Abstract

Thermal sprayed tribological coatings have been used extensively in aerospace applications, primarily to overcome critical challenges such as abrasive wear, corrosion, erosion, oxidation and fatigue at high temperatures and pressures. Such coatings can also play a critical role in optimizing the efficiency of gas turbine engines, thereby reducing fuel consumption and CO2 emissions. High Velocity Oxy-Fuel (HVOF) thermal spraying with its higher gas jet velocity and lower flame temperature as compared to Air Plasma Spray (APS) is a promising deposition technique that can be used to deposit nickel- and copper- based tribological coatings. More specifically, dense coatings with lower oxide content and higher hardness have made this process a promising technique for producing wear resistant coatings capable of operating effectively in extreme environments.
The main objective of this research is to study the tribological properties of NiGraphite and Cu-Al systems deposited by HVOF and APS deposition processes in order to compare and determine the most suitable thermal spraying parameters. This work consists of two research studies, the first of which focuses on the tribological performance of HVOF-sprayed nickel graphite coatings with different compositions at room temperature and 450 °C. The second study evaluates the temperature response (room temperature, 300 °C and 450 °C) on the hardness and sliding wear behavior of Cu-10Al coatings deposited by HVOF and APS.
In both studies, the tribological tests were performed using a ball-on-flat tribometer and the wear profiles were extracted using a laser confocal microscope. Ex-situ characterization of the coatings was performed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), image analysis, and Vickers microhardness testing at room and elevated temperatures. The HVOF 75Ni-25Gr coating showed the lower wear rates compared to 85Ni-15Gr at 450°C, while the wear rates of both coatings were similar at room temperature. The APS Cu-10Al coating showed better wear resistance compared to the HVOF coating at all test temperature.