The microstructure of WC-Co coatings produced by HVOF spraying with liquid fuel

Abstract

High velocity oxy-fuel (HVOF) spraying is now frequently used to produce high quality WC-Co coatings on surfaces which are subjected to certain kinds of erosive wear in service. An examination has been made of coatings produced by modified HVOF technology which makes use of liquid fuels rather than gaseous ones employed hitherto. It has been demonstrated that liquid fuel, i.e. diesel, promotes higher temperatures in the spray stream and this gives rise to an increased level of WC decomposition. Coatings contain reacted and unreacted zones and a model has been developed to account for their distribution. Observations on the coatings have demonstrated the composition of reaction products, i.e. W 2 C, Wand also a solid solution of carbon and tungsten in the cobalt matrix which is amorphous as a result of rapid cooling when the spray particles impact with the substrate. The coatings produced have lower porosity levels and higher hardness values than those associated with conventional plasma spraying.