Carbon-Carbon Composites

Dr. Dmitri Kopeliovich

Carbon-Carbon Composites are composite materials consisting of a carbon matrix reinforced by carbon fibers.

• Structure of Carbon-Carbon Composites
• Fabrication of Carbon-Carbon Composites by Liquid Phase Infiltration process
• Fabrication of Carbon-Carbon Composites by Chemical Vapor Deposition process
• Properties of Carbon-Carbon Composites
• Oxidation protection of Carbon-Carbon Composites
• Applications of Carbon-Carbon Composites

Carbon-Carbon (C/C) Composites may be manufactured with different orientation of the reinforcing phase (carbon fibers): unidirectional structure, bi-directional structure (cloth made of multiple carbon fiber yarns), multi-directional structure (3D, 4D, 5D, etc.).
Multi-directional reinforcement provides maximum level of mechanical properties in the directions of the woven structure.
The simplest multi-directional reinforcement consists of 3D orthogonal structure woven of straight carbon fiber yarns.

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• Preparation of carbon/Graphite fiber preform of the desired structure and shape.
• Infiltration of the preform with a liquid precursor: petroleum pitch/phenolic resin/coal tar.
• Pyrolysis/carbonization (chemical decomposition by heat in the absence of Oxygen) of the polymer precursor at 1000-1830ºF (538-1000ºC) under normal or high pressure.
• Infiltration – pyrolysis cycle is repeated several (3-10) times until the desired density is achieved.
• Graphitization heat treatment. At this stage amorphous carbon is transformed into crystalline graphite. The temperature of the treatment may vary within the range 2700-5400°F (1500-3000°C). Typical graphitization temperature is 4530°F (2500°C). Graphitization of carbon-carbon composites results in increase of Modulus of Elasticity and strength of the composite.

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• Preparation of carbon/Graphite fiber preform of the desired structure and shape.
• Densification of the composite by Chemical Vapor Deposition (CVD) technique. The CVD process involves infiltration of the preform with a pressurized hydrocarbon gas (propane, methane, propylene, acetylene, benzene) at 1800-2200ºF (982-1204ºC). The gas is pyrolyzed forming carbon deposition on the fiber surface. The process duration is determined by the thickness of the preform, through which the gas diffuses.
• Graphitization heat treatment. At this stage amorphous carbon is transformed into crystalline graphite. The temperature of the treatment may vary within the range 2700-5400°F (1500-3000°C). Typical graphitization temperature is 4530°F (2500°C). Graphitization of carbon-carbon composites results in increase of Modulus of Elasticity and strength of the composite.

Fabrication of Carbon-Carbon Composites by Chemical Vapor Deposition process results in higher (as compared to Liquid Phase Infiltration technique) Modulus of Elasticity and mechanical strength.

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• Excellent thermal shock resistance;
• Low Coefficient of Thermal Expansion;
• High Modulus of Elasticity (up to 29000 ksi / 200 GPa);
• High Thermal Conductivity (about 700 BTU*in/(hr*ft²*ºF) / 101 W/m*K;
• Low density (about 114 lb/ft³ / 1.83*10³kg/m³);
• High strength;
• Low coefficient of friction (in the fiber direction);
• Excellent heat resistance in non-oxidizing atmosphere. C/C Composites retain their mechanical properties up to 5432ºF (3000ºC).
• High abrasion resistance;
• High electrical conductivity;
• Non-brittle failure.

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The main disadvantage of Carbon-Carbon Composites is their low oxidation resistance. Carbon materials react with Oxygen at temperatures above 900ºF (482ºC).

The following methods are used for oxidation protection of Carbon-Carbon Composites:

• Protection coatings. The ceramic coatings (commonly multi-layer) of carbides, nitrides and oxides. Protection coatings may be deposited by Chemical Vapor Deposition (CVD) (including pack cementation), Physical Vapor Deposition (PVD) or Plasma spraying method.
• Impregnation of oxidation inhibitors: inorganic salts, borate and silicate glasses, phosphates, boron oxides, polysiloxanes, halogen compounds.
• Replacement of the matrix material from carbon to SiC. C-SiC composites possess excellent oxidation resistance.

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• High performance braking systems (eg. brake discs for high speed aircrafts);
• Refractory material (eg. protection tubes and grids);
• Hot-pressed dies;
• Heating elements;
• Turbojet engine components (eg. rocket nozzles).

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• Ceramic Matrix Composites (introduction)
• Classification of infiltration methods of ceramic composites fabrication
• Reinforcing fibers for ceramic composites
• Interphases
• Fabrication of Ceramic Matrix Composites by Polymer Infiltration and Pyrolysis (PIP)
• Fabrication of Ceramic Matrix Composites by Chemical Vapor Infiltration (CVI)
• Fabrication of Ceramic Matrix Composites by Liquid phase Infiltration
• Fabrication of Ceramic Matrix Composites by Liquid Silicon Infiltration (LSI)
• Fabrication of Ceramic Matrix Composites by Direct Oxidation Process
• Fabrication of Ceramic Matrix Composites by Slurry Infiltration
• Fabrication of Ceramic Matrix Composites by Sol-gel process
• Self-lubricating ceramic composites
• Classification of composites
• Structure of composites
• Estimations of composite materials properties
• Carbon Fiber Reinforced Polymer Composites
• Carbon materials

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