Dissolution mechanisms and kinetics of δ phase in an aged Ni-based superalloy in hot deformation process. (15th October 2018) - He, Dao-Guang
Abstract: High-temperature compressive experiments of a Ni-based superalloy containing δ phase (Ni3 Nb) 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 ( C 12 – C 44 ) 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. Graphical abstract: Highlights: High-temperature compressive experiments of a Ni-based superalloy containing δ phase (Ni3 Nb) are conduct. The dissolution of δ phase is accelerated with increasing deformation temperature or true strain. Local stress concentration induced by the interactions between dislocation and δ phases twists δ phases. The dislocation-assisted Nb atoms diffusion play a major role for the dissolution of δ phases. The developed model is feasible to predict the dissolution behaviors of δ phases during hot deformation.