Interfacial dislocation based criterion for the prediction of rafting behavior in superalloys

Abstract

The effect that the morphological changes in {gamma}/{gamma}{prime} superalloys have on the mechanical properties of these materials is still an unresolved issue of the greatest interest. Experimental studies on [001] oriented single crystals have shown, for instance, that when a microstructure consisting of evenly spaced cuboids of {gamma}{prime} embedded in {gamma} was subjected to externally applied stresses at high temperature, then the coalescence occurred in an orientation-dependent way, and also that these rafting phenomenon can have a significant influence on the creep or fatigue life in load-bearing applications. In some alloys, the coalescence produced long rods or needles of {gamma}{prime} oriented parallel to the axis of stress, and others produced flat plates or rafts in an orientation perpendicular to the stress axis. In most alloys this orientation dependence was found to invert when a stress of opposite sign was applied. Recent attempts to predict the rafting behavior of these materials have suggested using a combined Monte Carlo/finite element approach which relies on the elastic strain energy and an isotropic interfacial energy term. While this approach succeeded in reproducing the map developed by Pineau and based on the elastic energy of inclusions, a large amount of computation was needed even formore » small lattices in simulations of the microstructural evolution. The present study, which is part of a wider research program on the mechanical performance of superalloys, is aimed at presenting a novel criterion providing an improved rafting prediction map and also a simpler way to model the energy anisotropy, so as to allow simulations of larger systems or for longer microstructural evolutions.« less