Optimization Of Thermophysical Properties And Anti-CMAS Corrosion Of Rare Earth Tantalate RETaO₄ Ceramic

As aero-engines continue to upgrade,traditional yttria-stabilized zirconia（YSZ）coatings are no longer able to meet the requirements,so it is necessary to explore new thermal barrier coating materials that can withstand higher operating temperatures.Rare earth tantalate（RETa O₄,RE is rare earth）ceramics have the potential to be a new generation of thermal barrier coating materials due to their low thermal conductivity,high thermal expansion coefficients,high melting point,and high-temperature phase stability.This paper takes RETa O₄ ceramics as the research object with comprehensive performance,and studies the influence of the crystal structure and defects on the thermophysical properties and CMAS(Ca O-Mg O-Al O_1.5-Si O₂)corrosion resistance of the materials,which builds a certain foundation for the development of thermal barrier coating materials.The research content of this study is as follows:(Gd_1-xY_x)Ta O₄ ceramics were prepared by solid-state reaction,and X-ray diffraction revealed that each sample crystallized in a monoclinic phase.The properties of(Gd_1-xY_x)Ta O₄ were optimized by adjusting the Gd/Y ratio.(Gd _1-xY_x)Ta O₄ ceramics exhibited low high-temperature thermal conductivity(1.37～2.05W?m^-1?K^-1),which was attributed to the high concentration of lattice defects.The phase transition temperature of(Gd _1-xY_x)Ta O₄ ceramics was above 1500°C,and the linear expansion coefficient s were 10.5×10^-6 K^-1（1200°C）,which were comparable to that of yttria-stabilized zirconia(11×10^-6 K^-1,1200°C).(Gd_1-xY_x)Ta O₄ had anisotropic thermal expansion,and by controlling the preferred orientation,thermal expansion mismatch could be minimized when(Gd_1-xY_x)Ta O₄ coatings were deposited as thermal barrier coatings on different substrates.The microstructure and thermal properties of(Y_0.5Gd_0.5)(Ta_0.5Nb_0.5)O₄ ceramic was studied.We determined the contribution of phonons and photons to the total thermal conductivity,and achieved low thermal conductivity by suppressing high-temperature thermal radiation.By introducing Nb atoms into the prepared ceramic lattice,the thermal expansion coefficients were increased,and it met the requirements of thermal barrier coatings.The improved wear resistance of(Y_0.5Gd_0.5)(Ta_0.5Nb_0.5)O₄was due to its relatively high Young’s modulus and hardness,which would contribute to its service performance as a coating.This work promotes the engineering application of RETa O₄ and RENb O₄ as high-temperature thermal barrier coatings.Three kinds of medium and high entropy rare earth tantalate ceramics(Y_0.33Gd_0.33Tm_0.33)Ta O₄,(Y_0.25Gd_0.25Ho_0.25Tm_0.25)Ta O₄and(Y_0.2Gd_0.2Dy_0.2Ho_0.2Tm_0.2)Ta O₄ were prepared.The results showed that high-entropy could significantly reduce the thermal conductivity of rare earth tantalates.Additionally,due to the delayed diffusion and lattice distortion effects induced by high-entropy ceramics,(Y_0.2Gd_0.2Dy_0.2Ho_0.2Tm_0.2)Ta O₄ exhibited the best resistance to CMAS corrosion,with a corrosion depth of 8.49μm after 10 hours of corrosion at1400℃,which was significantly better than YSZ with a corrosion depth of 225μm after 4 hours of corrosion at 1250℃.Meanwhile,(Y_0.2Gd_0.2Dy_0.2Ho_0.2Tm_0.2)Ta O₄ceramics showed better wear resistance,with a maximum microhardness dissipation coefficient of 0.68 under the same conditions,which was higher than YSZ（0.58）.