Fabrication of SiCN-Sc2Si2O7 coatings on C/SiC composites at low temperatures

SiCN-Sc2Si2O7 environmental barrier coatings were fabricated on the surface of C/SiC composites at low temperatures by adding Li2CO3 as sintering aids. With this addition, the fabrication temperature could be lowered about 100-200 °C. The shrinkage of the polysilazane-Sc2Si2O7 bars with and without Li2CO3 was tested by dilatometer. The results indicate that the shrinkage speed of the polysilazane-Sc2Si2O7 bar with Li2CO3 is faster than the one without Li2CO3, indicating that the Li2CO3 greatly promotes the sintering of polysilazane-Sc2Si2O7. Water-vapor corrosion behavior of the SiCN-Sc2Si2O7 coated C/SiC composites was carried out at 1250 °C. The results reveal that the SiCN-Sc2Si2O7 coatings can effectively protect the C/SiC composites. The corrosion resistance of SiCN-Sc2Si2O7 coatings is not degraded by adding Li2CO3.