Simulation of Deformation Coordination and Hardening Behavior in Ferrite-Ferrite Grain Boundary

The deformation coordination of grain boundaries determines the nucleation and evolution of microvoids and affects the damage and fracture behavior of materials. However, grain boundary deformation is extremely complex and difficult to predict owing to the difference in intergranular orientation and grain stress state. Among them, two important ways of coordinating deformations are the accumulation of dislocations at grain boundaries and intergranular transfer. The geometric relationship of the activated intergranular slip systems determines the difficulty of slip transfer and the uniformity of deformation at grain boundaries. Moreover, owing to the complex grain boundary conditions of polycrystalline materials, it is difficult to accurately measure the actual stress state and deformation of grain boundaries, so there is a substantial discreteness between the experimentally observed slip transfer behavior and theoretical prediction results. Herein, based on the advantages of the crystal plasticity finite element method (CPFEM) in polycrystalline model construction, grain orientation, and mechanical boundary condition setting, the ferrite-ferrite symmetrical tilt and twist bicrystal models under different stress states was used to analyze the impact of stress state and relative grain orientation on grain boundary strain coordination and hardening behavior. The results show that the intergranular slip transfer factor and the resolve shear stress factor determine the strain uniformity at the grain boundary. The deformation uniformity at the grain boundary is positively correlated with the slip transfer factor, which mainly controls the intergranular deformation coordination behavior. However, the deformation at the grain boundaries of soft-oriented grains (determined by stress state and orientation) is uniform, and the slip transfer factor has little effect on strain coordination. When the slip transfer factor and the resolve shear stress factor are very small, strain concentration at the grain boundary easily occurs, making intergranular deformation coordination difficult. Therefore, the prediction results of intergranular deformation coordination combined with the slip transfer factor and resolving the shear stress factor are reasonable. In addition, the flow stress of the bicrystal model is negatively correlated with the slip shear stress factor, and the uneven deformation at the grain boundary easily causes geometrically necessary dislocations to proliferate and promote grain boundary hardening.

Automated summary

The coordination of grain boundary deformation is crucial for understanding the nucleation and evolution of microvoids, as well as the damage and fracture behavior of materials. However, predicting grain boundary deformation is challenging due to the complex intergranular orientation and stress state. Two important ways of coordinating deformations are the accumulation of dislocations and intergranular transfer, which are influenced by the geometric relationship of activated intergranular slip systems. Although there is a discrepancy between experimentally observed slip transfer behavior and theoretical predictions, using the crystal plasticity finite element method (CPFEM) can analyze the impact of stress state and grain orientation on grain boundary strain coordination and hardening behavior.