-Ti-Nb alloy heat-treated with HBSS is small. It is assumed that there is an influence of HBSS besides the fine structure.

<p>It had been reported that Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy forms a dense oxide layer by high-temperature oxidation whereas CP Ti forms a multilayered oxide consisted of rutile monolayers and void layer. This morphological change is supposed to be mainly caused by Nb addition in Ti since the dense oxide layer of TNTZ consists of multiple oxide phases, at least with rutile TiO₂ and TiNb₂O₇. In this study, high-temperature oxidation at 1273 K for 3.6 ks in the air of Ti-xNb alloys (x=1, 5, 7, 10, 13, 15, 18, 20, 23, 26, 28, 30 and 32 mol%) was investigated to discuss the effect of Nb addition to Ti on its high-oxidation behavior, and on its oxide microstructure. From the results of the SEM observation, an oxide layer with a void layer was formed on Ti-xNb substrate from 1 mol%Nb up to 10 mol%Nb. However, densification of the oxide layer was confirmed at Ti-13Nb. Then, the dense oxide layer was formed up to 32 mol%Nb. XRD results indicated that only rutile-type TiO₂ was identified from 1 mol%Nb up to 10 mol%Nb, then both TiO₂ and TiNb₂O₇ were formed from 13 mol%Nb to 32 mol%Nb. These results indicate that dense oxide layer formation attributes to phase separation from TiO₂ to TiNb₂O₇. Until 10 mol%Nb, the thickness of oxide layer was suppressed by Nb addition, whereas the layer thickness increased with increasing Nb content from 13 mol%Nb. The maximum exfoliation resistance of the oxide layer was obtained at 20 mol%Nb. The results of oxide growth rate at each Ti-xNb alloys suggested that Nb diffusion in Ti may rate-determining process of the dense oxide layer formation.</p>

The effects of soft X-ray irradiation on fluorinated diamond-like carbon (F-DLC) films were investigated using synchrotron radiation (SR). The Vickers hardness of the F-DLC films substantially increased from an initial value of about 290 to about 800 HV at a dose of 50 mA&amp h and the remained constant at about 1100 HV at doses of more than 300 mA&amp h. This dose dependence was consistent with those of the film thickness and elemental composition. The depth profile of the elemental composition inside each F-DLC film obtained by the measurement of the X-ray photoelectron spectrum (XPS) during sputtering showed that the composition ratio of fluorine was approximately constant from the surface to the neighborhood of the substrate. Namely, fluorine atoms were desorbed by SR irradiation from not only the surface but also the substrate neighborhood. Modification by SR irradiation was found to occur in the entire F-DLC film of about 200 nm thickness.

<p>We studied the fabrication of a TiO₂/SiO₂ composite coating on Ti. At a temperature above 1100 K with oxygen partial pressure, a self-organized coating of rutile phase TiO₂ is formed on a Ti substrate. The thick TiO₂ coating (> 10 m) had a "piecrust-like" multilayer structure, which comprise TiO₂ monolayers and gaps. A composite coating containing SiO₂ was fabricated via a sol-gel method in vacuum to improve the exfoliation strength of the brittle, porous TiO₂ coating. Cross-sectional SEM images revealed sufficient amounts of SiO₂ in the gaps between the TiO₂ monolayers in the TiO₂/SiO₂ composite coating, even at the interface between the oxide coating and the substrate. Exfoliation stress of the composite coating was up to 10–15 times higher than for the self-organized TiO₂ coating alone, and the composite coating's failure mode was interfacial compared with cohesive for the self-organized TiO₂ coating.</p><p> </p><p>Mater. Trans. 57（2016） 2008-2014に掲載</p><p>本研究の背景をより正確にするため，実験方法，結果，考察の一部を修正し，文献の追加および順番を変更，Fig. 12を追加した．</p>

