CHAPTER 12Applications and Processing of Materials

(1) FORGINGDeforming a single piece of a normally hot metal (closed or open die).(2) ROLLINGFor production of sheet, strip, and foil (circular shapes, I-beams and railroad rails using rooved rolls). (3) EXTRUSION For rods and tubing.(4) DRAWINGFor rod, wire and tubing.The shape of a metal piece is changed by plastic deformation: forging, rolling, extrusion, and drawing,Hot working or cold working (denpending on forming temperatune)12-I. Processing and Applications of Metallic MaterialsA-1. Forming by deformation (low m.p. & ductile)A. Fabrication of Metallic Materials

A-2. Casting (low m.p.)A totally molten metal is poured into a mold cavity having the desired shape.Good for (1) large or complicated object, (2) low in ductility, (3)economical ,A number of different casting techniques sand casting die casting investment casting continuous casting

minerals metal blocks metal powder powder compacts metal products A-3. Powder Metallurgy (P/M)Compaction of powdered metal, followed by a heat treatment (sintering) to produce a dense piece.

P/M especiallys suitable for metals having low ductilities, and metals having high melting temperatures (same reason that P/M is the major fabrication technigue for ceramics): sintering temperatune = ~0.75m.p.atomization Shape forming sintering

A. Types And Applications Of CeramicsA-1. Glasses and Glass CeramicsApplications: containers, windows, lenses, and fiberglass.Noncrystalline silicates containing other oxides, notable CaO, Na2O, K2O, and Al2O3. A typical soda-lime glass: 70wt% SiO2 with Na2O (soda ) and CaO (lime). Two prime assets: optical transparency and the relative ease for fabrication.

Most inorganic glasses can be made to transform a noncrystalline state to crystalline by heat treatemet: devitrification, the product is a fine-grained polycrystalline material: glass-ceramic. A nucleating agent (frequently titanium dioxide) must be added to induce the crystallization or devitrification process. F13-1F12-10F12-11T13-1 Glasses Glass-ceramics12-II. Applications and Processing of Ceramics

Glass-ceramics trade names: Pyroceram, Corningware, cercor, and Vision.Applications: ovenware, tableware, electrical insulators, substrates for printed circuit boards, architectural cladding, heat exchangers and regenerators: primarily because of their good strength, excellent resistance to thermal shock, and their high thermal conductivity. A-2. Clay ProductsInexpensive: found naturally in great abundance.One of the most widely used ceramic raw materials:ease with which clay products may be formed: mix clay and water, amenable to shaping and then dried and fired at an elevated temperature.Desirable characteristics of glass-ceramic: ware will not experience thermal shock; relatively high mechanical strengths and thermal conductivities. Some glass-ceramics may be made optically transparent; others are opaque.

Two broad classifications: the structural clay products and the whitewares. Structural clay products: building bricks, tiles, and sewer pipes.Whiteware ceramics: become white after firing: porcelain, pottery, tableware, china, and plumbing fixtures (sanitary ware).A-3. RefractoriesCapacity to withstand high temperatures without melting or decomposing; remain unreactive and inert; ability to provide thermal insulation;Applications: furnace linings for metal refining , glass manufacturing, metallurgical heat treatment, and power generation Classifications: fireclay, silica, basic, and special refractories. Raw ingredients: consist of of both large (or grog) particles and fine particles, the fine particles normally are involved in the formation of a bonding phase.T13-2

Porosity must be controlled to produce a suitable refractory brick. Strength, load-bearing capacity, and resistance to attack by corrosive materials all increase with porosity reduction. At the same time, thermal insulation characteristics and resistance to thermal shock are diminished Fireclay RefractoriesContaining between 25 and 45 wt% alumina. According to the SiO2-Al2O3 phase diagram, Figure 12.27, the highest temperature possible without the formation of a liquid phase is 1587.Upgrading the alumina content will increase the maximum service temperature, Used principally in furnace construction. To confine hot atomopsheres, and to thermally insulate structural members from excessive temperatures. Strength is not ordinarily an important cosiderationF12-27Alumina and silica mixtures

