Diamond coatings on tungsten carbide and their erosive wear properties

Diamond coatings up to similar to 60-mum 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 eros ion testing. Two different sintered tungsten carbide (WC) substrates have b een investigated and compared, the binder being either 6% Co or 5% Ni by we ight. Significant differences in morphology, residual stress, adhesion and erosion performance are seen as a function of pre-deposition treatment, dep osition conditions and the source of the substrates. Adherent coatings coul d be deposited to a thickness of similar to 35 mum. They offer significantl y better erosion resistance compared to uncoated substrates, with the erosi on rate being lowered by up to a factor between similar to 5 and 20 for par ticle 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 m echanism. However, the life of the coating is dependent on the progression of sub-surface damage promoted by sub-surface shear stresses associated wit h the particle impacts. It is thought that the coating debonding is driven by the shear stresses interacting with the grain boundary porosity at the s ubstrate/coating interface. (C) 2001 Elsevier Science B.V. All rights reser ved.