Invited Speaker: Investigation of Interfacial Properties of Air Plasma Sprayed Thermal Barrier Coatings with 4-point Bending and Computed Tomography Technique

A modified 4-point bending technique has been employed to investigate the fracture behaviour of air plasma sprayed (APS) calcia stabilised zirconia (CSZ) thermal barrier coatings (TBCs) after annealing at 1050 °C for different time.  The delamination of TBCs under bending mainly occurs in the top coat, a few micrometers above the thermally-grown oxide (TGO). The calculated energy release rate increases first with the annealing time until a critical period, and then gradually decreases with further thermal treatments. X-ray micro-tomography technique was used to study the evolution of the interface in situ. The 3D microstructure of the interface was reconstructed and visualised. It was found that the interfacial roughness does not vary much with the thermal treatments. The change of the interfacial toughness under annealing can be attributed to the phase transformation and densification of CSZ top coat as well as the residual stress in TGO.