Carbon fiber carbon matrix composites manufacturing processes

A carbon-carbon composite is a carbon fiber reinforced carbon matrix material, where the carbon matrix phase is typically formed by the pyrolysis of a solid, liquid or gaseous organic precursor material. The matrix can be either a graphitizable or a non—graphitizable carbon and the carbonaceous reinforcement is in fibrous form. The composite may also contain other components in particulate or fibrous forms.

The real development of carbon-carbon composites started in 1958, with US air force sponsored work, which later received a massive boost with the onset of the Space Shuttle Program. Carbon-carbon composites can be tailor-made to give a wide family of products by controlling the choice of fiber type, fiber presentation and matrix.

Many informative publications on carbon-carbon materials and composites are available, although all production processes remain strictly proprietary.

The precursor fiber type for reinforcing the carbon matrix can be oxidized PAN fiber, or either a PAN or pitch based carbon fiber. In some instances, for special application, such as the Shuttle, a cellulose based carbon fiber is used. The reinforcements can be unidirectional; have a random chopped fiber presentation as in a felt format; a woven product from continuous fiber presented in a 2D, 3D, or in a Multi-D format, or a non-woven carbon fiber. The chosen fiber architecture is most important for a given application and Lei et al describe how, for example, 3D braiding can be applied to carbon-carbon composites. One of the early forms of near net shape reinforcement used for carbon-carbon aircraft brakes was based on a weft knitted 3D fabric make by the pressure foot process.

The precursor matrix material can be a hydrocarbon gas, a thermoset resin such as a phenolic or furan, or a thermoplastic resin such as a pitch or thermoplastic polymer.

There are two primary methods of manufacturing carbon-carbon. One method is based on chemical vapor infiltration (CVI) also termed chemical vapor deposition (CVD), employing a number a techniques for the infiltration process:

  1. Isothermal CVI
  2. Thermal Gradient CVI (TG-CVI)
  3. Pressure gradient
  4. TG-CVI plus pulse CVI
  5. Other methods

The second manufacturing method is based on a liquid phase impregnation process, where the liquid matrix can be either a themoset or thermoplastic resin, including pitch based resins. There are three basic processes used for impregnation:

  1. Low pressure impregnation (LPI)
  2. Pressure impregnation and carbonization (PIC)
  3. Hot isostatic pressure impregnation carbonization (HIPIC)

It is also possible to combine the CVI and LPI processes.

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