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CHAPTER 12

CHAPTER 12. Applications and Processing of Materials. F 11.7. F 11.6. 12-I. Processing and Applications of Metallic Materials. A. Fabrication of Metallic Materials. A-1. Forming by deformation (low m.p. & ductile).

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CHAPTER 12

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  1. CHAPTER 12 Applications and Processing of Materials

  2. F 11.7 F 11.6 12-I. Processing and Applications of Metallic Materials A. Fabrication of Metallic Materials A-1. Forming by deformation (low m.p. & ductile) ˙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) (1) FORGING Deforming a single piece of a normally hot metal (closed or open die). (2) ROLLING For production of sheet, strip, and foil (circular shapes, I-beams and railroad rails using rooved rolls). (3) EXTRUSION For rods and tubing. (4) DRAWING For rod, wire and tubing.

  3. 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

  4. F 10.17 A-3. Powder Metallurgy (P/M) minerals  metal blocks metal powder powder compacts metal products Compaction of powderedmetal, followed by a heat treatment(sintering) to produce a densepiece. P/M especially’s suitable for metals having low ductilities, and metals having high meltingtemperatures (same reason that P/M is the major fabrication technigue for ceramics): sintering temperatune = ~0.75m.p. atomization sintering Shape forming

  5. 12-II. Applications and Processing of Ceramics A. Types And Applications Of Ceramics F13-1 A-1. Glasses and Glass Ceramics T13-1 F12-10 F12-11 ◎ Glasses • Applications: containers, windows, lenses, and fiberglass. • Noncrystalline silicates containing otheroxides, 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 heattreatemet: devitrification, the product is a fine-grainedpolycrystalline material: glass-ceramic. A nucleating agent (frequently titanium dioxide) must be added to induce the crystallization or devitrification process. ◎ Glass-ceramics

  6. 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. • Glass-ceramics trade names: Pyroceram, Corningware, cercor, and Vision. • Applications: ovenware, tableware, electricalinsulators, substratesforprintedcircuitboards, architectural cladding, heatexchangers and regenerators: primarily because of their good strength, excellent resistanceto thermal shock, and their high thermal conductivity. A-2. Clay Products • Inexpensive: 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.

  7. Two broad classifications: the structural clay products and the whitewares. Structural clay products: buildingbricks, tiles, and sewerpipes. Whiteware ceramics: become white after firing: porcelain, pottery, tableware, china, and plumbing fixtures (sanitary ware). A-3. Refractories T13-2 • Capacity to withstand high temperatures without melting or decomposing; remain unreactiveandinert; ability to provide thermalinsulation; • Applications: furnacelinings 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.

  8. Porosity must be controlled to produce a suitable refractory brick. Strength, load-bearing capacity, and resistance to attack by corrosive materials all increasewithporosityreduction. At the same time, thermalinsulation characteristics and resistance to thermal shock are diminished ◎ Fireclay Refractories Alumina and silica mixtures F12-27 • Containing between 25and 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 furnaceconstruction. To confine hot atomopsheres, and to thermally insulate structural members from excessive temperatures. • Strength is not ordinarily an important cosideration

  9. ◎ Silica Refractories F12-27 • Used in the arched roofs of steel-and glass-making furnaces; • Temperatures as high as 1650℃may be realized. The presence of even small • concentrations of alumina has an adverseinfluence • On the performance of these refractories. Thus, the aluminacontentshould • beheldto a minimum, normally to between 0.2 and 1.0 wt% ◎ Basic Refractories Rich in periclase, or magnesia (MgO), termed basic; use in some steel-making open hearth furnaces

  10. ◎ Special Refractories Some 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 (研磨材) F13-2 • Used to wear, grind, or cut away other material. • Prime requisite: hardness or wearresistance, high degree of toughness, refractoriness (high temperatures may be produced from abrasive frictional forces.)

  11. 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 heating • Coated abrasives: abrasive powder is coated on some type of paper or cloth Material (sandpaper) • Loose abrasive grains: icon carbide, and rouge (an iron oxide)

  12. A-5. Cements • Cements: cement, plaster of paris, and lime. • Characteristic feature: when mixed with water, they form a paste that subsequently setsandhardens, especially useful in: • solid and rigid strucures having just about and shape • as a bonding phase that chemically binds particulate aggregates into a single cohesive structure. • 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. 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

  13. 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 materials Other cement materials: are nonhydraulic compounds other than water(e.g., CO2) are involved in the hardening reaction.

