Influence of microstructure on cyclic deformation response and micromechanics of Ti–55531 alloy

Abstract

Abstract Cyclic deformation response and micromechanics in strain controlled low cycle fatigue of Ti–5Al–5Mo–5V–3Cr–1Zr (Ti–55531) alloy with bimodal microstructure (BM) and lamellar microstructure (LM) were comparatively investigated at ambient temperature. Results showed that cyclic hardening/softening behavior of Ti–55531 alloy was found to be significantly dependent on both the strain amplitude and microstructure. The cyclic softening rate of LM was always larger than that of BM at strain level below 1.0%; however, the opposite result was produced for strain amplitude above 1.0%. Dislocation features revealed that cyclic deformation of the alloy primarily relied on primary α (αp) and secondary α (αs) phases. At low strain levels, lasting hardening of BM was due to the interaction of multiple prismatic and basal slips, and pyramidal slip in αp particles, while slight softening of LM was owing to the activation of a few twins in lamellar αs. However, at high strain levels, dislocation annihilation and numerous twins were detected in both αp and αs phases in BM, which resulted in the larger cyclic softening rate of BM than that of LM. Evidently, besides dislocation annihilation, twinning was found to be another important softening mechanism, which was not revealed by other studies on Ti alloys.