New trends in directional coarsening of superalloys under stress

After a short summary of the most significant experimental results available in the literature, the different types of models proposed for directional coarsening under stress are discussed. We show that, in contrast with former models considering isolated precipitates in elastic media, local stresses resulting from both precipitate interactions and plastic relaxation of misfit stresses are of fundamental importance. In the latest approaches, directional coarsening is thought to result from cross-diffusion of chemical species in elastic energy gradients, in order to suppress non-relaxed matrix channels. The morphology and kinetics of directional coarsening is predicted by recent numerical simulations. Relations between directional coarsening and creep mechanisms are also discussed.