Mechanical testing of plasma-sprayed ceramic coatings on metal substrates: Interfacial fracture toughness and tensile bond strength

Plasma-sprayed ceramic coatings applied to metal components have uses in many diverse fields, including aerospace, electronics and, more recently, biomaterials. In all such applications success of the component relies on adequate bonding between the ceramic coating and metal substrate. In this study, a convenient and reliable test method to assess the fracture toughness of this metal/ceramic interface was developed by modifying an existing homogeneous short-bar configuration. Additionally, conventional tensile adhesive bond strength testing was conducted. For the alumina-coated Ti-6Al-4V model system studied, an interface toughness value of 1.84±0.20 MPa m^1/2 was obtained. An interfacial tensile bond strength of 13.6±2.9 MPa was also measured for this system. Further refinement of this modified short bar technique taking into account experimental compliance behaviour and potential complex or mixed-mode stress intensities is needed to confirm these preliminary toughness values, which nevertheless offer a potentially more sensitive means of monitoring the mechanical integrity of this metal/ceramic interface.