Atomic scale investigation of grain boundary structure role on deformation and crack growth dynamics in Aluminum

Abstract: The role that grain boundary (GB) structure plays on the plasticity of interfaces with preexisting cracks and on the interface crack dynamics was investigated using MD for both <100> and <110> aluminum STGBs. In simulations with a crack at the interface, this research shows how the maximum normal strength of the interface correlates with the respective GB energy, the GB misorientation, and the GB structural description. For instance, the normal interface strength for GBs containing D structural unit (SU) or stacking faults in the GB structural description ({\Sigma}13 (510) {\theta}=22.6{\deg} and {\Sigma}97 (940) {\theta}=47.9{\deg}) shows a noticeable decrease in interface strength, as compared to other evaluated <100> GBs that contained favored SUs. In the case of <110> interfaces, the presence of the E SU in the GB structure lowers the maximum normal interface strength by 35%. Further investigation of the deformation at the crack tip in GBs containing the E structure revealed that the E SU underwent atomic shuffling to accommodate intrinsic stacking faults (ISFs) along the interface, which in turn acts as a site for partial dislocation nucleation. Interestingly, regardless of GB misorientation, GB interfaces examined here containing the E structure in their structural period exhibited relatively small variation in maximum normal strength of interface. The GB volume ahead of the crack tip underwent structural rearrangement which, in turn, influenced the crack propagation mechanism. In most GBs, the crack propagation was due to alternating mechanisms of dislocation emission, followed by propagation of dislocation (blunting) and cleavage/crack advance. Moreover, the crack growth rates along the GB interface were strongly influenced by the initial free volume at the interface, i.e., faster crack growth was observed along interfaces with higher initial free volume.