Self-enhancement of cryogenic wear resistance in Fe₅₀Mn₃₀Co₁₀Cr₁₀ high-entropy alloy via boron doping and reversible phase transformation

Although face-centered cubic alloys have good performance at low temperatures, their wear resistance is poor, which limits their engineering applications. The cryogenic tribological properties of Fe₅₀Mn₃₀Co₁₀Cr₁₀ high-entropy alloy (HEA), both undoped and doped with 500 ppm boron, were investigated from 0 to −120 °C. The influence of boron on the structure, hardness, and wear resistance of the HEA has been fully studied. The doping of boron significantly reduces the wear rate of HEA to 5.01 × 10⁻⁵ mm³/(N m) at −80 °C, while that of the undoped HEA stays nearly constant across temperatures. Smaller grain size and nanoscale borides enhance the hardness of the HEA, reducing the effect of abrasive wear on the wear rate of the boron-doped HEA. Leveraging the unique stacking fault energy characteristics of Fe₅₀Mn₃₀Co₁₀Cr₁₀ HEA, a significant increase in wear resistance of the boron-doped HEA in low-temperature environments is achieved. At −80 °C, the boron-doped HEA exhibits multiple phase transitions and a hierarchical structure under the influence of friction stress. This structure provides multiple protections for the HEA matrix, including surface hardness enhancement and plastic deformation support in the lower layer. The construction of such a self-formed hierarchical structure offers a novel microstructural strategy for improving the wear resistance of alloys.