Process Residual Stresses and High Temperature Oxidation Performance of Thermal Barrier Coatings

Abstract

Abstract Thermal barrier coatings (TBCs) allow increasing combustion temperatures of gas turbines and diesel engines thus improving the system performance. Residual stresses due to the differences of thermal expansion coefficient between metallic bond coat and ceramic top coat as well as the stresses due to the oxidation of the bond coat and the consequent increase in the thermally grown oxide (TGO) layer lead to ceramic debonding and subsequent failure of the thermal barrier system in service conditions. Extensive research has been carried out to minimize such events by applying multilayered coatings, intermediate diffusion or protective layers and other methods. In this work the TBC systems were obtained by applying distinct bond coats and top coats. The bond coats were applied by High Velocity Oxygen Fuel (HVOF) and the ceramic top coats were applied by Air Plasma Spraying (APS). Residual stresses were measured by the Modified Layer Removal Method (MLRM). Isothermal high temperature oxidation tests were performed and the results were correlated with the post spraying stress state and the coating thermal history. Results show that the residual stresses are mainly influenced by the thermal history regarding the quenching of individual splats and the plastic deformation of ceramic deposits.