Effects of alloying on the interface energy of the δ- and η-phase in nickelbase superalloys

Abstract

Wrought 718-type nickel-base superalloys are forged at temperatures where the strengthening phases ( or ) are dissolved, but additional phases (δ-phase of Ni3Nb type or the η-phase of Ni3Ti-type) are present to ensure a fine-grained microstructure. The precipitation of these phases is influenced by the interfacial energy. We use density functional theory calculations at 0 K to study the interfacial energy of the δ- and η-phase with a coherent interface orientation. By transferring alloying elements from the center of a phase to the boundary, we calculate the influence of these elements on the interface energy. A simple model that uses the change in volume caused by the alloying element and its chemical binding energy in the different phases is presented and shown to be able to reasonably predict the interface transfer energy of the elements in most cases.