Effect of molar volume of diffusing elements and cross terms of Onsager formalism (vacancy wind effect) on estimated diffusion coefficients in ternary and multicomponent solid solutions

Abstract

The correlation between intrinsic and tracer diffusion coefficients considering the molar volume of the diffusing elements and cross phenomenological constants of Onsager (contributing to the vacancy wind effect) is established in guidance to Manning's analysis. Manning established this correlation assuming constant molar volume. A recent study in binary systems indicated a significant error in estimated data for consideration of constant molar volume if the molar volumes of the diffusing elements are significantly different. It also indicated that considering ideal molar volume variation is essential if a system's non-ideal molar volume variation is unknown. This could not have been practiced until now in ternary and multicomponent systems because of the unavailability of this correlation. This equation scheme is established in this study for conventional diffusion couples (all elements produce diffusion profiles) and constrained, such as pseudo-binary and pseudo-ternary diffusion couples (in which only two or three elements produce the diffusion profiles, respectively). The difference in data calculated considering a constant molar volume and neglecting the vacancy wind effect (which is mainly practiced until today) is compared with the data considering the molar volume of diffusing elements and vacancy wind effect in NiCoFeCr and an imaginary quaternary multi-principal element system. This indicates a significant error in estimated data when considering a constant molar volume if the molar volumes of the diffusing elements are reasonably different. Therefore, the outcome of this study is expected to bring a significant change in diffusion analysis in ternary and multicomponent systems.