Research On Modification Of Lanthanum Zirconate Based On Surface Coating

Thermal barrier coating?TBC?can effectively reduce the surface temperature of high-temperature components and protect high-temperature components of engines.It focuses on the research in the field of gas turbines.At present,Yttrium stabilized zirconia?YSZ?was widely used as thermal barrier coating material,which possesses low thermal conductivity,high thermal expansion coefficient and good thermal shock resistance,but the sintering of YSZ above 1473K causes the coating to failure.Therefore,it has become a research hotspot of high-performance thermal barrier coating materials.La₂Zr₂O₇ has broad application prospects in the field of thermal barrier coatings due to its good thermal stability,low thermal conductivity,resistance to sintering and oxygen barrier properties.But it has shortcomings such as low thermal expansion coefficient and poor toughness,hindering its practical application.The YSZ-coated La₂Zr₂O₇ composite ceramic structural material will enhance the advantages of the two materials to achieve the modification of La₂Zr₂O₇ material.In this paper,the liquid crystal precipitation method was used to successfully synthesize YSZ-coated La₂Zr₂O₇ powder,and the micro structure and phase structure of the powder and sintered composite ceramics were analyzed and characterized.The results showed that the microstructure of the powder was YSZ-coated core-shell structure,the shell is YSZ crystal grains,and the core is La₂Zr₂O₇ crystal grains,and the core-shell structure can also be maintained after sintering.The phase analysis confirmed the existence of the La₂Zr₂O₇ phase and the YSZ phase of the powder,and there was no impurity phase,and the powder did not undergo phase transformation after sintering at 1500?.The thermophysical properties such as thermal stability,thermal conductivity and thermal expansion coefficient of YSZ-coated La₂Zr₂O₇ composite ceramics after sintering were tested.It was found that the YSZ-coated La₂Zr₂O₇ material has good thermal stability below 1000?.The thermal conductivity test results show that the coating of YSZ improves the thermal conductivity of La₂Zr₂O₇ material.Although its thermal conductivity increases with temperature increasing,the thermal conductivity is only slightly higher in the range of room temperature to 1000 ?.Pure La₂Zr₂O₇ material is still much lower than YSZ material.The thermal conductivity from room temperature to 1000? is below 2.0 W/m·K,which has good thermal insulation properties.The results of thermal expansion coefficient show that the coating of YSZ improves the thermal expansion coefficient of La₂Zr₂O₇ material.The thermal expansion coefficient is 10.24?m/?m·??from room temperature to 400?,which is close to YSZ and much higher than pure La₂Zr₂O₇.The mechanical properties of YSZ-coated La₂Zr₂O₇ composite ceramics were characterized by nano-indentation experiments and micro-crack observation.The results of nano-indentation experiments show that the hardness of composite ceramics is 8.33 GPa which is not much different from that of pure La₂Zr₂O₇,but the elastic modulus is significantly reduced to 131.53 GPa,indicating that the coating of YSZ increases the toughness of La₂Zr₂O₇.The micro-crack morphology observation shows that the coating of YSZ makes the width and length of the micro-cracks generated in the sample under the same load decrease correspondingly,the crack direction is more tortuous,the crack deflection and bridging phenomenon are more frequent,making the micro-crack difficult to expand,increased the toughness of La₂Zr₂O₇.