Effect of WC size on interface fracture toughness of WC–Co HVOF sprayed coatings

The interface fracture toughness of high velocity oxygen fuel (HVOF) sprayed coatings on carbon steel made of various types of WC–12 wt.% Co powders with different WC particle sizes of 0.2 to 7.0 μm was evaluated by the pre-notched four-point bending test to clarify the size effect of WC particles and to explore the superior adhesion mechanisms of this coating system. The correlation between the splat microstructure and the toughness variation was investigated by observing a cross-section of WC–Co splats around the interface using the focused-ion-beam (FIB) technique. The interface fracture toughness of WC–12 wt.% Co coating/carbon steel under a mixed Mode I/Mode II loading condition increases from 600 to 1800 J/m2 as the WC particle size increases. Compaction of the underlying microstructure, the intrusion of WC particles into the substrate, and the volume fraction of the metallic binder phase in the coating are key factors in achieving excellent adhesion of this coating system.