Day 22: Overview of Advantages of Ceramics • temperature resistance • high hardness • low density • corrosion resistance
Special Design Considerations for Ceramics • brittleness • difficulty of manufacture.
Strength Richerson, 1992
Common Structural Ceramics • silicon carbide (SiC) • silicon nitride (Si3N4) • zirconia (ZrO2) • alumina (Al2O3)
Manufacturing Ceramics • The following methods are used to shape the ceramics. Please not that (wetted) powder is key.
Sintering • This is a process in which the small chunks of powder loose their identity, as the whole (porous) part is bonded. Temperature and often pressure are needed. Shrinkage has to be understood.
Die Pressing (Uniaxial Pressing) • Most common and rapid for small ceramic components where speed of manufacture means more than strength and uniformity. • Pressure, and densification is variable through the mold. The object will have varying properties, and maybe differential shrinkage on sintering. • Hot pressing is a combination of sintering and die-pressing happening at once.
Isotactic Pressing • Pressure transmitted to the powder from a compressed fluid. • More uniformity, less porosity • An elastomer (rubber mold) serves as the interface. • Slower rate of production. • Best for cylindrical shapes, eg. Spark plug. Hot isotact pressing (HIP) combines sintering and isotactic pressing.
Extrusion • We add a plasticizing agent, which is later cooked away during sintering.
Slip Casting • Make a slurry by adding liquid to the powder. • Pour into a porous mold. • Fluid is absorbed by the mold leaving a drier layer of powder along the walls. • Pour off remaining slurry, slip. Opening the mold reveals the thin-walled object. • Ready to be sintered.
Injection Molding • This method holds the most promise for mass production of complex shapes as evidenced by its use in producing ceramic turbocharger rotors. A combination of 60-70% powder mixed with an organic binder to provide flow is injected into a mold. Prior to sintering, burnout of the binder must be done. Current restrictions include small wall thickness. Because of the cost of equipment, this is only cost-effective for large volumes, and for simple shapes, the dry pressing methods are more cost-effective.
Reaction Bonding • A solid powder and a gas or liquid react during sintering to densify and bond. • In Reaction Bonded Silicon Nitride, silicon powder is fired in the presence of high pressure nitrogen gas, and the reaction forms Si3N4. • Advantage: very low shrinkage. • Disadvantage: high porosity and lower strengths.
More Reaction Bonding • Reaction bonded silicon carbide, RBSC, is made by infiltrating liquid silicon into a compact of carbon and silicon carbide. The Si reacts with the carbon to form SiC which then bonds with the original SiC particles. Pores are filled with liquid Si. Consequently, high temperature strength falls off at silicon's melting temperature. Dimensional changes with RBSC can be less than 1%. One interesting variation is to use carbon fibers rather than carbon particles.
Engine Products Kyocera engine products include cam rollers, turbocharger rotors, glow plugs, cylinder liners, seals, pistons, piston pins, valve and valve guides, fuel injection parts and various custom made components made from a wide selection of advanced ceramic materials. Ceramic Seal Assembly Ceramic Piston Head and Rings Ceramic Turbocharger Rotor Ceramic Cam Roller
Textile Manufacturing Kyocera's wide range of ceramic materials, such as alumina, cermet, sapphire, zirconia and silicon nitride, coupled with excellent forming and finishing capabilities provides the basis for expanding the applications of ceramic textile components. Guides and Finish Tips http://americas.kyocera.com/kicc/industrial/textiles.html
Seal, Pump and Valve Kyocera seal, pump and valve products include alumina faucet discs, alumina and silicon carbide automotive water pump seals, alumina appliance seals, alumina blood seals, zirconia containment shells and various custom made components made from a wide range of advanced ceramic materials. Shafts and Valves Pump Parts http://americas.kyocera.com/kicc/industrial/seal.html
Hip implants • Advantages of Ceramics • Low friction • Biocompatibility • Compressive strength http://ceramics.org/ceramictechtoday/tag/capacitor/ http://www.amjorthopedics.com/html/new/0605.asp
Hip implants • Disadvantage of Ceramics • Low Ductility http://emedicine.medscape.com/article/398669-media
THERMAL SHOCK RESISTANCE http://americas.kyocera.com/kicc/industrial/seal.html
Alumina Alumina is the most widely used advanced ceramic material. It offers very good performance in terms of wear resistance, corrosion resistance and strength at a reasonable price. Its high dielectric properties are beneficial in electronic products.Applications include armor, semiconductor processing equipment parts, faucet disc valves, seals, electronic substrates and industrial machine components. http://americas.kyocera.com/kicc/industrial/types.html
Silicon Carbide Silicon carbide has the highest corrosion resistance of all the advanced ceramic materials. It also retains its strength at temperatures as high as 1400°C and offers excellent wear resistance and thermal shock resistance.Applications include armor, mechanical seals, nozzles, silicon wafer polishing plates and pump parts. http://americas.kyocera.com/kicc/industrial/types.html
Silicon Nitride Silicon nitride exceeds other ceramic materials in thermal shock resistance. It also offers an excellent combination of low density, high strength, low thermal expansion and good corrosion resistance and fracture toughness.Applications include various aerospace and automotive engine components, papermaking machine wear surfaces, armor, burner nozzles and molten metal processing parts. http://americas.kyocera.com/kicc/industrial/types.html
Zirconia Zirconia has the highest strength and toughness at room temperature of all the advanced ceramic materials. The fine grain size allows for extremely smooth surfaces and sharp edges.Applications include scissors, knifes, slitters, pump shafts, metal-forming tools, fixtures, tweezers, wire drawing rings, bearing sleeves and valves. http://americas.kyocera.com/kicc/industrial/types.html
Summary of Materials • Hot-pressed silicon nitride (HPSN) has the strongest specific strength (strength/density) at 600oC of any material. It has excellent thermal shock resistance. • Sintered silicon nitride (SSN) has high strength and can be formed into complex shapes. • Reaction-bonded silicon nitride (RSBN) can be formed into complex shapes with no firing shrinkage. • Hot-pressed silicon carbide (HPSC) is the strongest of the silicon carbide family and maintains strength to very high temperatures (1500oC). • Sintered silicon carbide (SSC) has high temperature capability and can be formed into complex shapes • Reaction-bonded silicon carbide (RSBC) can be formed into complex shapes and has high thermal conductivity. • Partially stabilized zirconia (PSZ) is a good insulator and has high strength and toughness. It has thermal expansion close to iron, facilitating shrink fit attachments.