&lt;p&gt;It had been reported that Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy forms a dense oxide layer by high-temperature oxidation whereas CP Ti forms a multilayered oxide consisted of rutile monolayers and void layer. This morphological change is supposed to be mainly caused by Nb addition in Ti since the dense oxide layer of TNTZ consists of multiple oxide phases, at least with rutile TiO&lt;sub&gt;2&lt;/sub&gt; and TiNb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;. In this study, high-temperature oxidation at 1273 K for 3.6 ks in the air of Ti-&lt;i&gt;x&lt;/i&gt;Nb alloys (&lt;i&gt;x&lt;/i&gt;=1, 5, 7, 10, 13, 15, 18, 20, 23, 26, 28, 30 and 32 mol%) was investigated to discuss the effect of Nb addition to Ti on its high-oxidation behavior, and on its oxide microstructure. From the results of the SEM observation, an oxide layer with a void layer was formed on Ti-&lt;i&gt;x&lt;/i&gt;Nb substrate from 1 mol%Nb up to 10 mol%Nb. However, densification of the oxide layer was confirmed at Ti-13Nb. Then, the dense oxide layer was formed up to 32 mol%Nb. XRD results indicated that only rutile-type TiO&lt;sub&gt;2&lt;/sub&gt; was identified from 1 mol%Nb up to 10 mol%Nb, then both TiO&lt;sub&gt;2&lt;/sub&gt; and TiNb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt; were formed from 13 mol%Nb to 32 mol%Nb. These results indicate that dense oxide layer formation attributes to phase separation from TiO&lt;sub&gt;2&lt;/sub&gt; to TiNb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;. Until 10 mol%Nb, the thickness of oxide layer was suppressed by Nb addition, whereas the layer thickness increased with increasing Nb content from 13 mol%Nb. The maximum exfoliation resistance of the oxide layer was obtained at 20 mol%Nb. The results of oxide growth rate at each Ti-&lt;i&gt;x&lt;/i&gt;Nb alloys suggested that Nb diffusion in Ti may rate-determining process of the dense oxide layer formation.&lt;/p&gt;

&lt;p&gt;It had been reported that Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy forms a dense oxide layer by high-temperature oxidation whereas CP Ti forms a multilayered oxide consisted of rutile monolayers and void layer. This morphological change is supposed to be mainly caused by Nb addition in Ti since the dense oxide layer of TNTZ consists of multiple oxide phases, at least with rutile TiO&lt;sub&gt;2&lt;/sub&gt; and TiNb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;. In this study, high-temperature oxidation at 1273 K for 3.6 ks in the air of Ti-&lt;i&gt;x&lt;/i&gt;Nb alloys (&lt;i&gt;x&lt;/i&gt;=1, 5, 7, 10, 13, 15, 18, 20, 23, 26, 28, 30 and 32 mol%) was investigated to discuss the effect of Nb addition to Ti on its high-oxidation behavior, and on its oxide microstructure. From the results of the SEM observation, an oxide layer with a void layer was formed on Ti-&lt;i&gt;x&lt;/i&gt;Nb substrate from 1 mol%Nb up to 10 mol%Nb. However, densification of the oxide layer was confirmed at Ti-13Nb. Then, the dense oxide layer was formed up to 32 mol%Nb. XRD results indicated that only rutile-type TiO&lt;sub&gt;2&lt;/sub&gt; was identified from 1 mol%Nb up to 10 mol%Nb, then both TiO&lt;sub&gt;2&lt;/sub&gt; and TiNb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt; were formed from 13 mol%Nb to 32 mol%Nb. These results indicate that dense oxide layer formation attributes to phase separation from TiO&lt;sub&gt;2&lt;/sub&gt; to TiNb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;. Until 10 mol%Nb, the thickness of oxide layer was suppressed by Nb addition, whereas the layer thickness increased with increasing Nb content from 13 mol%Nb. The maximum exfoliation resistance of the oxide layer was obtained at 20 mol%Nb. The results of oxide growth rate at each Ti-&lt;i&gt;x&lt;/i&gt;Nb alloys suggested that Nb diffusion in Ti may rate-determining process of the dense oxide layer formation.&lt;/p&gt;

In this study, we investigate the effects of focused ion beam (FIB)-induced damage and specimen size on the mechanical properties of Si nanowires (NWs) by a microelectromechanical system (MEMS)-based tensile testing technique. By an FIB fabrication technique, three types of Si NWs, which are as-FIB-fabricated, annealed, and FIB-implanted NWs, are prepared. A sacrificial-oxidized NW is also prepared to compare the mechanical properties of these FIB-based NWs. The quasi-static uniaxial tensile tests of all the NWs are conducted by scanning electron microscopy (SEM). The fabrication process and specimen size dependences on Young's modulus and fracture strength are observed. Annealing is effective for improving the Young's modulus of the FIB-damaged Si. Transmission electron microscopy (TEM) suggests that the mechanism behind the process dependence on the mechanical characteristics is related to the crystallinity of the FIB-damaged portion. (C) 2017 The Japan Society of Applied Physics

