Oxidation protection of tri‐layer La ₂ Zr ₂ O ₇ /Yb ₂ Si ₂ O ₇ /SiC‐coated C _f /SiC composites at high temperature

Abstract Ytterbium silicate (Yb ₂ Si ₂ O ₇ ) and lanthanum zirconate (La ₂ Zr ₂ O ₇ ) ceramic powders were synthesized by the sol–gel method. A novel tri‐layer La ₂ Zr ₂ O ₇ /Yb ₂ Si ₂ O ₇ /SiC environmental barrier coating was prepared on the surface of C/SiC composites to improve the service temperature of the coating (above the Si melting point, 1683 K). Results show that both Yb ₂ Si ₂ O ₇ and La ₂ Zr ₂ O ₇ ceramic powders had extremely high purity and were accompanied by a large number of nanoparticles. The tri‐layer La ₂ Zr ₂ O ₇ /Yb ₂ Si ₂ O ₇ /SiC coating can efficiently prevent the oxidation failure of C/SiC composites in 1773 K air environment for more than 100 h with slight weight loss of 5.71 × 10 ⁻³ g·cm ⁻² and the matching weight loss rate of 5.71 × 10 ⁻⁵ g·cm ⁻² ·h ⁻¹ . No significant chemical reaction was observed between Yb ₂ Si ₂ O ₇ middle and La ₂ Zr ₂ O ₇ outer coatings during the oxidation process at 1773 K, indicating that the tri‐layer La ₂ Zr ₂ O ₇ /Yb ₂ Si ₂ O ₇ /SiC coating had better oxidation stability in 1773 K air environment.