Numerical Study Of Microstructural Effect On The Thermal Conductivity Of Thermal Barrier Coatings (TBCs)

Thermal barrier coatings(TBCs)are metal-ceramic composite coatings,which consist of top ceramic coatings with excellent performance of heat insulation and metal bond coatings.As the protective coatings of aero-engine and gas turbine,they can not only protect hot-end components from high-temperature oxidation,abrasion and corrosion,but also increase the temperature of inlet air and engine efficiency.With the increasing development of aviation,thermal power and shipping,the demand for high temperature environment of hot-end components is also rising,which has already overweighed the limiting temperature of Ni-based single crystal superalloy.In order to make the metal substrate work in a safe temperature range,the thermal barrier coatings with insulation function have been usually utilized.Therefore,the application of TBCs is crucial for the aero-engine and gas turbine to run safely and steadily in high temperature condition.As thermal conductivity of TBCs draws much attention as the key parameter of the measurement of the thermal insulation performance,it is of great significance to study it.It is not easy to calculate the effective thermal conductivity of TBCs by simple analytical models due to the complex porous microstructure,such as pores and cracks.In addition,the influence of size effects and phonon interface scattering on thermal conductivity becomes significant when the grain size decrease to the nanoscale.Thus,it is of great importance to relate the thermal conductivity to the porous microstructure.Through the SEM image of TBCs,the characteristics of microstructure can be analyzed,including the porosity,pore size and pore shape.A random pore generation algorithm,QSGS,is employed to reconstruct the porous structure.Combined with the LBM algorithm,the effects of various porous structures on thermal conductivity is studied.To model the thermal conductivity more precisely,the more real porous structures are reconstructed from the binarized SEM images.This paper not only studies the effects of micro porous structure on the thermal conductivity of conventional TBCs and functionally graded TBCs,but also puts much emphasis on the effects of nanostructural YSZ on the thermal conductivity of TBCs.The influence of size effects and phonon interface scattering on thermal conductivity is studied through solving the phonon Boltzmann transport equation(PBTE)and the simulated results are matched with the experimental data well.A thorough study has been carried out on the thermal conductivity of conventional TBCs,functionally graded TBCs and nano-YSZ TBCs,which could help us have a further understanding of the thermal insulation performance of TBCs and provide us a theoretical guide to design TBCs with a high thermal insulation property.