Preparation and phase composition optimization of yttrium silicates/SiC multilayer coating coated carbon/carbon composites

Abstract

In order to optimize the phase composition and improve the oxidation resistance of yttrium silicates coating, Y₂SiO₅-Y₂Si₂O₇-Y₄Si₃O₁₂ coatings with different phase composition were deposited on the surface of SiC pre-coated carbon/carbon (C/C) composites using a hydrothermal electrophoretic deposition process. The as-prepared multilayer coatings were characterized by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The influence of phase composition on the morphologies and anti-oxidation properties of the multicomposition yttrium silicates coatings were investigated. The phase composition of the coating was optimized. Results show that Y₂SiO₅/Y₂Si₂O₇/Y₄Si₃O₁₂ mass ratio has strong effect on the morphology and oxidation resistance of yttrium silicates coatings. It is found that a low thermal expansion coefficient (CTE) district existed in the Y₂SiO₅-Y₂Si₂O₇-Y₄Si₃O₁₂ ternary phase diagram. When the optimized phase composition of Y₂SiO₅/Y₂Si₂O₇/Y₄Si₃O₁₂ in the low CTE district reaches Y₂SiO₅ = 20.1 wt%, Y₂Si₂O₇ = 8.3 wt%, and Y₄Si₃O₁₂ = 71.6 wt%, dense and homogenous yttrium silicates coatings with perfect oxidation resistance are achieved. After 80 h oxidation in 1773 K, weight loss of the coated C/C composites is only 2.17 × 10⁻³ g.cm⁻².