Yb2O3 and Gd2O3 doped strontium zirconate for thermal barrier coatings

Yb2O3 (10 mol%) and Gd2O3 (20 mol%) doped SrZrO3 was investigated as a material for thermal barrier coating (TBC) applications. The thermal expansion coefficients (TECs) of sintered bulk Sr(Zr0.9Yb0.1)O2.95 and Sr(Zr0.8Gd0.2)O2.9 were recorded by a high-temperature dilatometer and revealed a positive influence on phase transformations of SrZrO3 by doping Yb2O3 or Gd2O3. The results for the thermal conductivities of Sr(Zr0.9Yb0.1)O2.95 and Sr(Zr0.8Gd0.2)O2.9 indicated that both dopants can reduce the thermal conductivity of SrZrO3. Mechanical properties (Young's modulus, hardness, and fracture toughness) of dense Sr(Zr0.9Yb0.1)O2.95 and Sr(Zr0.8Gd0.2)O2.9 showed lower Young's modulus, hardness and comparable fracture toughness with respect to YSZ. The cycling lifetimes of Sr(Zr0.9Yb0.1)O2.95/YSZ and Sr(Zr0.8Gd0.2)O2.9/YSZ double layer coatings (DLC), which were prepared by plasma spraying, were comparable to that of YSZ at operating temperatures <1300 °C. However, the cycling lifetime of Sr(Zr0.9Yb0.1)O2.95/YSZ DLC was ∼25% longer, whereas Sr(Zr0.8Gd0.2)O2.9/YSZ DLC had a shorter lifetime compared to the optimized YSZ coating at operating temperatures >1300 °C.