Thermal barrier coatings with high-entropy oxide as a top coat

Abstract A pyrochlore-structured La2(Zr0.2Ce0.2Hf0.2Sn0.2Ti0.2)2O7 high-entropy oxide was designed and synthesized, and its properties were tested. Traditional two-layer structured thermal barrier coatings (TBCs) with a La2(Zr0.2Ce0.2Hf0.2Sn0.2Ti0.2)2O7 top-coat were prepared by plasma spraying. A phase-pure defective-fluorite high-entropy-oxide top coat was thus obtained. The results confirmed the possibility of synthesizing pyrochlore-structured La2(Zr0.2Ce0.2Hf0.2Sn0.2Ti0.2)2O7. The material exhibited a low thermal conductivity, which increased with increasing temperature. The coefficient of thermal expansion (CTE) of La2(Zr0.2Ce0.2Sn0.2Hf0.2Ti0.2)2O7 ranged from 7.55 × 10−6 °C−1 to 8.63 × 10−6 °C−1 for the corresponding range of room temperature to 1000 °C. After 10 thermal cycles at 1050 °C, the La2(Zr0.2Ce0.2Hf0.2Sn0.2Ti0.2)2O7 top coat spalled in the TBC. Spallation did not occur at the interface between the bond coat and the thermally grown oxide layer, while it is in the top coat near the bond coat. Owing to the low fracture toughness and low CTE, the thermal cycling lifetime of TBCs with the La2(Zr0.2Ce0.2Hf0.2Sn0.2Ti0.2)2O7 top coat was short.