Study On Thermophysical Properties And CMAS Corrosion Behavior Of (Gd_0.9Yb_0.1)₂(Zr_1-xCe_x)₂O₇ Ceramic For Thermal Barrier Coatings

Thermal barrier coating is a protective coating mainly used on high temperature hot end parts of aviation engines to increase the service temperature of the engine.With the continuous development of the times,the traditional 8YSZ（8 wt.%Yttria-stabilized zirconia）coating material can no longer meet the latest requirements of active aviation engines.Compared with the traditional 8YSZ coating material,the rare earth zirconate material has lower thermal conductivity,better phase stability at high temperature,and better sintering resistance,which is considered as one of the candidate materials to replace the existing thermal barrier coating materials.In this paper,chemical co-precipitation calcination mothed was used to prepare four different kinds of(Gd_0.9Yb_0.1)₂(Zr_1-xCe_x)₂O₇（x=0,0.1,0.2,0.3）ceramic materials with zirconia,ytterbium oxide,zirconia oxychloride,cerium nitrate as the main raw materials.The structure,micro-morphology,thermophysical properties,mechanical properties and CMAS（CaO、MgO、Al₂O₃ and SiO₂）corrosion behavior of these four ceramic blocks were studied.The main contents and results of the research are as follows:（1）The preparation technology and microstructure of(Gd_0.9Yb_0.1)₂Zr₂O₇ ceramics with different content of Ce⁴⁺were studied.The calcination process of the precursor powder is optimized,with the increase of the calcination temperature,the crystallinity of the precursor powder gradually increases,and the crystal activation energy is63.72±8.85 kJ·mol^-1.Four ceramic blocks(Gd_0.9Yb_0.1)₂(Zr_1-xCe_x)₂O₇（x=0,0.1,0.2,0.3）were prepared by sintering at 1600℃in air atmosphere for 6 h,analysing the phase analysis of the four ceramic blocks,the results showed that the four ceramic blocks are single-phase defective fluorite structure,no impurity phase,which indicates that the doped Ce⁴⁺is completely dissolved into the crystal lattice of(Gd_0.9Yb_0.1)₂Zr₂O₇ ceramic material,forming a stable ceramic solid solution material.With the increase of Ce⁴⁺doping content,the XRD diffraction peaks of the four ceramic blocks gradually shifted to the low angle direction,and the lattice constant also increased approximately linearly with the increase of doping content.（2）The thermophysical and mechanical properties of(Gd_0.9Yb_0.1)₂Zr₂O₇ ceramic materials doped with different contents of Ce⁴⁺were studied.At 800℃,the thermal conductivity of(Gd_0.9Yb_0.1)₂(Zr_1-xCe_x)₂O₇（x=0,0.1,0.2,0.3）ceramic blocks decreases first and then increase with the increase of Ce⁴⁺doping content,and the lowest thermal conductivity is 0.8964 W/（m·k）at x=0.1.When x≥0.2,the thermal conductivity of the ceramic blocks are greater than that of the undoped(Gd_0.9Yb_0.1)₂Zr₂O₇ ceramic block.At 1000℃,the thermal expansion coefficient of the ceramic blocks material after doping with Ce⁴⁺increase with the increase of doping content.The thermal expansion coefficient of the ceramic blocks material have increased from 10.595×10^-66 K^-1 to11.148×10^-66 K^-1 when it has never been doped,which has been significantly improved.The hardness and fracture toughness of the ceramic blocks increase with the increase of Ce⁴⁺doping content,increasing from 6.83 Gpa to 8.05 Gpa when Ce⁴⁺was undoped,and the fracture toughness increases to 1.25 MPa·m^1/2 from undoped to 1.65 MPa·m^1/2when Ce⁴⁺was undoped.（3）The CMAS corrosion behavior of(Gd_0.9Yb_0.1)₂Zr₂O₇ ceramic materials doped with different contents of Ce⁴⁺at 1250℃was studied.The results showed that the corrosion products generated after the reaction of the four ceramic blocks(Gd_0.9Yb_0.1)₂(Zr_1-xCe_x)₂O₇（x=0,0.1,0.2,0.3）with CMAS are basically the same,mainly Ca₂RE₈（SiO₄）₆O₂（RE=Gd,Yb,Ce）、CaAl₂Si₂O₈、MgAl₂O₄、c-ZrO₂ and CeO_2.The cross section of the ceramic block after CMAS corrosion is divided into three areas,which are the CMAS residual layer,the corrosion reaction layer and the uncorroded part.The corrosion thickness of the four ceramic blocks(Gd_0.9Yb_0.1)₂(Zr_1-xCe_x)₂O₇（x=0,0.1,0.2,0.3）after being etched for 5 h is about 40μm,and after 10 h is about 60μm.At 1250℃,the ceramic blocks corroded for 5 h and 10 h produced needle-shaped and spherical products at the interface between the CMAS residual layer and the corrosion reaction layer.The analysis results show that the needle-shaped product is apatite and the spherical product is c-ZrO₂.After the reaction of four kinds of ceramic blocks with CMAS,the apatite with higher melting point in the corrosion products fills the corrosion channels and forms a dense barrier,which effectively inhibits the further corrosion of the ceramic blocks by CMAS.