312 International Journal of Applied Ceramic Technolog-Liut, et al. Vol.8,No.2,2011 Sample B carbon fiber 0.00,2040608101 150kv128mn Fig 3. The load-displacement curves of the three kinds of chieved a flexural strength of 530, 117, and 504 MPa, and a fracture toughness of 17.5, 3.3, and 18.6 Mpa" respectively. The elastic modulus of SiC fiber(270 GPa) was higher than that of the carbon fiber(230 GPa)and the matrix porosity of sample a was smaller than those of samples B and C. As a result, the fexural modulus of sample A was 96GPa, much higher than those of sample arbon fiber B(66 GPa)and sample C Typical failure curves of three kinds of composites are shown in Fig 3. The Flexural curve of sample A was similar to that of SiC/Py C/SiC composite& The flexural 15owV 13.6mm x200 SE/(M) curve of sample A showed an initially linear elastic be- havior and then a nonlinear beh avioN th there existed debonding and sliding at the fiber/matrix nterphase zone, which led to the pullout of fibers However, there was no nonlinear stage in the fexural curve of sample B, which exhibited a brittle fracture behavior like monolithic ceramics, indicating that no debonding and sliding occurred at the interphase zone Flexural load-displacement curve of sample C showed early linear behavior with the increasing load, and then a noncatastrophic failure behavior was observed after the maximum loa nd 4 shows the fexural fracture surface mor phologies of three kinds of composites In sample A, SiC 15.0 fibers showed apparent pullout in the fiber bundle, while carbon fibers showed no pullout, as shown in Fig. 4a. These fracture features indicated that PyC works flexural fracture surface morphologies of three kinds of composites. (a) sample A showing SiC fibers were pulled out and no carbon on SiC fibers and not on carbon fibers. As a result, the fibers were pulled out;:(b)sample B showing no carbon fibers debonding and sliding of Py C interphase mainly occurred were pulled out; and(c)sample C showing carbon fibers were between SiC fiber and SiC matrix In sample B, the frac- pulled out. ture morphology of carbon fiber bundles was fat,achieved a flexural strength of 530, 117, and 504 MPa, and a fracture toughness of 17.5, 3.3, and 18.6Mpa m1/2, respectively. The elastic modulus of SiC fiber (270 GPa) was higher than that of the carbon fiber (230 GPa) and the matrix porosity of sample A was smaller than those of samples B and C. As a result, the flexural modulus of sample A was 96 GPa, much higher than those of sample B (66 GPa) and sample C (64 GPa). Typical failure curves of three kinds of composites are shown in Fig. 3. The flexural curve of sample A was similar to that of SiC/PyC/SiC composite.8 The flexural curve of sample A showed an initially linear elastic be￾havior and then a nonlinear behavior, indicating that there existed debonding and sliding at the fiber/matrix interphase zone, which led to the pullout of fibers. However, there was no nonlinear stage in the flexural curve of sample B, which exhibited a brittle fracture behavior like monolithic ceramics, indicating that no debonding and sliding occurred at the interphase zone. Flexural load-displacement curve of sample C showed nearly linear behavior with the increasing load, and then a noncatastrophic failure behavior was observed after the maximum load. Figure 4 shows the flexural fracture surface mor￾phologies of three kinds of composites. In sample A, SiC fibers showed apparent pullout in the fiber bundle, while carbon fibers showed no pullout, as shown in Fig. 4a. These fracture features indicated that PyC works on SiC fibers and not on carbon fibers. As a result, the debonding and sliding of PyC interphase mainly occurred between SiC fiber and SiC matrix. In sample B, the frac￾ture morphology of carbon fiber bundles was flat, as Fig. 3. The load–displacement curves of the three kinds of composites. a b c SiC fiber carbon fiber carbon fiber carbon fiber Fig. 4. Scanning electron microscopic (SEM) images of the flexural fracture surface morphologies of three kinds of composites: (a) sample A showing SiC fibers were pulled out and no carbon fibers were pulled out; (b) sample B showing no carbon fibers were pulled out; and (c) sample C showing carbon fibers were pulled out. 312 International Journal of Applied Ceramic Technology—Liu, et al. Vol. 8, No. 2, 2011