Diffusion in High Entropy Alloys

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Diffusion in High Entropy Alloys (HEAs) is investigated using novel tracer-interdiffusion couple technique and compiled in an extended tracer diffusion database based on the pair-diffusion concept. While in the first funding period the focus lay on the establishment of the experimental and theoretical techniques as well as the general data base development, the proposed extension aims to examine systematically the tracer-interdiffusion couple method accounting for various situations which may be met in real multi-principal element alloys, including full miscibility, phase formation, complex interdiffusion paths, and strong volumetric changes. Simultaneously, the model description of diffusion in multicomponent HEAs has to be extended to account for vacancies as a separate species, ordering with appearance of different sub-lattices, influence of interstitially dissolved atoms and molar volume change along the interdiffusion path. The elaboration of the methodologies of experimental analysis and theoretic description will be done in a concerted way applying a combined experiment-modelling ansatz based on the CALPHAD-type description and the developed pair-wise diffusion model.Our research is motivated by the urgent need to provide reliable kinetic databases for adequate prediction of diffusion phenomena in multi-principal element alloys including both HEAs and compositionally complex alloys (CCAs). Furthermore, we will develop an automated assessment software for atomic mobilities and combine with the novel mobility database.A close and fruitful interaction with partners in the framework of SPP 2006 CCA-HEA will motivate and support the transfer of our insights and methods to other material classes and in particular to BCC HEAs and selected CCAs.