Effects of Fe, Cr and Mn on inter-diffusion in CoNi-containing multiple principal alloys

Inter-diffusion in eight alloys from the binary CoNi alloy to the quinary FeCrMnCoNi high entropy alloy (HEA) was studied by the diffusion couple experiments. It was found that the FeCrMnCoNi HEA does not exhibit sluggish diffusion in both the absolute temperature scale and the homologous temperature scale. Effects of specific elements were analyzed: Mn increases inter-diffusion in the absolute temperature scale but decreases it in the homologous temperature scale; Cr decreases inter-diffusion in both temperature scales; Fe decrease inter-diffusion in the absolute temperature scale but in the homologous temperature scale, the interaction between Fe and other elements could become important. The relationship between the pre-exponential factor and homologous activation energy indicates that the atomic diffusion process may not change qualitatively from binary to multiple principal alloys.