Effect of particle and carbide grain sizes on aHVOAF WC-Co-Cr coating for the future applicationon internal surfaces: microstructure and wear

The use of nanoscale WC grain or finer feedstock particles are two possible methods of improving the properties and performance of WC-Co-Cr coatings. Finer powders are being pursued for the development of coating internal surfaces, as less thermal energy is required to melt the finer powder compared to coarse powders, permitting spraying at smaller stand-off distances. Three WC-10Co-4Cr coatings, with two different particle sizes and two different carbide grain sizes, were sprayed using a high velocity oxy-air fuel flame spraying (HVOAF: the flame spraying process using both, oxigene and air to burn the fuel) thermal spray system developed by Monitor Coatings Ltd. in the UK. in the UK. The powder and coating microstructure were characterised using XRD and SEM. Fracture toughness and dry sliding wear performance were investigated using a ball-on-disc tribometer with a WC counter-body. It was found that the finer powder had a higher hardness but relatively lower fracture toughness. When performing sliding wear testing at the lower 96N load the nanostructured coating performed best; however at 240N this coating was displayed the highest specific wear rates, with the other two powders performing to a similar, better standard.