Papers by Author: Akihiro Suzuki

Abstract: A V-4Cr-4Ti alloy and pure V were oxidized in flowing argon for 0.5-8h and subsequently annealed in vacuum for 16h at 973K. The oxygen of 1000-9000ppm was introduced into the V-alloys with little nitrogen, where oxygen was concentrated in region near the surface. By the annealing, oxygen was homogeneously diffused into depth of 150µm. The diffusion depth of oxygen in V-4Cr-4Ti is much smaller than that of pure V, because of Ti-O precipitates formed as oxygen trap. The study indicated that it is feasible to control oxygen level and distribute in the surface region of the vanadium alloys.

Abstract: Microstructures of Ti-29Nb-13Ta-4.6Zr (TNTZ) aged at temperatures between 573 and 723 K after solution treatment at 1063 K have super fine omega phase, or􀀂 both super fine alpha and omega phases, respectively in beta phase with an average grain diameter of 20 µm. Plain fatigue strength of TNTZ aged after solution treatment is much greater than that of as-solutionized TNTZ in both low cycle fatigue and high cycle fatigue life regions. This is due to the improvement of the balance of strength and ductility by the precipitation of alpha phase. Fretting fatigue strength of TNTZ conducted with various heat treatments decreases dramatically as compared with their plain fatigue strength in both low cycle fatigue and high cycle fatigue life regions. In this case, the decreasing ratio of fretting fatigue life increases with increasing the small crack propagation area where both the tangential force and frictional force at the contact plane of pad exist. In fretting fatigue in air, the ratio of fretting damage (Pf/Ff), where Pf and Ff stand for plain fatigue limit and fretting fatigue limit, respectively, increases with increasing elastic modulus. In fretting fatigue in Ringer’s solution, the passive film on specimen surface is broken by fretting action in TNTZ, which have excellent corrosion resistance, and, as a result, corrosion pits that lead to decreasing fretting fatigue strength especially in high cycle fatigue life region, are formed on its surface.