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

Alloy 718-type wrought nickel-based superalloys are the materials of choice for many high temperature applications. They are strengthened by the gamma ''-phase that forms small precipitates with a large lattice distortion. However, at temperatures above 650 degrees C, this phase may transform to the thermodynamically stable delta-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 gamma ''-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 delta-phase and some conclusions for the design of 718-type alloys are drawn.

Automated summary

Alloy 718-type wrought nickel-based superalloys, strengthened by the gamma ''-phase, may transform to the thermodynamically stable delta-phase at temperatures above 650 degrees C. Density functional theory calculations reveal the influence of aluminium and transition group elements on the stability and lattice parameters of the gamma ''-phase.