Concentration-dependent atomic mobilities in FCC CoCrFeMnNi high-entropy alloys

TL;DR

This study investigates how atomic mobility varies with concentration in a specific high-entropy alloy, revealing element-specific diffusion rates, complex diffusion behaviors, and proposing a new modeling approach to accurately describe diffusion processes.

Contribution

It provides the first detailed measurement of composition-dependent tracer diffusion coefficients in CoCrFeMnNi high-entropy alloy and introduces a generalized continuum model for multi-component interdiffusion.

Findings

Mn diffuses fastest among elements studied

Co exhibits S-shaped concentration dependence in mobility

The proposed model accurately predicts complex diffusion profiles

Abstract

The diffusion kinetics in a CoCrFeMnNi high entropy alloy is investigated by a combined radiotracer--interdiffusion experiment applied to a pseudo-binary Co$_{15}$Cr$_{20}$Fe$_{20}$Mn$_{20}$Ni$_{25}$ / Co$_{25}$Cr$_{20}$Fe$_{20}$Mn$_{20}$Ni$_{15}$ couple. As a result, the composition-dependent tracer diffusion coefficients of Co, Cr, Fe and Mn are determined. The elements are characterized by significantly different diffusion rates, with Mn being the fastest element and Co being the slowest one. The elements having originally equiatomic concentration through the diffusion couple are found to reveal up-hill diffusion, especially Cr and Mn. The atomic mobility of Co seems to follow an S-shaped concentration dependence along the diffusion path. The experimentally measured kinetic data are checked against the existing CALPHAD-type databases. In order to ensure a consistent treatment of tracer and chemical diffusion a generalized symmetrized continuum approach for multi-component interdiffusion is proposed. Both, tracer and chemical diffusion concentration profiles are simulated and compared to the measurements. By using the measured tracer diffusion coefficients the chemical profiles can be described, almost perfectly, including up-hill diffusion.