Effect of α-phase morphology on low-cycle fatigue behavior of TC21 alloy

•The effect of α-phase morphology on LCF behavior of TC21 is investigated.•Mechanisms of cyclic deformation in the α/β titanium alloys are analyzed.•Planar slip is predominate plastic deformation mode in the α phase.

Low-cycle fatigue behavior of TC21 alloy with equiaxed α phase embedded in the β transformed matrix (EM) and full lamellar α phase (LM) was investigated. The results show that the EM microstructure possesses higher strength, ductility and longer fatigue life than those of the LM one. Dislocation structures are straight dislocation lines in both EM and LM; however, more dislocation tangles and debris were observed in the α than in the β phase. The planar slip predominates cyclic deformation in the α phase, and promotes strain concentration and crack initiation at α phase boundaries.