Influence of alloying elements upon the theoretical tensile strength of Ni-based model superalloy: γ-Ni/γ′-Ni3Al multilayer

Abstract

The theoretical tensile strength of Ni-based model superalloys was investigated by density functional theory calculations. The superalloy was modeled as a γ-Ni/γ′-Ni3Al multilayer, and the strengthening effect induced by alloying elements X (X=Re, Ru, Cr, Mo, W, or Ta) close to the γ/γ′ interface was investigated. Theoretical calculations show that the tensile strength of the model superalloy is ∼1GPa higher than that of the γ′-Ni3Al phase, although the critical strain is ∼38% lower than that of the pure γ′-Ni3Al phase. Except for Ta, doping at the Al site of the γ-Ni/γ′-Ni3Al interface significantly increases the theoretical tensile strength (>7%) or critical strain (>10%) of the γ-Ni/γ′-Ni3Al multilayer. Local atomic disorder is observed in the Ni–Al sublayer of the γ′-Ni3Al block of the superalloy, wherein the Ni–Al atomic layer decomposes into an Al layer and a Ni layer when the strain exceeds a critical value. The charge density difference and partial density of states provide further insight into the changes of chemical bonds and charge redistribution during the tensile process. Charge transfer from Al to Ni in the γ′-Ni3Al precipitate of the superalloy could account for its higher tensile strength than the single γ′ phase. Moreover, covalent-like Ni–X bonds inhibit deformation of the system, resulting in tensile strengthening of doped γ-Ni/γ′-Ni3Al multilayers.