Research On Optimization Of Thermophysical Properties Of Potential Thermal Barrier Coating Material Rare Earth Tantalate

With the development of aero-engines and gas turbines to a higher thrust-to-weight ratio,the turbine inlet temperature in the combustion chamber is being raised further,resulting in the more demanding requirements for thermal barrier coatings?TBCs?materials.Because of the phase transition,accompanying with volumetric expansion caused cracking and failure of coating,will occure when the operating temperature is above 1200?C,the yttria-stabilized zirconia?YSZ?,the state-of-art TBCs materials,doesn't meet the demands of future aero-engines and gas turbines.It is imperative to explore novel TBCs materials.It is selected as the investigated object that the ferroelastic rare earth tantalate as potential TBCs materials in this thesis.Based on the phonons scattering mechanism,the optimation of their performances is conducted by the doping method,and the main contents contain:The Zr⁴⁺ions are introduced into the lattice of DyTaO₄ by dopping methods to form the Dy_1-xTa_1-xZr_2xO₄ compounds.Due to the phonons scattering caused by Zr⁴⁺ions,the thermal conductivities of DyTaO₄ are gradually decreased with the content increase of Zr⁴⁺ions,and the optimized consentrations of Zr⁴⁺ions for reducing thermal conductivity are 8.mol%-10.mol%at the temperature range from 100?C to 900?C.Compared with YSZ,the minimum thermal conductivity of Dy_1-xTa_1-xZr_2xO₄ ceramic is declined by 30%,and their thermal expansion coefficients are comparable to that of YSZ.YTaO₄ and DyTaO₄ with the same crystal structure are selected to synthesize(Y_1-xDy_x)TaO₄ by equivalent ion doping.The heat transfer investigation of(Y_1-xDy_x)TaO₄found that the thermal conductivity varied with the composition does not conform to phonon-defects scattering model.This is mainly originated from the competition for phonon scattering between partial solid solution atoms and the segregation of Y and Dy elements.Via chemical bond adjustment,the thermophysical properties of(Y_1-xYb_x)TaO₄ceramics with different structure are tailored.Due to the different chemical bond strength,m'-phase(Y_1-x-x Yb_x)TaO₄ ceramics possess lower thermal conductivity than that of m phase,and the lowest thermal conductivity of(Y_1-xYb_x)TaO₄ ceramics is declined by 54%compared with YSZ.However,the thermal expansion coefficients of m'-phase is much lower than that of m-phase,and the ferroelastic transformation and ferroelastic domain are also not existed in m'-phase(Y_1-xYb_x)TaO₄ ceramics.Further studies reveal that the heat transfer in(Y_1-xYb_x)TaO₄ ceramics is correlated to multiple mechanisms including Umklapp scattering process,phonon-defects scattering and heat radiation.Derived from the particularity and complexity of crystal structure in RE₃TaO₇compounds,the ZrO₂-Dy ₃TaO₇ is choosed as investigated object.The results suggest that the crystalline ZrO₂-Dy₃TaO₇ ceramics have glass-like thermal conductivity similar to that of amorphous materials.Moreover,the introduction of Zr⁴⁺ions can effectively reduce the thermal conductivity of Dy₃TaO₇,making it closer to amorphous limit.Due to the incorporation of Zr⁴⁺ions,the lattice relaxation in Dy₃TaO₇ is appeared,which leads to the increase in its'thermal expansion coefficients,and the highest value reach11×10^-6/K.