Microstructure Observation And Thermal Conductivity Estimation Of Thermal Barrier Coating Materials

Thermal barrier coatings(TBCs)are extensively used on the blades and vanes of high-temperature gas turbines and aero-engines,to provide thermal insulation and also to protect them from degradation in hot sections.So the most important design parameter for TBCs is the low thermal conductivity.Currently,the state-of-art duplex TBC system comprises the 7~8wt.%YSZ top coat sprayed on the top of the metal components,by means of Air Plasma Spray(APS)preparing technique.This TBC system has a very low thermal conductivity,not only because of the intrinsic low thermal conductivity of YSZ material,but also because of the complex microstructures containing lots of defects,such as pores and cracks,which further lower the thermal conductivity.For more in-depth understanding the mechanism of low thermal conductivity and achieve better properties,numerous researches about the microstructures and properties have been carried out.But the numerical relationship between them are still not so clear,and no effective model has been developed so far.Based on the facts above,our research has paid efforts on the microstructure characterization and established a new model to predict the thermal conductivity by microstructure observation.In the research,three types of YSZ powder and three praying distance parameters were applied in the APS process,thus we prepared nine different TBC samples.One more dense YSZ bulk sample was also sintered as a contrast to the coating samples.Microstructures were characterized including calculating grain size by EBSD,quantifying amorphous contents by TEM,classifying and calculating porosities by Image Analysis.Thermal conductivity was also measured by experiments.Models were established to estimate the thermal conductivity according to microstructure parameters.And finally our new model was proved to have a good agreement with the experimental results.In a word,our research has explored the complex microstructures caused by APS technique and clarified the relationship between those microstructures and thermal conductivity.This is a preliminary achievement into establishing the processmicrostructure-property relationship,which will be of great significance for the further development of TBCs.