What are Carbon-Carbon Composites?
• Amorphous carbon matrix composite
• Carbon matrix reinforced by graphitic carbon fibers
• First developed in 1958, but not intensively researched until the Space Shuttle Program
C/C composites are lightweight, highC/C composites are lightweight, high--strength composite materials capable strength composite materials capable of withstanding temperatures over of withstanding temperatures over 30003000°°C. C.
What are C/C Composites?
C/C composites use the strength C/C composites use the strength and modulus of carbon fibers to and modulus of carbon fibers to reinforce a carbon matrix to resist reinforce a carbon matrix to resist the rigors of extreme environments.the rigors of extreme environments.
Carbon-Carbon Composites• Carbon-Carbon Composites are the woven
mesh of Carbon-fibers.• Carbon-Carbon Composites are used for
their high strength and modulus of rigidity.• Carbon-Carbon Composites' structure can
be tailored to meet requirements.• Carbon-Carbon Composites are light weight
material which can withstand temperatures up to 3000°C
Properties of C/C Composites
• Excellent Thermal Shock Resistance(Over 2000oC)• Low Coefficient of Thermal Expansion• High Modulus of Elasticity ( 200 GPa )• High Thermal Conductivity ( 100 W/m*K )• Low Density ( 1830 Kg/m^3 )• High Strength• Low Coefficient of Friction ( in Fiber direction )• Thermal Resistance in non-oxidizing atmosphere• High Abrasion Resistance• High Electrical Conductivity• Non-Brittle Failure
Production of C/CProduction of C/C
•Three dimensional woven carbon fiber structure
•Pressure impregnation with liquid
•Heat treated at 2550°C
•Impregnation, DENSIFICATION and graphitization cycle repeated
Representative Weave Constructions
Fabrication of C/C Composites
• Liquid Phase Infiltration
• Chemical Vapor Deposition
PAN-based carbon fibers (the most popular type of carbon fibers).
• In this method carbon fibers are produced by conversion of polyacrylonitrile (PAN) precursor through the following stages:Stretching filaments from polyacrylonitrile precursor and their thermal oxidation at 200°C.
• The filaments are held in tension.Carbonization in Nitrogen atmosphere at a temperature about 1200°C for several hours.
• During this stage non-carbonelements (O,N,H) volatilize resulting in enrichment of the fibers with carbon.Graphitization at about 2500°C.
Carbon-Carbon Composites
• porous carbon-carbon composites(carbon bonded carbon fiber (CBCF))
Porosity content 70~90% high temperature insulation
Liquid Phase Infiltration• Preparation of C/C fiber pre-form of desired shape and
structure
• Liquid pre-cursor : Petroleum pitch/ Phenolic resin/ Coal tar
• Pyrolysis (Chemical deposition by heat in absence of O2
• It is processed at 540–1000°C under high pressure
• Pyrolysis cycle is repeated 3 to 10 times for desired density
• Heat Treatment converts amorphous C into crystalline C
• Temperature range of treatment :1500-3000°C
• Heat treatment increases Modulus of Elasticity and Strength
Manufacturing Process :
• Processing of CBCF
Discontinuous fibers(mm in length)
Ground recycled CBCF(rework)
binder(phenolic resin)
water
mixer slurry moulding
water
dryingCarbonization
(950℃)High temp heat
treatmentProduct99.9%℃
50% carbon yieldfrom phenolic
vacuum
(fiber alignment) gaseous impurities
low pressure
porous & anisotropic
Chemical Vapor Deposition
• Preparation of C/C fiber pre-form of desired shape and structure
• Densification of the composite by CVD technique• Infiltration from pressurized hydrocarbon gases
(Methane /Propane)at 990-1210°C• Gas is pyrolyzed from deposition on fibre surface• Process duration depends on thickness of pre-form• Heat treatment increases Modulus of Elasticity and
Strength• This process gives higher strength and modulus of
elasticity
• Dense carbon-carbon composites
Discontinuous fibersContinuous fibers
Impregnation with thermosetting resins
(phenolic, furan polyimide)
pitch(polynuclear aromatic hydrocarbons)
pyrolysis Carbonization2500℃
Chemical vapour deposition
DenseThick
enough?
product
Limitation of CVD
• Hydrocarbon Gases Infiltrating into interfilament surfaces and cracks , sometimes these gases deposite on outer cracks and leave lot of pores
• Reinfiltration and densification required
• Month long process(for specific applications)
– Stress-strain curve process dependent: Fig 4.30
Form of fiber reinforcement: Fig 4.31
– Fatigue property
Properties of Carbon-Carbon
http://www.hitco.com/products/corrosion/chemical/index.html
Uses of Carbon-Carbon Composites • Aircraft, F-1 racing
cars and train brakes
• Space shuttle nose tip and leading edges
• Rocket nozzles and tips
http://www.futureshuttle.com/conference/ThermalProtectionSystem/Curry_73099.pdf
http://www.fibermaterialsinc.com/frSW.htm
http://www.fibermaterialsinc.com/frSW.htm
Optical MicroscopySample 3:
SEM ImagesSample 3:
Application• High Performance Braking System• Refractory Material• Hot-Pressed Dies(brake pads)• Turbo-Jet Engine Components• Heating Elements• Missile Nose-Tips• Rocket Motor Throats• Leading Edges(Space Shuttle, Agni missile)• Heat Shields• X-Ray Targets
ApplicationsApplications
• NASA thermal protection systems
• Nozzle throat inserts
• Nosetips & leading edges
• Space motor nozzles
Products
• Variety of high temperature applications.
Heat Shields
• Baffle Heat Shield
• Flexi Heat Shield
Disadvantage :
• Low oxidation resistance
• Reacts with Oxygen at temperature above 490°C
Protection Method:
• Ceramic coatings(Carbides/ Nitrides/oxides of Si,Zr,Ta,Al etc.)
• Physical vapor deposition
• Plasma spraying
• Injecting with inorganic salts , borate & silicate glass.
• Replacement of C/C matrix material by Si-C.(inhibitors of B, Si, Zr compounds)
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