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Chapter 11: Applications and Processing of Metal Alloys

Chapter 11: Applications and Processing of Metal Alloys. ISSUES TO ADDRESS. • How are metal alloys classified and what are their common applications ?. • What are some of the common fabrication techniques for metals?. • What heat treatment procedures are used to improve the

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Chapter 11: Applications and Processing of Metal Alloys

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  1. Chapter 11: Applications and Processing of Metal Alloys ISSUES TO ADDRESS... • How are metal alloys classified and what are their common applications? • What are some of the common fabrication techniques for metals? • What heat treatment procedures are used to improve the mechanical properties of both ferrous and nonferrous alloys?

  2. Classification of Metal Alloys Steels Cast Irons <1.4wt%C 3-4.5wt%C microstructure: ferrite, T(ºC) graphite/cementite 1600 d L 1400 g +L g L+Fe3C 1200 1148ºC austenite Eutectic: 4.30 1000 g a +Fe3C + Fe C 800 a g 3 727ºC ferrite Eutectoid: cementite a +Fe3C 600 0.76 400 0 1 2 3 4 5 6 6.7 (Fe) Co, wt% C Metal Alloys Adapted from Fig. 11.1, Callister & Rethwisch 8e. Ferrous Nonferrous Steels Cast Irons <1.4wt%C 3-4.5 wt%C Adapted from Fig. 9.24, Callister & Rethwisch 8e. (Fig. 9.24 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.)

  3. Steels High Alloy Low Alloy low carbon Med carbon high carbon <0.25wt%C 0.25-0.6wt%C 0.6-1.4wt%C heat stainless Name plain HSLA plain plain tool treatable Cr,V Cr, Ni Cr, V, Additions none none none Cr, Ni, Mo Ni, Mo Mo Mo, W Example 1010 4310 1040 43 40 1095 4190 304, 409 0 + + ++ ++ +++ varies Hardenability - 0 + ++ + ++ varies TS increasing strength, cost, decreasing ductility + + 0 - - -- ++ EL high T pistons Uses auto bridges crank wear drills applic. gears struc. towers shafts applic. saws turbines wear sheet press. bolts dies furnaces applic. vessels hammers Very corros. blades resistant Based on data provided in Tables 11.1(b), 11.2(b), 11.3, and 11.4, Callister & Rethwisch 8e.

  4. Refinement of Steel from Ore Coke Limestone Iron Ore BLAST FURNACE heat generation gas ® C + O2 CO2 refractory vessel reduction of iron ore to metal ® CO2 + C 2CO layers of coke ® 3CO+ Fe2O3 2Fe +3CO2 and iron ore air purification slag ® CaCO3 CaO+CO2 Molten iron ® CaO + SiO2 + Al2O3 slag

  5. Ferrous Alloys Iron-based alloys Nomenclature for steels (AISI/SAE) 10xx Plain Carbon Steels 11xx Plain Carbon Steels (resulfurized for machinability) 15xx Mn (1.00 - 1.65%) 40xx Mo (0.20 ~ 0.30%) 43xx Ni (1.65 - 2.00%), Cr (0.40 - 0.90%), Mo (0.20 - 0.30%) 44xx Mo (0.5%) where xx is wt% C x 100 example: 1060 steel – plain carbon steel with 0.60 wt% C Stainless Steel >11% Cr • Steels • Cast Irons

  6. Cast Irons • Ferrous alloys with > 2.1 wt% C • more commonly 3 - 4.5 wt% C • Low melting – relatively easy to cast • Generally brittle • Cementite decomposes to ferrite + graphite Fe3C  3 Fe () + C (graphite) • generally a slow process

  7. T(ºC) 1600 L 1400 Liquid + Graphite g +L 1200 g 1153ºC Austenite 4.2 wt% C 1000  + Graphite a + g 800 740ºC 0.65 600  + Graphite 400 90 0 100 1 2 3 4 C, wt% C (Fe) Fe-C True Equilibrium Diagram • Graphite formation promoted by • Si > 1 wt% • slow cooling Adapted from Fig. 11.2, Callister & Rethwisch 8e. [Fig. 11.2 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.]

  8. Types of Cast Iron Adapted from Fig. 11.3(a) & (b), Callister & Rethwisch 8e. Gray iron • graphite flakes • weak & brittle in tension • stronger in compression • excellent vibrational dampening • wear resistant Ductile iron • add Mg and/or Ce • graphite as nodules not flakes • matrix often pearlite – stronger but less ductile

  9. Types of Cast Iron (cont.) Adapted from Fig. 11.3(c) & (d), Callister & Rethwisch 8e. White iron • < 1 wt% Si • pearlite + cementite • very hard and brittle Malleable iron • heat treat white iron at 800-900ºC • graphite in rosettes • reasonably strong and ductile

  10. Types of Cast Iron (cont.) Compacted graphite iron • relatively high thermal conductivity • good resistance to thermal shock • lower oxidation at elevated temperatures Adapted from Fig. 11.3(e), Callister & Rethwisch 8e.

