Evolution of partial dislocation slip–mediated deformation twins in single crystals: a discrete dislocation plasticity model and an analytical approach

Abstract

Deformation twinning is an essential plastic deformation mechanism that realizes the trade–off between strength and ductility. Twins nucleate and grow by the coordinated slip of partial dislocations on consecutive {111}–type slip planes. The route of twin growth is responsible for the evolution of twin morphology, which affects the non–coplanar dislocation slips by adjusting the twinning–associated mean free path. Incorporating such twinning mechanisms is critical for the accurate modelling and simulation of deformation behavior. In this study, a discrete dislocation plasticity (DDP) model was developed by integrating the source introduction methods and source activation criteria of Shockley partial dislocation. In the model, two twin nucleation mechanisms, i.e., the internal source and surface source, were considered concurrently, and the additional effect of stacking fault energy on the motion of partial dislocations was introduced. The evolution of partial dislocation slip–mediated deformation twins in micron–sized pillars of twinning–induced plasticity steel under uniaxial compression was investigated. The predicted twin morphologies and stress–strain curves from DDP simulation both agreed well with the experimental results, highlighting the inherent characteristics of partial–dislocation–based twinning behavior. The simulation results showed that the formation of nanometer–sized sharp twin tips was caused by the strong interaction between the front and rear dislocations on adjacent slip planes. In addition, a novel analytical model verified with the DDP simulation was proposed by considering the kinetics of the newly formed twin embryos. The competition between new twin activation and near–twin merging in determining the evolution of twin thickness was analyzed using the analytical model. The dependence of flow stress and twin morphology on the density and distribution of internal sources was demonstrated by considering the new twinning route. This research thus advances the understanding of partial dislocation slip–mediated twinning mechanisms.