Preparation and antioxidant mechanism of TiSi2–Si–SiC/SiC bilayer coating on matrix graphite

Abstract

A two-step pack cementation technique was applied to synthesize the TiSi2–Si–SiC/SiC bilayer coating on the surface of graphite spheres for improving its antioxidant performance. Then, an investigation was conducted into the microstructure, phase composition, formation mechanism, and the isothermal oxidation behavior in static air of the coating. According to the research results, the coating consists of an internal SiC layer and an external TiSi2–Si–SiC layer. In the external layer, the gap between SiC particles filled with Si phase ensures the sufficient compactness of the as-prepared coating, while the small TiSi2 particles are embedded in SiC particles. In the oxidizing environment, TiSi2 is preferentially oxidized to reduce the consumption of SiC, thus ensuring the stability of the coating. The structure of the external layer is capable to ensure the excellent antioxidant performance of the coating. After being oxidized in static air at 1500 °C for 200 h, the weight gain of the coated graphite sphere reached merely 0.96 w.t.% and the thickness of the oxide layer was approximately 20 μm.