Structure and low-temperature micromechanical properties of as-cast and SPD-processed high-entropy Co_{25<i>−x</i>}Cr₂₅Fe₂₅Ni₂₅C<i>_x</i> alloys

The effect of carbon additions on the structure and mechanical properties high-entropy alloys Co25−xCr25Fe25Ni25Cx (x = 0, 1, 3, at. %) in two structural states, as-cast coarse-grained (CG) samples nanocrystalline (NC) obtained by severe plastic deformation (SPD), was studied. SPD performed high-pressure torsion at room temperature. were investigated microindentation temperature range T 77−300 K. It found that state, all had a dendritic microstructure an inhomogeneous distribution elements. At x 0 dendrites enriched iron nickel, interdendrite regions chromium. regions, eutectic consisting multicomponent matrix fine M7C3 carbide, where M is predominantly chromium, formed. main phase fcc lattice, while solubility it about 1 %. led to effective refinement (the size coherent scattering 30−50 nm), increase dislocation density up (1−1.5)⋅1015 m−2 concentration stacking faults. microhardness CG increased monotonically with increasing concentration, NC maximum HV achieved % carbon. reason for this anomalous behavior grain decrease alloy 3 compared 1. As decreased from liquid nitrogen, 1.5−1.7 1.2−1.5 times, respectively, which indicates thermally-activated nature under indenter. results indicate role hardening due solid solution dispersion hardening, (according Hall-Petch relation) Taylor relation).