Ti-6Al-4V合金の水素チャージ下における疲労き裂の発生および伝ぱ

概要

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The fatigue crack initiation and propagation behaviors were investigated on the Ti-6Al-4V alloy specimens which were hydrogen charged in 3% sodium chloride or lN sulfuric acid aqueous solution. The number of cycles to crack initiation obtained for notched tpecimens, N_i, was smaller in the specimens tested under hydrogen charging than in those tested in air when the range of the apparent stress intensity factor ΔK_a was relatively large, while when ΔK_a was small, N_i was rather large for the charged specimens. The crack propagation velocity da/dN was smaller in the specimens tested under hydrogen charging than those tested in air. The decrease in da/dN of the former specimens corresponded to the increase in crack closure : i. e. , the relation between the range of effective stress intensity factor ΔK_<eff> and N_t for two conditions was expressed by the same line. According to an X-ray analysis, the main reason for the enhancement of crack closure in the hydrogen charged specimens seemed to be the expansion due to the hydride formation near the specimen surface but not on the crack propagation plane (a kind of phase-transformation-induced crack closure).
1991-01-25