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By :-
Sara Hamid Shahatha
Ceramic Matrix
Composites
Ceramic Matrix Composites
• Ceramic materials are in general brittle, and,
according to the fracture mechanics, the strength
is governed by the flaw size and the fracture
toughness.
• General approaches for producing strong
ceramics are to reduce the maximum size of
processing flaws or to enhance the fracture
toughness.
• The former approach, however, is limited by the
nature of the microstructure of ceramics, since a
grain boundary itself can be a flaw responsible for
brittle fracture, and surface flaws generated in use
may also reduce the strength of ceramics.
• The fracture toughness of ceramics is improved
by introduction of secondary phases into matrix
materials when the secondary phases are chosen to
act as barriers to crack propagation.
Ceramic Matrix Composites
Ceramic Matrix Composites
• Whiskers introduced into a ceramic matrix, for
example, can retard the crack propagation
because the stresses in a whisker spanning the
crack plane will tend to pull the crack shut. This
phenomenon, known as "crack bridging", leads to
higher fracture toughness due to the additional
stress required for further propagation of the
crack
Ceramic Matrix Composites
Ceramic matrix composites may be classified into two
categories:-
 Toughened Ceramics Reinforced with Particulates and
Whiskers and their properties are exhibit brittle behavior
in spite of considerable improvements in fracture
toughness and strength. The maximum in fracture
toughness is around 10 MPa.m1/2 or more.
 Continuous-fiber Composites, the fracture toughness
of this class of materials can be higher than 20 MPa.m1/2
when produced with weak interfaces between the fibers
and matrix.
Ceramic Matrix Composites
Some important point that should be considered when
study Ceramic-Matrix Composites :-
The matrix is relatively hard and brittle.
The reinforcement must have high tensile strength to
arrest crack growth.
The reinforcement must be free to pull out as a crack
extends, so the reinforcement-matrix bond must be
relatively weak
Types of Fibers and whiskers for
reinforcement
Types of Fibers and whiskers for reinforcement
(typical diameters – fibers 10 μm, whiskers 1-5
μm):-
 Carbon fibers
 SiC fibers
 Oxide fibers (glass fibers, mullite fibers, zirconia
fibers, alumina fibers)
 SiC whiskers
Types of Ceramic-Matrix
Composites
Carbon- Carbon Composites
Glass-Matrix Composites
SiC- SiC Composites
Eutectic Composites (Al2O3-Y3Al5O12)
The choice of method is
determined by
The choice of method is determined by the:-
 Geometry,
 The complexity of shape and
 The production volume of the component
 To put a rigidized or densified matrix in place, the precursor
of the matrix has to be positioned within the mass of
reinforcement. This can be done by a number of methods:-
 Powder dispersion
 Liquid precursors
 Gaseous infiltration
Powder Dispersion
Impregnating the reinforcement with a
suspension of matrix precursor in powder
form, either by passing the reinforcement
through a slurry or by pressure impregnation
of a preform, or by electrophoretic infiltration.
Liquid Precursors
Impregnating the reinforcement
preform with a liquid organic or
organometallic or inorganic substance,
typically a polymer or a sol, which on
heating rigidizes by curing or gelling, and
then decomposes to leave a ceramic
matrix.
Gaseous infiltration
Using a reactive gas mixture which
deposits a ceramic material within a
preform of the reinforcement, commonly
known as chemical vapor deposition
(CVD) or chemical vapor infiltration
(CVI), and typically performed at high
temperature.
Ceramic-Matrix Composites
may be fabricated using these methods
oHot Pressing
oHot Isostatic Pressing
oLiquid Phase Sintering Techniques
Application
CMC materials overcome the major
disadvantages of conventional technical
ceramics, namely brittle failure and low
fracture toughness, and limited thermal shock
resistance. Therefore, their applications are in
fields requiring reliability at high-temperatures
(beyond the capability of metals) and
resistance to corrosion and wear. These
include:-
 Heat shield systems for space vehicles, which are
needed during the re-entry phase, where high
temperatures, thermal shock conditions and heavy
vibration loads take place.
 Components for high-temperature gas turbines such
as combustion chambers, stator vanes and turbine
blades.
 Components for burners, flame holders, and hot gas
ducts, where the use of oxide CMCs has found its
way.
Application
Brake disks and brake system
components, which experience extreme
thermal shock (greater than throwing a
glowing part of any material into water).
 Component for slide bearings under
heavy loads requiring high corrosion and
wear resistance.
