The Effects of Grain-boundary Orientations on Failure Behavior in F.C.C. Polycrystalline Systems

A multiple-slip rate-dependent crystalline constitutive formulation that is coupled to the evolutionary equations of mobile and immobile dislocation densities is used with specialized finite-element methodologies to obtain a detailed microstructural prediction of the inelastic deformation and interrelated physical mechanisms that affect different failure modes in f.c.c. crystalline materials. The effects of grain and grain-boundary (GB) orientations, grain shape and size, GB strength, and mechanical properties on the inelastic finite deformation and failure mode mechanisms in polycrystalline aggregates with Σ3 and Σ17b GBs have been investigated. Results from this study are consistent with experimental observations that microstructures with desired material properties, such as resistivity to crack nucleation, can be potentially achieved by the control of grain aggregate size and CSL GB orientations. Furthermore, it is also shown that transgranular failure modes can occur in aggregates with a high frequency of Σ3 GBs, whereas intergranular fracture modes can occur with a high frequency of Σ17b GBs.