Theory of intergranular creep cavity nucleation, growth and interaction

Abstract

Creep cavitation is modeled assuming random continuous cavity nucleation, coupled growth by diffusion and plastic deformation, diffusive cavity interactions and cavity interconnection and finally, failure at a critical a real damage fraction. Nucleation is simulated by Monte-Carlo techniques using an empirically-derived nucleation law for copper that depends on the steady-state creep strain. For initially fully-dense materials, cavity nucleation dominates the cavity number density until interconnection and coarsening become important late in rupture life. In this situation, Monkman-Grant behavior is obtained and cavity sizes approach stable log-normal distributions. However, when a small fraction of cavities pre-exist, the cavity density is dominated by cavity interactions and the density remains relatively constant despite continuous nucleation. In this case, cavity growth controls the rupture time and cavity size distributions tend to approach log-normal distribution more slowly. These diffusive interactions diminish for larger but more widely-spaced pre-existing cavities because of limited interactions between the pre-existing and nucleating cavities. The sensitivity of the rupture life on dihederal angle and nucleation rate are also examined, and the statistics of failure are quantified.