Effect of SiC Whiskers on Properties of SiC Coating for Carbon/carbon Composites

摘要

Using SiC whiskers as the reinforcement materials, a kind of whisker-toughened SiC coating (SiCw-toughened SiC coating) was produced on the surface of carbon/carbon (C/C) composites by pack cementation technique. SEM and XRD were adopted to analyze the microstructure and phase composition of as-prepared coating. The thickness and hardness of the as-coated C/C composites were tested by Vickers Sclerometer. The thermal expansion coefficient of the coated C/C composites was analyzed by TMA thermal mechanical analyzer. The oxidation test of SiCw-toughened SiC coated C/C was also carried out in air at 1573K. The results show that SiC whiskers can efficiently decrease the size and frequency of cracks in coating after adding SiC whiskers in SiC coating. The thickness of SiCw-toughened SiC coating is 134am, while that of SiC coating is up to 164μm. After adding SiCw in SiC coating, the hardness of the coated C/C composites increases, which is 1497kg/mm2. The thermal expansion coefficient of the as-coated C/C composites is 1.55×10-6/K from 532K to 703K and is 1.92×10-6/K from 713K to 873K. While the thermal expansion coefficient of C/C composites coated SiC coating without SiC whiskers is 1.91×10-6/K from 532K to 873K. Moreover, the oxidation protective ability of SiC coating can be improved by the introduction of SiCw. The as-prepared SiCw-toughened SiC coating can protect C/C composites from oxidation at 1573K in air for 21h and the weight loss is 8%, but the weight loss of SiC coating without SiC whiskers has up to 18% after oxidation for the same time.