Thermal Properties And Microstructures Analysis Of YSZ And YSZ-Al₂O₃ Thermal Barrier Coatings

The most widely used TBC is YSZ because of its excellent mechanic and thermal performance.However,as the service temperature of the engine increases,materials with lower thermal conductivity are required.Researchers have done a number of studies to reduce the thermal conductivity of the TBCs.Current studies mainly focus on doping modification on the basis of YSZ and developing new materials to replace it.The method of doping Al₂O₃ in YSZ has received widespread attention.In this paper,atmospheric plasma spraying YSZ and YSZ-Al₂O₃ coatings were used as research objects to study the relationship between thermal properties and coating microstructure.The main achievements are as follows:?1?At 800 ?,the thermal conductivity of YSZ?YSZ-15 wt.% Al₂O₃ and YSZ-35 wt.% Al₂O₃ coatings are 1.86,1.73 and 1.35 W/?m·K?,respectively.The YSZ-Al₂O₃ coatings possess much lower thermal conductivity compared to YSZ coating which is attributed to the smaller grains,more oxygen vacancies and the large atomic weight difference between Al and Zr.The mentioned factors improve the phonon scattering thereby reducing the thermal conductivity;?2?The lower thermal expansion coefficients?TECs?of YSZ-Al₂O₃ coatings is attributed to the smaller lattice parameters due to the substitutional Al3+ doping at Zr4+ sites.The decrease in lattice parameter values increases the crystal lattice energy,and the TEC is inversely proportional to the lattice energy.Moreover,the TEC of the YSZ-35 wt.% Al₂O₃ coating is much lower than the YSZ coating,which is due to the precipitation of Al₂O₃ and the formation of amorphous phases.Compared to Zr O2 phase,the Al₂O₃ phase possess lower TECs values.The amorphous phase can account for larger expansion tolerance compared to the corresponding crystalline phase due to its loose atomic arrangement.