The Effect Of Yb₂O₃Doping On The Structue And Propeties Of Y₂O₃-Ta₂O₅-ZrO₂Ceramic

With the development of aircraft engine toward higher flow ratio and thrust weightratio, alloys can not meet requirement, so thermal barrier coatings （TBCs） are widelyapplied and developed. In the thermal barrier coatings system, heat insulation is mostlyachieved by the top ceramic material. Yttria partly stabilized zirconia is widely used asthermal barrier coatings. However, its using temperature is limited to1200oC. If applyingabove1200oC, it will transform form t to m phase and accompanied by a volumeexpansion, leading to the density and thermal conductivity increase. Therefore, it is vital tosearch novel ceramic materials to substitute for YSZ.In this paper, Yb₂O₃-Y₂O₃-Ta₂O₅-ZrO₂ceramics were synthesized by a solid statereaction method. The phase compositions and phase stabilities, fracture microstructures,thermal diffusion coefficients, thermal expansion coefficients and volume densities wereidentified by X-ray diffraction technology （XRD）, Scanning electron microscope （SEM）,laser-flash apparatus （LFA）, thermal dilatometer and Archimedes principle, respectively.The heat capacities of these ceramics were calculated according to Neumann-Kopp rule.Theoretical thermal conductivities of these ceramics were calculated in accordance with apoint defect model.XRD patterns indicated that Yb₂O₃-Y₂O₃-Ta₂O₅-ZrO₂ceramics sintered at1600oC for6hours were composed of single tetragonal phase and had relatively high tetragonality.The tetragonalities of Yb₂O₃-Y₂O₃-Ta₂O₅-ZrO₂materials were lower than that of Y₂O₃-Ta₂O₅-ZrO₂. These ceramics heat treated at200¹500oC for24⁴00h still consisted ofpure tetragonal phase, which indicated Yb₂O₃-Y₂O₃-Ta₂O₅-ZrO₂ceramic materials hadgood phase stabiliy.SEM photographs of the ceramics sintered at1600oC for6hours shown thatoverburning phenomenon happened in Yb₂O₃-Y₂O₃-Ta₂O₅-ZrO₂(Yb³⁺≤8mol.%) systemand the grains were clear in Yb₂O₃-Y₂O₃-Ta₂O₅-ZrO₂（Yb3+＞8mol.%）system. With theincrease of Yb³⁺ content, the grain sizes became uniform. The sintering resistance of Y₂O₃- Ta₂O₅-ZrO₂was enhanced by Yb2O3doping after1500oC for150hours.The heat capacities, thermal diffusivities and thermal conductivities of Y₂O₃-Ta2O5-ZrO2were decreased by ytterbia doping between room temperature and1000oC. Moreover,14YbTYSZ had the lowest the thermal conductivity, which was ranged from1.50W/m·Kto1.68W/m·K. The trends of measured thermal conductivities for all compositions agreedwith these of thermal conductivities calculated on the basis of point defect model. Themodel predicted that thermal conductivity was affected by three factors, which includedmass difference, radius difference between substituting atom and substituted atom, andfield of stress around the point defect. The field of stress played a leading role in reductionof thermal conductivity. In addition, the thermal expansion coefficients of Yb2O3-Y₂O₃-Ta₂O₅-ZrO₂system were slightly lower than that of Y₂O₃-Ta₂O₅-ZrO₂from roomtemperature to1300oC.