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Diffusion in High Entropy Alloys

Subject Area Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
Term from 2016 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 314231017
 
Final Report Year 2023

Final Report Abstract

Within the current proposal, true tracer diffusion in FCC High Entropy Alloys (HEAs) was measured using the radiotracer technique. Furthermore, a so-called augmented tracer-interdiffusion couple technique has been developed and the experimental data were compiled in an extended tracer diffusion database based on the pair-diffusion concept, again elaborated and further developed within the proposal. In the first funding period, the focus lay on the establishment of the experimental and theoretical techniques, extensive measurements of atomic mobilities (the tracer diffusion coefficients) as well as the general data base developments. As a result, in total 7 papers were published which are already highly cited (in total more than 600 times so far after Scopus). The reports on tracer diffusivities of all elements in CoCrFeNi and CoCrFeMnNi alloys are used already by the community as basis information on the element mobility in FCC CoCrFeMnNi HEAs. During the second funding period, we examined systematically the augmented tracer-interdiffusion couple method accounting for various situations which may be met in real multi-principal element alloys, including full miscibility, 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 was done in a concerted way applying a combined experiment-modelling ansatz based on the CALPHAD-type description and the developed pair-wise diffusion model. As a result, reliable kinetic databases were elaborated allowing adequate prediction of the diffusion phenomena in multi-principal element alloys including both HEAs and compositionally complex alloys (CCAs). Furthermore, an automated assessment software for atomic mobilities was developed and combined with the novel mobility database. A close and fruitful interactions with partners in the framework of SPP 2006 CCA-HEA have been established (our activities were included as an associated project) allowing transfer of our insights and methods to other material classes and in particular to BCC HEAs and selected CCAs. The project marked an important milestone in both experimental investigations of diffusion in highentropy alloys as well as adequate and reliable developments of mobility databases of general usage.

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