Measurement of Interdiffusion and Tracer Diffusion Coefficients in FCC Co-Cr-Fe-Ni Multi-Principal Element Alloy

Abstract

Average effective interdiffusion coefficients of individual components and tracer diffusion coefficient of Ni were experimentally determined in FCC CoCrFeNi high entropy alloys. Average effective interdiffusion coefficients of individual elements in CoCrFeNi alloys were determined using the Dayananda-Sohn approach. Cr had the highest while Ni had the lowest magnitude of the average effective interdiffusion coefficient in the CoCrFeNi alloy. The tracer diffusion coefficient of Ni was determined without the application of radiotracers using the novel analytical method proposed by Belova et al. based on linear response theory coupled with the Boltzmann-Matano approach and Gaussian distribution function. Both average effective interdiffusion coefficients and tracer diffusion coefficients in CoCrFeNi were compared with the relevant high entropy alloys with varying entropy of mixing. The diffusion of individual elements in Al-containing high entropy alloys (e.g., Al-Co-Cr-Fe-Ni and Al-Co-Cr-Fe-Ni-Mn), with higher entropy of mixing, was higher than that in CoCrFeNi alloy, with relatively lower entropy of mixing. Therefore, diffusion cannot a priori consider to be sluggish in alloys with higher configurational entropy. Moreover, potential energy fluctuations determined in quinary and senary Al-containing high entropy alloys were higher than that in quaternary CoCrFeNi alloy. This also suggests that the diffusivity of a component may not be always lower in the alloys which possess higher fluctuations in potential energy or configurational entropy of mixing.