Effect of GdO Addition on the Microstructure and Properties of GdO-YbO-YO-ZrO (GYYZO) Ceramics.

Gd and Yb elements have high chemical stability, which can stabilize the solid solution in ZrO. GdO and YbO have high melting points, and good oxidation resistance in extreme environments, stable chemical properties. Therefore, GdO and YbO were added to ZrO to stabilize oxides, improve the high temperature stability, and effectively decrease the thermal conductivity at high temperature. In this work, 5 wt% YbO and 5 wt%, 10 wt%, 15 wt% GdO were doped into 8 wt% YO stabilized ZrO (8YSZ) powders as thermal barrier coating materials, and sintered at 1650 °C for 6 h, 12 h, 24 h. The effects of GdO addition on the microstructure, density, thermal conductivity, hardness, and fracture toughness of GdO-YbO-YO-ZrO (GYYZO) bulk composite ceramics were investigated. It was found that the densification of the 8YSZ bulk and GYYZO bulk with 15 wt% GdO reached 96.89% and 96.22% sintered at 1650 °C for 24 h. With the increase of GdO addition, the hardness, elastic modulus and fracture toughness of the GYYZO bulk increased and the thermal conductivity and thermal expansion coefficient of the GYYZO bulk decreased. GYYZO bulk with 15 wt% GdO sintered at 1650 °C for 24h had the highest hardness, elastic modulus and fracture toughness of 15.61 GPa, 306.88 GPa, 7.822 MPa·m, and the lowest thermal conductivity and thermal expansion coefficient of 1.04 W/(m·k) and 7.89 × 10/°C at 1100 °C, respectively. The addition of GdO into YSZ could not only effectively reduce the thermal conductivity but also improve the mechanical properties, which would improve the thermal barrier coatings' performances further.