Unveiling the Co effect on the temporal evolution kinetics of ?' phase in Ni-Al-Co model superalloys via CALPHAD-informed phase field simulations

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