Influence of transition group elements on the stability of the γ″-phase in nickelbase alloys

Abstract

Alloy 718-type wrought nickel-based superalloys are the materials of choice for many high temperature applications. They are strengthened by the γ″-phase that forms small precipitates with a large lattice distortion. However, at temperatures above 650 °C, this phase may transform to the thermodynamically stable δ-phase. It is therefore important to understand the influence of alloying elements on the stability of these phases. In this paper, density functional theory calculations at 0 K are performed to determine the effect of aluminium and of the transition group elements on the stability and the lattice parameters of the γ″-phase. It is shown that the substitution energy is mainly determined by two parameters, the charge transfer and the change in the lattice constant. Solution energies are compared to those in the δ-phase and some conclusions for the design of 718-type alloys are drawn.