On the Self - and Impurity Diffusion in High Entropy Alloys

Abstract

General trends in self- and impurity diffusion data are analyzed in high entropy alloys. Our analysis is based on the similarity of inter-atomic potentials in metals, which is in fact equivalent to a three-parameter description of the system (the mass, m, the lattice spacing, a, and the melting point, Tm, are only used). This leads to the so-called law of corresponding states in metals, manifested in many empirical rules (e.g. compensation laws or the proportionality between the self-diffusion activation energy and the melting point) if one uses dimensionless/reduced variables (like the homologous temperature: T*=T/Tm). It was shown in our previous papers, using the concept of a hypothetical crystal composed of simple atomic species whose properties are an average of the components, that the tracer diffusion of any species (let it be either one of the constituent atoms or a foreign atom) can be considered as impurity diffusion in the pure many-component matrix. Using this concept, we illustrate that the diffusion coefficients, Di, follow the same rule which obtained for impurity diffusion in pure metals: lnDi=A(T*)(Tmi/Tm-1)+r, with the same fitting parameters A(T*) and r. According to this, the diffusion of the constituent elements in high entropy alloys indeed shows some sluggish character, which can be attributed to a more or less temperature independent factor.