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

High-temperature compressive experiments of a Ni-based superalloy containing delta phase (Ni3Nb) are conducted. The dynamic dissolution behavior of delta phase in hot deformation process is quantitatively investigated. The dissolution mechanisms of delta phase are analyzed by Transmission Electron Microscopy (TEM) and first-principles calculations. Results reveal that the dissolution of delta phase is accelerated with increasing deformation temperature or deformation degree. But, the dissolution of delta phase becomes weaken as the strain rate is raised. The shear modulus (G) and bulk modulus (B) of delta phase decrease with increasing temperature or reducing pressure. The positive Cauchy pressure (C-12-C-44) and the larger ratio of B/G (greater than 1.75) reveal that delta phase is ductile at high temperatures or pressures. The intense interactions between dislocations and delta phase induce the stress concentration and the rapid diffusion of Nb atoms, which accelerate the precipitation/dissolution of delta phase. A phenomenological model is established for depicting the dissolution behavior of delta 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 delta phase in hot deformation process. (C) 2018 Elsevier Ltd. All rights reserved.