The effect of microstructure on fretting fatigue crack initiation life and crack propagation life of Ti-4.5Al-3V-2Mo-2Fe with Widmanstätten α structure was investigated in comparison with equiaxed α structure in this study. The crack propagation life is more predominant for fretting fatigue compared with the case of plain fatigue in low cycle fatigue life region in both structures. While, the crack initiation life is more predominant for fretting fatigue in high cycle fatigue life region in both structures. The crack propagation resistance of Ti-4.5Al-3V-2Mo-2Fe with Widmanstätten α structure is larger than that of the alloy with equiaxed α structure. The fretting fatigue strength of the alloy with Widmanstätten α structure improves slightly in low cycle fatigue life region. The effect of microstructure on crack deflection is small. The crack propagation rate increases remarkably because of the acceleration of crack propagation due to the frictional force. The fretting fatigue life of the alloy is remarkably lower than its plain fatigue life because of the decrease in crack initiation life and crack propagation life due to the fretting action during crack propagation phase.

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The effects of microstructure and contact pressure on fretting fatigue characteristics of a Ti-4.5Al-3V-2Mo-2Fe alloy with a Widmanstätten α structure were investigated in comparison with that with an equiaxed α structure in this study. In fretting fatigue of the Ti-4.5Al-3V-2Mo-2Fe alloy with a Widmanstätten α structure in a high cycle fatigue life region, and that with an equiaxed α structure in low and high cycle fatigue life regions, the fretting fatigue life does not change linearly with contact pressure, and the fretting fatigue life shows the minimum at a certain contact pressure. In a low cycle fretting fatigue region of the alloy with Widmanstätten α structure, the fretting fatigue life changes linearly with changing in contact pressure. At contact pressures over a certain value, fretting fatigue life of the alloy tends to become nearly constant in each fatigue life region. At relatively lower contact pressures, the main small crack in the alloy with equiaxed α structure tends to be formed at uneven wear damaged parts by fretting wear in the slip region in each fatigue life region. At relatively higher contact pressures, the main small crack in the alloy with equiaxed α structure tends to be formed at the boundary between slip and stick regions in each fatigue life region. The main small crack in the alloy with Widmanstätten α structure tends to be formed in the slip region in each fatigue life region.

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In this study, the effect of surface roughness on glossiness and surface color for a pure titanium and a TiN coating surface was investigated based on the experimental discussions. CIELAB (L^*a^*b^* color system) was applied to the evaluation method of surface color. Specimens were machined so that the arithmetical mean roughness, Ra, is less than 1.0 μm. From the results of experiments, the arithmetical mean roughness, Ra, decreased, as the glossiness, Gs (60°), increased. Especially, the glossiness value in the roughness range Ra ≤ 0.2 μm was distributed from 50 to 400. Moreover, the arithmetical mean roughness, Ra, decreased, as the lightness, L^*, and a, b chroma, C^*_ab, decreased. The TiN coated surface with vividness had a pronounced tendency to decreasing lightness, L^*, and a, b chroma, C^*_ab. This was attributable to the smaller difference of elevation of the spectral reflectance curve by reason that the short wavelength was diffused more than the long wavelength.

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Recently, Ti-4.5Al-4Cr-0.5Fe-0.2C has been developed. This alloy has excellent hot workability superior to the most widely used Ti-6Al-4V and comparable good mechanical properties, and contains only eutectoid-type beta stabilizers such as Cr and Fe in composition. Generally, eutectoid-type beta stabilizers embrittle the alloy after high temperature exposure because of the precipitation of intermetallic compounds such as TiCr₂. In this study, we investigated the tensile properties of Ti-4.5Al-4Cr-0.5Fe-0.2C after exposure at various elevated temperatures for various times. It is found that the precipitation of TiCr₂ makes this alloy brittle and that it takes place faster at 773 K than 523 K; embrittlement occurred after 8 h when exposed at 773 K while the alloy maintained good ductility even after 1000 h when exposed at 573 K. In order to suppress the precipitation of TiCr₂, after exploring alloy compositions for both good ductility after exposure and good hot workability, Ti-4.5Al-2Cr-1.7Mo-1.3V-0.5Fe-0.2C, where Mo and V substitute Cr in Ti-4.5Al-4Cr-0.5Fe-0.2C, has been obtained. The new alloy has shown to be able to suppress precipitation of TiCr₂ and to maintain much better ductility than Ti-4.5Al-4Cr-0.5Fe-0.2C after long time exposure at 773 K.

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Refraction-enhanced X-ray imaging method using extremely parallel X-ray beams from a so-called third generation synchrotron radiation source was applied to observe titanium-hydride in titanium polycrystals and titanium-aluminide. Hydride in titanium was formed by an annealing in 1 atm hydrogen gas and electrolytic-charging for cross-sectional observation. Although the hydride in titanium cannot be observed by conventional radiography that utilizes absorption of X-rays, we visualized a high-contrast projection image of hydride using refraction-contrast radiography. This is a promising new technique for non-destructive inspection in bulk material systems with only small differences between refraction indexes such as hydride in titanium.

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