SiC/Si–ZrSi2–ZrB2-HfB2/SiC coating for oxidation protection of C/C composites prepared by three-step method

Abstract

Abstract In this paper, a SiC/Si–ZrSi2–ZrB2-HfB2/SiC coating was designed, including a SiC inner layer, a middle self-healing layer and a SiC outer layer, and prepared for C/C composites by three-step method. The SiC inner layer was prepared by chemical vapor deposition, while the middle self-healing layer containing Si, ZrSi2, ZrB2 and HfB2 was prepared by a novel method combining brushing-sintering with pre-oxidation treatment. After pre-oxidation of the self-healing layer at 1300 °C for 1.5 h, the SiC outer layer was applied by chemical vapor deposition (CVD). The phase compositions, surface morphologies and element distributions of the coating were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. The oxidation tests demonstrated that the coating has good oxidation resistance attributed to the dense structure of the middle self-healing layer and the synergistic effects among three layers. After exposure to air at 1100 °C for 210 h, 1200 °C for 165 h, and 1300 °C for 120 h, the weight loss of the coated composites was 0.76%, 0.84% and 1.25%, respectively. After 50 times of thermal cycling oxidation from 1300 °C to room temperature, the weight loss of the coated composites was 0.19%.