C/SiC composites

Fig. 3. Load—deflection curve for a SiC—C—SiC composite in four-point bending. Note the extreme change in behavior fora composite fabricated with a 0.17-p.m carbon layer between the SiC fiber and the SiC matrix as compared with a composite with no interfacial layer (28).

Fig. 9. Stress-strain curves for 2D-C/SiC composites with different fiber/matrix bonding... 

Fig. 2 The typical tensile-stress/strain curves of the [0/90] plain weave C/SiC composites up to high temperatures... 

The largest commercial production facilities employ the isothermal-isobaric CVl process to produce mostly SiC/SiC or C/SiC composites. The hot zones of these reactors measnre 3 m or larger and can accommodate hundreds of parts. 

High, Si steel fabrication issues Coated materials (Pt) cost issue Ceramics promising, but have fabrication and joining issues Dry wall boiler design with ceramics may be option Data needed with iodine contamination Incoloy 800HT may address intergranular corrosion C—SiC composites should be examined... 

Figure 1.12 Crack deflection and fibre pull-out in 3-D C/SiC composites (a) crack deflection along the interface [60] and (b) fibre pull-out [58]...

According to Equation (5.7) the increase in processing temperature and preform thickness leads to larger values of Valid poor density uniformity. As stated previously, CVI processes preferably operate in a chemical-reaction-controlled regime where the ratio of k/D is small. For Fick diffusion, discussed in Section2.3.1, the diffusivity D is inversely proportional to the pressure and thus operates at lower pressures. Furthermore, coarser pore structures correspond to more uniform deposition. Figure 5.5 shows the microstructures of C/SiC composites prepared at different 9 numbers. 

Figure 5.10 shows the microstructure of a pyrocarbon interphase in C/SiC composites. 

Figure 5.11 shows the typical failure behaviour of 3-D C/SiC composites, which is quite different from that of monolithic ceramics. The present composite materials exhibit a non-catastrophic failure behaviour and a remarkable failure displacement of around 1.2 mm. 

Figure 5.11. Fracture behaviour of 3D C/SiC composite from RT to 1600°C [24] (a) stress-displacement curve and (b) fracture surface...

The toughening mechanism of fibre-reinforced ceramic-matrix composites is due to the pull-out phenomenon of the fibre from the matrix. For 3-D C/SiC composites three kinds of pull-out are observed from the fracture, namely the fibre pull-out, the fibre cluster pull-out and the bundle pull-out illustrated in Figure 5.12a, b and c respectively. 

Figure 5.12. Fracture surface of 3D C/SiC composites [24] (a) fibre pull-out, (b) fibre...

The equations for monolithic ceramics together with the experimental results of the notched specimen are used to determine the fracture toughness (represented as KIC) of the 3-D C/SiC composites created with the single edge notched beam (SENB) method. Its value is calculated as 20.3 MPa-m1/2, which is much higher than that of monolithic ceramic materials (3 to 5 MPa-m1/2). It should be noted that... 

Figure 5.14. Failure behaviour of 3-D C/SiC composite sample with a notch [24]...

Instrumented Charpy impact tests on unnotched samples are conducted to determine the energy absorbing capability and dynamic fracture behaviour of the C/SiC composites. The dynamic fracture toughness (ak) is calculated using the following equation ... 

Figure 5.35. Structure characteristics of HT-CVI C/SiC composites [51] (a) macro-structure and (b) micro structure...

Figure 5.44. SEM graphs of multilayered matrix composite by P-CVI (a) details of four sequences on a single fibre [23], (b) fracture surface of 2.5-D C/SiC composite [59], (c) fracture surface of a single fibre [59]...

Tang SF, Deng JY, Wang SJ, Liu WC (2007) Fabrication and characterization of C/SiC composites with large thickness, high density and near-stoichiometric matrix by heaterless chemical vapor infiltration. Mater Sci Eng A465 290-294... 

Tang SF, Deng JJ, Du HF, Liu WC, Yang K (2005) Fabrication and micro structure of C/SiC composites using a novel heaterless chemical vapor infiltration technique. J Am Ceram Soc 88 3253-3255... 

Both columnar and equiaxed microstructures are obtained from polycrystal growth. Columnar micro structure is composed of columnar grains of preferred orientation that grow from the first nucleated location on a substrate surface. The microstructure is attributed to high supersaturation and low temperature and hence more limited diffusion. A columnar microstructure is suitable for high-temperature structural applications, such as thermal barrier coatings. Figure 6.6 shows the typical columnar CVD SiC microstructure in C/SiC composites. 

NONDESTRUCTIVE TESTING OF DEFECT IN A C/SiC COMPOSITE Hui Mei, Xiaodong Deng, and Laifei Cheng... 

This paper highlighted the recent efforts to apply three NDT methods, i.e., the infrared thermography. X-ray radiography, and industrial computed tomography (CT), to detect the blind holes in a C/SiC composite panel, and then to evaluate the abilities of these used NDT techniques for detecting the artificial defects. 

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