Thermal-physical Properties And Molten Salt Corrosion Resistance Of Sc₂O₃ And CeO₂ Co-doped ZrO₂ Ceramics With High Strength And Toughness For TBC Application

The service environment of aero-engines is becoming more and more crucial with continuous aerospace technology development,which imposes stringent requirements on high-performance thermal barrier coating（TBC）materials.Currently,6-8wt.%yttria-stabilized zirconia（6-8wt.%YSZ）has been widely used as a thermal barrier in the gas turbine.However,the increased thermal conductivity,decreased mechanical properties,and reduced corrosion resistance lead eventually to spalling and delaminating due to the phase transformation and sintering issues above 1200℃.In this regard,it is of great significance to develop novel TBC materials for long-term service above 1200°C.In this work,CeO₂、Sc₂O₃and Zr O₂powders were used as raw materials,and a high-temperature solid reaction method was introduced for preparing Sc₂O₃and CeO₂co-doped Zr O₂TBC materials.The rare earth oxides co-doping effects and intrinsic mechanism on the microstructure and thermal physical properties of the Zr O₂based TBC ceramic materials were explored.The phase structure and microstructural evolution of ceramic materials were investigated by X-ray diffraction analysis（XRD）and scanning electron microscope（SEM）.The mechanical properties and strength-toughness mechanisms were studied by means of a Vickers hardness tester and elastic modulus tester.The rare-earth doping effect on the thermal physical properties of the TBC ceramic materials was investigated by using a high-temperature thermal expansion tester and laser thermal conductivity tester.Based on the optimal regulation of mechanical and thermophysical properties,the Na₂SO₄+V₂O₅molten salt corrosion resistance behaviors and damage evolutions of rare earth oxide doped zirconia ceramic materials were investigated.Eventually,the correlation between phase microstructure and macroscopic performance of Sc₂O₃and CeO₂co-doped Zr O₂TBC materials is investigated.The following conclusions were drawn from the above results:The XRD results indicate that the phase structure of Zr O₂ceramic materials obtained by sintering at 1500℃for 6h is noticeably influenced by Sc₂O₃doping content.In general,the 10C0SSZ sample exists in a large number of monoclinic phases and the samples of10C2SSZ and 10C4SSZ tend to appear in the tetragonal phase,and 10C6SSZ shows a more stable cubic phase structure.The SEM results show that the grain size of the ceramic material increases abnormally with the increase of Sc₂O₃doping content,the grain boundary is clear,and the relative density is above 95%.The results of mechanical properties show that the changes of phase structure and microstructure of Zr O₂ceramics co-stabilized by Sc₂O₃and CeO₂have little effect on Vickers hardness and elastic modulus,but instead have a greater effect on the fracture toughness.It can be seen from the spectrum test that martensitic transformation occurs at the indentation of tetragonal phase material.10C2SSZ shows excellent mechanical properties.The hardness,elastic modulus and fracture toughness are 12.0GPa、197.9GPa and 9.9MPa·m^1/2,respectively.The fracture toughness decreases to 5.4 MPa·m^1/2and 5.0MPa·m^1/2.The thermophysical performance results show that the Sc₂O₃and CeO₂co-stabilized Zr O₂ceramics exhibit relatively high average thermal expansion coefficients in the range from room temperature to 1300°C.The average linear expansion coefficients of the ceramics decreased with the increase of Sc₂O₃doping content,between 11.90×10^-6K^-1～12.24×10^-6K^-1,respectively.The heat capacity of the ceramic material increases with the increase of Sc₂O₃doping content in the temperature range from room temperature to1026.85°C.The thermal diffusivity of the ceramics decreases with the increase of Sc₂O₃doping content from room temperature to 1000°C.The thermal conductivity value is similar to the variation law of thermal diffusivity,from room temperature to 800°C,the increase of temperature and the increase of Sc₂O₃content have a greater impact on thermal conductivity,from 800°C to 1000°C,the thermal conductivity of each component is basically the same.The thermal conductivities of 10C2SSZ,10C4SSZ and 10C6SSZ are1.69-2.54Wm^-1K^-1,1.68-2.02Wm^-1K^-1and 1.73-1.93Wm^-1K^-1,respectively.The 10C2SSZ component exhibits excellent comprehensive thermophysical properties.The high temperature corrosion resistance of Na₂SO₄+V₂O₅results show that the content of the stabilizer and corrosion temperature play a dominant role in the corrosion products and corrosion behavior of ceramic materials.The corrosion products at 800℃and1000℃are mainly composed of Ce VO₄and m-Zr O₂.The content of the m-phase increases with the increase of temperature and initially decreases and then increases with Sc₂O₃doping content.The doping of Sc₂O₃and CeO₂can enhance the resistance to molten salt corrosion of Zr O₂-based thermal barrier coating ceramic materials.In summary,the Sc₂O₃-CeO₂co-doped Zr O₂based ceramics present excellent mechanical properties,thermophysical properties and corrosion resistance to molten salt,and is a promising potential candidate for new thermal barrier coating ceramic materials.