Composition Optimization And Cmas Corrosion Behavior Study Of YSZ/Al₂O₃ Composite Thermal Barrier Coatings

Calcium-magnesium-alumina-silicate（CMAS）attack is becoming a more critical issue with ever-increasing demand for higher operating temperature in future high-efficiency gas-turbines.Conventional YSZ thermal barrier coatings have been proved not resistant to CMAS attack.In the present study,YSZ/Al₂O₃ composite was designed to act as anti-CMAS layer due to its good performance in mitigating CMAS infiltration.Porous YSZ/Al₂O₃ ceramic pellets with different concentrations of Al₂O₃ were employed for composition optimization.Besides,YSZ/Al₂O₃ composite thermal barrier coatings were fabricated by air plasma spray.Scanning electron microscope,x-ray diffraction,Raman spectroscope as well as energy dispersive spectrometer were adopted to investigate the microstructure and CMAS corrosion behavior of the YSZ/Al₂O₃composite layer.The results indicate that the CMAS infiltration could be effectively reduced by adding Al₂O₃,for the reason that Al₂O₃ reacts actively with molten CMAS and form composites having higher melting temperature,such as anorthite.However,the effectiveness of CMAS mitigation strongly depends on the concentration of Al₂O₃.Considering thermal properties of the coatings,the optimal composition is 70 wt.%8YSZ+30 wt.%Al₂O₃.Laminated structures were observed within YSZ/Al₂O₃ composite layer,which helps to eliminate the propagation of vertical cracks within such coatings.Theoretical calculations of thermal conductivity and coefficient of thermal expansion（CTE）were carried out for the studied composite layer.The results indicate that the composite coatings have relatively low thermal conductivity,which is around 1.0 W·m^-1·K^-1 at1000℃,and comparably similar CTE with 8YSZ.