Antioxidation property of a multilayer coating for carbon/carbon composites in a wind tunnel at 1500℃

To protect carbon/carbon (C/C) composites against oxidation at 1500℃ in a wind tunnel, a multilayer coating was prepared on them by a combination of pack cementation, chemical vapor deposition and slurry coating. Xray diffraction, scanning electron microscopy and energy dispersive spectroscopy were used to analyze the phase, microstructure and elemental distribution of the coating. Results show that a threelayer structure is formed including a multiphase MoSi2SiCSi inner layer, a SiC middle layer and a borosilicate glass outer layer with thicknesses of about 80, 20 and 80μm, respectively. The threelayer coating can protect the C/C composites from failure at 1500℃ for 53 h in a wind tunnel. The cracking of the coating by thermal shock and gasfired impact is the main cause for the failure of the coating.