Study On Preparation And Properties Of GdTaO₄-Gd₂Zr₂O₇ Composite Thermal Barrier Coatings Ceramic Materials

Thermal barrier coatings are widely used in high-temperature hot-end components of aero-engines to increase the service temperature of the components,thereby prolonging the service life of the engine.Nowadays,the traditional thermal barrier coating material 8YSZ（8 wt.%Yttria-stabilized Zirconia）is far from being able to meet the higher thrust-to-weight ratio requirements of aeroengines.Therefore,it is urgent to develop new thermal barrier coatings materials.Compared with 8YSZ,gadolinium zirconate（Gd₂Zr₂O₇,GZ）and gadolinium tantalate（Gd Ta O₄,GT）has lower thermal conductivity,better high-temperature phase stability and higher temperature sintering resistance,which are a promising new generation of thermal barrier coatings ceramic materials.However,the lower thermal expansion coefficient and fracture toughness of GZ are not desireable.In this paper,GT and GZ are combined and the thermophysical properties,mechanical properties and CAMS corrosion resistance of Gd Ta O₄-Gd₂Zr₂O₇（GT-GZ）composite ceramic materials are studied.The main contents are as follows:（1）The preparation process of GT-GZ composite ceramics was studied.GZ and GT ceramic powders were prepared by the solid-phase reaction method,and the two powders of GZ and GT in different proportions were compounded by the ball mill mixing method,and then compressed and sintered to obtain GT-GZ composite ceramic blocks with different proportions.By adjusting the preparation process,the optimal sintering temperature is 1500℃,and the holding time is 6 h.（2）The phase structure and micro morphology of GT-GZ composite ceramics have been studied.When the GT content is less than 50 mol%,the XRD patterns of GT-GZ composite ceramics only present a single GZ diffraction peak,and the microscopic morphology only shows a single phase which belongs to GZ and without the second phase formed.When the GT content is 70 mol%and 90 mol%,XRD present two diffraction peaks of GT and GZ and the microscopic morphology present two phases of GT and GZ.As the GT content increases,the GZ characteristic peak in the GT-GZ composite material shifted to a large angle as a whole.At high temperatures,GT and GZ have a good chemical compatibility,and the two phases undergo solid solution,formed a solid solution with GZ as the solvent and GT as the solute.（3）The thermophysical and mechanical properties of GT-GZ composite ceramics were studied.At 800 ℃,the thermal conductivity of GT-GZ composite ceramics firstly decreases and then increases with the raising of GT content.GT5-GZ5composite ceramic has the lowest thermal conductivity with a value of0.920 Wm^-1k^-1.At 1400 ℃,the GT1-GZ9 composite ceramic has the highest thermal expansion coefficient with a value of 11.73×10^-6k^-1,which is 12.56%higher than that of a single GZ ceramic.The hardness of GT-GZ composite ceramics achieved the lowest value of 5.11GPa and the highest value of 9.70GPa when the content of GT was 30 mol%and 70 mol%,respectively,GT7-GZ3 has the highest fracture toughness of 2.30 Mpa·m^1/2.（4）The CMAS corrosion behavior of GT-GZ composite ceramic blocks at 1250oC was studied.The results shows that the corrosion products mainly include cubic zirconia c-Zr O₂,zirconia solid solution Ca_0.15Zr_0.85O_1.85,apatite Stone Ca₂Gd₈（Si O₄）₆O₂and spinel Mg Al₂O₄when the GT content is less than 50 mol%.But when the GT content is higher than 50 mol%,the corrosion products mainly include cubic zirconia c-Zr O₂,zirconia solid solution Ca_0.15Zr_0.85O_1.85,calcium tantalate Ca₂Ta₂O₇and gadolinium silicate Gd₂Si₂O₇.The cross-section of GT-GZ composite ceramic blocks was divided into three areas:CMAS residual layer,CMAS corrosion reaction layer and ceramic layer.With the increase of GT content,the corrosion reaction layer thickness of GT-GZ composite ceramics firstly decreases and then increases.When the GT content is 50 mol%,the thickness of the corrosion reaction layer of GT5-GZ5 composite ceramics is the smallest,which is 8.43μm for 5 h and16.92μm for 10 h,respectively.In the corrosion reaction layer,the particle shape of the reaction layer is mainly needle-like and spherical,the needle-like shape is apatite Ca₂Gd₈（Si O₄）₆O₂,and the spherical shape is cubic phase zirconia c-Zr O₂and oxide Zirconium solid solution Ca_0.15Zr_0.85O_1.85.when the GT composite content is less than50 mol%,When the GT composite content is higher than 50 mol%,the particle morphology of the corrosion reaction layer is mainly small spherical,and the main corrosion products are cubic zirconia c-Zr O₂and zirconia solid solution Ca_0.15Zr_0.85O_1.85,calcium tantalate Ca₂Ta₂O₇and silicon Gadolinium acid Gd₂Si₂O₇.