We studied the fabrication of a TiO2/SiO2 composite coating on Ti. At a temperature above 1100 K with oxygen partial pressure, a self-organized coating of rutile phase TiO2 is formed on a Ti substrate. The thick TiO2 coating (&gt;10 mu m) had a "piecrust-like" multilayer structure, which comprise TiO2 monolayers and gaps. A composite coating containing SiO2 was fabricated via a sol-gel method in vacuum to improve the exfoliation strength of the brittle, porous TiO2 coating. Cross-sectional SEM images revealed sufficient amounts of SiO2 in the gaps between the TiO2 monolayers in the TiO2/SiO2 composite coating, even at the interface between the oxide coating and the substrate. Exfoliation stress of the composite coating was up to 10-15 times higher than for the self-organized TiO2 coating alone, and the composite coating's failure mode was interfacial compared with cohesive for the self-organized TiO2 coating.

Frictional and wear behavior of SUS 316L stainless steel, commercially pure Ti (Grade 2), and Ti-6Al-7Nb in artificial saliva and in deionized water were investigated at 310K using a ball-on-disc type frictional test machine with a Ti counterface. The present study aims to obtain information on the in vitro frictional behaviors of Ti-based dental metallic materials, and to investigate the morphological and compositional changes of the surface damages caused by wear and friction. The surface morphology and chemical composition of the-wear track was investigated. The results obtained from the frictional test indicates an interpolated dynamic frictional coefficient ranging between 0.3 to 0.5 in both water and artificial saliva, which suggests that solid contact was predominant. The volume loss in water was always higher than that in artificial saliva and the volume loss of Ti-6Al-7Nb and SUS316L decreased with increase in the applied dead load. Microstructural observations suggests adhesive wear to be dominant in specimens tested in artificial saliva, whereas sharper grooves and cracks were frequently observed in the specimens tested in water. The results indicate that surface enbrittlement was caused by oxygen, and the strength of the materials was related to the wear and frictional parameters.

Frictional and wear behavior of SUS 316L stainless steel, commercially pure Ti (Grade 2), and Ti-6Al-7Nb in artificial saliva and in deionized water were investigated at 310K using a ball-on-disc type frictional test machine with a Ti counterface. The present study aims to obtain information on the in vitro frictional behaviors of Ti-based dental metallic materials, and to investigate the morphological and compositional changes of the surface damages caused by wear and friction. The surface morphology and chemical composition of the-wear track was investigated. The results obtained from the frictional test indicates an interpolated dynamic frictional coefficient ranging between 0.3 to 0.5 in both water and artificial saliva, which suggests that solid contact was predominant. The volume loss in water was always higher than that in artificial saliva and the volume loss of Ti-6Al-7Nb and SUS316L decreased with increase in the applied dead load. Microstructural observations suggests adhesive wear to be dominant in specimens tested in artificial saliva, whereas sharper grooves and cracks were frequently observed in the specimens tested in water. The results indicate that surface enbrittlement was caused by oxygen, and the strength of the materials was related to the wear and frictional parameters.

Surface and bulk properties' changes of a hydrogenated diamond-like carbon (H-DLC) film exposed to synchrotron radiation (SR) in the soft X-ray region were investigated by a nano-indenter, an atomic force microscope (AFM), and a combination of Rutherford Backscattering Spectroscopy (RBS) and Elastic Recoil Detection Analysis (ERDA) techniques. The surface of H-DLC films became flat and the hydrogen content of H-DLC films decreased with increasing SR dose. On the other hand, Vickers hardness showed the complicated dependency on the SR dose. It was found that modification processes of H-DLC films by SR exposure included three reactions: flattening on the surface, hydrogen desorption, and etching by SR exposure. (C) 2014 Elsevier B.V. All rights reserved.

Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy has excellent mechanical properties and bone conductivity. For dental application, TNTZ surfaces were converted to white oxidized layer by a simple heat treatment in air to achieve the formation of aesthetic surfaces. The oxidized layer formed by the heat treatment at 1000 degrees C for 0.5 or 1 hr was whiter and joined to TNTZ substrate more strongly than that formed by the treatment at 900 degrees C. The layer consisted of TiO2 (rutile), TiNb2O7, and TiTa2O7 and possessed similar to 30 mu m in thickness for the sample heat-treated at 1000 degrees C and similar to 10 mu m for that heat-treated at 900 degrees C. The surface average roughness and the wettability increased after the heat treatment. The spreading and proliferation level of mouse osteoblast-like cell (MC3T3-E1 cell) on the heat-treated sample were almost the same as those on as-prepared one. The cell spreading on TNTZ was better than those on pure titanium (CP Ti) regardless of the heat treatment for the samples. There was no deterioration in the in vitro cell compatibility of TNTZ after the oxidized layer coating by the heat treatment.

Formation behavior of wear-induced layer in Fe-Ni alloys is investigated. The wear-induced layer i s observed just below worn surface and it has very fine microstructure. Moreover, reverse transformation occurs around worn surface, and volume fraction of austenite (γ) phase increases. As a result, microstructure and hardness of the wear-induced layer become the same regardless of initial microstructure. From these results, it is found that both microstructural refinement and reverse transformation occur during wear. These phenomena are induced by large shear strain and frictional heat due to wear. Based on these obtained results, formation behavior of the wear-induced layer in stainless steel (SUS304) is also investigated. As well as Fe-Ni alloys, the wear-induced layer with fine microstructure is formed just below worn surface of SUS304. However, strain-induced martensitic transformation occurs without reverse transformation. This is because that amount shear strain induced by wear is not enough to cause reverse transformation. Finally, it is concluded that phase transformation induced by wear is controlled by both the amount of shear strain and the frictional heat.

The training treatments in the shape memory alloy are known as useful method to improve the shape memory effect. In our previous study, it was shown that the training treatments can also improve both the damping capacity and the hardness of the Fe-Mn alloy. In this study, training effects on damping capacity in solution treated Mn -22.5mass%Cu -5.08mass%Ni -1.96mass%Fe alloy have been investigated. As training treatments, the thermal training (only thermal cycling) and the thermo-mechanical training (thermal cycling with deformation) are carried out. Internal friction was measured at room temperature (R. T.) using a free-decay method. Although training effect cannot be found for the samples trained at higher annealing temperature (600 degrees C and 700 degrees C), damping capacity of the alloy is improved by thermal training annealed at 400 degrees C and 500 degrees C. The trade-off between the damping capacity and mechanical properties can be overcome by the training at lower temperature.

This study involves experimental investigation on severe plastic deformation (SPD) of Ti using novel equal-channel angular pressing (ECAP) at ambient temperature. Ti wire is tightly encapsulated in a hollow host material made of Al-based functionally graded material (FGM). The host material is prepared by embedding Al-Al3Ti alloy into Al. Three types of the Al-Al3Ti alloys with different Al3Ti volume fractions are used to prepare the host materials. ECAP for specimens is carried out for up to eight passes by route A. The microstructure and hardness of ECAPed specimens are investigated. The changes in microstructure and the increase in the hardness value of Ti with increased number of ECAP passes are evidences showing that Ti is successfully deformed by this technique. (C) 2012 The Japan Society of Applied Physics

Solid particles in discontinuous reinforcement metal matrix composites (DRMMCs) drastically improve their strength. Since the strength of DRMMCs is improved by the Orowan mechanism, smaller particles, such as nanoparticles, are effective as dispersoids. In this study, the effects of nanoparticles on the sliding wear behavior of DRMMCs are investigated using Cu-based composites containing 0.6, 1.2, and 1.7 vol% SiO2 particles. Wear resistance of the Cu-SiO2 composite is improved by increasing the volume fraction of SiO2 particles. Moreover, the amount of wear for the Cu SiO2 composites increases with increasing sliding distance and then becomes saturated beyond about 1000 m. Vickers hardness for all specimens becomes the same regardless of the volume fraction of SiO2 particles as the sliding distance increases. This behavior can be explained by the work-hardening rate of the Cu matrix and the critical hardness for adhesion with a counter-material. It is found that nanoparticles in DRMMCs improve wear resistance by increasing the work-hardening rate of the metal matrix. (C) 2012 The Japan Society of Applied Physics

