Effect of random variations in microstructure on the development of final creep failure in polycrystalline aggregates

Planar analyses of a unit cell containing many grains are used to study the effect of random variations in the microstructure on failure times in a metal subject to creep at high temperatures. The model accounts for intergranular failure by cavity nucleation and growth to coalescence, or by grain boundary sliding, and the deformations of the grains are represented by power-law creep and elasticity. Two kinds of microstructural variations are considered: variations in the size and shape of grains, and variations in the cavity nucleation properties. Failure times are determined for various levels of deviation from a uniform periodic array of hexagonal grains. For variations in grain geometry, the times are correlated with the relative change in the average density of grain boundary facets, while the variance of the distribution is used for the simulations with random nucleation properties. For each case analysed, the time to first cavity coalescence as well as the time to find failure by link-up of pain boundary microcracks are determined.