Abstract
Carbon-carbon composites have been prepared with and without addition of 15 wt% of the glass-forming oxidation inhibitors boron and zirconium diboride. Samples of the composites carbonised at 850°C were further heat treated over a range of heat-treatment temperatures to 2650°C. Mechanical properties of the heat-treated composites were measured by 3-point bend testing and their oxidation behaviour at 850°C in air determined by TGA. The mechanical properties of composites without inhibitor additives were unaffected by heat treatment to 2250°C. However, at 2650°C strength and modulus were reduced. Composites containing inhibitors exhibited reduced mechanical properties on heat treatment above their carbonisation temperature, with the most marked reduction above 2300°C. Scanning electron microscopy showed that at temperatures above 2320°C with boron and 2330°C with ZrB 2 the carbonaceous-composite components reacted with the inhibitors, probably forming carbides. The oxidation resistance of composites without inhibitors and those containing ZrB 2 increased with increasing heat-treatment temperature to a maximum at 2250°C before decreasing at 2650°C. Boron appeared the most effective oxidation inhibitor. The oxidation behaviour of the inhibitor-loaded composites appeared unaffected by the reaction of the carbonaceous-composite components and the inhibitors at temperatures above 2320°C.
Published Version
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