Difference of the phase transformation behavior at deformation-induced layer depending on surface treatment methods was investigated using Fe-33mass%Ni alloy. As specimens, two kinds of specimens were prepared. One specimen has austenite (gamma) single structure, and the other specimen consists of both martensite (alpha') and gamma phases. Using these specimens, shot-peening tests were performed, and then phase transformation behavior induced by the shot-peening was compared with that by sliding wear reported in previous literature. The deformation-induced layer induced by shot-peening has very fine microstructure consisted of both alpha' and gamma phases. The microstructure in the deformation-induced layer formed by shot-peening becomes similar with increasing duration of shot-peening regardless of initial microstucture. On the other hand, the deformation-induced layer induced by sliding wear is reported to have gamma single structure regardless of initial microstructure. This microstructural difference between shot-peening and sliding wear comes from the difference of heat generation during the surface treatment. Therefore, it is concluded that phase transformation behavior in deformation-induced layer depends on surface treatment method.

The training treatments in the shape memory alloy are known as useful method to improve the shape memory effect. In our previous study, it was shown that the training treatments can also improve both the damping capacity and the hardness of the Fe-Mn alloy. In this study, training effects on damping capacity in solution treated Mn -22.5mass%Cu -5.08mass%Ni -1.96mass%Fe alloy have been investigated. As training treatments, the thermal training (only thermal cycling) and the thermo-mechanical training (thermal cycling with deformation) are carried out. Internal friction was measured at room temperature (R. T.) using a free-decay method. Although training effect cannot be found for the samples trained at higher annealing temperature (600 degrees C and 700 degrees C), damping capacity of the alloy is improved by thermal training annealed at 400 degrees C and 500 degrees C. The trade-off between the damping capacity and mechanical properties can be overcome by the training at lower temperature.

Metal-bonded diamond grinding wheel was fabricated by a centrifugal mixed-powder method. The centrifugal mixed-powder method is a novel and effective casting process to obtain functionally graded material (FGM). At the beginning, we performed fundamental experiments using Al-Si alloy system for the purpose of knowing the migration behavior of mixed-powder under centrifugal force. Al-Si hypereutectic alloyed-powder or mixed-powder of Al and Si particles was placed into the mold, and then Al molten metal was cast under a centrifugal force. Cross sectional microstructure observation and quantitative analysis of Si content were conducted using an electron probe microanalyzer. Amount of Si decreased with receding from a mixed-powder region. Si concentration gradient in the sample fabricated Al-Si powder was smaller than the one fabricated using mixed-powder of Al and Si particles. Subsequently, phi 20 mm Cu/diamond grinding wheel was fabricated by the casting method. Graded diamond distribution was successfully obtained.

This study involves experimental investigation on severe plastic deformation (SPD) of Ti using novel equal-channel angular pressing (ECAP) at ambient temperature. Ti wire is tightly encapsulated in a hollow host material made of Al-based functionally graded material (FGM). The host material is prepared by embedding Al-Al3Ti alloy into Al. Three types of the Al-Al3Ti alloys with different Al3Ti volume fractions are used to prepare the host materials. ECAP for specimens is carried out for up to eight passes by route A. The microstructure and hardness of ECAPed specimens are investigated. The changes in microstructure and the increase in the hardness value of Ti with increased number of ECAP passes are evidences showing that Ti is successfully deformed by this technique. (C) 2012 The Japan Society of Applied Physics

