Gamma prime coarsening and age-hardening behaviors in a new nickel base superalloy

Abstract

By means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), phase extraction, small-angle X-ray scattering (SAXS), and microhardness testing, the coarsening kinetics of gamma prime and age-hardening behavior have been investigated in a newly developed nickel base superalloy aged at elevated temperatures for times of up to 4000 h. The precipitates of the alloy as standard precipitation treatment are γ′, MC, and M 23C 6. Coarsening of γ′ precipitates proceeds by Ostwald ripening controlled by volume diffusion of solute atoms in the alloy. The activation energy for γ′ coarsening is evaluated as 247 kJ mol −1. Due to the different growth rate of γ′ precipitates, room temperature microhardness of the alloy decreases notably with an increase in ageing temperature, while it decreases slowly with ageing time from 500 to 4000 h.