Composites
„ Metal Matrix Composites
„ Polymer Matrix Composites
„ Ceramic Matrix Composites
Composites
„ Combine materials with the objective of getting a
more desirable combination of properties
„
Ex: get flexibility & weight of a polymer plus the
strength of a ceramic
„ Principle of combined action
„ Mixture gives “averaged” properties
Terminology/Classification
• Composites:
-- Multiphase material w/significant
proportions of each phase.
woven
fibers
• Matrix:
-- The continuous phase
-- Purpose is to:
- transfer stress to other phases
- protect phases from environment
-- Classification:
metal
MMC, CMC, PMC
ceramic
polymer
0.5 mm
cross
section
view
• Dispersed phase:
-- Purpose: enhance matrix properties.
MMC: increase σy, TS, creep resist.
CMC: increase Kc
PMC: increase E, σy, TS, creep resist.
-- Classification: Particle, fiber, structural
0.5 mm
Reprinted with permission from
D. Hull and T.W. Clyne, An
Introduction to Composite Materials,
2nd ed., Cambridge University Press,
New York, 1996, Fig. 3.6, p. 47.
Composite Survey
Composites
Particle-reinforced
Largeparticle
Dispersionstrengthened
Fiber-reinforced
Continuous
(aligned)
Structural
Discontinuous
(short)
Aligned
Randomly
oriented
Laminates
Sandwich
panels
Composite Survey: Particle-I
Particle-reinforced
Fiber-reinforced
• Examples:
- Spheroidite matrix:
ferrite (α)
steel
(ductile)
60 μm
- WC/Co
cemented
carbide
matrix:
cobalt
(ductile)
Vm :
10-15 vol%!
Structural
particles:
cementite
(Fe3 C)
(brittle)
particles:
WC
(brittle,
hard)
Adapted from Fig.
10.19, Callister 7e.
(Fig. 10.19 is
copyright United
States Steel
Corporation, 1971.)
Adapted from Fig.
16.4, Callister 7e.
(Fig. 16.4 is courtesy
Carboloy Systems,
Department, General
Electric Company.)
600 μm
- Automobile matrix:
rubber
tires
particles:
C
(stiffer)
(compliant)
0.75 μm
Adapted from Fig.
16.5, Callister 7e.
(Fig. 16.5 is courtesy
Goodyear Tire and
Rubber Company.)
Composite Survey: Particle-II
Particle-reinforced
Fiber-reinforced
Structural
Concrete – gravel + sand + cement
- Why sand and gravel?
Sand packs into gravel voids
Reinforced concrete - Reinforce with steel rerod or remesh
- increases strength - even if cement matrix is cracked
Prestressed concrete - remesh under tension during setting of
concrete. Tension release puts concrete under compressive force
- Concrete much stronger under compression.
- Applied tension must exceed compressive force
Post tensioning – tighten nuts to put under tension
nut
threaded
rod
Composite Survey: Particle-III
Particle-reinforced
Fiber-reinforced
Structural
• Elastic modulus, Ec, of composites:
-- two approaches.
E(GPa)
350
Data:
Cu matrix 300
w/tungsten 250
particles
200
150
upper limit: “rule of mixtures”
Ec = VmEm + VpEp
0
lower limit:
1 Vm Vp
=
+
Ec Em Ep
20 40 60 80
(Cu)
Adapted from Fig. 16.3,
Callister 7e. (Fig. 16.3 is
from R.H. Krock, ASTM
Proc, Vol. 63, 1963.)
10 0 vol% tungsten
(W)
• Application to other properties:
-- Electrical conductivity, σe: Replace E in equations with σe.
-- Thermal conductivity, k: Replace E in equations with k.
