Activated slip systems in bimodal Ti-6Al-4V plastically deformed at low and moderately high temperatures

Activated slip systems were investigated by analyzing slip traces and measuring the distribution of the Schmid factor to understand the controlling mechanism behind the change in effective stress seen in bimodal Ti-6Al-4V. It was ascertained that both basal and prismatic slips are dominant at 77 K and 225 K. It was suggested that the critical resolved shear stress (CRSS) for basal and prismatic slips are close to each other at 77 K and 225 K. The activation of basal alongside prismatic slips was unexpected, owing to previous reports which determined that the CRSS of prismatic slips is lower than that of basal slips in single-phase Ti-6.6Al. It is presumed that the difference arises between single phase Ti-6.6Al and bimodal Ti-6Al-4V from the boundary of alpha/beta interfaces in bimodal Ti-6Al-4V, which acts as obstacles for prismatic and pyramidal slips. In addition to those, it was found that pyramidal slips are dominant at 550 K in this study. The reasons for the higher activation of pyramidal slips in comparison with basal and prismatic slips at 550 K are also discussed. Present study evidenced that the change in the dominant active slip systems is responsible for the change in the trend of temperature dependence interpreted in the effective stress.