Evaluation of cracking and delamination strength of thermally sprayed WC-Co coating by ring compression test method

Abstract

In order to evaluate the cracking and delamination strength of tungsten carbide cobalt (WC-Co) coatings sprayed on ductile substrates, a ring compression test method was proposed. WC-Co coatings were sprayed on three types of steel (SS400, S45C, SCM435) rings with various outer diameters by high velocity air fuel, high velocity oxygen fuel and plasma spraying methods. During the ring compression test, the WC-Co coatings were divided by parallel cracks perpendicular to the loading direction before delamination occurred. The cracking strength of the WC-Co coatings was independent of the outer diameter of the substrate, but depended on the material of the substrate and the spraying method of the coating. The equation to evaluate the interfacial fracture toughness was derived by expanding the equation obtained for the tensile and four-point bending test methods. The interfacial fracture toughness became constant when the outer diameter of the substrate exceeded 100mm. Large values of the interfacial fracture toughness obtained for the coating, sprayed on the SS400 substrate and sprayed by the high velocity oxygen fuel method.