Unveiling the Co effect on the temporal evolution kinetics of γ′ phase in Ni–Al–Co model superalloys via CALPHAD–informed phase field simulations

Abstract

Co is a valuable γ solid solution strengthening element in nickel-based superalloys that improves their microstructure and creep resistance. However, the impact of Co additions on the kinetics of γ′ precipitation remains controversial. In this study, we conducted CALPHAD-informed phase field simulations to quantitatively analyze the γ′ precipitation process in Ni–Al–Co model superalloys and uncover the Co effect on the temporal evolution kinetics of the γ′ phase. Our simulations revealed that the γ′ coarsening rate initially decreases, then increases at 1173 K with increasing Co content, a change that can be attributed to the competition between the γ/γ′ lattice misfit and interdiffusion coefficients. Although Co is a γ-stabilized element, our calculations and previous experiments show an anomalous increase in γ′ volume fraction with increasing Co concentration, which is linked to variations in elemental partitioning behaviors between the γ matrix and γ′ phase. Furthermore, the unique partitioning behavior of Ni suggests partial replacement of Al atoms at the corner site of γ′-Ni3(Al, Ni) sublattice by Ni atoms. Our research offers a new perspective on the effect of Co concentration on the kinetics of γ′ precipitation in Ni–Al–Co model superalloys and outlines a guideline for designing novel multicomponent superalloys with superior microstructural stability.