This paper focuses on the microstructure, phase composition, mechanical, tribological and corrosion properties of high-entropy alloys (HEAs) in the CoCrCuFeNi system depending on copper content, which was varied from 0 to 20 at. % with an increment of 5%. CoCrCuFeNi alloys were manufactured by powder metallurgy methods: mechanical alloying and hot pressing of element mixtures. The solubility limit of copper in CoCrFeNi solid solution was found to be 9 at. %. Segregation of irregularly shaped copper grains sized 1–30 μm is observed at concentrations above this solubility limit. As copper concentration increases, the phase composition of CoCrCuFeNi alloys changes from the single phase based on FCC1 solid solution (Cu = 0–5 at. %) to the dual-phase FCC1 + FCC2 alloy (Cu = 10–20 at. %), where FCC1 is the main phase and FCC2 is the secondary copper-rich phase. Tribological tests have shown that doping the CoCrFeNi alloy with copper increased wear resistance by 23% due to solid solution hardening. As copper content rises above 20%, the content of the secondary FCC2 phase increases, while wear resistance and alloy hardness decline. An analysis of wear tracks and wear products has shown that abrasion of CoCrCuFeNi alloys occurs via the abrasive-oxidative wear mechanism. The corrosion tests of CoCrCuFeNi HEAs in 3.5% NaCl solution had demonstrated that doping the alloy with copper at low concentrations (5–10%) leads to decreasing of corrosion resistance, possibly due to the formation of undesirable oxide Cu₂O along with protective Cr₂O₃. At high copper concentrations (15–20%) galvanic corrosion is suppressed due to coarsening of FCC2 grains and thus decreasing the specific contact surface area between the cathode (FCC2) and the anode (FCC1).

This paper focuses on the study of the structure and mechanical properties of CoCrCu_xFeNi high-entropy alloys and their adhesion to single diamond crystals. CoCrCu_xFeNi alloys were manufactured by the powder metallurgy route, specifically via mechanical alloying of elemental powders, followed by hot pressing. The addition of copper led to the formation of a dual-phase FCC + FCC2 structure. The CoCrCu_0.5FeNi alloy exhibited the highest ultimate tensile strength (1080 MPa). Reductions in the ductility of the CoCrCu_xFeNi HEAs and the tendency for brittle fracture behavior were observed at high copper concentrations. The equiatomic alloys CoCrFeNi and CoCrCuFeNi demonstrated high adhesion strength to single diamond crystals. The diamond surface at the fracture of the composites having the CoCrFeNi matrix had chromium-rich metal matrix regions, thus indicating that chromium carbide, responsible for adhesion, was formed at the composite–diamond interface. Copper-rich areas were detected on the diamond surface within the composites having the CoCrCuFeNi matrix due to the predominant precipitation of the FCC2 phase at the interfaces or the crack propagation along the FCC/FCC2 interface, resulting in the exposure of the Cu-rich FCC2 phase on the surface.

The article presents the results of comprehensive thermodynamic modeling and laboratory tests conducted for smelting a complex ferroalloy of silicon, manganese, and chromium (Fe-Si-Mn-Cr) from chromium, medium-grade manganese ores, and high-ash coals from Kazakhstan. Thermodynamic analysis was performed using HSC Chemistry software to model the Fe-Si-Mn-Cr smelting process over a temperature range of 900 °C–1800 °C. This analysis involved six actual charge compositions with solid reductant (C_solid) consumption ranging from 5 to 20 kg per 100 kg of Cr and Mn ore mixture. The mechanism of the combined carbothermic reduction of Cr, Mn, Si, and Fe was investigated using the Cr-Si-Al-Ca-Mn-Mg-O-C system. According to thermodynamic data, the optimal consumption of Csolid per 100 kg of ore mixture is 17 kg, and the optimal temperature range for smelting ferroalloys is between 1600 and 1700 °C. Laboratory tests were conducted in a high-temperature Tamman furnace at 1700 °C, resulting in experimental samples of the new complex ferroalloy with an average composition of 14.85% Fe, 14.05% Si, 7.55% Mn, 57.54% Cr, and 6.01% C, with P < 0.03% and S < 0.02%. The phase composition included (Cr, Fe, Mn)₃Si and carbides Cr₂₃C₆ and (Fe, Mn)₃C. The resulting alloy is suitable for alloying high-carbon and tool steels.

Protective coatings were applied by electrospark deposition (ESD) using zirconium electrodes to improve the performance of the Ni-containing alloy obtained using the selective laser melting (SLM) technology. The kinetics of mass transfer was studied in 5 different frequency-energy processing modes. An analog-to-digital converter was used to determine the average number of pulse discharges, single-pulse energy, and the total energy of pulse discharges for 1 min of processing (ΣЕ) for all the modes used. In low-energy processing modes (ΣЕ = 1459÷2915 J), a weak mass transfer was observed, and the cathode weight gain was recorded only in the first minutes. As the processing time increased, a decrease in the substrate weight was observed. The roughness of coatings (Ra) varied in the range of 3.9–7.2 μm. In high-energy modes (ΣЕ = 5197÷17212 J), due to intense electrode heating, a steady cathode weight gain was observed, but the formed coatings featured by increased roughness: Ra = 7.4÷8.6 μm. The Ra parameter for the original SLM samples was 10.7 μm. The formed coatings featured by a thickness of 15–30 μm, high continuity (up to 100 %), hardness of 9.0–12.5 GPa, elastic modulus of 122–145 GPa, and friction coefficient of 0.36–0.49. The ESD processing promoted an increase in wear resistance of the SLM alloy by 7.5–20 times, and oxidation resistance by 10–20 % (t = 1150 °C, τ = 30 h). It was found that the coating obtained in the low-energy ESD mode with energy ΣЕ = 2915 J featured the best performance (hardness, modulus of elasticity, roughness, wear resistance and oxidation resistance).