Microplasticity in polycrystalline materials from thermal cycling

In this work, we present a finite deformation, fully coupled thermomechanical crystal plasticity framework. The model includes temperature dependence in the kinematic formulation, constitutive law and governing equilibrium equations. For demonstration, we employ the model to study the evolution and formation of residual stresses, residual statistically stored dislocation density and residual lattice rotation due solely to solid state thermal cycling. The calculations reveal the development of microplasticity within the microstructure provided that the temperature change in the thermal cycle is sufficiently large. They also show, for the first time, that the thermal cycling generates an internally evolving strain rate, where the contributions of mechanical strain and plasticity depend on temperature change. The calculations suggest a strong connection between the maximum temperature of a given cycle and the magnitude of the residual stresses generated after the cycle. A pronounced influence of elastic anisotropy on the heterogeneity of the residual stress distribution is also demonstrated here. Finally, we calculate lattice rotation obtained from thermal cycling ranging from \(\pm 0.4^{\circ }\) and show the relation between changes in predominant slip systems with short range intragranular lattice rotation gradients. The model can benefit metal process design, especially where large strains and/or large temperature changes are involved, such as bulk forming and additive manufacturing.