The Effect of Temperature on Wear Performance of High-Velocity Oxy-Fuel Sprayed WC-10Co-4Cr Coating on AA7075-T6 Substrate

Abstract

In this study, the friction wear performance of a High-velocity oxy-fuel (HVOF) sprayed WC-10Co-4Cr coated AA7075-T6 substrate was investigated against a WC-4Co ball at different temperatures using a pin-on-disk tribometer. WC-10Co-4Cr coating was deposited with a commercial HVOF-K2 spray (GTV MF-HVOF-K 1000 compact), O-2 and kerosene as fuel gases with flow rates of 900 L/min and 26 L/h, respectively. Spraying was carried out with a rotation speed of 200 rpm, a particle feed rate of 1.8 rpm at a distance of 380 mm and a scanning distance of 5 mm. As HVOF spray, a commercial WC-10Co-4Cr powder (GTV 80.76.1.G) with a particle density of 4.63 g/cm(3) was utilized. The diffusion of coating to the substrate was investigated by scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX). The hardness of the as-sprayed coating was measured using a micro Vickers hardness tester. The friction and wear tests were performed at a sliding speed of 100 mm/s for 1800 s under a fixed load of 3 N at 25, 100, 200 and 300 degrees C. The wear rate increased five times at 300 degrees C testing compared to room temperature (RT), but the average coefficient of friction (COF) value increased from 0.30 to 0.48 for 200 degrees C testing and then decreased to 0.36 for 300 degrees C. The powder and coating microstructures were analyzed using x-ray diffractometer (XRD) analysis. Morphological characterizations were accomplished by SEM and a wide field confocal microscope (WCM/profilometer), and wear mechanisms were examined. The wear mechanism was abrasive until 100 degrees C, but a temperature increase allowed for adhesive wear, plastic deformation and oxidation fatigue. Oxide layers and crack propagation took place in accordance with applied load and thermal expansion of the AA7075-T6 substrate. Oxide layers on the worn surface enabled the coefficient of friction to decrease after 200 degrees C. Oxide delamination and pile-ups were observed at 300 degrees C.