Composite Survey: Fiber-I
Particle-reinforced
Fiber-reinforced
Structural
„ Fibers very strong
„ Provide significant strength improvement to
material
„ Ex: fiber-glass
„ Continuous glass filaments in a polymer matrix
„ Strength due to fibers
„ Polymer simply holds them in place
Composite Survey: Fiber-II
Particle-reinforced
Fiber-reinforced
Structural
„ Fiber Materials
„
Whiskers - Thin single crystals - large length to diameter ratio
graphite, SiN, SiC
„ high crystal perfection – extremely strong, strongest
known
„ very expensive
– Fibers
• polycrystalline or amorphous
• generally polymers or ceramics
• Ex: Al2O3 , Aramid, E-glass, Boron, UHMWPE
– Wires
• Metal – steel, Mo, W
„
Fiber Alignment
Adapted from Fig.
16.8, Callister 7e.
aligned
continuous
aligned
random
discontinuous
Composite Survey: Fiber-III
Particle-reinforced
Fiber-reinforced
Structural
• Aligned Continuous fibers
• Examples:
-- Metal: γ'(Ni3Al)-α(Mo)
-- Ceramic: Glass w/SiC fibers
by eutectic solidification.
formed by glass slurry
Eglass = 76 GPa; ESiC = 400 GPa.
matrix: α (Mo) (ductile)
(a)
2 μm
fibers: γ ’ (Ni3Al) (brittle)
From W. Funk and E. Blank, “Creep
deformation of Ni3Al-Mo in-situ
composites", Metall. Trans. A Vol. 19(4),
pp. 987-998, 1988. Used with permission.
(b)
fracture
surface
From F.L. Matthews and R.L.
Rawlings, Composite Materials;
Engineering and Science, Reprint
ed., CRC Press, Boca Raton, FL,
2000. (a) Fig. 4.22, p. 145 (photo by
J. Davies); (b) Fig. 11.20, p. 349
(micrograph by H.S. Kim, P.S.
Rodgers, and R.D. Rawlings). Used
with permission of CRC
Press, Boca Raton, FL.
Composite Survey: Fiber-IV
Particle-reinforced
Fiber-reinforced
• Discontinuous, random 2D fibers
• Example: Carbon-Carbon
-- process: fiber/pitch, then
burn out at up to 2500ºC.
-- uses: disk brakes, gas
turbine exhaust flaps, nose
cones.
(b)
(a)
Structural
C fibers:
very stiff
very strong
C matrix:
less stiff
view onto plane less strong
fibers lie
in plane
• Other variations:
-- Discontinuous, random 3D
-- Discontinuous, 1D
Adapted from F.L. Matthews and R.L. Rawlings,
Composite Materials; Engineering and Science,
Reprint ed., CRC Press, Boca Raton, FL, 2000.
(a) Fig. 4.24(a), p. 151; (b) Fig. 4.24(b) p. 151.
(Courtesy I.J. Davies) Reproduced with
permission of CRC Press, Boca Raton, FL.
Composite Survey: Fiber-V
Particle-reinforced
Fiber-reinforced
Structural
• Critical fiber length for effective stiffening & strengthening:
fiber strength in tension
σf d
fiber length > 15
τc
fiber diameter
shear strength of
fiber-matrix interface
• Ex: For fiberglass, fiber length > 15 mm needed
• Why? Longer fibers carry stress more efficiently!
Shorter, thicker fiber:
σd
fiber length < 15 f
τc
σ(x)
Longer, thinner fiber:
fiber length > 15
σf d
τc
σ(x)
Adapted from Fig.
16.7, Callister 7e.
Poorer fiber efficiency
Better fiber efficiency
Composite Strength:
Longitudinal Loading
Continuous fibers - Estimate fiber-reinforced composite
strength for long continuous fibers in a matrix
„ Longitudinal deformation
σc = σmVm + σfVf
volume fraction
∴
Ece = Em Vm + EfVf
Ff
EfVf
=
Fm E mVm
but
εc = εm = εf
isostrain
longitudinal (extensional)
modulus
f = fiber
m = matrix
Composite Strength:
Transverse Loading
„ In transverse loading the fibers carry less of the load
- isostress
σc = σm = σf = σ
∴
1
Vm Vf
=
+
Ect E m Ef
εc= εmVm + εfVf
transverse modulus
Composite Strength
Particle-reinforced
Fiber-reinforced
Structural
• Estimate of Ec and TS for discontinuous fibers:
σf d
-- valid when fiber length > 15
τc
-- Elastic modulus in fiber direction:
Ec = EmVm + KEfVf
efficiency factor:
-- aligned 1D: K = 1 (aligned )
-- aligned 1D: K = 0 (aligned )
-- random 2D: K = 3/8 (2D isotropy)
-- random 3D: K = 1/5 (3D isotropy)
Values from Table 16.3, Callister 7e.
