On the difference in carbon- and nitrogen-alloying of equiatomic FeMnCrNiCo high-entropy alloy

[Display omitted] •N-alloying increases both strength and ductility of FeMnCrNiCo alloy.•N-alloying up to 3 at. % provides a solid-solution hardening mainly.•C-alloying (1, 3 at. %) favors a heterophase structure in FeMnCrNiCo alloy.•Increase in C-concentration causes a growth in strength but reduces elongation. Microstructure and tensile properties of Fe20Mn20Cr20Ni20Co20, Fe20Mn20Cr20Ni20Co20-xCx and Fe20Mn20Cr20Ni20Co20-xNx (x = 1 at.% and 3 at.%) high-entropy cast alloys have been studied. Interstitial-doped alloys possess an austenitic structure with expanded crystal lattice and dendritic segregations of the alloying elements. Alloying with 1 at.% of C or N provides high solid-solution strengthening effects. Despite inhomogeneous dendritic microstructure, a yield strength and an elongation (349 MPa and 59%) in Fe20Mn20Cr20Ni20Co17N3 alloy exceed those for N-free alloy (163 MPa and 55%). Carbon-alloying produces more inhomogeneous microstructure and a precipitate hardening as compared to nitrogen-alloying and is accompanied with embrittlement of Fe20Mn20Cr20Ni20Co17C3 alloy.