Abstract
The thermal and mechanical stability of SiC fibers at elevated temperature is an important property for the practical application of SiC fiber-reinforced ceramic matrix composites and is related to the heat-treating atmosphere. In this study, the high-temperature behavior of KD SiC fibers with low oxygen content was investigated in both Ar and N2 at temperatures from 1400 to 1800 °C through scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Auger electron spectroscopy, resistivity measurements, and tensile tests in order to understand the effects of atmospheres on the degradation of the fibers. The results show that high-temperature treatment caused more severe strength degradation in Ar than in N2. In particular, the fibers heat treated in N2 at 1700 °C retained a relatively high strength of 1.52 GPa, 60 % of their original strength, while the fiber strength was completely lost after heat treatment in Ar. Fiber strength degradation was mainly caused by a combination of crystal growth and surface flaws. The formation of huge grains and porosity in the fiber surfaces, owing to the thermal decomposition of the SiC x O y N z and SiC x O y phases, significantly degraded the strength for fibers heat treated in Ar. However, the suppressing effect of N2 on the decomposition of the SiC x O y N z phase in the fiber surfaces and nitrided case on the decomposition of the SiC x O y phase in the fiber cores, led to higher SiC fiber temperature stability in N2 rather than Ar.
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Acknowledgements
This work is supported by the National Natural Science Foundation of China (Grant Nos. 51172280 and 51403233), the Aid Program for Science and Technology Innovation Research Team in Higher Educational Institution of Hunan Province, and the Aid Program for Innovation Group of National University of Defense Technology.
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Cao, S., Wang, J. & Wang, H. High-temperature behavior and degradation mechanism of SiC fibers annealed in Ar and N2 atmospheres. J Mater Sci 51, 4650–4659 (2016). https://doi.org/10.1007/s10853-016-9780-3
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DOI: https://doi.org/10.1007/s10853-016-9780-3