  11. Production of Cast Irons Adapted from Fig.11.5, Callister & Rethwisch 8e.

  12. Limitations of Ferrous Alloys • Relatively high densities • Relatively low electrical conductivities • Generally poor corrosion resistance

  13. Nonferrous Alloys • Cu Alloys • Al Alloys Brass:Zn is subst. impurity -low r: 2.7 g/cm3 (costume jewelry, coins, -Cu, Mg, Si, Mn, Zn additions corrosion resistant) -solid sol. or precip. Bronze : Sn, Al, Si, Ni are strengthened (struct. subst. impurities aircraft parts (bushings, landing & packaging) gear) NonFerrous • Mg Alloys Cu-Be : r -very low : 1.7g/cm3 Alloys precip. hardened -ignites easily for strength - aircraft, missiles • Ti Alloys • Refractory metals -relativelylowr:4.5g/cm3 -high melting T’s vs 7.9 for steel • Noble metals -Nb, Mo, W, Ta -Ag, Au, Pt -reactiveathighT’s - oxid./corr. resistant - space applic. Based on discussion and data provided in Section 11.3, Callister & Rethwisch 3e.

  14. Metal Fabrication • How do we fabricate metals? • Blacksmith - hammer (forged) • Cast molten metal into mold • Forming Operations • Rough stock formed to final shape Hot working vs. Cold working • • Deformation temperature high enough for recrystallization • • Large deformations • • Deformation below • recrystallization temperature • • Strain hardening occurs • • Small deformations

  15. Metal Fabrication Methods (i) • Forging (Hammering; Stamping) (wrenches, crankshafts) • Rolling (Hot or Cold Rolling) (I-beams, rails, sheet & plate) force roll die A d A often at elev. T A A o blank o d roll force Adapted from Fig. 11.8, Callister & Rethwisch 8e. • Drawing (rods, wire, tubing) • Extrusion (rods, tubing) A o die container A d die holder tensile force A o ram A billet extrusion d force die die container die must be well lubricated & clean ductile metals, e.g. Cu, Al (hot) FORMING CASTING MISCELLANEOUS

  16. Metal Fabrication Methods (ii) MISCELLANEOUS FORMING CASTING • Casting- mold is filled with molten metal • metal melted in furnace, perhaps alloying elements added, then cast in a mold • common and inexpensive • gives good production of shapes • weaker products, internal defects • good option for brittle materials

  17. Metal Fabrication Methods (iii) Sand Sand molten metal MISCELLANEOUS FORMING CASTING • Sand Casting (large parts, e.g., auto engine blocks) • What material will withstand T >1600ºCand is inexpensive and easy to mold? • Answer: sand!!! • To create mold, pack sand around form (pattern) of desired shape

  18. Metal Fabrication Methods (iv) I wax II III MISCELLANEOUS FORMING CASTING • Investment Casting (low volume, complex shapes e.g., jewelry, turbine blades) • Stage I — Mold formed by pouring plaster of paris around wax pattern. Plaster allowed to harden. • • Stage II — Wax is melted and then • poured from mold—hollow mold cavity remains. • Stage III — Molten metal is poured into mold and allowed to solidify.

  19. Metal Fabrication Methods (v) • Continuous Casting -- simple shapes (e.g., rectangular slabs, cylinders) molten solidified MISCELLANEOUS FORMING CASTING • Die Casting -- high volume -- for alloys having low melting temperatures

  20. Metal Fabrication Methods (vi) • Welding (when fabrication of one large part is impractical) pressure filler metal (melted) base metal (melted) fused base metal heat heat-affected zone area unaffected unaffected Adapted from Fig. 11.9, Callister & Rethwisch 8e. (Fig. 11.9 from Iron Castings Handbook, C.F. Walton and T.J. Opar (Ed.), 1981.) contact piece 1 piece 2 densify • Heat-affected zone: (region in which the microstructure has been changed). densification point contact by diffusion at at low T higher T MISCELLANEOUS FORMING CASTING • Powder Metallurgy (metals w/low ductilities)

  21. Thermal Processing of Metals • Stress Relief: Reduce • Spheroidize (steels): stresses resulting from: Make very soft steels for - plastic deformation good machining. Heat just - nonuniform cooling below Teutectoid & hold for - phase transform. 15-25h. • Full Anneal (steels): Types of Make soft steels for Annealing good forming. Heat g to get , then furnace-cool to obtain coarse pearlite. • Process Anneal: Negate effects of • Normalize (steels): Deform cold working by steel with large grains. Then heat (recovery/ treat to allow recrystallization recrystallization) and formation of smaller grains. Annealing: Heat to Tanneal, then cool slowly. Based on discussion in Section 11.7, Callister & Rethwisch 8e.

