The structure and mechanical properties of as-cast and thermomechanicaly processed (cold rolling followed by annealing at 700 °C and 900 °C) Fe₄₀Mn₄₀Cr₁₀Co₁₀ (at.%) high-entropy alloys doped with different amounts (0, 0.5, and 2.0 at.%) of N were examined. The as-cast Fe₄₀Mn₄₀Cr₁₀Co₁₀ alloy (N0) contained σ-phase particles at the boundaries of the fcc grains. The addition of 0.5 (N0.5) and 2.0 (N2) at.% of nitrogen suppressed the formation of the σ-phase due to which the alloys consisted of only the fcc phase. Annealing after rolling resulted in the development of static recrystallization and precipitation of additional phases: the σ-phase was found in the N0 and N0.5 alloys, and hexagonal M₂N nitrides were found in the N2 alloy. The strength of the as-cast alloys at room temperature increased with increasing nitrogen concentration due to interstitial solid solution strengthening. Cold rolling and subsequent annealing resulted in considerable strengthening of the program alloys. The strength of the alloys increased with the N content and decreased with increasing annealing temperature. The best combination of mechanical properties at room temperature was attained in the N2 alloy after annealing at 700 °C, and at 77 K, was demonstrated by the N0.5 alloy after annealing at 900 °C.

The effect of the carbon content (0-2 at.%) on the structure and mechanical properties at room and cryogenic temperatures of CoCrFeNiMn-based high entropy alloys with reduced Cr concentration was studied. The as-cast alloys were cold rolled to a thickness reduction of 80% and annealed at 800°C for 1 hour. As a result, a fully recrystallized microstructure with a grain size of 6.4 μm was produced in the carbon-free alloy. The recrystallized grain size was much smaller (1.5 μm in the alloy with 2.0 at.% of C) due to the pinning effect of the precipitated M₂₃C₆ carbides. The yield strength of the alloys increased with an increase in the carbon concentration from 313 MPa to 636 MPa, while the elongation to fracture slightly decreased from 56% to 43%, respectively, in the alloys with 0 and 2 at.% of C. A decrease in the test temperature to 77K resulted in a significant increase in both the strength and ductility of the alloys. The alloys had high values of impact toughness of 140 J/cm² and 85 J/cm², respectively, in the alloys with 0 and 2 at.% of C. A decrease in the testing temperature did not have a noticeable effect on the impact toughness.

The temperature dependence of the mechanical properties of the CoCrFeNi medium-entropy alloy (MEA) manufactured by laser-directed energy deposition (L-DED) and additionally annealed at 1200 °C for 24 h was studied. The microstructure of the as-deposited alloy was represented by a single-phase face-centered cubic structure with coarse columnar grains and a high density of dislocation. Annealing resulted in the development of recrystallization and a reduction in dislocation density. The CoCrFeNi alloy produced by L-DED demonstrated mechanical properties comparable with those of the fine-grained equiatomic CoCrFeMnNi alloy, produced by casting followed by thermomechanical processing. Namely, as-deposited CoCrFeNi had a yield strength (YS) and ultimate tensile strength (UTS) of YS = 370 MPa and UTS = 610 MPa at room temperature, and YS = 565 MPa and UTS = 965 MPa at cryogenic temperature, along with a ductility of ~60%. Annealing resulted in a decrease in strength to YS = 180/350 MPa at 293/77 K. A quantitative analysis of various strengthening mechanisms showed that some strength increment of the as-deposited alloy was ensured by the high dislocation density formed during L-DED.

For this work, the behavior of the ZhS6K alloy (Russian grade) in the process of direct laser deposition was investigated. Two samples, a “small” one (40 × 10 × 10 mm³) and “large” one (80 × 16 × 16 mm³), were fabricated with direct laser deposition. In both samples, the typical dual-phase γ/γ’ microstructure with cuboidal shape of the γ’ precipitates was observed. Both specimens revealed a similar tendency to continuous increasing in hardness from the bottom to the top associated with the refinement of γ’ precipitates. The “small” sample was essentially crack-free, while the “large” one underwent extensive cracking. The possible effects of various factors, including thermal history, size, and shape of the gamma grains, on cracking behavior were discussed.

In the present work, the microstructural evolution and mechanical properties of the high-entropy alloy CoCrFeMnNi were investigated after severe plastic deformation by high-pressure torsion (HPT) at 20 and 300°C, as well as after additional post-deformation annealing at 300°C for 1 h. It was established that HPT at 20°C leads to the formation of an ultrafine-grained structure with an average grain size of ~40 nm and a high defect density, which results in an increase in microhardness up to 600 HV and in tensile strength up to 1820 MPa, accompanied by a reduction in ductility to ~3%. Increasing the HPT temperature to 300°C causes the average grain size to grow to ~400 nm due to the activation of dynamic recrystallization processes. At the same time, the precipitation of nanoscale particles is observed, which provides dispersion strengthening and contributes to an increase in ductility up to 12% while maintaining a high strength of ~1486 MPa. Additional post-deformation annealing at 300°C for 1 h leads to partial relaxation of the defect structure and stabilization of equilibrium grains, accompanied by a reduction in strength to ~1000 MPa and an increase in ductility up to 20%. Thus, it has been shown that adjusting the parameters of thermomechanical treatment enables targeted control over the contributions of different strengthening mechanisms (grain boundary, dislocation, and dispersion) and allows achieving the desired balance of strength and ductility in the CoCrFeMnNi alloy. The results demonstrate the feasibility of tailoring the strength–ductility balance of the CoCrFeMnNi alloy through optimization of thermomechanical processing parameters.