Wear-resistant CrCoNi-(Ti, Al) medium-entropy alloy coatings prepared by laser cladding on CrCoNi medium-entropy alloy and their microstructural characteristics

Three medium-entropy alloy (MEA) coatings (CrCoNi, CrCoNi-Ti and CrCoNi-Al) were prepared by laser cladding on a CrCoNi MEA alloy to obtain enhanced surface wear resistance. The CrCoNi coating is composed of columnar grains (face centered cubic (FCC) structure) with typical epitaxial growth features, while the CrCoNi-Ti coating is mainly comprised of FCC irregularly-shaped grains with high-density substructures. As for the CrCoNi-Al coating, it consists of lamellar structures with alternating equiaxed and columnar grains, both of which mainly correspond to BCC phase with a small amount of FCC phase. Compared to the substrate, the hardnesses of the CrCoNi, CrCoNi-Ti, and CrCoNi-Al coatings are enhanced by 7.3 %, 79.1 %, and 209.6 %, respectively. Wear experiments show that the CrCoNi coating is less wear-resistant than the substrate, while there are 14.1 % and 39.7 % enhancements for the CrCoNi-Ti and CrCoNi-Al coatings, respectively. Characterizations of the worn surfaces suggest that all the specimens involve three wear mechanisms: adhesive, abrasive and oxidation wear. Comprehensive analyses suggest that the superior surface properties of the CrCoNi-Ti and CrCoNi-Al coatings can be associated with the solid-solution, second-phase, grain-boundary, and heterostructure-induced strengthening after adding Ti and Al.