Microstructure, tensile strength and thermostability of W-core SiC fibers with or without carbon coating

SiC fibers with carbon coating (SiC/C fiber) were prepared by three-stage chemical vapor deposition on W filament. In order to determine their thermal stability, tensile test was then performed after thermal exposure at 900 °C and 1000 °C in vacuum. The microstructure and chemical composition of the fibers were investigated by scanning electron microscopy, transmission electron microscopy and electron probe microanalysis, respectively. The results show that the average room-temperature strength of the 900 °C thermally-exposed SiC/C fiber had little loss in comparison with the as-prepared fibers, while a notable strength degradation occurred for the fiber after 1000 °C thermal exposure. The degradation of the tensile strength is due to the growth of W/SiC interfacial reaction layer and the coarsening of SiC grains in the SiC-2-I zone. In addition, the formation mechanism of the W/SiC interfacial reaction zone and its microstructure evolution were also discussed.