  22. a) b) c) Heat Treatment Temperature-Time Paths • Full Annealing A • Quenching P • Tempering (Tempered Martensite) B A 100% 50% 0% Fig. 10.25, Callister & Rethwisch 8e.

  23. flat ground specimen (heated to g Rockwell Chardness tests phase field) 24ºC water Hardness, HRC Distance from quenched end Hardenability -- Steels • Hardenability – measure of the ability to form martensite • Jominy end quench test used to measure hardenability. Adapted from Fig. 11.11, Callister & Rethwisch 8e. (Fig. 11.11 adapted from A.G. Guy, Essentials of Materials Science, McGraw-Hill Book Company, New York, 1978.) • Plot hardness versus distance from the quenched end. Adapted from Fig. 11.12, Callister & Rethwisch 8e.

  24. Reason Why Hardness Changes with Distance T(ºC) 0% 100% P 600 ® A 400 M(start) 200 ® A M M(finish) Pearlite 0 Martensite Fine Pearlite Martensite + Pearlite 0.1 1 10 100 1000 Time (s) • The cooling rate decreases with distance from quenched end. 60 40 Hardness, HRC 20 distance from quenched end (in) 0 1 2 3 Adapted from Fig. 11.13, Callister & Rethwisch 8e. (Fig. 11.13 adapted from H. Boyer (Ed.) Atlas of Isothermal Transformation and Cooling Transformation Diagrams, American Society for Metals, 1977, p. 376.)

  25. 100 10 3 2 Cooling rate (ºC/s) 60 100 %M 80 4340 Hardness, HRC 50 40 4140 8640 1040 5140 20 0 10 20 30 40 50 Distance from quenched end (mm) 800 T(ºC) TE 600 A B 400 M(start) 200 M(90%) 0 -1 3 5 Time (s) 10 10 10 10 Hardenability vs Alloy Composition • Hardenability curves for five alloys each with, C = 0.4 wt% C Adapted from Fig. 11.14, Callister & Rethwisch 8e. (Fig. 11.14 adapted from figure furnished courtesy Republic Steel Corporation.) • "Alloy Steels" (4140, 4340, 5140, 8640) -- contain Ni, Cr, Mo (0.2 to 2 wt%) -- these elements shift the "nose" to longer times (from A to B) -- martensite is easier to form

  26. Influences of Quenching Medium & Specimen Geometry • Effect of specimen geometry: When surface area-to-volume ratio increases: -- cooling rate throughout interior increases -- hardness throughout interior increases Position center surface Cooling rate low high Hardness low high • Effect of quenching medium: Medium air oil water Hardness low moderate high Severity of Quench low moderate high

  27. Precipitation Hardening 700 T(ºC) CuAl2 L 600 a +L +L A 500 q a+q C 400 300 0 10 20 30 40 50 B (Al) wt% Cu composition range available for precipitation hardening Temp. Pt A (sol’n heat treat) Pt C (precipitate ) Time Pt B • Particles impede dislocation motion. • Ex: Al-Cu system • Procedure: -- Pt A: solution heat treat (get a solid solution) -- Pt B: quench to room temp. (retain a solid solution) -- Pt C: reheat to nucleate small q particles withina phase. • Other alloys that precipitation harden: • Cu-Be • Cu-Sn • Mg-Al Adapted from Fig. 11.24, Callister & Rethwisch 8e. (Fig. 11.24 adapted from J.L. Murray, International Metals Review30, p.5, 1985.) Adapted from Fig. 11.22, Callister & Rethwisch 8e.

  28. Influence of Precipitation Heat Treatment on TS, %EL • Minima on %EL curves. many small “aged” precipitates non-equil. 30 solid solution fewer large precipitates 400 “overaged” 20 300 tensile strength (MPa) %EL (2 in sample) 10 149ºC 149ºC 200 204ºC 204ºC 100 0 1min 1h 1day 1mo 1yr 1min 1h 1day 1mo 1yr precipitation heat treat time precipitation heat treat time • 2014 Al Alloy: • Maxima on TS curves. • Increasing T accelerates process. Adapted from Fig. 11.27, Callister & Rethwisch 8e. (Fig. 11.27 adapted from Metals Handbook: Properties and Selection: Nonferrous Alloys and Pure Metals, Vol. 2, 9th ed., H. Baker (Managing Ed.), American Society for Metals, 1979. p. 41.)

  29. Summary • Ferrous alloys: steels and cast irons • Non-ferrous alloys: -- Cu, Al, Ti, and Mg alloys; refractory alloys; and noble metals. • Metal fabrication techniques: -- forming, casting, miscellaneous. • Hardenability of metals -- measure of ability of a steel to be heat treated. -- increases with alloy content. • Precipitation hardening --hardening, strengthening due to formation of precipitate particles. --Al, Mg alloys precipitation hardenable.

  30. ANNOUNCEMENTS Reading: Core Problems: Self-help Problems:

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