Effect of synergistic variation in Ti and Zr elements on the microstructure and properties of laser cladding AlCoCrFeNi high-entropy alloy coatings

AlCoCrFeNiTi1-xZrx (x = 0, 0.25, 0.5, 0.75, and 1.0) high-entropy alloy coatings were prepared on the surface of 45# steel by laser cladding, and the results showed that the coatings gradually changed from a double body-centered cubic (BCC) + metal carbide (MC) phase to a BCC + face-centered cubic (FCC) + MC phase with the increase in x. The grain morphology transitioned from equiaxed crystals to dendrites and was gradually refined. The solid solution strengthening, fine grain strengthening, and diffusion strengthening made the coatings' microhardness increase substantially to approximately 2.6 to 3.2 times of that of 45# steel. The wear resistance of the coatings was approximately 5.9 to 16.0 times that of the 45# steel, with the highest microhardness and the greatest wear resistance when x = 0.5. The wear mechanism of coatings was mainly abrasive wear and oxidation wear. The corrosion resistance of the coatings was better than that of 45# steel, but the corrosion resistance of the coatings gradually decreased with the increase in x. The increase in grain boundary density makes the galvanic corrosion intensify, and the corrosion resistance of the coating when x = 0, which was approximately 4.2 to 74.0 times that of other coatings. Grain refinement allows for more rapid formation of protective oxide layers with the increase in x, in this study, the resistance of the coating to high-temperature oxidation (800 °C) increased and then decreased with the increase in x, and the coating showed the greatest high-temperature oxidation resistance (800 °C) when x = 0.75, which was 1.4 to 3.5 times that of other coatings. However, the generation of microcracks reduced the high-temperature oxidation resistance of the coating when x = 1.0.