(Source for Table 16.3 is H. Krenchel,
Fibre Reinforcement, Copenhagen:
Akademisk Forlag, 1964.)
-- TS in fiber direction:
(TS)c = (TS)mVm + (TS)fVf
(aligned 1D)
Composite Production Methods-I
„ Pultrusion
„
Continuous fibers pulled through resin tank, then
preforming die & oven to cure
Adapted from Fig.
16.13, Callister 7e.
Composite Production Methods-II
„ Filament Winding
„
„
Ex: pressure tanks
Continuous filaments wound onto mandrel
Adapted from Fig. 16.15, Callister 7e. [Fig.
16.15 is from N. L. Hancox, (Editor), Fibre
Composite Hybrid Materials, The Macmillan
Company, New York, 1981.]
Composite Survey: Structural
Particle-reinforced
Fiber-reinforced
Structural
• Stacked and bonded fiber-reinforced sheets
-- stacking sequence: e.g., 0º/90º
-- benefit: balanced, in-plane stiffness
Adapted from
Fig. 16.16,
Callister 7e.
• Sandwich panels
-- low density, honeycomb core
-- benefit: small weight, large bending stiffness
face sheet
adhesive layer
honeycomb
Adapted from Fig. 16.18,
Callister 7e. (Fig. 16.18 is
from Engineered Materials
Handbook, Vol. 1, Composites, ASM International, Materials Park, OH, 1987.)
Composite Benefits
• CMCs: Increased toughness
Force
103
particle-reinf
1
un-reinf
10 -4
6061 Al
εss (s-1)
10 -6
10 -8
10 -10
metal/
metal alloys
.1 G=3E/8 polymers
.01 K=E
.1 .3 1 3 10 30
Density, ρ [mg/m3]
Bend displacement
Increased
creep
resistance
ceramics
E(GPa)
PMCs
2
10
10
fiber-reinf
• MMCs:
• PMCs: Increased E/ρ
6061 Al
w/SiC
whiskers
20 30 50
Adapted from T.G. Nieh, "Creep rupture of
a silicon-carbide reinforced aluminum
composite", Metall. Trans. A Vol. 15(1), pp.
139-146, 1984. Used with permission.
σ(MPa)
100 200
Metal Matrix Composites
„ The most common MMCs are:
Aluminium matrix
„ Magnesium matrix
„ Titanium matrix
„ Copper matrix
„
Aluminium matrix
„ Widest group of MMC
„ Some of the reinforcements are:
Continuous fibres: B, SiC, Al2O3, Graphite.
„ Discontinuous fibres: Al2O3, Al2O3-SiC.
„ Whiskers: SiC
„ Particulates: SiC, BC.
„
Al-SiC MMC
Aluminium matrix
„ Properties of Al-MC:
High strength even at elevated temperatures
„ High stiffness
„ Low density
„ High thermal conductivity
„ Excellent abrasion resistance
„
„ Applications
„
Pistons, pushrods, brakes components,
bicycles, golf clubs.
Magnesium matrix
„ Some of the reinforcements are:
Continuous fibres: Al2O3,
Graphite.
„ Whiskers: SiC
„ Particulates: SiC, BC.
„ Properties
„ Low density
„ High stiffness
„ Good strength at elevated
temperatures
„ Good creep resistance
„ Applications
„ Racing car components,
gearboxes, compressors.
„
Mg-MgB2 MMC
Mg-Mg2Si MMC
Titanium matrix
„ Some of the reinforcements are:
„ Continuous fibres: SiC, B.
„ Particulates: TiC.
