A study of isothermal variation of concentration-dependent interdiffusion coefficient in 100% Cu-100% Ni and 50% Cu 50%Ni -100% Cu diffusion couples
Goncalves Lopes, Juliane
Concentration-dependent interdiffusion coefficients (𝐷̃(𝐶)) are a fundamental parameter in the analysis of diffusion effects in materials. It is usually assumed in the literature that this parameter is mainly a function of concentration and temperature. However, recent studies have suggested that 𝐷̃(𝐶) may also change with time isothermally due to the development of internal stresses and strains during the diffusion process. The objective of this work is to verify if time affects the interdiffusion coefficient of a copper-nickel (Cu-Ni) system at a temperature range of 900°C-1000°C. A newly developed analytical method is used to address the shortcomings of conventional methods, such as the Boltzmann-Matano, Sauer-Freise and Hall techniques which neglect the presence of an initial solute distribution and therefore may produce unreliable results. The results of this study show that 𝐷̃(𝐶) of a Cu-Ni system indeed isothermally varies with time at all temperatures investigated as a result of diffusion-induced stress (DIS), in contrast to common assumptions in the literature. This finding draws attention to the need to take time into account as a fundamental factor in diffusion analysis, which would result in a more in-depth and accurate understanding of the interdiffusion phenomenon in materials.