Room temperature plastic flow behaviour of Ti–6.8Mo–4.5Fe–1.5Al and Ti–10V–4.5Fe–1.5Al: Effect of grain size and strain rate

The effect of β grain size and strain rate on the plastic flow behaviour of Ti–6.8Mo–4.5Fe–1.5Al (Ti metal LCB) and its equi-molybdenum DMRL alloy Ti–10V–4.5Fe–1.5Al was evaluated and compared. The 0.2% yield strength in both alloys was found to obey the Hall–Petch relation. However, σ0 (friction stress) was higher and ky (unpinning constant or stress concentration factor) was lower for the Mo containing alloy as compared to the V containing alloy. The strain rate was also found to influence the flow behaviour of both alloys. Flow softening was observed at strain rate of 10−2 s−1 for the Mo containing alloy at room temperature itself. However, at lower strain rates (10−4 and 10−5 s−1), there was no flow softening, although no significant work hardening was seen. The strain hardening parameter γ = dσ/σdɛP was calculated to explain the tensile deformation behaviour as a function of strain rate. The effect of strain rate on the flow behaviour was explained on the basis of velocity of mobile dislocation, localized adiabatic heating and planar slip due to the presence of ω-phase.