Preparation of a Gradient Anti-Oxidation Coating for Aircraft C/C Composite Brake Disc and Its High-Temperature In Situ Self-Healing Performance.

We studied a gradient anti-oxidation coating of C/C composite materials for aircraft brake discs with a simple process and low costs. The gradient coating consists of two layers, of which the inner layer is prepared with tetraethyl orthosilicate (Si (OC2H5)4), C 2 H 5 OH, H 3 PO 4 and B 4 C, and the outer layer is prepared with Na 2 B 4 O 7 .10H 2 O, B 2 O 3 , and SiO 2 powder. The experimental results show that after being oxidized at 700 °C for 15 h, the oxidation weight loss of the sample with the coating was only -0.17%. At the same time, after 50 thermal cycles in air at 900 °C, the sample's oxidation weight loss was only -0.06%. We conducted the 1:1 dynamic simulation test for aircraft brake discs, and the brake disc did not oxidize, thus meeting the requirements for aircraft use. In addition, the anti-oxidation mechanism of the coating was analyzed via scanning electron microscopy (SEM), X-ray diffraction (XRD), differential thermal analysis (DSC-TGA), and high-temperature in situ SEM.