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ISSUES TO ADDRESS... What are the common fabrication techniques for metals? How do the properties vary throughout a piece of metal that has been quenched?

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Presentation on theme: "ISSUES TO ADDRESS... What are the common fabrication techniques for metals? How do the properties vary throughout a piece of metal that has been quenched?"— Presentation transcript:

1 ISSUES TO ADDRESS... What are the common fabrication techniques for metals? How do the properties vary throughout a piece of metal that has been quenched? How can properties be modified by a post heat treatment? How is the processing of ceramics different than for metals? 1 CHAPTER 14: SYNTHESIS, FABRICATION, AND PROCESSING OF MATERIALS

2 2 REFINEMENT OF STEEL FROM ORE

3 3 Forging (wrenches, crankshafts) FORMING Drawing (rods, wire, tubing) often at elev. T Rolling (I-beams, rails) Extrusion (rods, tubing) Adapted from Fig. 11.7, Callister 6e. METAL FABRICATION METHODS- I

4 7 Hot working -- recrystallization --less energy to deform --oxidation: poor finish --lower strength Cold working -- recrystallization --less energy to deform --oxidation: poor finish --lower strength Cold worked microstructures --generally are very anisotropic! --Forged--Fracture resistant! Reprinted w/ permission from R.W. Hertzberg, "Deformation and Fracture Mechanics of Engineering Materials", (4th ed.), John Wiley and Sons, Inc., (a) Fig. 10.5, p. 410 (micrograph courtesy of G. Vander Voort, Car Tech Corp.); (b) Fig. 10.6(b), p. 411 (Orig. source: J.F. Peck and D.A. Thomas, Trans. Metall. Soc. AIME, 1961, p. 1240); (c) Fig , p. 415 (Orig. source: A.J. McEvily, Jr. and R.H. Bush, Trans. ASM 55, 1962, p. 654.) (a) (b)(c) --Swaged FORMING TEMPERATURE

5 plaster die formed around wax prototype 5 CASTING Sand Casting (large parts, e.g., auto engine blocks) Investment Casting (low volume, complex shapes e.g., jewelry, turbine blades) Die Casting (high volume, low T alloys) Continuous Casting (simple slab shapes) METAL FABRICATION METHODS- II

6 6 JOINING Powder Processing (materials w/low ductility) Welding (when one large part is impractical) Heat affected zone: (region in which the microstructure has been changed). Adapted from Fig. 11.8, Callister 6e. (Fig from Iron Castings Handbook, C.F. Walton and T.J. Opar (Ed.), 1981.) METAL FABRICATION METHODS- III

7 7 Annealing: Heat to T anneal, then cool slowly. Based on discussion in Section 11.7, Callister 6e. THERMAL PROCESSING OF METALS

8 8 Ability to form martensite Jominy end quench test to measure hardenability. Hardness versus distance from the quenched end. Adapted from Fig , Callister 6e. (Fig adapted from A.G. Guy, Essentials of Materials Science, McGraw-Hill Book Company, New York, 1978.) Adapted from Fig , Callister 6e. HARDENABILITY--STEELS

9 9 The cooling rate varies with position. Adapted from Fig , Callister 6e. (Fig adapted from H. Boyer (Ed.) Atlas of Isothermal Transformation and Cooling Transformation Diagrams, American Society for Metals, 1977, p. 376.) WHY HARDNESS CHANGES W/POSITION

10 13 Jominy end quench results, C = 0.4wt%C "Alloy Steels" (4140, 4340, 5140, 8640) --contain Ni, Cr, Mo (0.2 to 2wt%) --these elements shift the "nose". --martensite is easier to form. Adapted from Fig , Callister 6e. (Fig adapted from figure furnished courtesy Republic Steel Corporation.) HARDENABILITY VS ALLOY CONTENT

11 11 Effect of quenching medium: Medium air oil water Severity of Quench small moderate large Hardness small moderate large Effect of geometry: When surface-to-volume ratio increases: --cooling rate increases --hardness increases Position center surface Cooling rate small large Hardness small large QUENCHING MEDIUM & GEOMETRY

