Homework answers / question archive / Hahn ENGR45 Name:__________________ TTT Diagram Assignment Part 1: Identify the microstructure formed in the steel alloy based on the TTT-Diagram after each heat treatment step: 800 Austenite (stable) T(°C) TE A P 600 400 B A 200 0% M+A M+A 50% 90% M+A 10 -1 10 10 3 10 5 time (s) 1: a: Quench to from 800oC to 650oC and hold for 10 seconds: b: Next, quench the alloy to approximately 350oC and hold for 102 seconds c: Next, quench the alloy to approximately 175oC and hold for 10 seconds d: Finally, quench the alloy to room temperature Hahn ENGR45 800 Name:__________________ Austenite (stable) T(°C) TE A P 600 400 B A 200 0% M+A M+A 50% 90% M+A 10 -1 10 10 3 10 5 time (s) 2: a: Quench to from 800oC to 350oC and hold for 102 seconds: b: Quench the alloy to room temperature c: Reheat the alloy to 700oC and hold for 105 seconds (HINT: This heat treatment is one we did in Lab 4) Hahn ENGR45 Name:__________________ Part 2: Use the TTT-Diagram to “map out” heat treatment steps for the following desired microstructures (You can physically draw the treatment as lines on the diagram, and/or list the steps) 800 Austenite (stable) T(°C) TE A P 600 400 B A 200 0% M+A M+A 50% 90% M+A 10 -1 10 3: 50% Pearlite, 50% Tempered Martensite 4: 50% Bainite, 45% Martensite, 5% Austenite 10 3 10 5 time (s) Chapter 15: Characteristics, Applications & Processing of Polymers ISSUES TO ADDRESS

Hahn ENGR45 Name:__________________ TTT Diagram Assignment Part 1: Identify the microstructure formed in the steel alloy based on the TTT-Diagram after each heat treatment step: 800 Austenite (stable) T(°C) TE A P 600 400 B A 200 0% M+A M+A 50% 90% M+A 10 -1 10 10 3 10 5 time (s) 1: a: Quench to from 800oC to 650oC and hold for 10 seconds: b: Next, quench the alloy to approximately 350oC and hold for 102 seconds c: Next, quench the alloy to approximately 175oC and hold for 10 seconds d: Finally, quench the alloy to room temperature Hahn ENGR45 800 Name:__________________ Austenite (stable) T(°C) TE A P 600 400 B A 200 0% M+A M+A 50% 90% M+A 10 -1 10 10 3 10 5 time (s) 2: a: Quench to from 800oC to 350oC and hold for 102 seconds: b: Quench the alloy to room temperature c: Reheat the alloy to 700oC and hold for 105 seconds (HINT: This heat treatment is one we did in Lab 4) Hahn ENGR45 Name:__________________ Part 2: Use the TTT-Diagram to “map out” heat treatment steps for the following desired microstructures (You can physically draw the treatment as lines on the diagram, and/or list the steps) 800 Austenite (stable) T(°C) TE A P 600 400 B A 200 0% M+A M+A 50% 90% M+A 10 -1 10 3: 50% Pearlite, 50% Tempered Martensite 4: 50% Bainite, 45% Martensite, 5% Austenite 10 3 10 5 time (s) Chapter 15: Characteristics, Applications & Processing of Polymers ISSUES TO ADDRESS

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Hahn ENGR45 Name:__________________ TTT Diagram Assignment Part 1: Identify the microstructure formed in the steel alloy based on the TTT-Diagram after each heat treatment step: 800 Austenite (stable) T(°C) TE A P 600 400 B A 200 0% M+A M+A 50% 90% M+A 10 -1 10 10 3 10 5 time (s) 1: a: Quench to from 800oC to 650oC and hold for 10 seconds: b: Next, quench the alloy to approximately 350oC and hold for 102 seconds c: Next, quench the alloy to approximately 175oC and hold for 10 seconds d: Finally, quench the alloy to room temperature Hahn ENGR45 800 Name:__________________ Austenite (stable) T(°C) TE A P 600 400 B A 200 0% M+A M+A 50% 90% M+A 10 -1 10 10 3 10 5 time (s) 2: a: Quench to from 800oC to 350oC and hold for 102 seconds: b: Quench the alloy to room temperature c: Reheat the alloy to 700oC and hold for 105 seconds (HINT: This heat treatment is one we did in Lab 4) Hahn ENGR45 Name:__________________ Part 2: Use the TTT-Diagram to “map out” heat treatment steps for the following desired microstructures (You can physically draw the treatment as lines on the diagram, and/or list the steps) 