Silica RefractoriesUsed in the arched roofs of steel-and glass-making furnaces;Temperatures as high as 1650may be realized. The presence of even small concentrations of alumina has an adverse influence On the performance of these refractories. Thus, the alumina content should be held to a minimum, normally to between 0.2 and 1.0 wt% Basic RefractoriesRich in periclase, or magnesia (MgO), termed basic; use in some steel-making open hearth furnacesF12-27

Special RefractoriesSome are relatively high-purity oxide materials: alumina, silica, magnesia, beryllia (BeO), ziconia (ZrO2), and mullite (3Al2O3-2SiO2); Others include: carbide compounds, e.g., silicon carbide (SiC). (Graphite are very refractory, but find limited application Because they are susceptible to oxidation at temperatures in excess of about 800.)A-4. Abrasives ()Used to wear, grind, or cut away other material.Prime requisite: hardness or wear resistance, high degree of toughness, refractoriness (high temperatures may be produced from abrasive frictional forces.)F13-2

Diamonds,( natural and synthetic, relatively expensive), silicon carbide, tungsten Carbide (WC), aluminum oxide (or corundum), and silica sand.Used in several forms: bonded to grinding wheels, as coated abrasives, and as loose grains. Bonded to grinding wheels: The abrasive particles are bonded to a wheel by means of a glassy ceramic or an organic resin. A continual flow of air currents or liquid coolants within the pores that surround the refractory grains prevents excessive heatingCoated abrasives: abrasive powder is coated on some type of paper or cloth Material (sandpaper) Loose abrasive grains: icon carbide, and rouge (an iron oxide)

A-5. CementsCements: cement, plaster of paris, and lime. Characteristic feature: when mixed with water, they form a paste that subsequently sets and hardens, especially useful in: solid and rigid strucures having just about and shapeas a bonding phase that chemically binds particulate aggregates into a single cohesive structure.Produced by: grinding and mixing clay and lime-bearing minerals, heating to about 1400, ground into a very fine powder with added a small amount of gypsum (CaSO4-2H2O). The setting and hardening of this material result from relatively complicated hydration reactions that occur between the various cement constituents and the water, for example Similar to that of the glassy bonding phase that forms when clay products and some refractory bricks are fired. One important difference: cementitious bond develops at room temperature.

2CaO-SiO2+xH2O = 2CaO-SiO2-xH2O (13.1)Setting (i.e., the stiffening of the once-plasticpaste) takes place soon after within several hours. Hardening of the mass follows as a result of further hydration, a relatively slow process that may continue for as long as several years. (not one of drying)Portland cement is termed a hydraulic cement: its hardness develops by chemical reactions with water. It is used in concrete to bind aggregates of inert particles (sand and/or gravel): composite materialsOther cement materials: are nonhydraulic compounds other than water(e.g., CO2) are involved in the hardening reaction.

A-6. Advanced CeramicsTraditional ceramics IntroductionGlasses and Glass CeramicsClay ProductsRefractoriesABRASIVES ()CEMENTSAdvanced ceramics:Chemical (corrosion resistance)MechanicalOpticalElectricalOpto electricalMagneticBiologicalSensor LuminescenceSuperconductionPiezoelectric

B. Fabrication of Ceramic MaterialsPhysical Forms of Inorganic (ceramic) materialsPowders (zero-dimensional materials)Fibers, whiskers () (one-dimensional materials)Films, coatings (two-dimensional materials)Monolithic, bulk (three-dimensional materials)

Fabrication of Monolithic Ceramics Powder Metallurgy (P/M) (high m.p. and brittleness forming by deformation (X), casting (X) )(starting materials)

() pressingPowderBinder and Lubricantdieapplying pressure(to achieve compaction)the desired shapedensificationLubricant(in general, wax, e.g., paraffin poly (ethylene glycol)) to provide lubrication so that the powder is free flowing (fill all corners of the die and to achieve compaction) minimize die stickingB-1. Major Techniques of Shape Forming for Ceramic Fabrication () pressing, () casting, () plastic forming, () others

