Microstructural Modeling of Intergranular Fracture in Tricrystals With Random Low- and High-Angle Grain Boundaries

Intergranular (IG) fracture behavior near triple junctions (TJs) in f.c.c. tricrystals with a variety of grain boundary (GB) misorientations has been investigated. Based on a dislocation-density GB interaction scheme, critical fracture conditions were coupled to evolving dislocation-density pileups and local stresses by using a dislocation-density-based crystalline plasticity formulation within a nonlinear finite-element framework to elucidate the effects of local GB structure, dislocation-GB interactions, and misorientations on IG crack propagation in f.c.c. crystalline materials. Tricrystals with low-angle GBs had higher fracture toughness than tricrystals with high-angle GBs. In TJs with a combination of random low- and high-angle GBs, the formation of dislocation-density pileups in the high-angle GB led to IG crack propagation along the high-angle GB rather than along the low-angle GB. These predictions, which are consistent with experimental observations, indicate that fracture behavior near TJs is controlled by highly local, evolving, and interrelated events, such as dislocation-density pileups and GB misorientations.