THE EVOLUTION OF INTERGRANULAR MICROCRACKS DUE TO SURFACE AND GRAIN-BOUNDARY DIFFUSION INDUCED BY MULTI-FIELD

Based on the classical theory of surface diffusion and grain-boundary diffusion and its weak statement, a finite element program is developed to simulate the evolution of intergranular microcracks in metal materials due to the stress and electromigration-induced surface and grain-boundary diffusion. The effects of the ratio of grain-boundary diffusion to surface diffusion, the magnitude of the stress, the electric field and the aspect ratio on the evolution of intergranular microcracks are investigated in detail. The results show that the intergranular microcrack can split into two little microcracks or can propagate. The increase of the ratio of grain-boundary diffusion to surface diffusion and the magnitude of the electric field promote crack propagation, while the magnitude of the stress impedes crack propagation. The splitting time of the microcrack decreases with the magnitude of the stress increasing, while it increases with the aspect-ratio increasing. When , the splitting time decreases obviously with the increase of the electric field, that is, the electric field accelerates the microcrack splitting. However, the effect of the electric field is not obvious on the splitting time when .