„ Properties
„ High strength
„ High stiffness
„ High creep resistance
„ High thermal stability
„ High wear resistance
„ Applications
„ F-16 jet’s landing gear, turbine engine components
(fan blades, actuator pistons, shafts, discs).
Copper matrix
„ Some of the reinforcements are:
„ Continuous fibres: SiC, Graphite.
„ Particulates: SiC, BC, TiC.
„ Wires: Nb-Ti, Nb-Sn.
„ Properties
„ Low coefficient of thermal expansion
„ High stiffness
„ Good electrical conductivity
„ High thermal conductivity
„ Good wear resistance
„ Applications
„ Electronic relays, electrically conducting springs.
Advantages of MMC over PMC
„ Higher temperature capability
„ Fire resistance
„ Higher transverse stiffness and strength
„ No moisture absorption
„ Higher electrical and thermal conductivities
„ Better radiation resistance
Advantages of MMC over metals
„ Higher specific strength
„ Higher specific stiffness
„ Better fatigue resistance
„ Better elevated temperature properties
„ Lower coefficients of thermal expansion
„ Better wear resistance
Disadvantages of MMC over metals
„ Higher cost of some systems
„ Relatively immature technology
„ Complex fabrication methods for fiber
reinforced systems
„ Limited service experience
Fabrication of MMC
„ Liquid state fabrication (LSF)
„ Solid state fabrication (SSF)
Liquid State Fabrication
„ Involves incorporation of dispersed phase
into a molten matrix metal, followed by
solidification.
„ Good “wetting” (interfacial bonding) between
the dispersed phase and the liquid matrix
should be obtained.
„ Wetting may be achieved through coating the
dispersed phase particles.
L S F 1: Stir Casting
„
„
„
„
Mixing through mechanical stirrer.
Then cast through conventional casting methods.
Content of dispersed phase limited (30vol%).
Dispersed phase not perfectly distributed.
„ Clusters of dispersed particles
„ Segregation due to gravity and density.
„ May improve through Rheocasting – mixing in
semi-solid condition.
„ Simple and low cost
L S F 2: Infiltration
„ Dispersed phase soaked in molten matrix
metal.
„ Two types of infiltration:
„
Spontaneous infiltration
„
„
The motive force of an infiltration process comes
from the capillary force of the dispersed phase.
Forced infiltration
„
The motive force comes from external pressure
applied to the liquid matrix phase.
Gas Pressure Infiltration
„ Pressurised gas applied on the molten metal, forcing
it to penetrate into a preformed dispersed phase.
„ Used for manufacturing large composite parts.
„ Allows the use of
non-coated fibers
due to short
contact time of
the fibers with
the hot metal.
„ Low damage to
the fibers.
Squeeze Casting Infiltration
„ Pressure applied through a movable mold part, forcing the
molten metal to penetrate into a preformed dispersed phase.
„ Used for manufacturing simple small parts (automotive engine
pistons).
„ Steps in SCI:
„
„
„
„
„
A preform is placed into the
lower fixed mold half.
A molten metal is pured into the
lower mold half.
The upper movable mold half
moves downward and forces the
liquid metal to infiltrate the
preform.
The infiltrated material solidifies
under the pressure.
Part is removed.
Pressure Die Infiltration
„ Forced infiltration method using a die casting technology.
„ Steps in PDI:
„
„
„
A preform is placed into a die
Molten metal is then poured
into the pressure chamber
through a sprue
The molten metal penetrates
into the preform under the
pressure of a movable piston.
Solid State Fabrication
„ Formed as a result of bonding matrix metal
and dispersed phase due to mutual diffusion
ocurring between them in solid states at
elevated temperature and pressure.
„ Two types of SSF:
Diffusion bonding
„ Sintering
„
Diffusion Bonding
„ Matrix in form of foils, Dispersed phase in form of
layers of long fibers, stacked in a particular order and
then pressed at elevated temperature – ended with a
multilayer structure.
„ Suitable for
simple shape
parts –
(plates,
tubes).
Sintering
„ Powder of a matrix metal mixed with powder of
dispersed phase for subsequent compacting and
sintering in solid state.
