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Ceramics Metals Metals Vs. Ceramics Properties And Use Of Ceramic Materials Advanced Ceramics Advanced ceramic materials have been developed over the past half century

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advanced ceramics
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
engine components
Engine Components

Rotor (Alumina)

Gears (Alumina)

turbo charger
Turbo Charger

Ceramic Rotor

blow molding
Blow Molding

Softened

glass

tempered glass
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.
hardening processes
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.
slip casting
Slip Casting

Sinter

and

Serve

powder pressing process
Powder Pressing Process

Filling

Mould

Green part

ejected - then

sintered

Compaction

sintering process
Sintering Process

Pressed Ceramic

Particles

Sintered for

a short time

Sintered for

a long time

glass ceramics
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.
refractories
Refractories
  • Used to provide thermal protection of other materials in very high temperature applications, such as steel making (Tm=1500°C), metal foundry operations, etc.
  • They are usually composed of alumina (Tm=2050°C) and silica along with other oxides: MgO (Tm=2850°C), 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.
ceramic armor
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.
slide22
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 APC’s