Wear resistance and adhesive failure of thermal spray ceramic coatings deposited onto graphite in response to ultrasonic nanocrystal surface modification technique

In this study, thermal spray ceramic (TSC) coatings sprayed onto a graphite were subjected to ultrasonic nanocrystal surface modification (UNSM) technique. The surface roughness of the as-received Cr₃C₂, ZrO₂ and Al₂O₃ coatings was reduced by about 28, 24 and 9% after UNSM treatment, which can be explained that the high peaks were removed during UNSM treatment, where a flat surface area is enlarged due to the partially elimination of single- and interconnected micro-pores. In addition, the number of cracks is also reduced by filling up the cracks by a smashed coating powder due to the continuous high-frequency strikes of a tip to the surface of the coating resulting in increase in surface hardness of the as-received Cr₃C₂, ZrO₂ and Al₂O₃ coatings by about 14, 10 and 6% after UNSM treatment, respectively. The wear resistance and adhesive failure of the coatings were improved after UNSM treatment as well representing a remarkable influence on the friction and wear performance, and the critical load of the coatings. Hence, it is expected that a hybrid use of TSC coatings with UNSM technique is beneficial to improving the surface and adhesion behavior of the coatings to be applied to a graphite mold to produce a glass.