Influence of Adding ZrO<sub>2 </sub>on the Properties of La<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> Ceramic

Abstract

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, 10%, 20%, 30%)were prepared by pressureless sintering process. The microstructure and properties of the samples were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), three-point bend tests, SENB, laser impulse thermal conductivity instrument and high-temperature expansion instrument. Owing to the partial solid solubility in the La2Zr2O7-xZrO2 ceramics, ZrO2 exists in the form of m-ZrO2 and t-ZrO2. With the addition of ZrO2, the mechanical properties of La2Zr2O7-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·m1/2. When the addition amount of ZrO2 reaches 10%, the bending strength comes to the greatest value 202.4 MPa. The thermal conductivity of the La2Zr2O7-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 ZrO2 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.