Impact of a Subsonic Dissociated Air Flow on the Surface of HfB2–30 vol % SiC UHTC Produced by the Sol–Gel Method

Abstract

A new method, which included the sol–gel synthesis of a HfB₂–(SiO₂–C) reactive composite powder and its subsequent consolidation by hot pressing (1700°C, 30 MPa, 15 min) with simultaneous carbothermic synthesis of nanocrystalline silicon carbide, was used to produce HfB₂–SiC ultra-high-temperature ceramic material promising for using in an air atmosphere at temperatures above 2000°C. Its elemental and phase compositions, as well as its microstructure were investigated. The density and calculated porosity were 7.6 g/cm³ and 13.5%, respectively. The behavior of a cylindrical sample of the material was studied on long-term (40 min) exposure to a subsonic dissociated air flow in a high-frequency induction plasmatron. The change in the temperature of the surface of the material was examined in the context of its relationship with the HfB₂ and SiC oxidation and the evaporation of the oxidation products. The phase composition and microstructure were determined in regions of the oxidized surface of a HfB₂–SiC sample containing 30 vol % SiC that were heated on exposure to high-enthalpy flows to 2600–2700°C and in regions the temperature of which was 1850–1950°C. By scanning electron microscopy, the thickness, microstructure, and composition of the oxidized layer were found.