Deformation-induced martensitic transformation in a new metastable β titanium alloy

A new metastable beta titanium alloy, Ti-4Al-7Mo-3V-3Cr (wt.%), was designed using d-electron method, aiming to tailor the deformation mechanism. Microstructural and X-ray diffraction analysis of deformed specimens conforming with the theoretical prediction of d-electron method, confirmed the formation of stress-induced martensite (SIM) and mechanical twinning as the deformation mechanisms. The effect of initial grain size, strain level and strain rate on the formation of SIM were investigated. The results showed that in a given grain size, the volume fraction of SIM initially increases intensively and then follows with lower rate reaching a saturation at 35% reduction. It was observed that after a decrease in the martensite laths interspace down to less than 2 mu m as a result of increasing the strain, some secondary martensite laths forms within the primary ones. It was found that with an increase in grain size from 150 mu m to 250 mu m, the volume fraction of SIM increases while a further increase in grain size up to 500 mu m leads to a decrease in SIM volume fraction. The compression test results at different strain rates ranging from 0.7 x 10(-4) to 0.7 x 10(-1) s(-1) showed SIM transformation occurs at all strain rates and although the triggering stress for SIM transformation increases continuously with an increase in strain rate, the volume fraction of SIM is independent of the strain rate. (C) 2015 Elsevier B.V. All rights reserved.