Anti-oxidation property of a multi-layer coating for carbon/carbon composites in a wind tunnel at 1500°C

To protect carbon/carbon (C/C) composites against oxidation at 1500°C 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 80 μm, respectively. The three-layer coating can protect the C/C composites from failure at 1500°C 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.