A new type of gradient structure FeCoCrNiWMo high entropy alloy layer by plasma solid-state surface metallurgy

In this paper, the FeCoCrNiWMo HEA layer with metallurgical bonding and gradient structure was successfully prepared by plasma solid-state surface metallurgy for the first time. The microstructure, composition, growth and deposition kinetics of HEA layer was studied by XRD, SEM and EDS. The results show that the FeCoCrNiWMo HEA layer consists of HCP and FCC phase. In the equipotential mode, the high vacancy concentration gradient layer can't be formed continuously on the substrate surface. In addition, the serious lattice distortion and the increase of atomic packing density caused by different atomic sizes decrease the density of vacancy formation. So the composite strengthening layer structure of HEA layer (deposit layer + diffusion layer) is formed on the substrate surface instead of conventional alloying layer. According to Boltzmann's hypothesis, the entropy value of calculating the surface mixing entropy of HEA layer is >1.5 R, which accords with the definition of high-entropy alloy. Compared with the substrate, the wear resistance and high-temperature oxidation resistance of the HEA layers are improved to some extent and the wear mechanism of substrate and HEA layers is mainly abrasive wear, which is accompanied by adhesive wear and oxidation wear. The results show that it is reasonable and feasible to prepare a new type metallurgical bonding and gradient structure of wear resistant and high-temperature oxidation resistant HEA layer by plasma solid-state surface metallurgy.