In this study, as a novel centrifugal mixed-powder method, reaction centrifugal mixed-powder method was applied for Mg&amp;ndash;Si system to fabricate Mg/Mg&lt;sub&gt;2&lt;/sub&gt;Si functionally graded materials (FGMs). In advance, the mixed powder of Mg and Si particles is inserted into a rotationable mold, and then the molten Mg is poured into the mold with the powder mixture. As a result, the molten metal matrix penetrated into the space between the particles due to the pressure exerted by the centrifugal force. At the same time, Mg particles were melted by the heat from the molten Mg, and it allowed the occurrence of Mg/Si reaction. Using this method, Mg/Mg&lt;sub&gt;2&lt;/sub&gt;Si FGMs with gradual distribution of Mg&lt;sub&gt;2&lt;/sub&gt;Si particles was successfully fabricated. Particles size and morphology of Mg&lt;sub&gt;2&lt;/sub&gt;Si particles in the FGMs depend on the amount of Si particles in mixed powder. This is because the reaction heat due to the reaction of Si particles and molten Mg is influenced by the amount of Si particles. Therefore, it can be concluded that the reaction heat is important factor for the reaction centrifugal mixed-powder method, and it controls the microstructure of the FGMs.

In this study, as a novel centrifugal mixed-powder method, reaction centrifugal mixed-powder method was applied for Mg-Si system to fabricate Mg/Mg 2Si functionally graded materials (FGMs). In advance, the mixed powder of Mg and Si particles is inserted into a rotationable mold, and then the molten Mg is poured into the mold with the powder mixture. As a result, the molten metal matrix penetrated into the space between the particles due to the pressure exerted by the centrifugal force. At the same time, Mg particles were melted by the heat from the molten Mg, and it allowed the occurrence of Mg/Si reaction. Using this method, Mg/Mg 2Si FGMs with gradual distribution of Mg 2Si particles was successfully fabricated. Particles size and morphology of Mg 2Si particles in the FGMs depend on the amount of Si particles in mixed powder. This is because the reaction heat due to the reaction of Si particles and molten Mg is influenced by the amount of Si particles. Therefore, it can be concluded that the reaction heat is important factor for the reaction centrifugal mixed-powder method, and it controls the microstructure of the FGMs. © 2012 The Japan Institute of Light Metals.

Metallic materials for dentistry such as Ti alloys, the Pt group or Au group alloys have excellent mechanical properties as a load bearing material, however, they are inferior in point of esthetic. Ti-29Nb-13Ta-4. 6Zr alloy is beta-type Ti alloy with excellent mechanical property as a biomedical load-bearing material, and on which it is found that a firm yellowish-white oxide layer is formed by heat treatment at a particular temperature. Therefore, the detailed study regarding the oxide film formation in Ti-29Nb-13Ta-4. 6Zr and its properties will be interesting in terms of biomedical applications. In the present study, the oxide formation behavior investigation was carried out with focusing on oxide exfoliation behavior and esthetic property. Our recent results revealed that multilayer oxide film covers Ti-29Nb-13Ta-4. 6Zr substrate, and which each layer has different color. From cross sectional observation, a dense white oxide layer formed on top, and whose thickness increased with increasing heat treatment temperature and duration time. CIELab measurement results suggest that L* increases with increasing layer thickness.

Ti and Ti alloys are widely used as metallic implants, because of their good mechanical properties and nontoxic behavior. However, they have problems as the implant-materials, namely, high Young&apos;s modulus comparing that of bone and low bonding ability with bone. There is a need to develop the Ti and Ti alloys with lower Young&apos;s modulus and good bonding ability. In previous study, Ti composite containing biodegradable poly-L-lactic-acid (PLLA) fiber has been fabricated to improve these problems. However, this composite has low strength because of the imperfect sintering of Ti matrix. To improve its strength, sintering of Ti matrix should be completed. In this study, Ti-NaCl composite material was fabricated by spark plasma sintering (SPS) method using powder mixture of Ti and NaCl to complete the sintering of Ti matrix. To obtain porous Ti samples, Ti-NaCl composite were put into hot water of 317 K. The porous Ti was dipped into PLLA melt in order to introduce PLLA into the pores of porous Ti. Finally, Ti/PLLA composite was obtained, and PLLA plays a role as reinforcement of Ti matrix. It was found that the Ti/PLLA composite has gradient structure and mechanical properties. (C) 2011 Elsevier B.V. All rights reserved.

