The experimental and theoretical study on influence of Al and Cu contents on phase abundance changes in AlxCuyFeCrNiCo HEA system

Abstract

Two series of AlxCuyFeCrNiCo (0.0≤x≤1.5, 0.5≤y≤2) high entropy alloys were prepared using arc melting and sintering techniques. For all samples, XRD and EDX measurements were performed. Three different structures (two fcc and one bcc) were detected using X-ray diffraction technique, while four chemically different phases were identified by EDX, with presence and stoichiometry dependent on the Al and Cu concentrations. Cu-rich and FeCrNiCo-rich phases were identified, having fcc structures with different lattice parameters. AlNi-rich and Cr-rich phases crystallize in bcc/B2 and bcc structures with similar lattice parameters indistinguishable using standard XRD technique. The preparation method did not influence meaningfully on phase composition and stoichiometry of the analyzed system. The increase of Cu content caused mostly increase of the Cu-rich phase abundance. In turn, the increase of Al led to vanishing of the FeCrNiCo-rich phase and appearance of Cr-rich as well as AlNi-rich phases. The KKR-CPA electronic structure calculations were performed to have information about phase preference and structural stability. The reduction of total energy of multi-phase AlxCuyFeCrNiCo system in comparison to the single-phase one is evidenced. It appears that further lowering of total energy can be achieved when admitting atoms ordering in AlNi-rich phase in frame of B2 crystal structure.