Abstract
In order to evaluate the delamination strength of brittle coating on ductile substrate, the four-point bending test method was proposed by expanding the tensile test method. The delamination energy was derived as a function of bending moment, curvature of specimen at delamination of coating and material's constants by theoretical analysis where the change of strain energy both in coating and substrate at delamination were considered. The method was applied to the specimen with WC-Co coating on an annealed tool steel prepared by high-velocity flame spraying. With increasing bending moment, the coating is divided repeatedly by cracks with almost the same interval. The crack interval at the delamination increases and the delamination energy of coating decreases with an increase in coating thickness. The four-point bending method is also effective to evaluate the delamination strength of brittle coating.
