H Liu et aL/ Materials Science and Engineering A 525(2009)121-127 KD.2 0100200300400500600700800 Binding energy/ev Fig 4. Raman spectra of KD-1 and KD-2 SiC fibers D-2 KD-1 Binding energy/ev Fig 3. Survey XPS spectra of KD-1 and KD-2 SiC fibers (a)and the Si 2p spectrum of KD-2 SiC fibers(b). Fig. 5. XRD patterns of KD-1 and KD-2 SiC fibers. 4 Raman spectra of KD-1 and KD-2 SiC fibers are shown in Fig 4 he Raman spectrum of KD-1SiC fibers, only carbon spectra con- The broad bands around a 20 value of 35.7 in KD-1 and KD-2Sic sisting of broad peaks at about 1350 and 1600 are detected which are assigned to the sp and sp 2 bonded carbon respectively fibers are attributed to p-Sic[24] For KD-2 SiC fibers, besides the typical d and G bands assigned to carbon, a peak at about 1150 is detected, which may be due 3. 2. Mechanical properties of the KD Sicy/SiC composites to the disordered and hydrogenated sp bonded carbon [21, 22).A peak detected at about 1030cm-I should be assigned to the Si-o-Si The properties of the KD-1 and KD-2 SiC /Sic composites are symmetric stretching vibration bands, which are due to Si-o-Si shown in Table 2. It can be seen that the density and porosity of linkages in a network structure having a smaller bond angle [23]. the two composites are nearly the same, but the flexural strength In Fig 4, no Sic spectra( mainly consisting of peaks around 796 and of the KD-1 Sicr/SiC composite is about 7 times that of the KD-2 972cm-l)were detected. That is because the Raman scattering effi- SiCr/SiC composite. The load /displacement curves of the two com- ciency of carbon is at least ten times that of Sic [21 whereas the posites are represented in Fig. 6. It is observed that the KD-2 SiCr/Sic enetration depth of the laser beam in SiC fibers can reach about composite shows a standard brittle fracture behavior, but the KD-1 0.1 um. The lack of Sic spectra is due to the carbon excess of Kd Sic SiC/Sic composite exhibits a toughened fracture behavior, and fails bers(see Table 1). So, it can be concluded that KD-1 and KD-2 SiC fibers have PyC and silicon-based oxide surface layers respectively, Table 2 which are in agreement with the results of the XPs analysi Properties of the KD-1 and KD-2 SiC/SiC composites. XRD patterns of KD-1 and KD-2 SiC fibers are represented in Fig. 5. No obvious XRD peaks are observed, which show that both Composites Density (gcm-) Porosity(%) Flexural strength(MPa) KD-1 and KD-2 SiC fibers are amorphous structures, and the PyCand KD-1 silicon-based oxide surface layers are also noncrystalline structures.H. Liu et al. / Materials Science and Engineering A 525 (2009) 121–127 123 Fig. 3. Survey XPS spectra of KD-1 and KD-2 SiC fibers (a) and the Si 2p spectrum of KD-2 SiC fibers (b). Raman spectra of KD-1 and KD-2 SiC fibers are shown in Fig. 4. In the Raman spectrum of KD-1 SiC fibers, only carbon spectra con￾sisting of broad peaks at about 1350 and 1600 cm−1 are detected, which are assigned to the sp3 and sp2 bonded carbon respectively. For KD-2 SiC fibers, besides the typical D and G bands assigned to carbon, a peak at about 1150 cm−1 is detected, which may be due to the disordered and hydrogenated sp3 bonded carbon [21,22]. A peak detected at about 1030 cm−1 should be assigned to the Si–O–Si asymmetric stretching vibration bands, which are due to Si–O–Si linkages in a network structure having a smaller bond angle [23]. In Fig. 4, no SiC spectra (mainly consisting of peaks around 796 and 972 cm−1) were detected. That is because the Raman scattering effi- ciency of carbon is at least ten times that of SiC [21], whereas the penetration depth of the laser beam in SiC fibers can reach about 0.1 m. The lack of SiC spectra is due to the carbon excess of KD SiC fibers (see Table 1). So, it can be concluded that KD-1 and KD-2 SiC fibers have PyC and silicon-based oxide surface layers respectively, which are in agreement with the results of the XPS analysis. XRD patterns of KD-1 and KD-2 SiC fibers are represented in Fig. 5. No obvious XRD peaks are observed, which show that both KD-1 and KD-2 SiC fibers are amorphous structures, and the PyC and silicon-based oxide surface layers are also noncrystalline structures. Fig. 4. Raman spectra of KD-1 and KD-2 SiC fibers. Fig. 5. XRD patterns of KD-1 and KD-2 SiC fibers. The broad bands around a 2 value of 35.7◦ in KD-1 and KD-2 SiC fibers are attributed to -SiC [24]. 3.2. Mechanical properties of the KD SiCf/SiC composites The properties of the KD-1 and KD-2 SiCf/SiC composites are shown in Table 2. It can be seen that the density and porosity of the two composites are nearly the same, but the flexural strength of the KD-1 SiCf/SiC composite is about 7 times that of the KD-2 SiCf/SiC composite. The load/displacement curves of the two com￾posites are represented in Fig. 6. It is observed that the KD-2 SiCf/SiC composite shows a standard brittle fracture behavior, but the KD-1 SiCf/SiC composite exhibits a toughened fracture behavior, and fails Table 2 Properties of the KD-1 and KD-2 SiCf/SiC composites. Composites Density (g cm−3) Porosity (%) Flexural strength (MPa) KD-1 2.04 18.4 211.7 KD-2 2.06 17.6 30.5