Twinning, phase transformation and dislocation evolution in single crystal titanium under uniaxial strain conditions: A molecular dynamics study

We perform molecular dynamics simulations to investigate the microstructural evolution and role of twinning on omega-phase transformation in single crystal Ti for loading perpendicular to the c-axis under uniaxial strain conditions. We find that both tension twinning and omega-phase evolve simultaneously and compete with each other. The number of activated tension twin variants not only affects the overall twin volume fraction but also the omega-phase volume fraction. For the case where four twin variants activate, the overall twin volume fraction is lowest and omega-phase volume fraction is highest in comparison to the case where only two twin variants activate. Significant amount of unconsumed parent HCP structure occurs for the case where four twin variants activate in comparison to the case where only two twin variants activate. This suggests that the number of activated twin variants and the spatial distribution of twins belonging to these variants play an important role on the amount of unconsumed parent HCP structure. The presence of high dislocation density for the case where four twin variants activate in comparison to the case where only two variants activate indicates that the number of activated twin variants also affects the overall dislocation density. The foregoing observations can be useful to develop a dynamic material strength model which can account for the coupled evolution of plasticity and phase transformation.