Microstructure and wear performance of Ni-10 wt.%Al coatings plasma sprayed on Ni-based superalloys with a sound field

Abstract

We investigated the microstructure and wear performance of Ni-10wt.%Al coatings deposited by plasma spraying on a Ni-based superalloy loaded with a 100-Hz sound field. Applying the sound field greatly increased both the compactness and bonding strength of the coating. The coatings sprayed with and without a sound field both showed a lamellar structure. Electron backscattering diffraction analysis showed that the sound field helped to align the long axis of the γ-Ni grain perpendicular to the substrate rather than along the fine equiaxed crystal, as present in the coating sprayed without the sound field. Additionally, spraying with the sound field produced a γ-Ni phase with strong 〈001〉 orientation. The wear performance of the Ni-10 wt.%Al coating sprayed with the sound field was much better than that sprayed without the sound field. We attributed the microstructure transformation, preferred orientation, and performance enhancement of the coating to the application of the sound field during plasma spraying. Sound pressure and acoustic streaming enhanced the wettability of molten droplets on the substrate as well as the filling ability of molten droplets in the gaps between solidified particles. Applying the sound field enhanced the heat loss of molten droplets close to the substrate, causing a temperature gradient during solidification.