Uncovering the damage behavior of heterogeneous grains in Mg-RE alloys

Grain boundaries are often prone to damage due to local stress concentration and strain accumulations. However, the influence of heterogenous grain characteristics on damage behavior is not only a function of grain size, but also its orientations. In this study, a Crystal Plasticity Fast Fourier Transform (CPFFT) model has been coupled with phase field to simulate this heterogeneous grain effects on damage behavior. Using the heterogeneous grains from Electron Back Scatter Diffraction (EBSD) measurements of Mg-2Y and Mg-2Gd alloys, the damage propagation subjected to uniaxial tension has been simulated and it was found that grain size, Schmid factor, grain boundary misorientation angle, and geometric compatibility factor collectively influence the crack initiation and propagation. The inhomogeneous plastic deformation within the polycrystals, consequently manifesting diverse behaviors of damage evolution. Therefore, it is the coordination of heterogeneous crystal orientation and grain size which inhibits the initiation and propagation of cracks, thereby retarding the plastic instability and improving the material ductility.