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

摘要

The theoretical tensile strength of Ni-based model superalloys was investigated by density functional theory calculations. The superalloy was modeled as a gamma-Ni/gamma'-Ni3Al multilayer, and the strengthening effect induced by alloying elements X (X = Re, Ru, Cr, Mo, W, or Ta) close to the gamma/gamma' interface was investigated. Theoretical calculations show that the tensile strength of the model superalloy is similar to 1 GPa higher than that of the gamma'-Ni3Al phase, although the critical strain is similar to 38% lower than that of the pure gamma'-Ni3Al phase. Except for Ta, doping at the Al site of the gamma-Ni/gamma'-Ni3Al interface significantly increases the theoretical tensile strength (>7%) or critical strain (> 10%) of the gamma-Ni/gamma'-Ni3Al multilayer. Local atomic disorder is observed in the Ni-Al sublayer of the gamma'-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 gamma'-Ni3Al precipitate of the superalloy could account for its higher tensile strength than the single gamma' phase. Moreover, covalent-like Ni-X bonds inhibit deformation of the system, resulting in tensile strengthening of doped gamma-Ni/gamma'-Ni3Al multilayers. (C) 2016 Elsevier B.V. All rights reserved.