Microstructure evolution and cyclic deformation behavior of Ti-6Al-4 V alloy via electron beam melting during low cycle fatigue

Abstract

Low cycle fatigue (LCF) behavior of Ti-6Al-4 V alloy constructed via electron beam melting (EBM) was investigated. The relationship among fatigue property, internal stress and microstructure was established to characterize cyclic-deformation behavior and LCF life of EBM Ti-6Al-4 V alloy. The LCF life of EBM Ti-6Al-4 V is almost comparable to the wrought counterparts under low strains and higher than that of selective laser melted Ti-6Al-4 V reported. Tension-compression asymmetry and cyclic softening behavior were found at various strains. Considering the asymmetry of hysteresis loops, internal stresses during tension and compression were distinguished. The anisotropy of tension-compression enhances with increasing strain due to the increase of back stress and the decrease of friction stress. Sub-grain boundaries along with fragmented β phase were observed. The formation of sub-grains and dislocation annihilation in α grains reduce the friction stress, resulting in cyclic softening.