w. Yang et al. Materials Science and Engineering 4345(2003)28-35 Table 2 The fabricated Tyranno-SA/SiC composites pecten L D Interlayer structure and thickness(nm) Fiber volume fraction (% Density(Mg m) Porosity (% T-NL 2.78(0.01) T-C50 F/CSO(/M TC200 423343 2.61(0.03) F/SiCSO23)/CSOIS)/M 2.58(0.04) 16.4 SiC/C150 F/SC15025C15028M 2.370.05) -a Included in the parenthesis are the standard deviations. The standard deviations of the thickness of interlayers were obtained using a same method as described in Ref. [18] examinations of other interlayered composites also bonding and crack deflection had occurred at SiC/PyC confirmed successful deposition of the interlayers with interface or at the matrix/PyC interface for the former quite well through-thickness uniformity, as indicated while at the fiber surface for the latter before the failure Table 2. Composites T-C50 and T-SiC/C150 showed of the composites. Therefore, it is likely that a first Sic lower densities compared with the others, resulting in layer on the fiber is able to control the interfacial the porosities over 20% debonding to occur within the SiC/PyC interlayers or at the matrix/PyC interface, rather than at the fib 3.2. Fracture behaviors surface. For composites T-C50 and T-SiC/C150, sig- nificant inter-fabric layers delaminating occurred during the bending tests, as indicated by the large inter-fabric Transverse cracks initiated at the tensile surfaces of e s ens from composite T-NL and propagated layers pores in Fig 4(composite T-C50) almost vertically to the compression surfaces. SEM Typical load-displacement curves of the composites fracture surface examination revealed a smooth and are shown in Fig. 5. Composite T-NL exhibited low load flat fracture surface. with no evidence of fiber/matrix fiber/matrix maximum and displayed brittle failure mode, with no signs of toughening. This is in consistent with the flat debonding and fiber pullout. Multiple deflection or fracture surface. Improved toughness was indicated in transverse cracks occurred in the PyC or SiC/PyC layered composites. Fig. 2 shows the transverse crack the curves for the interlayered composites. Both the load propagation behaviors in composite T-C100. Cracks maximums and displacement at load maximums were nitiated at both tensile and compression surfaces. The increased. Initially, the load increased linearly with the main crack initiated at tensile surface and was multi- increasing of displacement, reflecting the elastic re- deflected by the 0/90 fiber bundles. Fiber pullouts were ponse of the composites. Deviation of the curves to observed at the fracture surface as shown in Fig 3(a and the linearity occurred at certain loads, followed by a b). Similar fracture behaviors were observed with nonlinear domain of deformation until the load max composites T-C200 and T-SiC/C80. Fig. 3(c and imum, due mainly to the matrix cracking, interfacial show the fracture surface and fiber pullouts of compo- debonding and fibe ng, and individual fiber fail site T-SiC/C80. It is seen from Fig 3(b and d) that the ures. Finally, the composites failed owing to the failures interlayer(s)was pulled out together with the debonded of the fibers. Some differences of the load maximums are fibers for composite T-SiC/C80, while no PyC layer demonstrated by the various composites Composite T flake was found attaching on the pulled out fibers for C100 yielded the highest load maximum at a displace- composite T-C100. This indicates that interfacial de- ment up to -0.18 mm (a)T-C200 Matrix Fig. 1. SEM images of the interlayers in composites: (a)T-C200: and (b)T-SiC/C150.examinations of other interlayered composites also confirmed successful deposition of the interlayers with quite well through-thickness uniformity, as indicated in Table 2. Composites T-C50 and T-SiC/C150 showed lower densities compared with the others, resulting in the porosities over 20%. 3.2. Fracture behaviors Transverse cracks initiated at the tensile surfaces of the specimens from composite T-NL and propagated almost vertically to the compression surfaces. SEM fracture surface examination revealed a smooth and flat fracture surface, with no evidence of fiber/matrix debonding and fiber pullout. Multiple deflection of transverse cracks occurred in the PyC or SiC/PyC layered composites. Fig. 2 shows the transverse crack propagation behaviors in composite T-C100. Cracks initiated at both tensile and compression surfaces. The main crack initiated at tensile surface and was multi￾deflected by the 0/908 fiber bundles. Fiber pullouts were observed at the fracture surface as shown in Fig. 3(a and b). Similar fracture behaviors were observed with composites T-C200 and T-SiC/C80. Fig. 3(c and d) show the fracture surface and fiber pullouts of compo￾site T-SiC/C80. It is seen from Fig. 3(b and d) that the interlayer(s) was pulled out together with the debonded fibers for composite T-SiC/C80, while no PyC layer flake was found attaching on the pulled out fibers for composite T-C100. This indicates that interfacial de￾bonding and crack deflection had occurred at SiC/PyC interface or at the matrix/PyC interface for the former while at the fiber surface for the latter before the failure of the composites. Therefore, it is likely that a first SiC layer on the fiber is able to control the interfacial debonding to occur within the SiC/PyC interlayers or at the matrix/PyC interface, rather than at the fiber surface. For composites T-C50 and T-SiC/C150, sig￾nificant inter-fabric layers delaminating occurred during the bending tests, as indicated by the large inter-fabric layers pores in Fig. 4 (composite T-C50). Typical load/displacement curves of the composites are shown in Fig. 5. Composite T-NL exhibited low load maximum and displayed brittle failure mode, with no signs of toughening. This is in consistent with the flat fracture surface. Improved toughness was indicated in the curves for the interlayered composites. Both the load maximums and displacement at load maximums were increased. Initially, the load increased linearly with the increasing of displacement, reflecting the elastic re￾sponse of the composites. Deviation of the curves to the linearity occurred at certain loads, followed by a nonlinear domain of deformation until the load max￾imum, due mainly to the matrix cracking, interfacial debonding and fiber sliding, and individual fiber fail￾ures. Finally, the composites failed owing to the failures of the fibers. Some differences of the load maximums are demonstrated by the various composites. Composite T￾C100 yielded the highest load maximum at a displace￾ment up to
/0.18 mm. Table 2 The fabricated Tyranno-SA/SiC composites Specimen I.D. Interlayer structure and thickness (nm)a Fiber volume fraction (%) Density (Mg m3 ) a Porosity (%) T-NL F/M 44 2.78(0.01) 10.6 T-C50 F/C50(8)/M 42 2.41(0.03) 20.4 T-C100 F/C100(19)/M 43 2.63(0.04) 15.1 T-C200 F/C200(34)/M 43 2.61(0.03) 14.6 T-SiC/C80 F/SiC150(23)/C80(15)/M 44 2.58(0.04) 16.4 T-SiC/C150 F/SiC150(25)/C150(28)/M 43 2.37(0.05) 21.8 a Included in the parenthesis are the standard deviations. The standard deviations of the thickness of interlayers were obtained using a same method as described in Ref. [18]. Fig. 1. SEM images of the interlayers in composites: (a) T-C200; and (b) T-SiC/C150. 30 W. Yang et al. / Materials Science and Engineering A345 (2003) 28 /35