Complex Modification of the Surface Layer of a High-Entropy Al-Cr-Fe-Co-Ni Alloy by Electron-Ion-Plasma Treatment

Abstract

Using the technology of wire-arc additive manufacturing (WAAM – wire arc additive manufacture), a high-entropy alloy (HEA) of non-equiatomic composition Al, Cr, Fe, Co, Ni was manufactured. Using the methods of modern physical materials science, an analysis of the elemental and phase composition, defective substructure, mechanical and tribological properties of the HEA surface layer, formed as a result of complex modification, combining the deposition of a film (B + Cr) and irradiation with a pulsed electron beam in an argon medium, was carried out. In the initial state, the alloy has a simple cubic lattice with a lattice parameter of 0.28795 nm; the average grain size of the HEA is 12.3 µm. Chemical elements (at. %) 33.4 Al; 8.3 Cr, 17.1 Fe, 5.4 Co, 35.7 Ni, which form HEA, are distributed quasi-periodically. The irradiation regime was revealed (energy density of the electron beam ES = 20 J/cm2, pulse duration 200 µs, number of pulses 3 pulses, frequency 0.3 s more than 5 times), allowing to increase microhardness (almost 2 times) and wear resistance (more than 5 times), reduce the coefficient of friction by 1.3 times. Regardless of the value of ES, HEA is a single-phase material and has a simple cubic crystal lattice. High-speed crystallization of the surface layer leads to the formation of a subgrain structure (150–200) nm. It is shown that an increase in the strength and tribological properties of HEA is due to a significant (4.5 times) decrease in the average grain size, the formation of particles of chromium and aluminum oxyborides, and the incorporation of boron atoms into the crystal lattice of HEA.