800 Austenite (stable) T(°C) TE A P 600 400 B A 200 0% M+A M+A 50% 90% M+A 10 -1 10 3: 50% Pearlite, 50% Tempered Martensite 4: 50% Bainite, 45% Martensite, 5% Austenite 10 3 10 5 time (s) Chapter 15: Characteristics, Applications & Processing of Polymers ISSUES TO ADDRESS... • What are the tensile properties of polymers and how are they affected by basic microstructural features? • Hardening, anisotropy, and annealing in polymers. • How does the elevated temperature mechanical response of polymers compare to ceramics and metals? • What are the primary polymer processing methods? Chapter 15 - 1 Mechanical Properties of Polymers – Stress-Strain Behavior brittle polymer plastic elastomer elastic moduli – less than for metals Adapted from Fig. 15.1, Callister & Rethwisch 10e. • Fracture strengths of polymers ~ 10% of those for metals • Deformation strains for polymers > 1000% – for most metals, deformation strains < 10% Chapter 15 - 2 Mechanisms of Deformation—Brittle Crosslinked and Network Polymers Initial Near Failure σ(MPa) Initial x brittle failure Near Failure x plastic failure aligned, crosslinked polymer ε network polymer Chapter 15 - 3 Mechanisms of Deformation — Semicrystalline (Plastic) Polymers σ(MPa) Inset figures along plastic response curve adapted from Figs. 15.12 & 15.13, Callister & Rethwisch 10e. fibrillar structure x brittle failure onset of necking plastic failure near failure x unload/reload ε crystalline block segments separate undeformed structure amorphous regions elongate crystalline regions align Chapter 15 - 4 Mechanisms of Deformation— Elastomers σ(MPa) x brittle failure x plastic failure elastomer x ε initial: amorphous chains are kinked, cross-linked. Stress-strain curves adapted from Fig. 15.1, Callister & Rethwisch 10e. Inset figures along elastomer curve (green) adapted from Fig. 15.15, Callister & Rethwisch 10e. final: chains are straighter, still cross-linked (Fig. 15.15 adapted from Z. D. Jastrzebski, The Nature and Properties of Engineering Materials, 3rd edition. Copyright © 1987 by John Wiley & Sons, New York. Reprinted by permission of John Wiley & Sons, Inc.) deformation is reversible (elastic)! • Compare elastic behavior of elastomers with the: -- brittle behavior (of aligned, crosslinked & network polymers), and -- plastic behavior (of semicrystalline polymers) (as shown on previous slides) Chapter 15 - 5 Thermoplastics vs. Thermosets • Thermoplastics: -- little crosslinking -- ductile -- soften w/heating -- polyethylene polypropylene polycarbonate polystyrene • Thermosets: T viscous liquid mobile liquid Callister, rubber Fig. 16.9 tough plastic crystalline solid Tm Tg partially crystalline solid Molecular weight Adapted from Fig. 15.19, Callister & Rethwisch 10e. (From F. W. Billmeyer, Jr., Textbook of Polymer Science, 3rd edition. -- significant crosslinking Copyright © 1984 by John Wiley & Sons, New York. Reprinted by (10 to 50% of repeat units) permission of John Wiley & Sons, Inc.) -- hard and brittle -- do NOT soften w/heating -- vulcanized rubber, epoxies, polyester resin, phenolic resin Chapter 15 - 6 Influence of T and Strain Rate on Thermoplastics • Decreasing T... -- increases E -- increases TS -- decreases %EL • Increasing strain rate... -- same effects as decreasing T. σ(MPa) 80 4ºC 60 20ºC 40 Plots for semicrystalline PMMA (Plexiglas) 40ºC 20 0 60ºC 0 0.1 0.2 ε to 1.3 0.3 Adapted from Fig. 15.3, Callister & Rethwisch 10e. (Reprinted with permission from T. S. Carswell and H. K. Nason, “Effect of Environmental Conditions on the Mechanical Properties of Organic Plastics,” in Symposium on Plastics. Copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428.) Chapter 15 - 7 Time-Dependent Deformation • Stress relaxation test: -- strain in tension to εo and hold. -- observe decrease in stress with time. tensile test • There is a large decrease in Er for T > Tg. 5 10 Er (10 s) 3 in MPa 10 rigid solid (small relax) transition region 1 10 10-1 εo strain