Crystal plasticity analysis of change in incompatibility and activities of slip systems in α-phase of Ti alloy under cyclic loading

Abstract

With respect to Ti-6Al-4V alloy (Ti-64) with duplex phases constructed by α-phase with an hcp structure and β-phase with a bcc structure, basal slips in α-phase can potentially lead to crack initiation under fatigue loading. Hence, it is necessary to quantitatively evaluate the activity of basal slip systems. However, the critical resolved shear stress (CRSS) for the basal slips in α-phase is equal to or slightly exceeds that for the prismatic slips, and mechanisms for the activation of slip systems are not completely understood. The present study involved conducting crystal plasticity analysis of α-phase subjected to cyclic loading and uniaxial tensile loading employing bicrystal models and uniaxial tensile analysis of tricrystal models. The results indicated that a trade-off relationship exists between the activities of slip systems. Specifically, the inactivation of prismatic <a> slip system in a crystal grain activates the basal slip system in the neighboring crystal grains due to the changes of incompatibility by work hardening around the grain boundary triple junction line. The changes in incompatibility can be explained by wedge disclination type deformation field.