Oxidation Resistance of the ZrSi2–MoSi2–ZrB2–ZrC Coating on the C/C–SiC Composite in High-Speed High-Enthalpy Air Plasma Flow

Abstract

The oxidation resistance of a coating, which is formed by firing deposition of layers from a ZrSi₂–MoSi₂–ZrB₂–Si powder mixture, on a C/C–SiC composite substrate is studied. Oxidation resistance tests are carried out under interaction with a high-speed air plasma flow at temperatures up to 2200°C. The performance of the coating is ensured by the formation (and evolution during operation) of a heterogeneous oxide film based on borosilicate glass modified with zirconium, which is an efficient barrier to oxygen diffusion and promotes the passivation of oxidation processes. An increase in the operating temperatures above 1750–1800°C leads to glass phase evaporation from the surface and the formation of a porous thermal barrier layer based on ZrO₂ and containing secondary phases Mo/MoO₂, Mo₃Si, and Mo₅Si₃. The temperature gradient across the coating thickness favors partial preservation of the glass phase in the inner layers due to a decrease in the vapor pressure, which results in the retardation of oxygen diffusion deep into the material. The temperature–time ranges of performance; the characteristics of mass loss, catalytic activity, and emissivity of the coating; and the main factors limiting the efficiency of its protective action are determined.