Failure process analysis of plasma sprayed coatings under tip load based on acoustic emission signals

Abstract

A detector combining the surface indentation method and the acoustic emission (AE) technique was developed for evaluating the interfacial bonding strengths of sprayed coatings. In order to assure the reliability and accuracy of the detecting equipment, the coating failure process and mode were analysed based on AE signals during indentation test. As test objects, Al₂O₃ coating, Al₂O₃–40 wt-%TiO₂ (AT40) coating and FeCrBSi coating with different microhardness were prepared by plasma spraying technique. The results indicated that the detector could effectively induce and define the cracking failure of coating and the measurement is simple and convenient. The failure process of ductile coating was basically very similar to that of brittle coating. The initial failures were both caused by crack initiation and propagation at the interfaces. Simultaneously, AE signals showed an obvious burst change. During the indentation tests, AE amplitude characterised the failure process accurately. The AE energy was more sensitive to coating fracture.