Microstructure evolution and strengthening mechanism of laser-cladding MoFexCrTiWAlNby refractory high-entropy alloy coatings

The MoFexCrTiWAlNby refractory high-entropy alloys (HEAs) were designed and the correlative coatings were fabricated by laser cladding on a M2 high-speed steel. The microstructure and performance evolution at various annealing temperatures of 600 degrees C-800 degrees C for 4 h, was carefully investigated. The as-cladded coatings consist mainly of body-centered-cubic (BCC) solid solution, MC carbide and C14 Laves phase plus small amounts of un-melted W-particles. The phase structures remain basically unchanged although the contents of Fe and Nb are changing. Meanwhile, the as-cladded MoFe1.5CrTiWAlNb1 HEA coatings exhibit high nano- and micro-hardness due to severe lattice distortion, carbides reinforcement together with laser rapid solidification. Therefore, it was selected for high-temperature experiment, which indicates that the dendrites and MC carbides are unaltered even annealed at 800 degrees C. However, the C14-Laves precipitates begin to form in the BCC matrix while annealing exceeded 600 degrees C. The hardness and wear resistance of the coating annealed below 700 degrees C increased slightly. Especially for the 650 degrees C-annealed coating shows the highest hardness and most excellent wear resistance strengthened by C14 precipitates. Additionally, a dense and thermostable oxide film was formed in an atmospheric environment of 800 degrees C, indicating a better oxidation resistance, compared with the M2 steels. (C) 2020 Elsevier B.V. All rights reserved.