The material property measurements of thermal barrier coatings from cyclic furnace, thermal rig, thermal expansion, acoustic emission and tensile adhesion test methods are critically examined. Some basic engineering properties of coatings such as the elastic modulus have not been measured without ambiguity. Data of this nature is essential to the success of modeling studies. Insights into the mechanical properties of coatings have been gained by carrying out instrumented tensile adhesion tests. The general view of the coating deformation process is that the individual lamellae slide over each other and this promotes a “pseudo-ductility” response in the coating. Monitoring of the acoustic emission response of coatings during thermal cycling experiments suggests that there are two distinct cracking processes. The macro-cracking behaviour, indicated by a change in the acoustic emission count rate, is the predominant mechanism which leads to coating failure. It is further shown that the acceptance tests used by industry, although useful in ranking coatings in terms of a particular property, present no fundamental knowledge concerning the material properties of coatings. It is only when the phenomenological characteristics of the thermo-mechanical response of coatings is understood that coating development will substantially progress.

The deformation behavior of thermally sprayed partially stabilized zirconia (PSZ) coatings are investigated using Hertzian indentation and four-point bend testing, with in situ acoustic emission monitoring. The experimental deformation curves, together with the corresponding acoustic emission responses and the fracture properties of the material are used in defining the deformation characteristics of the coating (ceramic overlay with metallic bond coal where applicable) and substrate composite system. Experiments are aimed in examining the influence of the bond coat and the coating properties on the form of deformation. Substrate temperature and pauses during spraying are demonstrated to strongly effect the coating properties and the resulting fracture/failure characteristics of the composite system.

Nanostructured and conventional titania (TiO2) coatings were thermally sprayed using air plasma spray (APS) and high velocity oxy-fuel (HVOF) processes. The fatigue and mechanical properties of these coatings were investigated. The fatigue strength of coatings deposited onto low-carbon steel showed that the nanostructured titania coated specimens exhibited significantly higher fatigue strength compared to the conventionally sprayed titania. SEM analysis of fracture surfaces revealed valuable information regarding the influence of these coatings on the performance of the coated component. Analysis of surface deformation around Vickers indentations was carried out. This investigation gives new understanding to the nature of fatigue and deformation of these coatings.