Design of High Entropy Alloys (HEA)

F. Tancret, E. Bertrand

High Entropy Alloys (HEA) constitute a new class of metallic materials, studied since 2004. They consist in mixtures of at least five elements, all with contents between 5 and 35 at.%, forming a single solid solution. Whereas most HEAs had been discovered fortuitously, though trial-and-error or in a rather empirical manner, we have undertaken the project, as a collaboration with the University of Cambridge and during the PhD studentship of Edern Menou (2016), of designing HEAs by combinatorial optimisation relying on modelling and machine learning. After experimental validation we have obtained alloys whose properties surpass those of HEAs having the same structure and microstructure, and sometimes even those of other categories of alloys. Among others, the highest substitutional solid solution hardening ever reported was achieved.

Keywords: Multi-element alloys, multi-principal element alloys, complex concentrated alloys, compositionally complex alloys

 

Using a combination of computational tools (physico-chemical criteria, computational thermodynamics Calphad / Thermo-Calc, physical solid solution hardening model, genetic algorithm multi-objective optimisation), we have designed by calculation thousands of HEAs having either a face centred cubic (FCC) or a body centred cubic (BCC) structure.

 

Several alloys have been fabricated and characterised. One of them (Al₃₅Cr₃₅Mn₈Mo₅Ti₁₇, at.%), with a single phase BCC structure, exhibits the highest substitutional solid solution hardening ever reported, with a Vickers hardness of 6.45 GPa (658 HV), associated to a density lower than 5.5 g/cm³.

 

References:

F. Tancret, I. Toda-Caraballo, E. Menou, P.E.J. Rivera Díaz-del-Castillo, “Designing high entropy alloys employing thermodynamics and Gaussian process statistical analysis”, Materials & Design, 115 (2017) 486-497

E. Menou, I. Toda-Caraballo, P.E.J. Rivera Díaz-del-Castillo, C. Pineau, E. Bertrand, G. Ramstein, F. Tancret, “Evolutionary design of strong and stable high entropy alloys using multi-objective optimisation based on physical models, statistics and thermodynamics”, Materials & Design, 143 (2018) 185-195

S. Gorsse, F. Tancret, “Current and emerging practices of CALPHAD toward the development of high entropy alloys and complex concentrated alloys”, Journal of Materials Research, 33(19) (2018) 2899-2923

E. Menou, F. Tancret, I. Toda-Caraballo, G. Ramstein, P. Castany, E. Bertrand, N. Gautier, P.E.J. Rivera Díaz-del-Castillo, “Computational design of light and strong High Entropy Alloys (HEA): Obtainment of an extremely high specific solid solution hardening”, Scripta Materialia, 156 (2018) 120-123

M. Traversier, P. Mestre-Rinn, N. Peillon, E. Rigal, X. Boulnat, F. Tancret, J. Dhers, A. Fraczkiewicz, “Nitrogen-induced hardening in an austenitic CrFeMnNi high-entropy alloy (HEA)”, Materials Science & Engineering A, 804 (2021) 140725

 

Collaborations

. Laboratoire des Sciences du Numérique de Nantes (LS2N) – Université de Nantes
. Laboratoire Georges Friedel (LGF) – Mines Saint-Étienne