New trends in directional coarsening of superalloys under stress

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