Heat Conduction And Microscale Radiative Thermal Transport In Functionally Graded Thermal Barrier Coatings(FGTBCs)

Thermal barrier coatings(TBCs)are widely used for gas turbines,especially aero-engines,to provide thermal insulation and protect superalloy blades.Conventional TBCs are duplex coatings consisting a ceramic top coat and an alloy bond coat.Despite the excellent thermal insulation performance of conventional TBCs,the mismatch between the coefficients of thermal expansion(CTE)of ceramic and alloy at higher temperature can cause the spalling and other types of failure of the coating during realistic applications.To tackle the issue,the functionally graded thermal barrier coatings(FGTBCs)were then developed.Mechanical properties and heat transfer mechanism are the two research topics of the most importance concerning TBCs.Currently,the mechanical properties and the heat transfer mechanism of TBCs,the mechanical properties of FGTBCs have been well studied.However the heat transfer mechanism of FGTBCs has been long left uninvestigated by academia.So in this thesis,over 50 different TBC and FGTBC samples are prepared by air plasma spraying(APS).Micro-structural features of the samples are characterized and analyzed.Since the microstructures in FGTBCs are quite different from those in the conventional TBCs,the thermal radiation and heat conduction characteristics must be different from previous research.The thesis presents a deep and thorough study on the micro mechanism for the heat transfer in FGTBCs via both theoretical and experimental approaches.The thermal radiative properties,mechanism,the features of heat conduction,along with their micro-structural effects,of FGTBCs are retrieved by experimental data and inversion models.The finally proposed radiation-conduction coupled heat transfer model for FGTBCs predicts the temperature distribution in FGTBCs and thus we evaluate the thermal insulation performance of FGTBCs.The results provide valuable guidance for better thermal design,for the development and further researches concerning FGTBCs.