Ti and Ti alloys are widely used as metallic implants, because of their good mechanical properties and nontoxic behavior. However, they have problems as the implant-materials, namely, high Young&apos;s modulus comparing that of bone and low bonding ability with bone. There is a need to develop the Ti and Ti alloys with lower Young&apos;s modulus and good bonding ability. In previous study, Ti composite containing biodegradable poly-L-lactic-acid (PLLA) fiber has been fabricated to improve these problems. However, this composite has low strength because of the imperfect sintering of Ti matrix. To improve its strength, sintering of Ti matrix should be completed. In this study, Ti-NaCl composite material was fabricated by spark plasma sintering (SPS) method using powder mixture of Ti and NaCl to complete the sintering of Ti matrix. To obtain porous Ti samples, Ti-NaCl composite were put into hot water of 317 K. The porous Ti was dipped into PLLA melt in order to introduce PLLA into the pores of porous Ti. Finally, Ti/PLLA composite was obtained, and PLLA plays a role as reinforcement of Ti matrix. It was found that the Ti/PLLA composite has gradient structure and mechanical properties. (C) 2011 Elsevier B.V. All rights reserved.

Formation of compositional gradient in Al/Al3Ti Functionally graded materials (FGMs) fabricated by the centrifugal method (CM) depends mainly on the centrifugal force and the processing temperature. In this study, a novel centrifugal method, reaction centrifugal mixed-powder method (RCMPM), was proposed to fabricate Al/Al3Ti FGMs under fixed centrifugal force (G 80). The effects of RCMPM processing temperature on the formation of Al3Ti intermetallics, its morphology and its distribution in the fabricated Al/Al3Ti FGMs have been investigated. Fine granular Al3Ti were observed at relatively lower processing temperature while the known coarse platelet-like particles of Al3Ti could be achieved at higher casting temperatures. Moreover, Ti3Al intermetallics compound and unreacted Ti phases are also observed along with Al3Ti particles. In addition, distribution of Al3Ti intermetallics size and their volume fraction showed a significant change when the Al/Al3Ti FGMs processed at different temperatures relative to the liquidus temperature of the master alloy. (C) 2011 The Japan Society of Applied Physics

An alternative technique of the equal-channel angular pressing (ECAP) process for difficult-to-work materials at ambient temperature is proposed by embedding a difficult-to-work material into an easy-to-work material. The easy-to-work material as a host material assists the deformation of the difficult-to-work material. The ECAP process is simulated by the finite element method (FEM). For this study, Ti as the difficult-to-work material is embedded into an Al-based functionally graded material (FGM) matrix. FEM is conducted with Ti embedded into a different host material type as well as a different die channel geometry. The strain distribution of the specimen after a single ECAP pass is analyzed. From the obtained results, it is found that the strain distribution in Ti is strongly influenced by the host material and the shape of the die channel. (C) 2011 The Japan Society of Applied Physics

We are developing functionally graded grinding wheels fabricated by a centrifugal mixed-powder method. As a first step of this fabrication method, a powder mixture of abrasive particles and metal matrix particles is inserted into a spinning mould. After that, a metal matrix ingot is melted and then the molten metal matrix is poured into the spinning mould with the powder mixture. As a result, the molten metal matrix penetrates into the space between the particles due to the pressure exerted by the centrifugal force. At the same time, the metal matrix powder is melted by the heat from molten matrix poured from the crucible. Finally, a ring-shaped sample with abrasive particles distributed on its surface (functionally graded grinding wheel) can be obtained. In this study, functionally graded grinding wheel fabricated by the centrifugal mixed-powder method will be reported.

Formation of compositional gradient in Al/Al3Ti Functionally graded materials (FGMs) fabricated by the centrifugal method (CM) depends mainly on the centrifugal force and the processing temperature. In this study, a novel centrifugal method, reaction centrifugal mixed-powder method (RCMPM), was proposed to fabricate Al/Al3Ti FGMs under fixed centrifugal force (G 80). The effects of RCMPM processing temperature on the formation of Al3Ti intermetallics, its morphology and its distribution in the fabricated Al/Al3Ti FGMs have been investigated. Fine granular Al3Ti were observed at relatively lower processing temperature while the known coarse platelet-like particles of Al3Ti could be achieved at higher casting temperatures. Moreover, Ti3Al intermetallics compound and unreacted Ti phases are also observed along with Al3Ti particles. In addition, distribution of Al3Ti intermetallics size and their volume fraction showed a significant change when the Al/Al3Ti FGMs processed at different temperatures relative to the liquidus temperature of the master alloy. (C) 2011 The Japan Society of Applied Physics