Lecture 7 Metal and Ceramic Matrix Composites(1).pdf

Composite lecture

1. Metal Matrix Composites and
Ceramic Matrix Composites
MS4622
Composite Materials
Jing YU
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2. Metal Matrix
Composites
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3. Why Fiber Reinforcement of Metals?
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•The improvement in stiffness of a metal can be profitably
obtained by incorporating high modulus fibers in a metal
matrix.
•Most of these high modulus fibers are also lighter than the
metallic matrix materials.
•For structural applications involving compression or flexural
loading of beams (for example, in an airplane, rocket, or
truck), it is the E/!
2
value, ! being the density, that should be
maximized.
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4. Type Aspect RatioDiameter, m Examples
Particle ~1-4 1-25 SiC, Al
2O
3, BN, B
4C
Short fiber or whisker ~10-1000 0.1-25 SiC, Al
2O
3, Al
2O
3 + SiO
2, C
Continuous fiber >1000 3-150 SiC, Al
2O
3, C, B, W
Types of Metal Matrix Composites
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Three kinds of metal matrix composites:
1.Particle reinforced MMCs
2.Short fiber or whisker reinforced MMCs
3.Continuous fiber or sheet reinforced MMCs
Length / Diameter
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5. Important Metallic Matrices
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Aluminum alloy (Al-Cu-Mg, Al-Zn-Mg-Cu, and Al-Li)
High tensile strength-to-weight ratio. Popular reinforcement is SiC
coated C-fibers.
•Applications: automotive engine cylinders – die cast
•Continuous fibers: boron, silicon carbide, alumina, graphite
•Discontinuous fibers: alumina, alumina-silica
•Whiskers: silicon carbide
•Particulates: silicon carbide, boron carbide
Magnesium matrix •Continuous fibers: graphite, alumina
•Whiskers: silicon carbide
•Particulates: silicon carbide, boron carbide
Titanium matrix •Continuous fibers: silicon carbide, coated
boron
•Particulates: titanium carbide
Copper matrix •Continuous fibers: graphite, silicon carbide
•Wires: niobium-titanium, niobium-tin
•Particulates: silicon carbide, boron carbide, titanium
carbide.
Superalloy matrices •Wires: tungsten
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6. Processing
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1. Liquid-state process
a) casting or liquid infiltration.
b) squeeze casting or pressure infiltration.
c) spray-forming.
2. Solid-state process
a) diffusion bonding.
b) deformation processing through mechanical processing (swaging,
extrusion, drawing or rolling).
c) deposition techniques: immersion plating, electroplating, spray
deposition, chemical vapor deposition (CVD), and physical vapor
deposition (PVD).
3. In Situ process
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7. Liquid - State Process - Casting Or
Liquid Infiltration
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8. Squeeze Casting Or
Pressure Infiltration
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•Pressure-assisted Solidification Process.
•Liquid metal is injected into a preform (an assembly of short fibres).
•Solidification of metal leads to MMC.
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9. Squeeze Casting or
Pressure Infiltration (Preform)
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A press forming of a preform
Suction forming of a preform
Porous
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10. Squeeze Casting or
Pressure Infiltration
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Pouring Pressurization Solidification Ejection
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11. Spray - Forming
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Preheated
to dry them
Particles
should be
optimized. Al stream
This process is
controlled by
computer
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12. Spray - Forming
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13. Solid - State Process
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a) Diffusion bonding.
b) Deformation processing through mechanical
processing (swaging, extrusion, drawing or rolling).
c) Deposition techniques: immersion plating,
electroplating, spray deposition, chemical vapor
deposition (CVD), and physical vapor deposition (PVD).
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14. Diffusion Bonding of Foils
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•Array of fibers placed between thin metallic foils.
•Followed by hot pressing.
•Commonly used for titanium reinforced with long fibers.
•This joining technique bonds two metals together without the use of alloy. Two
metals are pressed together with extreme force and at high temperatures.
Metal atoms diffuse into the adjacent material forming what is called a
Diffusion Bond. This technique is commonly performed on Copper and
Titanium components and requires very specific conditions such as
temperature, pressure, time at temperature, surface finish, and surface
flatness.
