Effect of strain rate on the mechanical response of a Ti₃Al-Nb-Mo alloy

In this study, the effect of strain rate and temperature on the substructure evolution and mechanical response of a Ti₃Al-Nb-Mo alloy (Ti-24.5Al-10.5Nb-1.5Mo) was investigated. The yield and flow stresses were found to decrease gradually with increasing temperature at the strain rate of 3000 s^-1 and no flow stress/temperature anomaly was observed. The variation of hardening behavior of Ti-24.5Al-10.5Nb-1.5Mo alloy with temperature and strain rate was found to be negligible, implying that the dynamic recovery mechanism for this alloy is rather athermal. Dynamic recovery of Ti-24.5Al-10.5Nb-1.5Mo alloy is thought to be quite difficult and slow because of its complicated dislocation core structure. Ti-24.5Al-10.5Nb-1.5Mo alloy exhibited predominantly planar dislocation debris after deformation. Following the room temperature deformation at low strain rate the majority of the dislocations were a-dislocations lying on the basal and 1st-order pyramidal slip planes and the 2nd-order pyramidal a/2+c slip on {1211}. Increasing the rate of deformation at room temperature to 6000 s^-1 resulted in the increased a-slip on prism planes and the lessor amount of basal slip. At elevated temperatures, the substructure after high rate deformation was found to be similar to that following high rate deformation at room temperature except for an increased amount of basal slip and somewhat higher incidence of the 2nd-order pyramidal slip. The evidence of an increased amount of shearing of the β_o phase was observed at elevated temperature, suggesting the decreased strength of the β_o phase.