12 12 Ex: Round bar, 1040 steel, water quenched, 2" diam. Adapted from Fig , Callister 6e. PREDICTING HARDNESS PROFILES

13 13 Pressing: GLASS FORMING Blowing: Fiber drawing: Adapted from Fig. 13.7, Callister, 6e. (Fig is adapted from C.J. Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.) CERAMIC FABRICATION METHODS-I

14 14 Quartz is crystalline SiO 2 : Basic Unit: Glass is amorphous Amorphous structure occurs by adding impurities (Na +,Mg 2+,Ca 2+, Al 3+ ) Impurities: interfere with formation of crystalline structure. (soda glass) Adapted from Fig , Callister, 6e. GLASS STRUCTURE

15 15 Specific volume (1 ) vs Temperature (T): Glasses: --do not crystallize --spec. vol. varies smoothly with T --Glass transition temp, T g Crystalline materials: --crystallize at melting temp, T m --have abrupt change in spec. vol. at T m Viscosity: --relates shear stress & velocity gradient: --has units of (Pa-s) Adapted from Fig. 13.5, Callister, 6e. GLASS PROPERTIES

16 16 Viscosity decreases with T Impurities lower T deform Adapted from Fig. 13.6, Callister, 6e. (Fig is from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262.) GLASS VISCOSITY VS T AND IMPURITIES

17 17 Annealing: --removes internal stress caused by uneven cooling. Tempering: --puts surface of glass part into compression --suppresses growth of cracks from surface scratches. --sequence: --Result: surface crack growth is suppressed. HEAT TREATING GLASS

18 Milling and screening: desired particle size PARTICULATE FORMING Mixing particles & water: produces a "slip" --Hydroplastic forming: extrude the slip (e.g., into a pipe) 18 Form a "green" component hollow component Dry and Fire the component --Slip casting: solid component Adapted from Fig. 11.7, Callister 6e. Adapted from Fig , Callister 6e. (Fig is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.) CERAMIC FABRICATION METHODS-IIA

19 13 Clay is inexpensive Adding water to clay --allows material to shear easily along weak van der Waals bonds --enables extrusion --enables slip casting Structure of Kaolinite Clay: Adapted from Fig , Callister 6e. (Fig is adapted from W.E. Hauth, "Crystal Chemistry of Ceramics", American Ceramic Society Bulletin, Vol. 30 (4), 1951, p. 140.) FEATURES OF A SLIP

20 20 Firing : --T raised to ( C) --vitrification: glass forms from clay and flows between SiO 2 particles. Drying : layer size and spacing decrease. Adapted from Fig , Callister 6e. (Fig is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.) Adapted from Fig , Callister 6e. (Fig is courtesy H.G. Brinkies, Swinburne University of Technology, Hawthorn Campus, Hawthorn, Victoria, Australia.) DRYING AND FIRING

21 Sintering: useful for both clay and non-clay compositions. Procedure: --grind to produce ceramic and/or glass particles --inject into mold --press at elevated T to reduce pore size. Aluminum oxide powder: --sintered at 1700C for 6 minutes. PARTICULATE FORMING 21 Adapted from Fig , Callister 6e. (Fig is from W.D. Kingery, H.K. Bowen, and D.R. Uhlmann, Introduction to Ceramics, 2nd ed., John Wiley and Sons, Inc., 1976, p. 483.) CERAMIC FABRICATION METHODS-IIB

22 CEMENTATION Produced in extremely large quantities. Portland cement: --mix clay and lime bearing materials --calcinate (heat to 1400C) --primary constituents: tri-calcium silicate di-calcium silicate Adding water --produces a paste which hardens --hardening occurs due to hydration (chemical reactions with the water). Forming: done usually minutes after hydration begins. 22 CERAMIC FABRICATION METHODS-III

23 23 Fabrication techniques for metals - Forming, casting, joining Hardenability - Increases with alloy content Fabrication techniques for ceramics - Glass forming (impurities affect forming temp.) - Particulate forming (needed if ductility is limited) - Cementation (large volume, room T process) Heat treating: used to - Alleviate residual stress from cooling - Produce fracture-resistant components by putting surface in compression SUMMARY

24 Reading: Core Problems: Self-help Problems: 0 ANNOUNCEMENTS


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