Annealing-induced microstructure and properties evolution of refractory MoFeCrTiWAlNb3 eutectic high-entropy alloy coating by laser cladding

Abstract

A refractory high-entropy alloy (HEA) coating with a composition close to MoFeCrTiWAlNb3 was fabricated by laser cladding on M2 high-speed steel. The as-cladded coating is mainly constituted by body-centered-cubic (BCC) solid solution, MC carbide and C14-Laves phase, and exhibits typical lamellar eutectic. To explore its performance at elevated temperature, these samples were annealed at 950 °C for 6 h–10 h in addition to a 4 h annealing treatment in the temperature range of 750 °C–950 °C. The results show that when the coating is annealed at 750 °C, its microstructure remains basically unchanged, and the hardness can reach 635 HV0.2. However, the hardness drops sharply due to the dissolution of the eutectic Laves phase as the annealing temperature increases. Interestingly, after annealing at 950 °C for 6 h–10 h, the hardness rises as the number of precipitated Laves phase and σ phase increases. The hardness and volume loss of the coating annealed at 950 °C for 8 h are 639 HV0.2 and 0.74 mm3, respectively, indicating that the coating has excellent high temperature softening resistance.