boron fibres
TRANSCRIPT
-
7/31/2019 Boron Fibres
1/21
Boron FibresBoron Fibres
-
7/31/2019 Boron Fibres
2/21
IntroductionIntroduction
Inherently brittle materialInherently brittle material
Produced by chemical vapour depositionProduced by chemical vapour deposition High temperature processHigh temperature processLimited substrate materialsLimited substrate materials Tungsten or Carbon fibre is usedTungsten or Carbon fibre is usedItself a composite fibreItself a composite fibre
First boron fibre obtained byFirst boron fibre obtained by WeintraubWeintraub in 1911in 1911Commercial production started during 1960Commercial production started during 1960At present, usage is very much limitedAt present, usage is very much limited
-
7/31/2019 Boron Fibres
3/21
FabricationFabrication
Thermal decomposition of a boron hydrideThermal decomposition of a boron hydride
Involves low temperaturesInvolves low temperatures
CarbonCarbon--coated glass fibres can be usedcoated glass fibres can be used
Weak due to lack of adherenceWeak due to lack of adherence
Much less dense owing to the trapped gasesMuch less dense owing to the trapped gases
Reduction of boron halideReduction of boron halide
2BX2BX33
+ 3H+ 3H22
2B + 6HX2B + 6HX
XX ClCl, Br, I, Br, I High temperature processHigh temperature process Refractory material substrateRefractory material substrate
heavyheavy
High & uniform quality fibresHigh & uniform quality fibres
-
7/31/2019 Boron Fibres
4/21
Schematic of boron
filament production by the CVD technique
-
7/31/2019 Boron Fibres
5/21
-
7/31/2019 Boron Fibres
6/21
Formation TemperatureFormation Temperature
Below critical temperature (CT)Below critical temperature (CT)
AmorphousAmorphousAbove CTAbove CT
CrystallineCrystalline
Stationary wireStationary wire
CT is 1000CT is 1000CCMoving wireMoving wire CT is higherCT is higherCT increases with speedCT increases with speed
-
7/31/2019 Boron Fibres
7/21
-
7/31/2019 Boron Fibres
8/21
Structure & MorphologyStructure & Morphology
Structural defects & morphological irregularitiesStructural defects & morphological irregularitiesdeteriorate the mechanical propertiesdeteriorate the mechanical properties
Depend on the conditions of depositionDepend on the conditions of depositionComposition of gases, gas dynamics, temperature,Composition of gases, gas dynamics, temperature,
etc.etc.
Temperature gradients & trace impurities areTemperature gradients & trace impurities areprocess irregularitiesprocess irregularities
Greater irregularities caused byGreater irregularities caused by
Fluctuations in electric powerFluctuations in electric powerInstability in gas flowInstability in gas flowOther operator induced variablesOther operator induced variables
-
7/31/2019 Boron Fibres
9/21
StructureStructure
Depends on deposition conditionsDepends on deposition conditions
Melt/CVD above 1300Melt/CVD above 1300CC
--rhombohedralrhombohedralLower temperature (
-
7/31/2019 Boron Fibres
10/21
-
7/31/2019 Boron Fibres
11/21
-
7/31/2019 Boron Fibres
12/21
Barrier coatingBarrier coating
SiC barrier coating prevents adverseSiC barrier coating prevents adverse
reactionreactionegeg. between Al & B. between Al & B
SiC is vapour deposited using a mixture ofSiC is vapour deposited using a mixture ofHH22
& methyl& methyl dichlorosilanedichlorosilane
-
7/31/2019 Boron Fibres
13/21
Corn-cob structure of boron fibre
Consisting of nodules separated by boundaries
Nodule size varies during the course of fabrication
-
7/31/2019 Boron Fibres
14/21
Residual stressesResidual stresses
Boron fibres have inherent residualBoron fibres have inherent residual
stressesstressesGrowth stresses in the nodules of boronGrowth stresses in the nodules of boron
Stresses induced by diffusion of boron into WStresses induced by diffusion of boron into Wcorecore
Stresses generated by difference in TECStresses generated by difference in TEC
Compressive stresses on surface due toCompressive stresses on surface due toquenching actionquenching action
-
7/31/2019 Boron Fibres
15/21
Residual stress pattern in boron fibre
-
7/31/2019 Boron Fibres
16/21
Fracture characteristicsFracture characteristics
Brittle materialBrittle material
distribution of strengthsdistribution of strengthsnot capable of deforming plasticallynot capable of deforming plastically
Imperfections lead to stress concentrationsImperfections lead to stress concentrations
Cracks originate at preexisting defectsCracks originate at preexisting defects
located at boronlocated at boron--core interface/ surfacecore interface/ surface
Surface defects are due to nodularSurface defects are due to nodular
structurestructure
-
7/31/2019 Boron Fibres
17/21
Radial cracks due to internal stresses
Cracks run from within the core to just inside
Characteristic brittlefracture of B fibre
-
7/31/2019 Boron Fibres
18/21
PropertiesProperties
YoungYoungs modulus is 380s modulus is 380--400 GPa400 GPa
Does not show intrinsic strength under tensileDoes not show intrinsic strength under tensileloadingloading
Average tensile strength is 3Average tensile strength is 3--4 GPa4 GPa
Intrinsic strength of B obtained in flexure testIntrinsic strength of B obtained in flexure test
Strength of 14 GPa observedStrength of 14 GPa observedDensity of 100Density of 100 mm B/W fibre is 2.6 g/ccB/W fibre is 2.6 g/ccMelting point is 2040Melting point is 2040CC
Thermal expansion coefficient is 8.3 X 10Thermal expansion coefficient is 8.3 X 10--66
CC--11
-
7/31/2019 Boron Fibres
19/21
-
7/31/2019 Boron Fibres
20/21
ApplicationsApplications
Used in a number of military aircraftsUsed in a number of military aircrafts
FF--14, F14, F--15 and US space shuttle15 and US space shuttleUsed for stiffening golf shafts, tennisUsed for stiffening golf shafts, tennis
rackets and bicycle framesrackets and bicycle framesOne big obstacle is high costOne big obstacle is high cost
Higher cost is due to the costly W substrateHigher cost is due to the costly W substrate
-
7/31/2019 Boron Fibres
21/21
Find out the final density of B fibre of diameter 100 m deposited on
a W fibre of diameter 12.5 m. Density values of B & W are 2.34 & 19.3 g/cm3
respectively.