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Manufacturing Techniques
Published in Sumit Sharma, Composite Materials, 2021
In gas-phase routes, that is, the so-called chemical vapor infiltration (CVI) process, the reinforcement (usually as a multidirectional preform) is densified by the matrix deposited from a gaseous precursor, for example, a hydrocarbon for carbon or a mixture of methyltrichlorosilane and hydrogen for silicon carbide. There are several versions of the CVI process. It is now well established that a fiber coating, referred to as the interphase, has to be deposited on the fiber prior to the infiltration of the matrix in order to control the fiber–matrix bonding and the mechanical behavior of the composite. CVI is a method of infiltrating fiber architectures with matrix particles via the vapor phase. Although this is a similar process to CVD in terms of gas reaction, decomposition conditions in CVI are chosen for in-depth decomposition rather than coating the surface of the substrate. Several techniques have been developed to introduce the reaction gases into the fiber architecture, such as temperature gradient, pressure gradient, and pulse CVI. Figure 3.27 shows the schematic of CVI technique.
Fabrication and Machining Methods of Composites for Aerospace Applications
Published in Chander Prakash, Sunpreet Singh, J. Paulo Davim, Characterization, Testing, Measurement, and Metrology, 2020
Atul Babbar, Vivek Jain, Dheeraj Gupta, Chander Prakash, Ankit Sharma
In chemical vapour infiltration (CVI), fibre-reinforced composite is made by infiltrating matrix material at high temperature in reactive gases environment into the fibrous preform. CVI is a similar technique like chemical vapour deposition (CVD). The CVD is used for the deposition process on the hot bulk surface, whereas CVI is for deposition on the porous surface. In CVD, the deposition of material is done by pyrolysing the gaseous pressure, on the external surface of a bulk substrate. CVI is also CVD but on the internal surface of a substrate. CVD is commonly used for augment substrate surface and to deposit conformal films where conventional techniques for surface modification are not competent. CVI is highly useful in atomic layer deposition process for depositing enormously thin layers of material. A CVI process differs from physical vapour deposition (PVD) processes, such as reactive sputtering and evaporation. PVD involves adsorption of molecular and atomic species on the substrate. The schematic representation of the CVI system has been shown in Figure 7.1.
Chemical vapour infiltration of composites and their applications
Published in Kwang Leong Choy, Chemical Vapour Deposition (CVD), 2019
Maria-Beatrice Coltelli, Andrea Lazzeri
CVI process is used especially for producing Cf/C composites or Cf/SiC composites. By CVI carbon or SiC is deposited on the fibres in the interior of the preform. The high wear resistance and the favourable friction properties of CMCs allow for their application in brakes, clutch-plates, and sliding contact bearings. CVI technology is used in brake discs in Formula 1 racing cars, as well as in the aerospace industry. When Formula1 racing cars are braked at full speed, this places an extreme load on the brakes and the parts subject to wear, in particular the ceramic brake discs.52 With the aid of CVI infiltration it is possible to make brake discs extremely dense and efficient (Figure 8.7a) and brakes based on CMCs were used in Porsche at the beginning of 2000.
Fabrication of SiCf/SiC composites through hybrid processing via chemical vapor infiltration, electrophoretic deposition, and liquid silicon infiltration
Published in Journal of Asian Ceramic Societies, 2021
Kati Raju, Young-Hoon Seong, Seyoung Kim, Soo-Hyun Kim, In-Sub Han, Hyung-Joon Bang, Sang-Kuk Woo, Hyun-Kwuon Lee
LSI has been demonstrated to be an effective technique for fabricating Cf/SiC and SiCf/SiC composites. Low fabrication costs, low residual porosities, short fabrication times, and ease of near-net-shaping are the main advantages of the LSI method. From an industrial point of view, this method is economically more viable despite having disadvantages such as the presence of residual silicon and fiber damage, which may limit composite performance. To overcome these drawbacks, the composites are coated with weak interphase layers such as PyC, BN, or SiC using the CVI method. To reduce the residual silicon and increase the SiC content in the final product, researchers infiltrate a slurry containing sources of both carbon and SiC into the preforms using a brush and/or vacuum before LSI. However, the reliability of the composites prepared by these methods is always a problem. In past years, much research has focused on the use of CVI and LSI techniques for the fabrication of long fiber-reinforced CMCs since their existence from longer times [12–16].