Effect of Microstructural Evolution on Wear and Cavitation Erosion Resistance of Laser-cladded CoCrNiNbx Medium-entropy Alloy Coatings

• • Microhardness peaks at 689 HV0.1 for CoCrNiNb0.6, 3.7 times that of the 316L substrate, directly extending the service life of pump impellers and turbine blades by reducing wear rates under abrasive slurries. • • Cavitation erosion resistance is maximized at x = 1.0, with mass loss an order of magnitude lower than the 316L baseline, enabling maintenance intervals for hydroelectric turbine runners to be extended from months to years. • • The FCC-to-FCC+HCP phase transition occurs as Nb content increases, with Nb segregation at interdendritic regions forming a semi-continuous HCP network that enhances strain hardening but risks embrittlement beyond x = 1.0, imposing a compositional ceiling for dynamic load applications. • • Optimal Nb range (x = 0.6–1.0) balances strength and toughness, delivering a 3.7-fold hardness increase while maintaining sufficient ductility to absorb high-frequency impact energy, validated by a 10× reduction in cavitation mass loss compared to the substrate.