Fabrication and oxidation resistant behavior of plasma sprayed Si/Yb2Si2O7/LaMgAl11O19 coating for Cf/SiC composites at 1673Â K

Cf/SiC composites were plasma sprayed with Yb2Si2O7/LaMgAl11O19 coatings with and without Si bond layer. Microstructure and oxidation protection of the coatings at 1673 K were investigated. The results showed that the coatings have the same phase constituent as that of the powders and uniformly distributed on the substrate. The bonding interface between the coating and substrate with Si bond layer is better than that of without Si bond layer. After 15 cycles of heating at 1673 K for 90 min, the weight losses of the coated samples with and without Si bond layer were 2.54% and 21.89%, respectively, however, for the uncoated sample, its weight loss was up to 36.47%. To certain extent, the Si bond layer efficiently healed the porosity on the surface of substrate and relieved the mismatch of coefficient of thermal expansion (CTE) between the coating and substrate, and therefore significantly improved the oxidation protection of the coating. The difference of CTEs between the coating and substrate, the chemical reactions between the LaMgAl11O19 and Yb2Si2O7 layers and the holes and cracks inside Cf/SiC composites were disadvantageous to the oxidation resistance of the coatings.