Microstructure and wear property of WMoTaNb refractory high entropy alloy coating by laser cladding

WMoTaNb refractory high entropy alloy (RHEA) coating was prepared successfully by laser cladding. The coating is a composite structure composed of BCC1 and BCC2 structural HEA with some tiny intermetallic compound (IMC). The surface EBSD results indicates that the BCC1 has a strong (0001) texture with the intensity of 63.96. BCC2 possesses higher content of solute atoms, such as Nb, Mo, Ta, W, than that in BCC1, resulting in the formation of higher KAM mean value in BCC2, which indicates BCC2 has greater stresses and strains than that of the BCC1. Large numbers of LAGBs and dislocation lines are found to exist in BCC2, while little LAGBs and dislocation can be seen in BCC1. The interfaces between BCC1/BCC2, BCC1/IMC-and coating/substrate were analyzed using TEM. By calculating the lattice mismatch of each phase interface, it can be seen that typical incoherent characteristics are presented in each interface and large stress-strain is existed within the RHEA coating by laser cladding. The microhardness value of the laser cladded WMoTaNb coating is 551 HV0.2, which is much higher than that of the substrate due to the dislocations interaction and solid solution strengthening in the coating. The friction coefficient of laser cladded WMoTaNb RHEA coating is in the range of 0.55-0.6 at room temperature, while the friction coefficient at 800 degrees C increases to the range of 0.8-1.3. The dissolution of Fe atoms deteriorates the wear performance of the coating at high temperature.