Investigation of failure mechanisms in WC–Co coated materials

WC–Co coated materials are increasingly used in aeronautical applications. The objective of the present study was to develop and validate a method for the characterisation of damage in coated material using a technique involving simultaneous use of both acoustic emission (AE) and scanning electron microscopy observations. Four point bending tests in association with in situ AE were conducted on WC–Co coated specimens prepared with high velocity oxy-fuel technology. Observation of the samples under a microscope shows two types of cracks: transverse cracks, which are regularly spaced on the surface of the coating and interfacial cracks. AE results for these tests were also investigated in terms of amplitude, hits, absolute energy and position of the event. These results show two different types of acoustic event in terms of absolute energy and amplitude. A transverse cracking model within a coating is then presented. This model is obtained by use of the integral equation method.