STUDY OF THE STRUCTURE OF NON-EQUIATOMIC ALLOYS OF THE CoCrNi SYSTEM ALLOYED WITH Nb AND Mn

10.25712/ASTU.1811-1416.2026.01.005

Abstract

The article presents the results of a comprehensive study of the structure and elemental composition of a nonequiatomic medium-entropy alloy of the CoCrNi system alloyed with niobium (Nb) and manganese (Mn), with a nominal composition of Nb₂Co₄₀Cr₁₄Ni₄₀Mn₄. The main objective of the study was to experimentally confirm the predicted single-phase state of the solid solution and analyze the microstructural features formed during vacuum-arc melting. A set of modern methods was used to study the alloy: X-ray diffraction analysis, scanning electron microscopy with energy-dispersive spectroscopy, and transmission electron microscopy. The X-ray diffraction method confirmed that the alloy has a face-centered cubic (FCC) lattice with a parameter of 3.568 Å. The experimental alloy composition was found to deviate slightly from the nominal value, and the presence of iron and aluminum impurities was detected. Microstructural analysis revealed a developed dendritic structure with a grain size distribution in the range of 50–80 µm. Elemental mapping demonstrated a uniform distribution of cobalt, chromium, nickel, and manganese in the matrix, while niobium exhibits a tendency to segregate in interdendritic regions, which is explained by its high melting point and positive heat of mixing with other components. Nanoscale transmission microscopy studies confirmed the formation of a single-phase fcc matrix with localized niobium-rich regions at grain boundaries. The obtained results are an important step in establishing the structure-property correlation in promising medium-entropy alloys and confirm the possibility of targeted control of their microstructure through alloying.