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)