Detonation sprayed WC-Co coatings: unique aspects of their structure and mechanical behaviour

Tungsten Carbide-Cobalt (WC-Co) Cermets are known for their excellent wear resistance. Conventionally, WC-Co cermets are produced by liquid phase sintering and such a process results in optimum combination and distribution of WC and Co phases and thus a good combination of hardness and toughness. In contrast to using bulk WC-Co, there are many applications wherein a thick coating of WC-Co over the surface of the engineering component (usually made from steel) represents a cost-effective option. Numerous thermal spray coating techniques have been extensively used to deposit thick WC-Co coatings on a variety of components and detonation spray coating represents one such coating technique capable of depositing hard and dense WC-Co coatings. However, as compared to bulk WC-Co, detonation sprayed WC-Co exhibit inferior properties and performance primarily because of the nature of the detonation spray coating process. In addition, depositing a WC-Co coating on a component automatically introduces an interface between the coating and the substrate and the properties of this interface also become important in determining the overall performance of the WC-Co coating. The purpose of this article is to describe in detail the unique aspects of the structure and mechanical behaviour of detonation sprayed WC-Co coatings and contrast the same with the behaviour of bulk, liquid-phase sintered WC-Co cermet.