Impact of CNTs Reinforcement on Microstructural Characteristics and Tribological Behavior of Plasma-Sprayed Conventional Ceramic Coatings

The reinforcement of carbon nanotubes (CNTs) in Al 2 O 3 –3wt%TiO 2 and WC-20wt%Co thermally sprayed ceramic coatings is expected to enhance their mechanical properties and microstructural features. Alumina–Titania coatings are deposited by air plasma spraying, (APS) and tungsten carbide–cobalt coatings are deposited by high velocity oxy-fuel (HVOF) spraying process. In this work, the CNTs-reinforced composite coatings are prepared to interpret the effect of CNTs on the microstructural characteristics after conducting wear analysis and to correlate with the properties of coatings that are obtained without adding CNTs. The CNTs percentage proportion in both HVOF and APS sprayed coatings systems is maintained constant at 2 wt%. The various loading conditions used for tests are low load (0.5 kgf), medium load (1.0 kgf), and the highest load (1.5 kgf). Wear tests are conducted using a ball-on-disk tribometer. It is observed that for both types of coatings, low coefficient of friction, less weight loss, and less wear rate occur in the coatings derived from CNT reinforcement as compared to the coatings obtained without the CNTs addition. This is primarily due to the presence of a protective layer over the worn-out surface, i.e., bridging of CNTs in between the splats. The coating systems microstructural characteristics clearly reveal that the coatings are thicker with less number of pores because of CNTs presence and this implies that the CNTs are the most appropriate additives for improving the wear resistance of ceramic composite coatings.