Diamond coatings on tungsten carbide and their erosive wear properties

Diamond coatings up to ∼60-μm thick have been grown by microwave plasma CVD (MPCVD) on sintered tungsten carbide (WC) substrates, and their erosive wear properties are investigated under high velocity air–sand erosion testing. Two different sintered tungsten carbide (WC) substrates have been investigated and compared, the binder being either 6% Co or 5% Ni by weight. Significant differences in morphology, residual stress, adhesion and erosion performance are seen as a function of pre-deposition treatment, deposition conditions and the source of the substrates. Adherent coatings could be deposited to a thickness of ∼35 μm. They offer significantly better erosion resistance compared to uncoated substrates, with the erosion rate being lowered by up to a factor between ∼5 and 20 for particle test velocities of 148 and 63 m s−1, respectively. The steady-state erosion rates of the coatings are a function of a gradual micro-chipping mechanism. However, the life of the coating is dependent on the progression of sub-surface damage promoted by sub-surface shear stresses associated with the particle impacts. It is thought that the coating debonding is driven by the shear stresses interacting with the grain boundary porosity at the substrate/coating interface.