Double Rare-Earth Oxides Co-Doped Strontium Zirconate as a New Thermal Barrier Coating Material

Advanced ceramic materials with perovskite structure have been developed for potential applications in thermal barrier coating (TBC) systems in an effort to overcome the properties of the pre-existing ones like 8wt% yttria stabilized zirconia (8YSZ). Y₂O₃ and Yb₂O₃ co-doped strontium zirconate with chemistry of Sr(Zr_0.9Y_0.05Yb_0.05)O_2.95 (SZYY) was synthesized using ball milling prior to solid-state sintering, and had a minor second phase of Yb₂O₃. The SZYY showed good phase stability not only from room temperature to 1400°C, but also at high temperature of 1450°C for a long period, analyzed by thermogravimetry-differential scanning calorimetry (TG-DSC) and X-ray diffraction (XRD), respectively. The thermal expansion coefficients (TECs) of the sintered bulk SZYY were recorded by a high-temperature dilatometer and revealed a positive influence on phase transitions of SrZrO₃ by codoping Y₂O₃ and Yb₂O₃. The thermal conductivities of SZYY were at least ~30% lower in contrast to that of SrZrO₃ and 8YSZ in the whole tested temperature range. The good chemical compatibility was observed for SZYY with 8YSZ or Al₂O₃ powders after 24 h heat treatment at 1250°C. The phase stability and the microstructure evolution of the as-sprayed SZYY coating during annealing at 1400°C were also investigated in this work.