„ The material of the separate particles diffuse to the
neighbouring powder particles at high temperature
(below melting).
„ Allows MMC
with up to 50%
dispersed
phase.
Hot Pressing
„ Sintering under a
unidirectional
pressure applied by
a hot press.
Hot Isostatic Pressing
„ Sintering under a
pressure applied from
multiple directions
through a liquid or
gaseous medium
surrounding the
compacted part and at
elevated temperature.
Hot Powder Extrusion
„ Sintering under a
pressure applied by an
extruder at elevated
temperature.
Polymer Matrix Composite
„ Polymer-Matrix Types
„ Polyesters
„
„
Phenolic Resins
„
„
Inexpensive and easy to process
For high temperature applications
Epoxy Resins
„
For high strength applications and creating
smooth surfaces
„ Typical reinforcements
„ Natural fibers, synthetics, carbon, graphite,
fiberglass, quartz, kevlar.
Manufacturing Processes
„ Sheet molding
Deposit resin on carrier film
„ Deposit fiber on resin
„ Add more resin on top with another
layer of carrier film
„ Smooth through rollers
„ Bulk molding
„ Premix the polymer with the fiber
„ Smooth through rollers
„ Pultrusion
„ Pull preheated prepreg through
heated, tappered die
„ Open mold
„ Spray-up
„ Tape laying machines
„ Filament winding
„
Applications of PMC
Ceramic Matrix Composites
„ Developed to overcome the brittleness and
lack of reliability.
„ Oxide matrices are more mature and stable
„
Alumina (Al2O3), Silica (SiO2), Mullite (3Al2O3 2SiO2), Barium aluminosilicate (BAS), Lithium
aluminosilicate (LAS), Calcium aluminosilicate
(CAS).
„ However, non-oxide matrices have superior
structural properties, hardness, corrosion
resistance.
„
SiC, Si3N4, BC, AlN.
Type of reinforcements
„ Whiskers, particles
SiC, Si3N4, AlN, TiB2, BC, BN.
„ Oxide ceramics not normally used because of
their incompatibility.
„
„ Continuous fibers
SiC, Glass, mullite, alumina, Carbon.
„ More expensive ($1000/lb c.w. $50/lb.)
„
Applications
„ Cutting tools, aerospace & military, engines,
wear & industrial, bioceramics.
„ Characteristics of CMCs:
High temperature stability.
„ High thermal shock resistance.
„ High hardness.
„ High corrosion resistance.
„ Light weight.
„ Nonmagnetic & nonconductive properties.
„
Processing
„ If discontinuous reinforcement is used, then
process traditionally:
Slip casting or Injection moulding
„ Sintering (Hot pressing / H.I.P.)
„
Typical microstructure for a
discontinuous reinforced ceramic
composite (SiC / Al2O3), normally
used as cutting tools.
Slip casting
• Mixing particles & water: produces a "slip"
• Form a "green" component
--Slip casting:
pour slip
into mold
absorb water
into mold
“green
ceramic”
solid component
pour slip
into mold
drain
mold
hollow component
• Dry and fire the component
“green
ceramic”
Adapted from Fig.
13.12, Callister 7e.
(Fig. 13.12 is from
W.D. Kingery,
Introduction to
Ceramics, John
Wiley and Sons,
Inc., 1960.)
Features of a slip
Shear
charge
neutral
weak van
der Waals
bonding
4+
charge
neutral
Si
3+
Al
OH
2O
Shear
e.g.: Structure of
Kaolinite Clay
Injection moulding
Processing
„ For continuous phase, processing involves
formation of fiber preform coated through
CVD.
Typical microstructure of (SiC / SiC)
CMC.
Applications (non-oxide matrices)
„ For high thermal conductivity, low thermal
expansion, light weight, good corrosion &
wear resistance.
Furnace pipe hangers
Hot gas recirculating fan
Radiant burner screen
Gas turbine engine combustor liner
Applications (oxide matrices)
„ For high tolerance to salt corrosion, oxidation,
high toughness, light weight, high thermal
shock resistance.
Burner stabiliser
ring
Heat exchanger
Hot gas filter