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15. Diffusion Bonding
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16. Step 1 Step 2 Step 3 Step 4 Step 5
Step 6 Step 7
Apply aluminum foilCut to shape
Lay up
desired piles
Vacuum
encapsulate
Heat to
fabrication
temperature
Applying pressure
and hold for
consolidation cycle
Cool. Remove and
clean part
Diffusion Bond Process
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Pressure and temperature
are very important.
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17. The Microstructure Made
by Diffusion Bonding
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SiC fiber/
Titanium matrix
composite
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18. In Situ Processes
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In in situ techniques, one forms the reinforcement phase in situ. The
composite material is produced in one step from an appropriate starting
alloy, thus avoiding the difficulties inherent in combining the separate
components as in a typical composite processing. Controlled
unidirectional solidification of a eutectic alloy is a classic example of in situ
processing.
.?+?
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19. In Situ Processes
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20. In Situ Processes
• Unidirectional solidification of a
eutectic alloy can result in one
phase being distributed in the
form of fibers or ribbon in the
other.

• One can control the fineness of
distribution of the reinforcement
phase by simply controlling the
solidification rate.
TaC fiber in nickel alloy matrix
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21. Properties of MMCs
Unidirectionally reinforced continuous fiber reinforced metal matrix
composites show a linear increase in the longitudinal Young’s modulus
of the composite as a function of the fiber volume fraction.
Properties of Al2O3/Al-Li
composites as a function of
fiber volume fraction (Vf): a
axial and transverse
Young’s modulus versus
fiber volume fraction, b axial
and transverse ultimate
tensile strength versus fiber
volume fraction
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22. Applications of MMCs
It is convenient to divide the applications of metal matrix composites into
aerospace and nonaerospace categories.
•In the category of aerospace applications, low density and other desirable
features such as a tailored coefficient of thermal expansion and thermal
conductivity, high stiffness, and strength are the main drivers.
•In the nonaerospace applications, cost and performance are important,
i.e., an optimum combination of these items is required.
One of the important applications of
MMCs in the automotive area is in
diesel piston crowns. This application
involves incorporation of short fibers of
alumina or alumina + silica in the
crown of the piston.
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23. Ceramic
Matrix
Composites
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24. CMCs - Introduction
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CMCs: ceramic matrices – reinforced with continuous fibers,
chopped fibers, whiskers, platelets, or particulates have
emerged as advanced engineering structural materials.
•Oxides: Al2O3, Zirconia, Titania, MgO, Silica – heat
resistance applications, cutting tools, structural
applications.
•Glass-ceramic (Li2O-Al2O3-SiO2, MgO, CaO) matrices –
refractory applications, heat shielding applications.
•SiC, B4C, TiC, & Si3N4– hard abrasive materials, erosion &
corrosion resistance. Nitrides show excellent oxidation
resistance.
•Si-Al-O-N (Sialon) – cutting tools, seals, bearings, wear
components etc.
- Important Matrix Materials:
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25. CMCs - Advantages
Ceramic materials:
•high strength and high stiffness at very high temperatures
•chemical inertness
•low density
•lack of toughness
Ceramics are prone to catastrophic failures in the presence of flaws
(surface or internal). They are extremely susceptible to thermal shock
and are easily damaged during fabrication and/or service.
It is therefore understandable that an overriding consideration in
ceramic matrix composites (CMCs) is to toughen the ceramics by
incorporating fibers in them and thus exploit the attractive high
temperature strength and environmental resistance of ceramic materials
without risking a catastrophic failure.
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26. Processing of CMCs
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Processing Methods:
•Cold pressing and sintering
•Hot pressing
•Reaction bonding process
•Liquid Infiltration
•Directed Melt Oxidation – “Dimox” or “Lanxide” Process
•Chemical Vapor Impregnation (CVI)
•Sol-Gel Processing
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27. Cold Pressing & Sintering
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•Matrix powder and fiber binder is mixed >>> formed
>>> sintered.
