Dissolution mechanisms and kinetics of δ phase in an aged Ni-based superalloy in hot deformation process

Abstract

High-temperature compressive experiments of a Ni-based superalloy containing δ phase (Ni3Nb) are conducted. The dynamic dissolution behavior of δ phase in hot deformation process is quantitatively investigated. The dissolution mechanisms of δ phase are analyzed by Transmission Electron Microscopy (TEM) and first-principles calculations. Results reveal that the dissolution of δ phase is accelerated with increasing deformation temperature or deformation degree. But, the dissolution of δ phase becomes weaken as the strain rate is raised. The shear modulus (G) and bulk modulus (B) of δ phase decrease with increasing temperature or reducing pressure. The positive Cauchy pressure (C12–C44) and the larger ratio of B/G (greater than 1.75) reveal that δ phase is ductile at high temperatures or pressures. The intense interactions between dislocations and δ phase induce the stress concentration and the rapid diffusion of Nb atoms, which accelerate the precipitation/dissolution of δ phase. A phenomenological model is established for depicting the dissolution behavior of δ phase in hot deformation process. The measured results are identical with the forecasted ones, which demonstrates the established model is feasible to accurately depict the dynamic dissolution behaviors of δ phase in hot deformation process.