HfB₂-SiC ceramics fabricated by reactive melt infiltration and its long-term oxidation behavior at 1650°C

High-density HfB₂-SiC ceramics were prepared by reactive melt infiltration (RMI) at a relatively low temperature (1500°C). The ceramics had the open porosity of 0.5 % and the uniform distribution of constituent phases. The long-term oxidation behavior of HfB₂-SiC ceramics in air was investigated at 1650°C. After oxidation for 100 h, the weight gain rates of ceramics varied within the range of 1.30–2.26 %. The oxidation products included SiO₂, HfO₂, and HfSiO₄ phases, among which the HfSiO₄ compound possessed the higher stability resulting from the reaction between the HfO₂ and SiO₂ phases. The samples all exhibited the typical feature of layered scale structure after HfB₂-SiC oxidation, which was composed of the outermost SiO₂ glass layer with the uneven thickness, followed by a relatively porous oxide layer containing white HfO₂ and slight HfSiO₄, below it was the unoxidized HfB₂-SiC. The presence of this multiphase glass layer endowed the samples with excellent oxidation resistance.