Synthesis and characterization of refractory TiZrNbWMo high-entropy alloy coating by laser cladding

A novel refractory high-entropy alloy (HEA) coating with composition close to TiZrNbWMo was synthesized on 45 # steel by laser cladding. Constituent phases, microstructure, chemical composition and microhardness of the coatings before and after annealing were investigated by XRD, SEM, TEM, EDS and micro/Vickers hardness test, respectively. Results showed that the TiZrNbWMo coating was ~ 513 μm in thickness. The microstructure of the coatings exhibited typical dendritic and interdendritic structure. The coating was composed of a major body-centered cubic (BCC) solid solution and a small amount of β-TixW1 − x precipitated phase due to high-entropy affect and laser rapid solidification. Apart from enhanced fraction of β-TixW1 − x precipitation, the structure and BCC solid solution phases remained almost unchanged after annealing at 800 °C, 1000 °C, and 1200 °C for 20 h, indicating that the coating had high thermal stability. The microhardness of as-clad HEA coating reached around 700 HV0.5, which was three times of 45 # steel substrate. The coating microhardness increased significantly after annealing, which was due to the solid solution strengthening of BCC matrix and formation of β-TixW1 − x precipitation. Notably, the highest value was up to 1300 HV0.5 after heat treatment at 800 °C. Therefore, the HEA coatings showed high microhardness and resistance to softening.