Abstract
The oxidation behaviour of HfB 2 –SiC monoliths and coatings has been studied in the 20– 1700 ∘ C temperature range in flowing O 2 /He mixtures ( P tot =1 bar, PO 2 = 1 –200 mbar). Two overlapping domains of oxidation were identified corresponding, respectively, to the reaction of HfB 2 and an intermediate phase containing Hf/Si/B/C in the 600– 800 ∘ C temperature range and SiC nanoparticles in the 800– 1000 ∘ C interval. A protective borosilicate glass is quickly formed at low temperature. The good oxidation resistance up to 1700 ∘ C and under low oxygen partial pressure (10 mbar) is discussed according to the degradation mechanisms involving compositional and microstructural changes and compared to previous results obtained on hot pressed HfB 2 –SiC composites. The specific microstructure of the materials studied in this work is of great importance for the composition of the protective glassy phase and leads to the formation of a refractory glass containing hafnium.
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