Modeling of grain-boundary effects and intergranular and transgranular failure in polycrystalline intermetallics

摘要

A three-dimensional multiple-slip dislocation-density-based crystalline formation and specialized finite-element formulation were used to investigate dislocation-density transmission and blockage in nickel-aluminide polycrystalline aggregates, which were subjected to dynamic loading conditions, with a macroscopic crack and different distributions of random low-angle and coincident site lattice (CSL) grain boundaries (GBs). An interfacial GB scheme was developed to determine whether dislocation-density pileups or transmissions occur as immobile and mobile dislocation densities evolve along different slip systems. The three-dimensional dislocation-density-based crystalline formulation is based on inter-related mechanisms that can occur due to the generation, trapping, interaction, and annihilation of mobile and immobile dislocation densities that are generally associated with large strain-high-strain-rate plasticity in L12-ordered intermetallics. A crack-tip shielding factor was also formulated to delineate between transgranular and intergranular crack growth. The current results indicate that aggregates with a high frequency of Σ33a GBs would be susceptible to blunted transgranular crack growth due to high dislocation-density transmission rates and shear-stress accumulations, and that an aggregate with a high frequency of Σ17b GBs would be susceptible to sharp intergranular growth due to a large number of dislocation-density pileups and an accumulation of large normal stresses ahead of the crack tip.