Application
Fig (1) Shows Ceramic Matrix Composite
Turbine Blade
Thank You For Listening

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Ceramic Matrix Composites

  • 1. By :- Sara Hamid Shahatha Ceramic Matrix Composites
  • 2. Ceramic Matrix Composites • Ceramic materials are in general brittle, and, according to the fracture mechanics, the strength is governed by the flaw size and the fracture toughness. • General approaches for producing strong ceramics are to reduce the maximum size of processing flaws or to enhance the fracture toughness.
  • 3. • The former approach, however, is limited by the nature of the microstructure of ceramics, since a grain boundary itself can be a flaw responsible for brittle fracture, and surface flaws generated in use may also reduce the strength of ceramics. • The fracture toughness of ceramics is improved by introduction of secondary phases into matrix materials when the secondary phases are chosen to act as barriers to crack propagation. Ceramic Matrix Composites
  • 4. Ceramic Matrix Composites • Whiskers introduced into a ceramic matrix, for example, can retard the crack propagation because the stresses in a whisker spanning the crack plane will tend to pull the crack shut. This phenomenon, known as "crack bridging", leads to higher fracture toughness due to the additional stress required for further propagation of the crack
  • 5. Ceramic Matrix Composites Ceramic matrix composites may be classified into two categories:-  Toughened Ceramics Reinforced with Particulates and Whiskers and their properties are exhibit brittle behavior in spite of considerable improvements in fracture toughness and strength. The maximum in fracture toughness is around 10 MPa.m1/2 or more.  Continuous-fiber Composites, the fracture toughness of this class of materials can be higher than 20 MPa.m1/2 when produced with weak interfaces between the fibers and matrix.
  • 6. Ceramic Matrix Composites Some important point that should be considered when study Ceramic-Matrix Composites :- The matrix is relatively hard and brittle. The reinforcement must have high tensile strength to arrest crack growth. The reinforcement must be free to pull out as a crack extends, so the reinforcement-matrix bond must be relatively weak
  • 7. Types of Fibers and whiskers for reinforcement Types of Fibers and whiskers for reinforcement (typical diameters – fibers 10 μm, whiskers 1-5 μm):-  Carbon fibers  SiC fibers  Oxide fibers (glass fibers, mullite fibers, zirconia fibers, alumina fibers)  SiC whiskers
  • 8. Types of Ceramic-Matrix Composites Carbon- Carbon Composites Glass-Matrix Composites SiC- SiC Composites Eutectic Composites (Al2O3-Y3Al5O12)
  • 9. The choice of method is determined by The choice of method is determined by the:-  Geometry,  The complexity of shape and  The production volume of the component  To put a rigidized or densified matrix in place, the precursor of the matrix has to be positioned within the mass of reinforcement. This can be done by a number of methods:-  Powder dispersion  Liquid precursors  Gaseous infiltration
  • 10. Powder Dispersion Impregnating the reinforcement with a suspension of matrix precursor in powder form, either by passing the reinforcement through a slurry or by pressure impregnation of a preform, or by electrophoretic infiltration.
  • 11. Liquid Precursors Impregnating the reinforcement preform with a liquid organic or organometallic or inorganic substance, typically a polymer or a sol, which on heating rigidizes by curing or gelling, and then decomposes to leave a ceramic matrix.
  • 12. Gaseous infiltration Using a reactive gas mixture which deposits a ceramic material within a preform of the reinforcement, commonly known as chemical vapor deposition (CVD) or chemical vapor infiltration (CVI), and typically performed at high temperature.
  • 13. Ceramic-Matrix Composites may be fabricated using these methods oHot Pressing oHot Isostatic Pressing oLiquid Phase Sintering Techniques
  • 14. Application CMC materials overcome the major disadvantages of conventional technical ceramics, namely brittle failure and low fracture toughness, and limited thermal shock resistance. Therefore, their applications are in fields requiring reliability at high-temperatures (beyond the capability of metals) and resistance to corrosion and wear. These include:-
  • 15.  Heat shield systems for space vehicles, which are needed during the re-entry phase, where high temperatures, thermal shock conditions and heavy vibration loads take place.  Components for high-temperature gas turbines such as combustion chambers, stator vanes and turbine blades.  Components for burners, flame holders, and hot gas ducts, where the use of oxide CMCs has found its way. Application
  • 16. Brake disks and brake system components, which experience extreme thermal shock (greater than throwing a glowing part of any material into water).  Component for slide bearings under heavy loads requiring high corrosion and wear resistance. Application
  • 17. Fig (1) Shows Ceramic Matrix Composite Turbine Blade
  • 18. Thank You For Listening