σ(t) time • Relaxation modulus: s (t) Er (t) = eo viscous liquid 10-3 (large relax) (amorphous polystyrene) Fig. 15.7, Callister & Rethwisch 10e. (From A. V. Tobolsky, Properties and Structures of Polymers. Copyright © 1960 by John Wiley & Sons, New York. Reprinted by permission of John Wiley & Sons, Inc.) 60 100 140 180 T(ºC) Tg • Representative Tg values (?C): PE (low density) PE (high density) PVC PS PC - 110 - 90 + 87 +100 +150 Selected values from Table 15.2, Callister & Rethwisch 10e. Chapter 15 - 8 Crazing During Fracture of Thermoplastic Polymers Craze formation prior to cracking – during crazing, plastic deformation of spherulites – and formation of microvoids and fibrillar bridges aligned chains fibrillar bridges microvoids crack Fig. 15.9, Callister & Rethwisch 10e. (From J. W. S. Hearle, Polymers and Their Properties, Vol. 1, Fundamentals of Structure and Mechanics, Ellis Horwood, Ltd., Chichester, West Sussex, England, 1982.) Chapter 15 - 9 Polymer Formation • There are two types of polymerization – Addition (or chain) polymerization – Condensation (step) polymerization Chapter 15 - 10 Addition (Chain) Polymerization – Initiation – Propagation – Termination Chapter 15 - 11 Condensation (Step) Polymerization Chapter 15 - 12 Polymer Additives Improve mechanical properties, processability, durability, etc. • Fillers – Added to improve tensile strength & abrasion resistance, toughness & decrease cost – ex: carbon black, silica gel, wood flour, glass, limestone, talc, etc. • Plasticizers – Added to reduce the glass transition temperature Tg below room temperature – Presence of plasticizer transforms brittle polymer to a ductile one – Commonly added to PVC - otherwise it is brittle Chapter 15 - 13 Polymer Additives (cont.) • Stabilizers – Antioxidants – UV protectants • Lubricants – Added to allow easier processing – polymer “slides” through dies easier – ex: sodium stearate • Colorants – Dyes and pigments • Flame Retardants – Substances containing chlorine, fluorine, and boron Chapter 15 - 14 Processing of Plastics • Thermoplastic – can be reversibly cooled & reheated, i.e. recycled – heat until soft, shape as desired, then cool – ex: polyethylene, polypropylene, polystyrene. • Thermoset – when heated forms a molecular network (chemical reaction) – degrades (doesn’t melt) when heated – a prepolymer molded into desired shape, then chemical reaction occurs – ex: urethane, epoxy Chapter 15 - 15 Processing Plastics – Compression Molding Thermoplastics and thermosets • polymer and additives placed in mold cavity • mold heated and pressure applied • fluid polymer assumes shape of mold Fig. 15.23, Callister & Rethwisch 10e. (From F. W. Billmeyer, Jr., Textbook of Polymer Science, 3rd edition. Copyright © 1984 by John Wiley & Sons, New York. Reprinted by permission of John Wiley & Sons, Inc.) Chapter 15 - 16 Processing Plastics – Injection Molding Thermoplastics and some thermosets • when ram retracts, plastic pellets drop from hopper into barrel • ram forces plastic into the heating chamber (around the spreader) where the plastic melts as it moves forward • molten plastic is forced under pressure (injected) into the mold cavity where it assumes the shape of the mold Fig. 15.24, Callister & Rethwisch 10e. (From F. W. Billmeyer, Jr., Textbook of Polymer Science, 3rd edition. Copyright © 1984 by John Wiley & Sons, New York. Reprinted by permission of John Wiley & Sons, Inc.) Barrel Chapter 15 - 17 Processing Plastics – Extrusion thermoplastics • plastic pellets drop from hopper onto the turning screw • plastic pellets melt as the turning screw pushes them forward by the heaters • molten polymer is forced under pressure through the shaping die to form the final product (extrudate) Fig. 15.25, Callister & Rethwisch 10e. Chapter 15 - 18 Processing Plastics – Blown-Film Extrusion Fig. 15.26, Callister & Rethwisch 10e. Chapter 15 - 19 Polymer Types – Fibers Fibers - length/diameter >100 • Primary use is