Effects of time on impurity diffusion and concentration-dependent interdiffusion coefficients in Cu-Ni system

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Afolabi, Samuel
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Considerable focus has been directed toward investigating the interdiffusion coefficients in binary systems, primarily due to their pivotal role in metallurgical processes and material performance assessments. An essential parameter in this context is the isothermal concentration-dependent interdiffusion coefficient. While interdiffusion coefficients are widely recognized as being influenced by temperature and concentration, the element of time can exert substantial influence due to the presence of diffusion-induced stress (DIS) within the system. The present research experimentally investigates the effect of time on concentration-dependent interdiffusion and impurity diffusion coefficients in Cu-Ni binary systems and their alloy compositions. The investigation delves into the effect of solute source concentration and anomalous behaviors of temperature as the attributable indications of DIS at play. To implement the research work, a newly devised numerical diffusion model by Olaye and Ojo [20] is integrated with a forward simulation approach in this study. This model incorporates different atomic diffusion coefficients and ensures solute conservation. The model also merges fully explicit finite difference analyses with the Leapfrog/Dufort-Frankel scheme, thus enabling the determination of concentration-dependent interdiffusion coefficients. This approach overcomes the limitations associated with traditional techniques like the Boltzmann-Matano, Hall, Wagner and Sauer-Freise methods. By applying this method, both the interdiffusion and impurity diffusion coefficients are investigated at various diffusion times. The results reveal that the interdiffusion and impurity diffusion coefficients show time variations as a result of DIS in the system. This phenomenon contrasts the widely accepted notion of the interdiffusion coefficient being solely dependent on concentration and temperature without considering time. Overlooking this critical aspect could have substantial implications in the analysis of diffusion data and an accurate understanding of microstructural transformations initiated by diffusion-controlled phase changes in metallic systems.
Concentration, Diffusion-coefficient, Forward simulation, Time, Diffusion-induced stress