Influence of adding ZrO₂ on the properties of La ₂Zr₂O₇ ceramic

La₂Zr₂O₇ as the thermal barrier coating material draws more and more attention because of its greater thermal physical properties than YSZ, while its further application is restricted by its poor mechanical properties. In this paper, certain ZrO₂ is added into the La₂Zr₂O₇ ceramics in order to improve its mechanical properties. La₂Zr₂O₇ ceramic superfine powder was synthesized by the co-precipitation method and samples of La₂Zr₂O₇-xZrO₂ (x= 0 ~ 30%) were prepared by pressureless sintering process. The microstructure and properties of the samples were investigated by SEM, XRD, three-point bend tests, SENB, laser impulse thermal conductivity instrument and high-temperature expansion instrument. Owing to the partial solid solubility in the La₂Zr ₂O₇-xZrO₂ ceramics, ZrO₂ exists in the form of m-ZrO₂ and t-ZrO₂. With the addition of ZrO₂, the mechanical properties of La₂Zr₂O ₇-xZrO₂ ceramics first increase, then decrease. When the addition amount of ZrO₂ reaches 20%, the fracture toughness comes to the greatest value 2.41 MPa·m^1/2. When the addition amount of ZrO₂ reaches 10%, the bending strength comes to the greatest value 202.4 MPa. The thermal conductivity of the La₂Zr₂O ₇-xZrO₂ ceramics is lower than YSZ. The thermal conductivity of the La₂Zr₂O₇-xZrO₂ ceramic decrease at 1400 °C as the addition amount of ZrO₂ increases, resulting from the higher intrinsic thermal conductivity of ZrO ₂ than that of La₂Zr₂O₇. The thermal expansion coefficient of the La₂Zr₂O₇- xZrO₂ ceramics decreases slowly after about 350 °C and decrease rapidly at about 1000 °C, and then increase rapidly due to the transformation of m-ZrO₂ to t-ZrO₂.