Improvement of film boiling chemical vapor infiltration process for fabrication of large size C/C composite

State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China
Materials Letters (Impact Factor: 2.49). 05/2006; 60(9):1269-1272. DOI: 10.1016/j.matlet.2005.11.012


An improved film boiling chemical vapor infiltration process was developed to fabricate a large size C/C composite with homogeneous density and microstructure. The C/C composite was prepared by processing a disc-shaped carbon felt preform, whose upper and lower sides were fixed and heated simultaneously by two flat surfaces of two heat sources, with kerosene as a precursor at 1050 °C for 3 h at an atmospheric pressure. The in-situ temperature distribution along the radial direction of the preform upper surface was analyzed to get better information and control of the process. Experimental results show that the average density of the composite of Φ 110×10 mm3 size is about 1.72 g/cm3 and its maximal difference along radial direction is 0.05 g/cm3. Polarized light microscopy (PLM) and scanning electron microscopy (SEM) reveal that the carbon fibers of the composite are surrounded by ring-shaped pyrocarbons with a thickness of ∼20 μm, and that pyrocarbons are delaminated to 4–6 layers. A schematic model is proposed to analyze the process by dividing the reactor into different regions associated with specific functions.

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    • "In this paper, by choosing kerosene as precursor, C/C composites were successfully fabricated by CVI with an improved device developed by us as shown in Section 2. The size of composites was much larger than that of samples reported by Wang et al. [6] and Ji et al. [12], which is important to extend their engineering applications especially in civil field such as brake discs for racing cars and fast trains. Moreover, several pieces of samples can be densified simultaneously. "
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    ABSTRACT: C/SiC composites were prepared by joint processes of chemical liquid–vapor deposition (CLVD) for 3h and Precursor Infiltration and Pyrolysis (PIP) for 5cycles, with a density of 1.97g/cm3, a flexural strength of 297±26MPa and a preparation period of only 10days. CLVD process combines the advantages of both continual vapor deposition of chemical vapor infiltration process and high liquid infiltration efficiency of PIP process, thus in 3h the composite reaches a density of 1.75g/cm3. SiC matrix in CLVD process prefers to deposit into small pores in bundles, while in PIP process into large pores between bundles and layers, thus a homogeneous structure is quickly obtained by joint processes. Furthermore the composite by CLVD process usually shows density gradient during the deposition front propagation, and post PIP process which is not sensitive with thickness, makes up this drawback.
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