  14. A-6. Advanced Ceramics • Advanced ceramics: • Chemical (corrosion resistance) • Mechanical • Optical • Electrical • Opto electrical • Magnetic • Biological • Sensor • Luminescence • Superconduction • Piezoelectric • Traditional ceramics • Introduction • Glasses and Glass Ceramics • Clay Products • Refractories • ABRASIVES (研磨材) • CEMENTS

  15. ◎ Raw Materials (原料) Starting Materials(原材料) synthesis fabrication Ceramic Parts (陶瓷產品) 31 32 34 35 33 powders films, coatings powders monolithic B. Fabrication of Ceramic Materials Physical Forms of Inorganic (ceramic) materials ˙Powders (zero-dimensional materials) ˙Fibers, whiskers (鬚晶) (one-dimensional materials) ˙Films, coatings (two-dimensional materials) ˙Monolithic, bulk (three-dimensional materials)

  16. Chemical synthesis powders Raw materials Shape forming sintering F 10.17 F 2.9 Green compacts Ceramic products ◎ Fabrication of Monolithic Ceramics：Powder Metallurgy (P/M)(high m.p. and brittleness  forming by deformation (X), casting (X) ) (starting materials)

  17. B-1. Major Techniques of Shape Forming for Ceramic Fabrication (一) pressing, (二) casting, (三) plastic forming, (四) others (一) pressing Binder and Lubricant applying pressure Powder die the desired shape (to achieve compaction) densification Lubricant：(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 sticking

  18. 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 problems：object with a long dimension (長的物體) (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. 28 29 30

  19. Plastic (可塑物) starting materials 水(water) hand forming 古老方法： (fraditional method) (clay：白土、紅土、陶土) F 6.14 F 6.7 (二) Casting (澆…於模中) cast porous mold e.g., gypsum (石膏) powder (suspended in a liquid) particulate compact in the mold into liquid (三) Plastic Forming 25-30% organic additives powder plastic (可塑物) (to achieve adequate plasticity for forming) (如塑膠之成形)

  20. F 6.16 46 47 48 49 F 6.14 injection molding (射出成形) firing (sintering) extrusion molding (擠壓成形) removing the organic additives (a major problem) (四) other Techniques (a) tape forming e.g., electronic substrates, LED chip submounts. (b) ceramic coating (c) CVD (d) SHS (HPCS, surface coating)

  21. B-2. Sintering (Densification) ◎Densification (Sintering) ：removal of pores among the starting particles, combined with growth together and formation strong bonding between adjacent particles. Sintering：material 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)

  22. Y2O3 AlNwith YAlO3 (YAP), Al2Y4O9 (YAM) AlN MgO Al2O3 Al2O3 with Al2O3 / MgO example 1 F 12.25 example 2 F 10.1 B-2-2. Initial Stage of Sintering ◎ the driving forces for sintering (i.e., material transport)(1) surface energy(2) capillary pressure(3) difference in vapor pressure(4) difference in solubility

  23. need to achieve mass transport (1) surface energy decrease in pore size (removal of pores) decrease in surface area (elimination of surface) decrease in energy (minimize the energy) F 10.9 F 10.13 F 10.2 Particle size ↓  mass transport rate ↑ ∵ shorter diffusion path

  24. (2) Capillary Pressure ∵P＞P ∴ the liquid in the tube is pushed up 90＜  ≦180° ∵P＞P ∴ the liquid in the tube is pushed down until balanced by lgh

  25. Pr+ P∞ Pr- ＞ ＞ Pr- Pr+ P∞

  26. Pr+ Pr-

  27. (3) Difference in Vapor Pressure F 2.3 F 10.18

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

  29. ◎ Mechanisms of Initial Stage Sintering F 10.21

  30. B-2-3. Subsequent Stage of Sintering：Grain Growth ˙Larger 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

  31. γgb 120° 120° γgb γgb 120° ˙Smaller grain  convex surface：r+ Larger grain  concave surface：r- Pr+ > r-  Gr+ > Gr- F 10.19 ˙Mass transport direction and boundary moving direction F 7.24 ˙Equilibrium grain geometroy：six sidedm 120° , and flat surface (grain boundary) F 10.16 γgb=2 × γgb cos 60°

  32. Powder  shape forming  sintering  ceramic products (loose) (geen density：the higher, the better) (high density, low porosity) (densification) B-2-4. Ideal Powders for Sintering ◎ The Fabrication Process to achieve maximum particle packing uniformity to obtain minimum shrinkage and porosity ◎ Indeal Powder (1) small particle size (i) higher packing density (ii) higher reactivity (iii) minimizing diffusion distance

  33. (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 (少量大晶粒  強度上的大弱點) (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

  34. Reactivity：The primary driving force for densification of a • compated powder at high temperature is the change • in surface energy. • size 越小  surface energy 越大  thermodynamic driving force 越大 • (to decrease their surface area by bonding together ) • size effects on density 2m 90% theoretical density ＜1m 95% theoretical density Si3N4 • size 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.

  35. desirable sintering lower temp. shorter time conditions lower temp： lower cost, easy processing Shorter time： lower cost, higher production rate, better property by reducing grain growth 2m  0.1m 4 hr  1 hr 1400℃  1100℃ 90% 

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