Change in Concentration-Dependent Diffusion Activation Energy and Frequency Factor with Time: Identified by Numerical Analyses of Experimental Data

Abstract

A newly developed fully explicit numerical diffusion model coupled with a forward simulation technique, to avoid flaws in conventional methods such as the Boltzmann–Matano, Sauer–Freise and Hall procedures, is used to compute the concentration-dependent activation energy and frequency factor for diffusion in two different alloy systems. In contrast to what has been commonly reported in the literature, the results show that the concentration dependence of activation energy and frequency factor can significantly change with time. In this situation, the use of concentration-dependent activation energy and frequency factor that does not vary with time to predict diffusion effect can lead to considerable error. Furthermore, when there is a time variation in the dependence of activation energy and frequency factor on concentration, a common expectation that diffusion-controlled kinetics would increase with an increase in temperature may not always apply for all time durations.