Influence of laser power on microstructure and high-temperature tribological properties of CoAlTiWTa RHEA coating on Inconel 718 superalloy

CoAlTiWTa refractory high-entropy alloy (RHEA) coatings were prepared on the surfaces of Inconel 718 superalloy by pulsed laser cladding under different powers up to 75 W. Phase constitution and microstructural characteristics of the coatings were characterized, and their tribological properties at high temperature were studied. The results show that the RHEA coating is composed of columnar grains with FCC structure. As the laser power increases from 25 W to 75 W, the grain size of the coating becomes smaller, the thickness increases, and the microhardness increases. The increase in hardness can be attributed to the inherent solid solution hardening of high-entropy alloys, and the combined effects of boundary strengthening and stress strengthening caused by high laser power-induced grain refinement and residual stress enhancement. At 600 °C, the average friction coefficients of the RHEA-coated and uncoated samples are 0.45 and 0.60, respectively. The RHEA-coated samples have narrower and shallower wear marks and lower wear rates, and this phenomenon becomes more and more obvious as the laser power increases. The improvement of wear resistance at high temperatures is mainly because the RHEA coating has higher hardness and better resistance to abrasive wear and oxidative wear compared to the uncoated Inconel 718 alloy.