Ultrasonic-Induced Grain Refinement in Laser Cladding Nickel-Based Superalloy Reinforced by WC Particles

Laser cladding was used to prepare three composite coatings, i.e., Inconel 718 nickel-based superalloy (IN718), IN718-50 wt.% WC created by adding tungsten carbide (WC) particles and IN718-50 wt.% WC assisted by ultrasonic vibration. The phase composition, microstructure evolution, microhardness, residual stress and tribological properties of the three coatings were studied. The addition of WC enhances hardness and improves tribological properties, but also causes aggregation and considerable formation of carbides associated with rough structure. Ultrasonic vibration greatly refines the solidification microstructure, as it can break the growing dendrites, reduce the aggregation of reinforced particles and refine solidified structure. The average microhardness of the latter two composite coatings was increased by 36.37% and 57.15%, respectively, compared with the first IN718 coating, and the last composite coating (ultrasonic assistance) had the lowest COF (0.494). The WC particles and refined carbides converted the wear mechanism from adhesive wear to abrasive wear. In addition, the resultant stress on the surface of the composite coating roughly doubled after adding 50 wt.% WC, and only increased by 49.53% with ultrasonic treatment. The simulation results indicate that acoustic cavitation mainly occurs in the middle and bottom of the molten pool and proper frequency ultrasonic is conducive to the generation of the cavitation effect.