Atomistic simulation of the effect of Ga on crack tip opening in Al bicrystals

Liquid metal embrittlement (LME) in the Al-Ga system is studied using molecular dynamics simulations. Crack tip opening loads are exerted on symmetric tilt Al bicrystals in the presence of liquid Ga. In general, the speed of crack propagation increases in the presence of Ga. However, there is significant variation in the dynamic behavior of the different boundaries studied here. We observe the formation of a sub-grain by grain boundary dissociation (grain boundary phase transformation) in [1 1 0] Sigma 9 and [1 1 0] Sigma 11 grain boundaries; this results in crack blunting even in the presence of Ga. In the Sigma 3 twin, the absence of alternating compressive and tensile stresses present in other boundaries results in fast Ga penetration after the crack path is formed. The structure of grain boundaries apart from thermodynamic considerations significantly affects LME.