Nanotexture Change Caused by Strain-Induced Anisotropic Diffusion During Creep of Ni-Base Superalloy

Abstract

In order to make clear the mechanism of the directional coarsening (rafting) of γ′ phases in Ni-base superalloys under uni-axial tensile strain, molecular dynamics (MD) analysis was applied to investigate dominant factors of strain-induced anisotropic diffusion of Al atoms and nanotexture change of fine dispersed γ′ precipitates. In this study, a simple interface structure model corresponding to the γ/γ′ interface, which consisted of Ni as γ and Ni3Al as γ′ structure, was used to analyze the effect of alloying element on diffusion properties. The diffusion constants of Al atoms were changed drastically by the dopant elements and their contents. When the lattice constant of the γ phase was increased and its melting point was decreased by the addition of Cr or Al atoms, the strain-induced anisotropic diffusion of Al atoms in the γ′ phase was accelerated. On the other hand, the addition of Co decreased the diffusion significantly. Therefore, changes of lattice constant and melting point depending on the chemical composition of the γ/γ′ interface are the dominant factors controlling the strain-induced anisotropic diffusion of Al atoms in the Ni-base superalloy.

Acceleration mechanism of the degradation of the lifetime of Ni‐based superalloys under creep‐fatigue loading at elevated temperatures

“…And also, the Nb and Mo provide age‐hardening in Alloy 625. Al and Ti were kept low to avoid the appearance of γ′ phase (Ni 3 Al) and, thus, the change of the micro texture caused by rafting 26 . The low content of Al and Ti also benefits in weldability 27 …”