Application of HVOF WC-Co-Cr coatings on the internal surface of small cylinders: Effect of internal diameter on the wear resistance

Due to the restrictions and mediocre performance of current methods of coating complex shaped parts in which line of sight processes currently struggle, the development of new coating methods is essential, with High Velocity Oxy-Fuel (HVOF) thermal spray coatings being a good candidate. In this study, a new compact High Velocity Oxy-Air Fuel (HVOAF) thermal spray torch designed to coat internal surfaces was traversed within cylindrical pipes of internal diameters (IDs) of 70 mm, 90 mm and 110 mm and a WC-10Co-4Cr coating was applied with a commercially available powder feedstock. Powder and coating microstructures were analysed using SEM/EDX and XRD. Fracture toughness and microhardness of the coatings were measured, and dry sliding wear performance was investigated at two loads: 96 and 240 N. It was found that the coating sprayed at 90 mm (medium ID) had a lower specific wear rates at both test loads due to the highest fracture toughness and microhardness; whereas, the coating sprayed at 110 mm (high ID) showed the highest specific wear rates at both low and high conditions due to poor fracture toughness. •WC-Co-Cr coatings were applied on internal surface of cylindrical pipes with IDs as low as 70 mm for the first time.•The changing internal diameter affects coating microhardness, fracture toughness and therefore dry sliding wear resistance.•The wear rate and mechanisms of wear were shown to vary at different IDs due to changes in coating mechanical properties.