Method for determining diffusion data in ternary and multicomponent alloys

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In the proposed project a novel method will be elaborated that allows determining atomic mobilities in multicomponent alloys including their temperature dependence with reasonable experimental effort. The new method will consist of a variation of a directional solidification experiment, a diffusion experiment in a temperature gradient, a diffusion calculation and an optimization algorithm. The fcc-Al phase of the Al-Mg-Zn system will be used as the model material to develop and verify the new method.Samples that exhibit systematically varying concentration gradients over an extended sample length will be created. For this, the solidification velocity during steady state solidification is abruptly changed several times and the steady state is re-adjusted. This creates fluctuations in the solidifying concentration which enclose relatively narrow concentration intervals.The samples will be annealed in a temperature gradient to induce diffusion processes with locally changing kinetics. During the evaluation of each single diffusion experiment, the concentration dependence of the atomic mobilities can be neglected and diffusion processes can be assumed to be solely temperature dependent. From the diffusion experiments, atomic mobilities in an expanded temperature interval will be accessible. The diffusion equation will be solved for ternary alloys with approximations for the diffusion parameters, and an optimization routine for these parameters will be implemented. Starting with the initial concentration profiles, the evolution of the concentration profiles during the diffusion heat treatment is calculated on the basis of the temperature dependent mobility functions. The optimization algorithm that is to be elaborated adapts the mobility functions by minimizing the total deviation between the concentration profiles obtained from the diffusion experiment and the diffusion calculation. Interaction effects of the chemical potential gradients that occur during multicomponent diffusion cause special features in the diffusion profiles such as increasing concentration gradients in the vicinity of concentration gradients of the other alloying elements. These features will provide detailed information on the individual mobility functions.The currently immense effort for building up or extending mobility databases will be drastically reduced by the new method.