PNNL

Abstract

Twinning in metals is a major plastic deformation mode. Here we present a phase-field model to describe twin formation and evolution in a polycrystalline FCC metal under loading and unloading. The model assumes that the twin nucleation, growth and de-twinning is a process of partial dislocation nucleation and slip on successive habit planes. Stacking fault energies, energy pathways ( surfaces), critical shear stresses for the formation of stacking faults, and dislocation core energies are used to construct the thermodynamic model. The simulation results demonstrate that the model is able to predict the nucleation of twins and partial dislocations as well as the morphology of the twin nuclei, and reasonably to describe twin growth and interaction. The twin microstructures at grain boundaries are in agreement with experimental observation . It is found that de-twinning occurs during unloading in performed simulations. However, strong dependence of twin structure evolution on loading history is observed.