Structure and Properties of a High-Entropy AlCrFeCoNi Alloy after Treatment with an Electron–Ion Plasma

With the help of wire arc additive manufacturing, a high-entropy alloy of AlCrFeCoNi was prepared: of a non-equiatomic composition, on which a B + Cr film with a thickness of ~1 μm was deposited by plasma-assisted RF sputtering. Subsequent processing consisted in electron-beam irradiation of the surface with the following parameters: energy density 20–40 J/cm², pulse duration 200 μs, frequency 0.3 s^–1, and number of pulses 3. A quasi-periodic distribution of chemical elements (at %) 33.4 Al, 8.3 Cr, 17.1 Fe, 5.4 Co, and 35.7 Ni is established. It is shown that, at the energy density of the electron beam E_s = 20 J/cm², the microhardness increases by a factor of two and the wear resistance by a factor of five, and the friction coefficient decreases by a factor of 1.3. High-speed crystallization of the surface layer leads to the formation of a subgrain structure with subgrain sizes (150–200 nm). The increase in strength and tribological properties during electron-beam processing is interpreted taking into account the reduction in grain size, the formation of chromium and aluminum oxyborides, and the formation of a solid solution of boron incorporation into the HEA crystal lattice.