High and medium entropy alloys: a combined experimental and theoretical study

Abstract: Alloys consisting of multiple principal elements in approximately equiatomic concentrations have been termed high (configurational) entropy alloys (HEAs). They represent a very interesting class of materials since certain combinations of elements in a single phase may exhibit a number of unusual physical properties with high potential for applications. The first part of the talk will provide a representative example of HEAs, the equiatomic CrMnFeCoNi alloy, which we studied using both experimental and theoretical tools. In particular, we found that the material undergoes two magnetic transformations at temperatures below 100 K while maintaining its fcc structure down to 3 K. Further, field-assisted cooling below 38 K resulted in a systematic vertical shift of the hysteresis curves. Strength and direction of the associated magnetization bias was proportional to the strength and direction of the cooling field. As a complement to our experiments, local magnetic moments of individual atoms in the CrMnFeCoNi alloy were studied by quantum-mechanical (electronic density functional theory) calculations [1]. The second part of the talk will be focused on materials containing lower number of principal elements for which the term medium entropy alloys (MEAs) is being currently coined. Phases appearing in Fe-Al-based superalloys will be discussed as examples of MEAs. In particular, thermodynamic, magnetic and mechanical properties of alloys from the Fe-Al binary system [2,3] and Fe-Al-Ti [3,4] and Fe-Al-Co [5] ternary systems will be discussed. Similarly as in the HEA case, our measurements were complemented by ab initio calculations providing an insight into nano-scale properties.

References:
[1] O. Schneeweiss, M. Friák, M. Dudová, D. Holec, M. Šob, D. Kriegner, V. Holý, P. Beran, E. P. George, J. Neugebauer, and A. Dlouhý, Physical Review B 96 (2017) 014437.
[2] P. Šesták, M. Friák, D. Holec, M. Všianská and M. Šob, Nanomaterials 8 (2018) 873.
[3] Y. Jirásková, N. Pizúrová, A. Titov, D. Janičkovič and M. Friák, Journal of Magnetism and Magnetic Materials 468 (2018) 91.
[4] M. Friák, A. Slávik, I. Miháliková, D. Holec, M. Všianská, M. Šob, M. Palm and J. Neugebauer, Materials 11 (2018) 1732.
[5] M. Friák, S. Oweisová, J. Pavlů, D. Holec and M. Šob, Materials 11 (2018) 1543.