Diffusion kinetics in crystals

In this study, the full diffusion kinetics behaviour for phenomenological coefficients, interdiffusion coefficients and tracer diffusion coefficients of atomic components in crystalline solids is investigated. The main theoretical approach for this investigation is the hierarchy of random alloy approximations. The combined analysis of tracer or self- diffusion coefficients with the interdiffusion coefficient is also performed. The basic information on the interrelation of the tracer and collective diffusion processes is provided by the chosen theory of diffusion kinetics. Furthermore, extensive Kinetic Monte Carlo (KMC) simulation results are used for the testing and development of analytical diffusion kinetics approaches for binary and multicomponent alloy systems. As part of the present research, the solution to a problem that is often encountered in the experimental investigation on the self- and interdiffusion coefficients is considered. Namely, in the case of a binary alloy it is often necessary (via the Darken-Manning equation) to find the tracer diffusion coefficient where the other tracer diffusion coefficient and interdiffusion coefficient are available. Several numerical tests are performed to examine the solution and compared them with the available experimental data. Further, in this study, the diffusion kinetics formalisms of Darken, Manning, Holdsworth and Elliott (HE), and Moleko, Allnatt and Allnatt (MAA) are analysed in detail. These formalisms are then extended and applied for the cases of multicomponent random alloy models. Moreover, a new version of the highly accurate MAA theory, called MAA-light, is developed for describing diffusion kinetics in multicomponent random alloys. In addition, the resulting expressions from the approaches are verified by means of KMC simulation and the possible range of the tracer diffusion coefficient ratio of the highest atomic mobility to the lowest atomic mobility is analysed. It is shown that the overall results for the theories are in reasonably good agreement with the simulation results. An iterative method for the case of the multicomponent system is also developed to find the uncorrelated parts of the tracer diffusion coefficients and tracer correlation factors with reasonable accuracy. In this research, the diffusion kinetics theory is focused on a special type of multicomponent alloy, namely, high entropy alloys (HEAs). The self-diffusion and interdiffusion kinetics are investigated by extending and applying three diffusion kinetics approaches in the case of the face centred cubic high entropy alloy CoCrFeMn_0.5Ni.