Study of dislocation-twin boundary interaction mechanisms in plastic deformation of twip steel by discrete dislocation dynamics and dislocation density-based modeling

Abstract

Deformation twins contribute to the unique deformation behaviors and characteristics in the plastic deformation of TWIP steels since twin boundary (TB) blocks the movement of dislocations and absorbs them in deformation process. On the other hand, dislocations can traverse TB. However, there is still no consensus on how TB influences the plastic deformation of TWIP steels among prior researches. Therefore, exploring the interaction between dislocation and TB is critical to understand the effects of twins on the macro deformation behaviors and exploit the strengthening potential of the alloys. In this study, a dislocation-TB interactions model for TWIP steel was proposed, developed and implemented in discrete dislocation dynamics (DDD) simulation, the complicated dislocation reactions at the TB were determined by the energy criterion, which serves as a feasible approach to represent the micro deformation characteristics under different tension directions with respect to the twin plane normal of TWIP steel micropillar. Furthermore, the effect of dislocation type and reaction characteristic at the TB in DDD are incorporated into the conventional dislocation density-based (DDB) model, and then the improved DDB model is used to quantitatively describe the macro plastic behavior of TWIP steel micropillar. The DDD simulation results show that the dislocation-TB interactions are related to the dislocation type and the angular relationship between loading direction and twin plane normal. The TB has a significant strengthening effect if the loading direction is perpendicular to the twin plane (0°) due to the increase of the back stress induced by the activated 60° dislocation pileups. For other orientations (45° and 90°), however, the strain hardening becomes negligible. Meanwhile, the stress and dislocation density-strain curves under different directions with respect to the twin plane normal are predicted by the improved DDB model and have a good agreement with the DDD simulation and experimental results. The research thus advances the understanding of dislocation-TB interaction mechanisms in plastic deformation of TWIP steels.