Reciprocating Wear of WC-17 Co Coatings in aqueous Environments

Abstract

Surface Engineering is briefly reviewed and the deposition of hard coatings by a High Velocity Oxygen Fuel process is described. Features of the deposit microstructure are discussed in terms of production parameters and their effect on both strength and wear behaviour. An experimental programme to create controlled reciprocating wear of the coatings in the presence of air, aqueous and aqueous abrasive media is described. The resulting wear is assessed quantitatively in terms of volume loss and change in surface roughness. Introduction ofseawater to the wearing interface reduces wear by a factor of four and the introduction of alumina slurries results in wear rates, and scar roughness values intermediate between those in seawater and air. The reduced wear rates in aqueous media are attributed to the cushioning effects of the liquid and the relatively benign effects of the abrasive to the replacement of early adhesive wear (in air) by abrasive wear. The fine (0.1 µm) abrasive is more damaging than the coarse (7 µm) one which is thought to be due to the easy embedding of the 0.1 µm alumina in the soft phase, which has a typical microstructural mean free path of about 0.5 µm.