Binder( in general polymers, e.g., cellulose and poly (vinyl alcohol))give the pressed part enough strength and toughness that is can be handled and even machined prior to densification.(2) lubrication both lubricant and binder should be removed (usually thermal decomposition) before densification.(1) Uniaxial Pressing Press he powder compact by applying a pressure in one direction problemsobject with a long dimension ()(due to powder- wall and powder- powder friction) 1. density variation (nonuniformity) 2. die wear(2) Isostatic Pressing (CIP) (hydrostatic pressing) apply pressure equally to the powder from all the sides This substantially reduces the problems of non- uniformity.282930

() Casting ()powder (suspended in a liquid)castintoporous mold e.g., gypsum ()liquidparticulate compact in the mold() Plastic Formingpowder25-30% organic additives(to achieve adequate plasticity for forming) ()plastic ()

injection molding ()extrusion molding ()firing (sintering)removing the organic additives (a major problem)() other Techniques (a) tape forming e.g., electronic substrates, LED chip submounts. (b) ceramic coating (c) CVD (d) SHS (HPCS, surface coating)

B-2. Sintering (Densification) Densification (Sintering) removal of pores among the starting particles, combined with growth together and formation strong bonding between adjacent particles. Sinteringmaterial transport (removal of pores, filling of material into pores) is necessary for sintering Two major types of sintering solid state sintering no sintering aids added no formation of liquid phase during sintering liquid phase sintering with addition of sintering aids liquid phase is formed during (before) sintering (forming low m.p. solution, e.g., eutetic composition)

the driving forces for sintering (i.e., material transport) (1) surface energy (2) capillary pressure (3) difference in vapor pressure (4) difference in solubilityexample 1F 12.25example 2F 10.1B-2-2. Initial Stage of Sintering

(1) surface energy decrease in pore size (removal of pores) decrease in surface area (elimination of surface) decrease in energy (minimize the energy)F 10.9F 10.13F 10.2Particle size mass transport rate shorter diffusion path

PP the liquid in the tube is pushed up90 180PP the liquid in the tube is pushed down until balanced by lgh(2) Capillary Pressure

Pr-PPr+

(3) Difference in Vapor PressureF 2.3F 10.18

(4) Difference in Solubility (liquid phase sintering with sintering aid)F 2.9

Mechanisms of Initial Stage SinteringF 10.21

B-2-3. Subsequent Stage of SinteringGrain GrowthLarger grains grow, and smaller grains shrink and disappear finally. i.e., grains with concave surface grow, and grains with convex surface shrink and disappear finally.Larger grains more sides larger angle concave surface Smaller grains LESS sides smaller angle convex surface

Smaller grain convex surfacer+ Larger grain concave surfacer- Pr+ > r- Gr+ > Gr-F 10.19Mass transport direction and boundary moving directionF 7.24Equilibrium grain geometroy six sidedm 120 , and flat surface (grain boundary)gb=2 gb cos 60 F 10.16

to achieve maximum particle packing uniformityto obtain minimum shrinkage and porosity Indeal Powder (1) small particle size (i) higher packing density (ii) higher reactivity (iii) minimizing diffusion distance The Fabrication ProcessB-2-4. Ideal Powders for Sintering

(2) Spherical shape: east to flow to achieve high paching density(3) freedom from agglomeration (otherwise resulting in void formation)(4) a narrow range of sizes ( ) (but A single particle size does not produce good packing, a proper range of distribution is required, e.g., bimodel or trimodel distribution.)(5) Chemical homogeneity(6) suitable crystalline structure(7) high purity

ReactivityThe primary driving force for densification of a compated powder at high temperature is the change in surface energy.size surface energy thermodynamic driving force (to decrease their surface area by bonding together )size effects on densitySi3N42m 90% theoretical density1m 95% theoretical densitysize effects on sintering temperature and time The small the particle size, the lower is the temperature required to achieve sintering and less time is required.

sinteringdesirableconditionslower temp.shorter timelower temp lower cost, easy processingShorter time lower cost, higher production rate, better property by reducing grain growth2m 0.1m4 hr 1 hr1400 110090%

Application of AlN on Semiconductor Substrate L A M S A PDimension50 50 1 mm

L A M S A PApplication of AlN on LED Substrate AlNW padW layerDimension9.5 9.5 1 mmGreen CompactSintered Body