Phase structure, thermophysical properties and thermal cycling behavior of novel (Sm0.2La0.8)2(Zr0.7Ce0.3)2O7 thermal barrier coatings

Samarium-lanthanum-zirconium-cerium composite oxide ((Sm0.2La0.8)2(Zr0.7Ce0.3)2O7, SmLZC) as a candidate material for novel thermal barrier coatings (TBCs) was prepared by electron beam-physical vapor deposition (EB-PVD). The phase structure, thermophysical properties, sintering-resistance and thermal cycling behavior of SmLZC ceramics and coatings were investigated in detail. The SmLZC ceramics consist of mixture structures of pyrochlore and fluorite, and no new phase appears after long-term annealing. The thermal conductivities of SmLZC ceramics first decrease gradually with the increment of temperature below 1273 K and then increase slightly above 1273 K. The minimum value of ∼0.85 W m−1 K−1 is detected at 1273 K. Thermal expansion coefficient of SmLZC is ∼10.78 × 10−6 K−1, which is larger than those of La2Zr2O7 (9.18 × 10−6 K−1) and La2(Zr0.7Ce0.3)2O7 (LZC, 10.51 × 10−6 K−1). The volume shrinkages of LZC and SmLZC are basically identical, only a bit of sintering-resistance improvement of SmLZC ceramics observed above 1773 K. The failure of the SmLZC coating is mainly a result of the occurrence of microcracks within ceramic coat, which cause the abnormal oxidation of bond coat. The microcracks of the ceramic coating are probably improved in a way both by adjusting the compositional ratio of ceramic ingot and by optimizing the process parameters.