A relatively new approach to obtaining metal materials containing several principal elements in equiatomic concentrations which look promising for replacin

A promising approach to the development of advanced metallic materials is based on a fundamentally new concept of avoiding the use of the main component but mixing several metal elements simultaneously. Such multicomponent alloys are called high-entropy alloys, the most studied of which is the Co-Cr-Fe-Ni-Mn alloy with attractive mechanical properties. The single-phase fcc structure is stable in this alloy, which allows it to be used as a “model” high-entropy alloy or a single-phase multicomponent solid solution. This paper is the first to experimentally evaluate the possibility of synthesizing strengthened high-entropy alloys with the basic system (Co-Cr-Fe-Ni-Mn) and strengthening precipitates based on borides and silicides of refractory metals (Mo and Nb), formed in situ during the combustion of thermite-type SHS systems. The microstructural analysis of the synthesized NiCrCoFeMn alloys with the complex modifying Mo(Nb)-Si-B additive showed that, at a higher content of the additive, the microstructure of the synthesis products exhibits the high-entropy alloy matrix and precipitates of new structural elements based on borides and silicides of refractory metals (Mo and Nb). The morphology and concentration of such precipitates depends on the concentration of the additive in the green mixture. The strengthening precipitates are of endogenous origin as they are formed in situ during SHS and are the result of chemical reactions occurring both directly in the combustion wave and during cooling of the high-temperature melt of the synthesis products. Control of SHS processes opens up new possibilities for the formation of metal-matrix composites based on high-entropy alloys.

Cast refractory alloys Mo–Nb–Si–B were prepared by centrifugal self-propagating high-temperature synthesis (SHS) from metallothermic mixtures containing MoO₃, Nb₂O₅, Al, Si, and B powders, and additive of Al₂O₃ as a temperature-moderating and chemically inert agent. Variation in the centrifugal acceleration and amount of the additive affected the composition and structure of cast Mo–Nb–Si–B alloys. In a wide range of values, the combustion temperature was found to exceed 3000 K, and the combustion products were obtained as two-layer ingots of target Mo–Nb–Si–B alloy (lower) and Al₂O₃ slag (upper).

FeCoNiCu(Cr, Mn, La, Ce)-Al high-entropy alloys (HEAs) were prepared via a combined centrifugal casting–self-propagating high-temperature synthesis process to serve as multifunctional catalyst precursors. The findings indicated that even with aluminum content reaching 50 wt %, the typical bcc structure inherent to HEAs was preserved. Doping additions (Cr, Mn, La, and Ce) led to pronounced microstructural changes, including alterations in morphology, porosity, and elemental distribution, while the primary phase constituents of the FeCoNiCuAl-based alloys remained consistent. It was found that La and Ce exhibited poor bulk incorporation into the HEAs, evidenced by a low surface content. Aluminum leaching and hydrogen peroxide stabilization converted these precursors into catalysts. These catalysts demonstrated high activity in the deep oxidation of propane and CO. The FeCoNiCu catalyst achieved the best results for CO oxidation, reaching 100% CO conversion at 250 °C. For propane oxidation, the FeCoNiCuCrMn catalyst was the most active, yielding 100% CO conversion at 300 °C and 97% propane conversion at 400 °C.