Metals Vs' Ceramics

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Metals Vs. Ceramics
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Properties And Use Of Ceramic Materials
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Advanced Ceramics

• Advanced ceramic materials have been developed
  over the past half century
• Applied as thermal barrier coatings to protect
  metal structures, wearing surfaces, or as
  integral components by themselves.
• Engine applications are very common for this
  class of material which includes silicon nitride
  (Si3N4), silicon carbide (SiC), Zirconia (ZrO2)
  and Alumina (Al2O3)
• Heat resistance and other desirable properties
  have lead to the development of methods to
  toughen the material by reinforcement with fibers
  and whiskers opening up more applications for
  ceramics

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Engine Components
Rotor (Alumina)
Gears (Alumina)
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Turbo Charger
Ceramic Rotor
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Candidate Materials for Turbocharger
g/cm3
MPa
GPa
(1000C)
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Glasses and Glass Processing
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Compositions of Commercial Glasses
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Pressed Glass Processing
Softened Gob
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Blow Molding
Softened glass
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Plate Glass Drawing Processes
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Tempered Glass
Small Scratches

• The strength of glass can be enhanced by inducing
  compressive residual stresses at the surface.
• Two methods are used
• Thermal Tempering
• Chemical Hardening
• The surface stays in compression - closing small
  scratches and cracks.

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Hardening Processes

• Tempering
• Glass heated above Tg but below the softening
  point
• Cooled to room temp in air or oil
• Surface cools to below Tg before interior
• when interior cools and contracts it draws the
  exterior into compression.
• Chemical Hardening
• Cations with large ionic radius are diffused into
  the surface
• This strains the lattice inducing compressive
  strains and stresses.

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Ceramic Processing
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Slip Casting
Sinter and Serve
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Powder Pressing Process
Filling Mould
Green part ejected - then sintered
Compaction
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Sintering Process
Pressed Ceramic Particles
Sintered for a short time
Sintered for a long time
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Glass Ceramics

• These are primarily silicates containing oxides
  such as Alumina (AL2O3), TiO2, LiO2, and others.
  
• In amorphous form, the glasses are transparent.
  Most glasses can be made to transform into a
  polycrystalline state by a suitable
  heat-treatment process, called devitrification.
• An initiator, such as TiO2, is added to begin the
  nucleation of ceramic crystals. The product is
  called a glass ceramic.
• Desirable properties include high strength and
  thermal conductivity, low thermal expansion,
  resistant to thermal shock, ease of fabrication.
  using conventional methods.

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Refractories

• Used to provide thermal protection of other
  materials in very high temperature applications,
  such as steel making (Tm1500C), metal foundry
  operations, etc.
• They are usually composed of alumina (Tm2050C)
  and silica along with other oxides MgO
  (Tm2850C), Fe2O3, TiO2, etc., and have
  intrinsic porosity typically greater than 10 by
  volume.
• Specialized refractories, (those already
  mentioned) and BeO, ZrO2, mullite, SiC, and
  graphite with low porosity are also used.

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Ceramic - Composite Armor
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Ceramic Armor

• Ceramic armor systems are used to protect
  military personnel and equipment.
• Advantage low density of the material can lead
  to weight efficient armor systems.
• Typical ceramic materials used in armor systems
  include alumina, boron carbide, silicon carbide,
  and titanium diboride.
• The ceramic material is discontinuous and is
  sandwiched between a more ductile outer and inner
  skin.
• The outer skin must be hard enough to shatter the
  projectile.

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• Most of the impact energy is absorbed by the
  fracturing of the ceramic and any remaining
  kinetic energy is absorbed by the inner skin,
  that also serves to contain the fragments of the
  ceramic and the projectile preventing severe
  impact with the personnel/equipment being
  protected.
• CF uses alumina ceramic/Kevlar composite system
  in sheets about 20mm thick and having a bulk
  density of about 2.5 g/cm3 to protect key areas
  of Hercules aircraft (cockpit crew/instruments
  and loadmaster station).
• This lightweight solution provided an efficient
  and removable/replaceable armor system. Similar
  systems used on APCs