Effect of carbide grain size on the sliding and abrasive wear behavior of thermally sprayed WC-Co coatings

The carbide size and cobalt content of thermally sprayed tungsten carbide/cobalt coatings (WC-Co) can influence their microstructure, fracture strength, friction response and abrasion resistance, In this paper, these properties have been determined for one commercially available and three experimental WC-17 wt. % Co thermally sprayed coatings. The experimental coatings were processed from starting powders containing median carbide size distributions of 1.2, 3.8 and 7.9 mu m, respectively. All the coatings were produced using a high velocity oxy-fuel (HVOF) spray process. The present results indicate that coatings with a higher percentage of finer carbide size distribution in the starting powder display a higher degree of decomposition of the WC phase to W2C phase and, consequently, display lower fracture toughness and abrasion resistance values. Unidirectional, unlubricated sliding veal tests did not reveal major differences in the sliding wear response of the coatings as a function of carbide size. The microscopic analysis of the sliding wear-tested surfaces showed particle delamination and fracture, providing insight into wear mechanisms in these materials.