超塑性用α+βチタン合金の疲労強度および疲労き裂進展特性 : 異方性と結晶粒径の影響

概要

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Behavior of fatigue strength and fatigue crack growth were investigated in thin sheet of titanium alloys, in order to clarify the influence of microstructure, stress ratio, and anisotropy. Fatigue tests were carried out with α+β titanium (Ti-6Al-4V) and β-rich α+β titanium (Ti-4Al-3V-2Fe-2Mo) alloys after the heat treatments of furnace cooled at superplastic forming temperatures 1173 K and 1073 K, and as received. The main results are summarized as follows ; 1) The fatigue strength of heat treated both materials were lower than as received. Main reason of fatigue strength being lower by heat treatment was caused by rearrangement of quantitative proportion of the β phase to α phase. 2) The fatigue crack growth rate of both materials were almost independent of the anisotropy and texture, regardless of the heat treatments condition to be superplastic forming temperature. 3) The fatigue crack growth rate of Ti 6A1-4V alloy was lower than that of Ti-4A1-3V-2Fe-2Mo alloy because the fatigue crack growth went zigzag direction by large grain size α and resistance of crack propagation was increased by the prior β phase mostly transformed from aciculate α.
社団法人日本機械学会の論文
1999-11-25