Atomic mobilities and interdiffusivities in Ni-rich fcc Ni-Co-Cr and Ni-Al-Co-Cr systems evaluated using composition profiles and HitDIC

Abstract

In this paper, 15 single-phase solid/solid diffusion couples in Ni-rich fcc Ni-Co-Cr and Ni-Al-Co-Cr systems were fabricated, and the corresponding concentration profiles of Ni, Co, Cr, and Al at 1423–1523 K were determined by means of the electron probe microstructure analysis technique. The atomic mobility descriptions in Ni-rich fcc Ni-Al-Co-Cr system were established directly from the present 15 concentration profiles with the aid of HitDIC software. The interdiffusion coefficients in fcc Ni-Co-Cr and Ni-Al-Co-Cr alloys were then evaluated based on the established atomic mobilities in fcc Ni-Al-Co-Cr system together with the reported thermodynamic descriptions. The reasonability of D̃CoCoNi and D̃CrCrNi in fcc Ni-Co-Cr alloy was validated by comparing with the corresponding experimental values in Ni-Co and Ni-Cr binary alloys. The diffusion rate of Cr is larger than that of Co in both Ni-Co-Cr and Ni-Al-Co-Cr alloys, and Al diffuses faster than Cr in Ni-Al-Co-Cr alloys. The comparison between the diffusion rates of Co and Cr in Ni-Al-Co and those in Ni-Al-Co-Cr alloys suggests the addition of Al speeds up the diffusion of Co and Cr in Ni-Al-Co-Cr alloys, and the acceleration is more pronounced as the temperature increases.