Elastoplastic phase-field simulation of martensitic transformation with plastic deformation in polycrystal

The martensitic transformation with plastic deformation in polycrystal is investigated by the elastoplastic phase-field model. The model can capture not only spatiotemporal change of martensitic microstructure, but also plastic deformation behavior to accommodate transformation-induced stress. In this paper, fcc → bcc martensitic transformation in Fe–Ni polycrystalline alloy is simulated in two-dimensions. The effects of self- and plastic accommodations on the transformation kinetics and morphology of microstructure are studied. The simulation results demonstrate that the martensite phase nucleates near crystal defects and grows into the parent phase. The morphology of the growing martensite phase presents a plate-like shape to minimize the elastic strain energy. The present simulation clearly shows that stress relaxation behavior is dominant factor which characterizes the morphology of martensite phase. The martensitic transformation only with the self-accommodation produces fine multivariant lamellar microstructure which accommodates internal stress-field. The high stress-field in the microstructure prevents completion of the transformation and causes formation of retained parent phase. In the martensitic transformation with the self- and the plastic accommodations, since the plastic deformation largely reduces the elastic strain energy, the self-accommodation driven by reduction of the elastic strain energy is suppressed. As a result, coarse multi-variant microstructure emerges in the grain where large amount of plastic strain is introduced. Furthermore, the parent phase can transform into the martensite phase completely.