in textiles. • Fiber characteristics: – high tensile strengths – high degrees of crystallinity – structures containing polar groups • Formed by spinning – extrude polymer through a spinneret (a die containing many small orifices) – the spun fibers are drawn under tension – leads to highly aligned chains - fibrillar structure Chapter 15 - 20 Polymer Types – Miscellaneous • • Coatings – thin polymer films applied to surfaces – i.e., paints, varnishes – protects from corrosion/degradation – decorative – improves appearance – can provide electrical insulation Adhesives – bonds two solid materials (adherands) – bonding types: 1. Secondary – van der Waals forces 2. Mechanical – penetration into pores/crevices • • Films – produced by blown film extrusion Foams – gas bubbles incorporated into plastic Chapter 15 - 21 Advanced Polymers Ultrahigh Molecular Weight Polyethylene (UHMWPE) • Molecular weight ca. 4 x 106 g/mol • Outstanding properties – – – – high impact strength resistance to wear/abrasion low coefficient of friction self-lubricating surface UHMWPE • Important applications – bullet-proof vests – golf ball covers – hip implants (acetabular cup) Adapted from chapteropening photograph, Chapter 22, Callister 7e. Chapter 15 - 22 Advanced Polymers Thermoplastic Elastomers Styrene-butadiene block copolymer hard component domain styrene butadiene Fig. 15.21(a), Callister & Rethwisch 10e. soft component domain Fig. 15.22, Callister & Rethwisch 10e. Chapter 15 - 23 Summary • Limitations of polymers: -- E, σy, Kc, Tapplication are generally small. -- Deformation is often time and temperature dependent. • Thermoplastics (PE, PS, PP, PC): -- Smaller E, σy, Tapplication -- Larger Kc -- Easier to form and recycle • Elastomers (rubber): -- Large reversible strains! • Thermosets (epoxies, polyesters): -- Larger E, σy, Tapplication -- Smaller Kc Chapter 15 - 24 Summary • Polymer Processing -- compression and injection molding, extrusion, blown film extrusion • Polymer melting and glass transition temperatures • Polymer applications -- elastomers -- fibers -- coatings -- adhesives -- films -- foams -- advanced polymeric materials Chapter 15 - 25 ANNOUNCEMENTS Reading: Core Problems: Self-help Problems: Chapter 15 - 26 Chapter 14: Polymer Structures ISSUES TO ADDRESS... • What are the general structural and chemical characteristics of polymer molecules? • What are some of the common polymeric materials, and how do they differ chemically? • How is the crystalline state in polymers different from that in metals and ceramics ? Chapter 14 - 1 What is a Polymer? Poly many mer repeat unit repeat unit repeat unit H H H H H H C C C C C C H H H H H H H H H H H H C C C C C C H Cl H Cl H Cl Polyethylene (PE) Poly(vinyl chloride) (PVC) repeat unit H C H H H C C CH3 H H H C C CH3 H H C CH3 Polypropylene (PP) Chapter 14 - 2 Polymer Composition Most polymers are hydrocarbons – i.e., made up of H and C Hydrocarbons can be saturated and unsaturated • Saturated hydrocarbons – Each carbon singly bonded to four other atoms – Example: • Ethane, C2H6 H H C H H C H H Chapter 14 - 3 Chapter 14 - 4 Unsaturated Hydrocarbons • Double & triple bonds somewhat unstable – can form new bonds – Double bond found in ethylene or ethene - C2H4 H H C C H H – Triple bond found in acetylene or ethyne - C2H2 H C C H Chapter 14 - 5 Polymer Composition -Most polymers tend to be extremely large due to their repetitive, long range chains -Consist of Carbon backbone -Consist of repetitive Monomers – Small molecules/units from which polymer is synthesized Chapter 14 - 6 Isomerism • Isomerism – two compounds with same chemical formula can have quite different structures for example: C8H18 • normal-octane H H H H H H H H H C C C C C C C C H = H3C CH2 CH2 CH2 CH2 CH2 CH2 CH3 H H H H H H H H ? H3C ( CH2 ) CH3 6 • 2,4-dimethylhexane CH3 H3C CH CH2 CH CH3 CH2 CH3 Chapter 14 - 7 Polymerization and Polymer Chemistry • Free radical polymerization R + H H H H C C R C C free