β型Ti-22V-4Al合金の疲労き裂進展挙動に及ぼす結晶粒径と時効条件の影響

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This paper presents the effect of microstructural modification on fatigue crack propagation (FCP) in a beta Ti-22V-4Al alloy. FCP experiments have been conducted using eight materials with different microstructures : two as solution treated materials (ST), three single aged materials (STA), and three two-step aged materials (STDA). Particular attention has been paid to the effect of grain size and aging condition. The results showed that in ST materials the coarse grained material exhibited higher FCP resistance than the fine grained material, but this grain size dependence was eliminated by aging, and two-step aging condition had very little influence on FCP behaviour. After allowing for crack closure, the effect of grain size was largely diminished and FCP behaviour was not affected by solution treatment temperature and aging condition. ST materials indicated the highest apparent and intrinsic FCP resistance and then STDA materials, STA materials in the decreasing order. Taking into account the difference in the modulus of elasticity in addition to crack closure, the difference in FCP resistance between STDA and STA materials was eliminated, but ST materials still showed higher FCP resistance.
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