Effect of pack cementation temperatures on component, microstructure and anti-oxidation performance of Al-modified SiC coatings on C/C composites

SiC coatings doped with Al were synthesized on the C/C composites using the pack cementation technique. We explored the microstructure, composition, as well as anti-oxidation performance of Al-doped SiC coatings with different preparation temperatures (1500-2100 degrees C). The results prove that the coatings prepared at 1500-1900 degrees C are discontinuous 3C-SiC/2H-SiC/C/Si/Al2O3 coatings with some holes and micro-cracks, while the coating prepared at 2100 degrees C is Al atoms dissolved 4H-SiC coating with inconspicuous cracks and a loose and porous surface structure. And the coating thickness and oxidation resistances are enhanced with increasing the pack cementation temperatures. Besides, the oxygen diffusion via the coating's invisible microdefects is the leading cause of the coating's oxidation produced at 2100 degrees C. The coating gained at 2100 degrees C shows the best antioxidation properties owing to the in situ formed Al2O3 as well as SiO2 oxide layer on their surface.