•Challenges include removal of binder, densification,
shrinkage, and shrinkage induced cracking.
•Aspect ratios of fibers, 3-D networks of fibers that
may form, CTE induced tensile stresses may
counter the driving force for sintering.
•Stack thin sheets or tapes in the green state and
consolidating them by a sintering operation.
•Fine ceramic powders is blended with a viscous
polymer solution and formed into a tape (roll casting
or tape casting) of about 200um thick, stacked and
sintered.
•In order to increase toughness, a weak interface
layers is sometimes added to provide crack
deflection.
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28. Hot Pressing
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•Hot pressing is a high-pressure, low-strain-rate
powder metallurgy process for forming of a
powder or powder compact at a temperature
high enough to induce sintering and creep
processes.
•Simultaneous application of pressure, high temp
>>> leads to an increased rate of densification
and pore free materials can be formed.
• Stages are:
- Incorporation of a reinforcing phase in to
an unconsolidated matrix
-Matrix consolidation by hot pressing
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29. Liquid Infiltration
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Proper control of the fluidity of the liquid matrix is the key to this technique.
Advantages
•The matrix is formed in a single
processing step.
•A homogeneous matrix can be
obtained.
Disadvantages
•The temperature are very high :
some unwanted reactions
between the reinforcement and
the matrix may happen.
•High viscosities of ceramic melts
cause problem to fill all space in
reinforcement.
•Thermal expansion mismatch:
matrix is likely to crack because of
the differential shrinkage.
Piston
Infiltrate
Preform
Heating
coils
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30. Liquid Infiltration Processing for
SiC/Si
3N
4 Composites
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1.Porous SiC or Si3N4 fibrous perform with binders is prepared.
2.The fibrous preform is evacuated in autoclave.
3.Samples are infiltrated with molten precursors, silazanes, or
polycarbosilanes, at 780 K in Ar or N2 with pressures ranging from 2 to 40
Mpa. Polymerization results.
4.Samples are cooled, treated with solvents.
5.Samples are placed in an autoclave (@800 – 1300 K) to decompose the
organosilicon matrix.
6.Step 2 through 5 are repeated to achieve adequate density of the matrix.
7.The material is finally annealed at 1300 – 1800 K.
Process Steps
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31. Chemical Vapor Impregnation (CVI)
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1.A vapor feed system
2.A CVD reactor
3.An effluent system
In C, CVD is used to impregnate large amounts of matrix material in
fibrous preforms.
CH
3SiCl
3 SiC(s) + 3 HCl
1200K
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32. An example of the Microstructure by CVI
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33. CVI with Pressure & Temperature Gradients
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Advantages of CVI technique
•Good mechanical properties at high temperature.
•Large, complex shapes can be produced in a near-net
shape.
•Considerable flexibility in the fibers and matrices.
Disadvantages
•The process is slow and expensive. 34

34. Properties of CMCs
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An important feature of CMCs is matrix microcracking, which does not
have a parallel in MMCs or PMCs.Typically, fibers such as boron,
carbon, and silicon carbide show failure strain values of ~ 1–2%.
Compare this with the failure strains of less than 0.05% for most
ceramic matrix materials.
In a strongly bonded CMC, fiber and matrix would fail simultaneously
at matrix failure strain. A weak interface, however, would lead to fiber
bridging of matrix microcracks.
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35. Toughness of CMCs
Mechanism Requirements
Fiber (whisker)
pullout
Fibers or whiskers having high
transverse fracture toughness
will cause failure along
fiber/matrix interface leading to
fiberpullout on further straining
Crack impedingFracture toughness of the
second phase (fibersor
particles) is greater than that of
the matrix locally. Crack is either
arrested or bows out (line
tension effect)
Interface
Debonding/
Crack deflection
Weak fiber/matrix interfaces
deflect the propagating crack
away from the principal direction
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36. Application of Ceramic Matrix Materials
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Applications are limited to high temperature applications.
Applications include military, aerospace, wear resistance, heat
resistance, furnace materials, energy conversion systems, gas
turbines, heat engines, energy efficient systems, transportation.
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38. Thank You
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