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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.
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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Low density (about 114 lb/ft³ / 1.83*10³kg/m³);
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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;
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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:
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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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