Ti-29Nb-13Ta-4.6Zr (TNTZ) which was developed for biomedical applications, is a β-type titanium alloy with a relatively low Young's modulus. However, its fabrication cost is high because the alloying elements of Nb and Ta, which are β-stabilizers with high melting points, are expensive and rare metals. In this study, Ti-Mn system alloys were developed as low-cost titanium binary alloys for biomedical applications, and their mechanical properties (tensile strength and Young's modulus) and biocompatibility (bone contact ratio) were investigated to evaluate their possible use as next generation metallic biomaterials. Ti-12Mn has a tensile strength of approximately 950 MPa, which is similar to those of annealed Ti-6Al-4V ELI (Extra Low interstitial) and insufficiently aged TNTZ. Ti-9.2Mn has the lowest Young's modulus of approximately 90 GPa among the alloys investigated. The mean values of bone contact ratios on Ti-12Mn were obtained 12, 52 and 96 weeks after the implantation of rabbit femurs and were found to be slightly lower than the values for commercially pure Ti, although a small amount of Mn element was detected at a interfacial bone tissue with the concentration gradient at 96 weeks after implantation. However, there appeared to be no significant effects of the release of Mn to the bone tissue on bone formation. From these results, it is considered that Ti-Mn system alloys are promising biomaterials with attractive mechanical properties and relatively good biocompatibility.
In order to reduce carbon emission, aluminum alloy has been being considered to get light weight car body in automotive industry. But it is difficult to obtain highly reliable joint of aluminum alloy and steel because of the production of hard and brittle intermetallic compounds during the welding process. In this study, aluminum alloys were welded to cold-rolling steel SPCC by resistance spot welding. Effects of welding conditions and alloy element Si, Cu and Mg in aluminum alloy on growth of intermetallic compounds at weld interfacial zones and weld strength of aluminum alloys/SPCC joints were investigated. The intermetallic compound layer was formed of Fe2Al5 adhering to the steel and FeAl3 adhering to aluminum alloy, and the thickness varied with positions along the interface. From EBSD results, the Fe2Al5 layer has columnar grains which grew with the 〈001〉 direction perpendicular to the interface of spot welded joint. Diffusion of Si in aluminum alloy happened at the interface, which might inhibit the growth of intermetallic compounds, whereas diffusion of Mg and Cu was not found at the interface by EPMA analysis results. Hardness of intermetallic compound Fe2Al5 was affected by the diffusion of Si in aluminum alloy. The tensile shear strength of joint increased with the increasing of welding time, and the maximum tensile shear load was obtained at welding time of 0.134 s and 0.167 s.
Transmission-EBSD (t-EBSD) method is proposed as a new method for nano-scale microstructures analysis of materials. t-EBSD uses TEM thin foil specimen. Electrons transmitted through the specimen form EBSD patterns. A EBSD detector used for standard EBSD (s-EBSD) is used to acquire these t-EBSD patterns. The patterns are indexed in the same manner as s-EBSD to get crystal orientation. The conditions to get good t-EBSD patterns, formation of t-EBSD patterns and spatial resolution of this method are studied in this paper. Specimen thickness affects seriously to the results of orientation mapping by t-EBSD. It is confirmed that t-EBSD patterns are formed at the bottom layer of the specimen. If the specimen is very thin, the patterns become very weak and noisy. If the specimen becomes thicker, t-EBSD patterns lose its contrast and sometimes patterns become weak with reverse contrast bands. This means that total thickness of the specimen is important for t-EBSD method, but overlapped grains look not so big problem to get t-EBSD patterns. Electron beam spread in the specimen is reduced due to thin foil specimen, and it improves spatial resolution of EBSD orientation map. It is confirmed that it can achieve about 10 nm spatial resolution and about 30 nm size grains can be detected with reasonable thickness specimen.
Based on the first-principles calculation combined with the cluster expansion technique, we developed a formalism enabling energetics for alloy nanoparticles with multiple shapes to be modeled. One of the essential drawbacks in conventional cluster expansion is that the Hamiltonian of cluster expansion depends on the shape of nanoparticles, which leads to difficulties in modeling more general energetics for nanoparticles. In order to overcome this problem, we introduced the concept of “virtual” vacancy into cluster expansion, which successfully makes the cluster expansion Hamiltonian, independent of the shape. We demonstrate that the proposed formalism can accurately describe the relative energies of alloy nanoparticles with possible composition and atomic configuration of a variety of shapes, which leads to comprehensively addressing a stable as well as metastable structure for alloy nanoparticles.
The ω-phase transformation and β-phase stability in Ti-xNb (28≤x≤40 at%) single crystals were investigated using electrical resistivity measurements, transmission electron microscopy (TEM) observations, and specific heat measurements. The crystal for x=28 exhibits distinct anomalous negative temperature dependence of the resistivity coefficient and thermal hysteresis accompanied by the presence of the athermal ω-phase and β-phase lattice modulation. Although the crystal for x=30 appears in the β-phase lattice modulation, it does not exhibit a clear negative temperature dependence of the resistivity coefficient or the athermal ω-phase. The crystal of x=30 also shows a relatively high absolute value of resistivity at 15 K among the crystals for 28≤x≤40 and a low Debye temperature in a normal conductive state. The crystal for x=30 that shows the lattice modulation, high resistivity, and low β-phase Debye temperature corresponds to the low stability of the β-phase. Moreover, the stability strongly depends on the Nb content in the binary Ti-Nb crystal.
Molten salt method with nitrate was proposed and carried out to fabricate TiO2 photocatalyst with visible light activity. The alumina balls with Ti films formed by mechanical coating technique were used for the source samples. The microstructures and composition of the compounds were characterized by SEM, XRD and EDS. The absorption characteristic was evaluated by methylene blue solution concentration. The photocatalytic activity under visible light or UV light was evaluated by the degradation constant k. Molten salt method with KNO3 nitrate is a simple and effective way to fabricate visible light active TiO2 photocatalyst. The fabricated TiO2 photocatalyst showed high absorption property and photocatalytic activity under visible light. The high performance of the fabricated TiO2 photocatalyst is due to the reaction of K element in the molten KNO3.