The roles of microstructure and mechanics in intergranular stress corrosion cracking

Abstract

Previous work on the prediction of intergranular stress corrosion cracking resistance in grain boundary engineered microstructures has used two dimensional percolation models, in which the grain boundaries are assumed to be either resistant or susceptible to cracking, depending on the grain boundary character. One limitation of such models is that they do not necessarily account for the mechanical crack driving force. Further, they cannot capture experimentally observed phenomena such as the formation of isolated ductile bridging ligaments by resistant boundaries. These arise due to the threedimensional character of crack propagation. A new mechanical crack propagation model is presented which, via finite element solutions, addresses these limitations. The model is based on a regular discrete representation of the materials microstructure and is applicable to both 2D and 3D behaviour. Results are reported for 2D-hexagonal microstructures, and are compared with percolation models. The results demonstrate the influence of stress on crack path, as well as the influence of the rupture strain of susceptible boundaries on crack behaviour. Further, the effect of crack bridging, which arises from ductile resistant boundaries is studied.