Structural modifications induced by ultrasonic vibration during plasma spray deposition Ni coating on Al substrate

In this study, a 28 kHz ultrasonic vibration was applied to the Al substrate during plasma spraying of Ni coatings. The microstructure, mechanical properties, and wear resistance of the coatings were investigated. With application of the ultrasonic vibration, the bonding between splats increased and porosity of the coatings decreased from 6.2 % to 3.4 %. Grain size in the coatings also decreased. The hardness and Young's modulus of the coating increased from about 2.8 GPa and 111.5 GPa to about 4.4 GPa and 183.4 GPa, respectively, by application of the ultrasonic vibration. The width and depth of the wear trace and the wear rate of the Ni coating sprayed using ultrasonic vibration also significantly decreased. These results are ascribed to the effects of acoustic pressure and acoustic streaming, cavitation, and heating of the ultrasonic vibration that promote wetting and filling ability and affect solidification of molten Ni droplets during the spraying process.