The effect of strain rate on deformation-induced α′ phase transformation and mechanical properties of a metastable β-type Ti–30Zr–5Mo alloy

Abstract

The effect of strain rate on stress-induced α′ phase transformation and room temperature tensile deformation flow behavior of a metastable β-type Ti–30Zr–5Mo alloy at strain rates ranging from 3 × 10−5 to 103 s−1 was investigated. The trigger stress for α′ phase transformation increases from 190 to 632 MPa with the strain rate increasing from 3 × 10−5 to 103 s−1, while the transformed volume of α′ phase decreases at the same time. The true strain at which stress-induced α′ phase transformation occurs also increases from 0.01 to 0.035 with the strain rate increasing from 3 × 10−5 to 103 s−1. Ultrahigh strain hardening rate of 8.7 GPa is observed at the strain rate of 3 × 10−5 s−1 due to the stress-induced α′ phase transformation. At a high strain rate of 103 s−1, the planar slip bands also form during deformation, indicating that the deformation becomes more localized with increasing strain rate. The ultimate tensile strength increases from 722 to 853 MPa with increasing the strain rate from 3 × 10−3 s−1 to 101 s−1 without sacrificing the elongation to fracture. The improved mechanical properties are attributed to the dislocation hindering mechanism of short-range obstacles associated with the stress-induced α′ phase transformation during deformation, and the adiabatic temperature rise caused by the deformation.