Wear and wear-corrosion performance of CoCrNi-based high-entropy alloys modified by Mo and C under ultrasonic-assisted laser cladding

Wear and corrosion damage have long been challenges to the service safety of engineering equipment, resulting in significant economic losses and highlighting the urgent need for the development of highly wear- and corrosion-resistant composite materials. In this study, CoCrNi-based high-entropy alloy composite coatings were prepared using ultrasonically assisted laser cladding. The effects of Mo and C additions, as well as ultrasonic treatment, on the microstructure, wear, and corrosion properties of the coatings were investigated. The results indicate that the incorporation of Mo and C promotes the formation of high-hardness strengthening phases, while the atomic size mismatch induces pronounced solid-solution strengthening. Under dry sliding conditions, the ultrasonically treated coating exhibited a ∼0.15 reduction in coefficient of friction (COF) and a ∼40 % decrease in wear volume compared to its counterpart without ultrasonic treatment. In wear-corrosion tests conducted in a 3.5 % NaCl solution, the ultrasonic-assisted coating demonstrated lower COF and wear volume, along with a remarkable reduction in passive current density (I_pass) by 90.2 % and 78.9 %, respectively. Microstructural analysis revealed that ultrasonic cavitation and acoustic streaming effects refined the grain size and promoted the formation of Cr/Mo-rich associated phases, mitigating carbide inhomogeneity. These microstructural improvements enhanced the coating homogeneity and wear and corrosion resistance, and optimized the wear mechanism.