Computational development, synthesis and mechanical properties of face centered cubic Co-free high entropy alloys

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The search for Co-free high entropy alloy (HEA) matrix for Stellite (Co-Cr) substitution in nuclear applications is addressed by computational and experimental investigations conducted within the Cr20-(Fe-Mn-Ni)80 system at 1100 °C. Calphad method is employed using Thermo-Calc and TCHEA3 to determine the single phase domain of the face centered cubic (FCC) solid solution. For each composition of this domain, the intrinsic lattice strength is calculated using two models from literature, namely Varvenne and Walbrühl. Then, four alloys of the Cr20-(Fe-Mn-Ni)80 plane, with atomic compositions Cr20Fe35Ni45, Cr20Fe30Mn5Ni45, Cr20Fe35Mn5Ni40, Cr20Fe30Mn10Ni40 are elaborated by arc-melting. Thermo-mechanical treatments (homogenization at 1100 °C, 80% cold-rolling reduction and annealing/recrystallization at 900 °C) are performed to obtain equiaxed recrystallized microstructures and different grain sizes for each alloy. As expected from thermodynamic calculations, all samples of all alloys are confirmed to be face centered cubic (FCC) by X-Ray Diffraction. Hall-Petch law parameters are established from tensile tests and intrinsic lattice strength are deduced. Experimental results are discussed regarding other HEAs and Co-Cr FCC alloys and intently compared to predictions from Varvenne and Walbrühl models. Results indicate that Co-free HEA from the Cr-Fe-Mn-Ni alloy system with intrinsic lattice strength similar or superior to the classical Cantor alloy may be identified.