A numerical analysis of intergranular penny-shaped microcrack shrinkage controlled by coupled surface and interface diffusion

An axisymmetric finite-element method is developed and applied to simulate healing evolution of intergranular penny-shaped microcracks. In the finite-element method, grain-boundary diffusion and surface diffusion are coupled by the boundary conditions at the triple circle of the penny-shaped microcrack surface and the grain-boundary plane. Matter is transported to the triple circle by grain-boundary diffusion and is taken away from the microcrack tips and deposited onto the microcrack surfaces by surface diffusion, resulting in shrinkage of the intergranular microcracks. The numerical simulations show that the evolution processes of intergranular microcracks are controlled by equilibrium dihedral angle (defined by surface and grain-boundary tensions), microcrack spacing, ratio of grain-boundary diffusion to surface diffusion, and the applied pressure.