The effect of grain size and stability on ambient temperature tensile and creep deformation in metastable beta titanium alloys

The effect of grain size in the range of 100–500 μm on the ambient temperature tensile and creep deformation behavior was investigated in a metastable Ti–9.4 wt% Mn alloy at 95% yield stress. It was observed that, as grain size increases the creep strain increases, the slip lines become coarser and the density of slip increases. An interrupt creep test showed that new slip lines were generated with time and most of the deformation occurred during the first few hours of testing. The effect of β-phase stability was studied by comparing the creep and tensile behavior of Ti–9.4 wt% Mn in this study, with previously reported results obtained for Ti–14.8 wt% V and Ti–13.0 wt% Mn at ambient (room) temperature. The Molybdenum Equivalency, which is a measure of the stability of these alloys, are 9.9, 14.3, and 19.9, respectively. The main mode of deformation in Ti–9.4 wt% Mn alloy was observed to be slip. The modes of deformation changed with the increase in stability from slip accompanied by Stress Induced Plate formation to only slip. It was also found that metastable ω-phase was present in lower stable alloys, irrespective of the observed mode of deformation. At 95% yield stress, the amount of creep strain in 200 h was found to increase with a decrease in stability of the β-phase.