Elevated temperature wear behavior of thermally sprayed WC-Co/nanodiamond composite coatings

This study investigates the effects of nanodiamonds (ND) on the wear behavior of WC-Co coatings during dry sliding under ambient and elevated temperature environments. The nanometric dimensions and exceptional hardness of ND are envisioned to enhance hardness while maintaining toughness, thereby enhancing wear resistance. ND reinforced WC-Co coatings were successfully fabricated by high velocity oxygen fuel spray (HVOF) and air plasma spraying (APS). The tribological behavior of WC-Co-ND composite coatings was evaluated at room temperature and at 300 °C using reciprocating dry sliding wear tests. At room temperature, the addition of ND led to an enhancement in wear resistance of 8.5% and 13% in HVOF and APS coatings, respectively. The composite coatings exhibited increased formation of a protective silica tribolayer, which was attributed to enhanced heat transfer induced by the excellent thermal conductivity of diamond. At 300 °C, however, the composite coatings exhibited poorer wear resistance than the counterpart WC-Co coatings as a result of the degradation of the ND phase. The loss of the diamond phase was believed to decrease hardness and weaken splat interfaces, which led to more facile delamination in HVOF coatings, as well as severe brittle wear and fracture in APS coatings.