Abstract
Decarburized layer was artificially formed on substrate specimens of tool steel (JIS: SKD5) by controlling the austenitizing time before quenching. The specimens were coated with WC-Co cermet by high-pressure high-velocity oxygen fuel (HP-HVOF) spraying. Tensile and edge-indent tests were carried out to evaluate the effect of decarburized layer on delamination strength of coating. During the tensile test, the coating is cracked parallelly many times with increasing load and finally delaminated along the interface between coating and decarburized layer. The tensile strength σc of coating has no remarkable change with decarburized layer thickness, while the interfacial fracture toughness Gc1/2 is lager for decarburized specimen than non-decarburized one and the Gc1/2 increases to an almost constant value with increasing layer thickness beyond 0.2mm. A Two-dimensional finite element method analysis reveals that the tensile stress and shear stress at the crack tip which are perpendicular and parallel to the interface and the tensile stress at the center of the coating are decreased by the existence of decarburized layer. The delamination energy Ed of decarburized specimens obtained by edge indent test is lower than that of non-decarburized specimen. The reason is that the decarburized layer is easy to be sheared during penetration of indenter.
