調和組織を有するTi-6Al-4V合金の微小疲労き裂発生および伝ぱ挙動

抄録

Titanium alloy (Ti-6Al-4V) with bimodal “harmonic structure”, which consists of a coarse-grained structure surrounded by a network structure of fine-grains, was produced by sintering mechanically milled powder to achieve high strength and good plasticity. In this study, we examine the behavior of small fatigue crack initiation and propagation of Ti-6Al-4V alloy with harmonic structure. In the material with harmonic structure, fatigue crack growth rate (da/dN) was high and threshold stress intensity range (ΔK_th) was low compared to the material with coarse acicular structure. On the other hand, the material with harmonic structure showed higher fatigue limit. This is because the fine-grained microstructure, which shows high fatigue strength, is formed in the harmonic structure. However, their fatigue crack growth resistance was lower compared to the coarse-grained microstructure.