Abstract The structure and properties of metallic multicomponent Fe–Ni–Co–Cr–Cux and Fe–Ni–Co–Cu–Crx system alloys (x is the component content, at %), which are the basis of the wide class of high-entropy alloys, are studied. The synthesized alloys are investigated using instrumental analysis methods (DTA, SEM-EPMA, XRD), and the concentration and temperature boundaries of the fcc solid solution have been determined.