Evaluation of fracture characteristics of ceramic coatings on stainless steel substrates using circumferentially notched tensile specimens

The durability of ceramic coated equipment mainly depends on the ability of coatings to sustain various in-service loading conditions. Understanding the fracture characteristics of coatings plays a crucial role in assessing the performance of many components, which have surface and/or sub-surface interactions. In this study, the fracture behaviour of TiN and TiAlN coatings was studied under tensile loading. The coatings were deposited onto stainless steel substrates by a cathodic arc deposition technique. The mechanical integrity of these coatings was studied using a new test specimen, known as the circumferentially notched tensile (CNT) specimen. One of the key aims was to study the effect of substrate shape on the crack initiation and propagation characteristics, to take into account the realistic shapes of mechanical components. Tensile tests were conducted on TiN and TiAlN coated stainless steel cylindrical substrates. The coated specimens after tensile loading were then examined using a scanning electron microscope to study the response of the coatings to the applied loads. The stress distributions at the critical load in the coating were numerically investigated. The interfacial shear strength and energy release rate were determined using experimental and numerical simulations. It was found that the shape of the substrate has a strong influence on the initiation and propagation of cracks in brittle coatings. Stress concentrations caused by the substrate's shape can lead to a premature failure of the coated components. The proposed new test method is found to be effective for evaluating the mechanical behaviour of coatings under the stress conditions encountered during real-life applications.