Oxidation and thermal shock resistant properties of Si/Yb2SiO5/NdMgAl11O19 coating deposited on Cf/SiC composites

Yb2SiO5 and NdMgAl11O19 (NMA) powders were synthesized by solid-state reactions. Triple-layer ceramic coatings based on the Si bond layer, Yb2SiO5 interlayer and NMA top layer were prepared on carbon fiber reinforced silicon carbide ceramic matrix (Cf/SiC) composites by atmospheric plasma spraying (APS). The coatings were subjected to thermal shock tests at 1300 °C, 1400 °C and 1450 °C, respectively. The results showed that the Si/Yb2SiO5/NMA coating significantly improved the oxidation resistance of Cf/SiC composites. The failure mechanism of the Si/Yb2SiO5/NMA coating was closely related to the thermal shock temperature. Below 1400 °C, the failure of the coating was connected with the mismatch of thermal expansion coefficient (CTE) between the coating and substrate, the reaction between Yb2SiO5 and NMA at the interface, the poor sintering property of Yb2SiO5 and NMA and the substrate itself. Above 1450 °C, the coating failed after only one thermal shock cycle due to the temperature higher than the melting point of the silicon. Keywords: Coating, Oxidation protection, Atmospheric plasma spraying, Thermal shock test