H Liu et aL/ Materials Science and Engineering A 525(2009)121-127 Fiber Fig 8. TEM cross-sectional images of the KD-1 SiC/SiC composite the strong chemical interfacial bonding and serious chemical dam- and FM debonding also cannot take place within the silicon-based age to fibers From Fig 2c and d, it can be found that the surface of oxide interphase. Consequently the desired mechanical reinfore <D-2 SiC fibers is relatively rough, which would lead to the strong ing mechanisms such as fiber pullout and fm debonding are not physical interfacial bonding: at the same time, the defects on the available, and a brittle fracture behavior occurs in the KD-2 SiC/Sic D-2 SiC fibers can result in a large stress concentration, and the composite. larger stress may fracture the Sic fiber during composite process- Schematic representations of the interphase structures ing (as shown in Fig. 10), which causes physical damage to Sic matrix crack propagation paths in the KD-1(Fig. 11a) and fibers. Therefore, the strong interfacial bonding and fiber damage(Fig. 11b)SiCr/SiC composites are described in Fig. 11, which cause undesirable interfacial stress. fiber fracture. and low in situ trate the effects of fiber surface characteristics on the interfacial ber strength, respectively. It is well known that the silicon-based microstructure and mechanical properties of the Kd Sic/Sic com- oxide is not a layered crystal structure, so that the crack deflection posites. Interp M 10 Fig 9. TEM images of the interphase in the KD-2 SiC/SiC composite(a-c)and the carbon elemental mapping ofc(d).H. Liu et al. / Materials Science and Engineering A 525 (2009) 121–127 125 Fig. 8. TEM cross-sectional images of the KD-1 SiCf/SiC composite. the strong chemical interfacial bonding and serious chemical dam￾age to fibers. From Fig. 2c and d, it can be found that the surface of KD-2 SiC fibers is relatively rough, which would lead to the strong physical interfacial bonding; at the same time, the defects on the KD-2 SiC fibers can result in a large stress concentration, and the larger stress may fracture the SiC fiber during composite process￾ing (as shown in Fig. 10), which causes physical damage to SiC fibers. Therefore, the strong interfacial bonding and fiber damage cause undesirable interfacial stress, fiber fracture, and low in situ fiber strength, respectively. It is well known that the silicon-based oxide is not a layered crystal structure, so that the crack deflection and FM debonding also cannot take place within the silicon-based oxide interphase. Consequently, the desired mechanical reinforc￾ing mechanisms such as fiber pullout and FM debonding are not available, and a brittle fracture behavior occurs in the KD-2 SiCf/SiC composite. Schematic representations of the interphase structures and matrix crack propagation paths in the KD-1 (Fig. 11a) and KD-2 (Fig. 11b) SiCf/SiC composites are described in Fig. 11, which illus￾trate the effects of fiber surface characteristics on the interfacial microstructure and mechanical properties of the KD SiCf/SiC com￾posites. Fig. 9. TEM images of the interphase in the KD-2 SiCf/SiC composite (a–c) and the carbon elemental mapping of ‘c’ (d)