高温におけるTi-6Al-4V合金の疲労強度に及ぼす人工微小欠陥の影響

概要

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The bending fatigue strength of Ti-6Al-4V alloy was investigated in the temperature range of 20℃ to 450℃. A small artificial defect was introduced in the form of a small hole drilled in the surface of an unnotched specimen. The diameter of the hole was about 0.1 mm and its depth was virtually the same as the diameter. The fatigue strength σ_F of the unnotched specimen was compared with the σ_<FN> of specimens with a small hole. The following results were obtained. (1)The fatigue strength is remarkably decreased even by such a small hole. The decrements of the fatigue strength caused by the hole, (σ_F-σ_<FN>)/σ_F are about 40%, 32%, 27% and 47% at 20℃, 250℃, 350℃ and 450℃, respectively. The values of σ_<FN> predicted by the Murakami's √<area> parameter model are about 3%〜17% smaller than the experimental results. The prediction seems to give a conservative estimation. (2)In the temperature range of 350℃ to 450℃, both σ_F and σ_<FN> are increased by solution hardening, dynamic strain aging and so on. Since the static yield strength is hardly influenced by such a strengthening factor, the temperature dependence of the yield strength may be used as the reference for evaluating the increments in the fatigue strength. It is concluded that the maximum increments of σ_F and σ_<FN> come to about 60%.
社団法人日本材料学会の論文
1995-04-15