Abstract
Oxidation behavior of boron-containing HfC/SiC nanocomposites (SHBC) at temperatures up to 1500 °C and with exposure time up to 100 h was investigated. Two strategies to improve the oxidation resistance of the HfC/SiC ceramics are proposed. First concept involves the incorporation of a small amount of boron (ca. 0.6 wt.%) into the nanocomposite via a single-source-precursor approach, which contributes significantly to the enhancement of its oxidation resistance. Parabolic oxidation rate constants of 10−3 to 10-4 mg2/(cm4 h) at 1300−1500 °C were measured for SHBC and were several orders of magnitude lower than those recorded for boron-free HfC/SiC. The second improvement concept is realized via passivation of the samples upon short-term oxidation at 1400 °C, providing an excellent oxidation resistance over a wide temperature range. This is a crucial step especially when considering the poor oxidation behavior of HfC and the sluggish formation of protective silica scale at moderate temperatures.
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