Abrasive wear behaviour of conventional and nanocomposite HVOF-sprayed WC-Co coatings

WC-Co cermets have been used traditionally as wear-resistant materials. Rec ent work has shown that nanostructured cermets offer improved properties ov er their conventional counterparts. This work examines the performance of s uch conventional and nanostructured materials in the form of coatings depos ited by high velocity oxy-fuel (HVOF) thermal spraying. WC-Co coatings were deposited under identical conditions using both conventional sintered and crushed and nanocomposite powder feedstocks. Both powders consisted of tung sten carbide (WC) grains in a cobalt binder. Characterisation of the coatin gs by a range of techniques showed that both coatings not only contained WC but also reaction products such as tungsten hemicarbide (W2C) and W and an amorphous Go-rich binder phase containing W and C. Due to differences in t he morphology of the powder feedstock and the WC grain size, the nanocompos ite coating contained a smaller fraction of unreacted WC than the conventio nal coating. Three body abrasive wear tests were performed using a modified dry sand rubber wheel apparatus with alumina and silica abrasives. a range of abrasive particle sizes and loads were used to assess the wear resistan ce of both coatings. It was found that the nanocomposite had a poorer wear resistance than the conventional coating under all the conditions examined. Wear was dominated by the loss of ductility in the Go-rich binder phase du e to its amorphisation. The differences in the wear behaviour of the coatin gs could, thus, be explained in terms of differences in powder characterist ics, the extent of reaction and decarburisation during spraying, and the su bsequent development of the microstructure in the coating during splat soli dification at high cooling rates. (C) 1999 Published by Elsevier Science S. A. All rights reserved.