radical H H monomer (ethylene) H H H H H H H H C C R C C C C H H H H H H R C C H H + initiation H H propagation propagation dimer • Initiator: example - benzoyl peroxide H C O O C H H H H 2 C O =2R H Chapter 14 - 8 Chemistry and Structure of Polyethylene Adapted from Fig. 14.1, Callister & Rethwisch 10e. Note: polyethylene is a long-chain hydrocarbon - paraffin wax for candles is short polyethylene Chapter 14 - 9 Bulk or Commodity Polymers Chapter 14 - 10 Bulk or Commodity Polymers (cont) Chapter 14 - 11 Bulk or Commodity Polymers (cont) Chapter 14 - 12 MOLECULAR WEIGHT • Molecular weight, M: Mass of a mole of chains. Low M high M Not all chains in a polymer are of the same length — i.e., there is a distribution of molecular weights Chapter 14 - 13 Degree of Polymerization, DP DP = average number of repeat units per chain H H H H H H H H H H H H H C C (C C ) C C C C C C C C H DP = 6 H H H H H H H H H H H H Mn DP = m where m = average molecular weight of repeat unit for copolymers this is calculated as follows: m = Sfi mi Chain fraction mol. wt of repeat unit i Chapter 14 - 14 Molecular Structures for Polymers secondary bonding Linear Branched Cross-Linked Network Adapted from Fig. 14.7, Callister & Rethwisch 10e. Chapter 14 - 15 Polymers – Molecular Shape Molecular Shape (or Conformation) – chain bending and twisting are possible by rotation of carbon atoms around their chain bonds – note: not necessary to break chain bonds to alter molecular shape Adapted from Fig. 14.5, Callister & Rethwisch 10e. Chapter 14 - 16 Chain End-to-End Distance, r Fig. 14.6, Callister & Rethwisch 10e. Chapter 14 - 17 Copolymers two or more monomers polymerized together • random – A and B randomly positioned along chain • alternating – A and B alternate in polymer chain • block – large blocks of A units alternate with large blocks of B units • graft – chains of B units grafted onto A backbone A– B– Fig. 14.9, Callister & Rethwisch 10e. random alternating block graft Chapter 14 - 18 Crystallinity in Polymers Fig. 14.10, Callister & Rethwisch 10e. • Ordered atomic arrangements involving molecular chains • Crystal structures in terms of unit cells • Example shown – polyethylene unit cell Chapter 14 - 19 Polymer Crystallinity (cont.) Polymers rarely 100% crystalline • Difficult for all regions of all chains to become aligned crystalline region • Degree of crystallinity expressed as % crystallinity. -- Some physical properties depend on % crystallinity. -- Heat treating causes crystalline regions to grow and % crystallinity to increase. amorphous region Fig. 14.11, Callister 6e. (From H.W. Hayden, W.G. Moffatt, and J. Wulff, The Structure and Properties of Materials, Vol. III, Mechanical Behavior, John Wiley and Sons, Inc., 1965.) Chapter 14 - 20 ANNOUNCEMENTS Reading: Core Problems: Self-help Problems: Chapter 14 - 21 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? Chapter 11 - 1 Classification of Metal Alloys Ferrous v. Nonferrous • Ferrous: Iron is prime constituent (Cast Iron, Steel alloys, etc) • Produced in larger quantities than any other metal type • Iron compounds are abundant in earth’s crust • Metallic Iron and Steel are typically easy/economical to extract, refine, alloy, and fabricate • Extremely Versatile • Nonferrous: Iron is NOT prime constituent Chapter 11 - 2 Ferrous Alloys Iron-based alloys • Steels • Cast Irons 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 Chapter 11 - 3 Classification of Metal Alloys Metal Alloys Ferrous Steels Steels 1600°C and is inexpensive and easy to mold? • Answer: sand!!! Sand Sand molten metal • To create mold, pack sand around form (pattern) of desired shape Chapter 11 - 23 Metal Fabrication Methods (iv) FORMING CASTING MISCELLANEOUS • 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. wax I • Stage II — Wax is melted and then poured from mold—hollow mold cavity remains. II • Stage III — Molten metal is poured into mold and allowed to solidify. III Chapter 11 - 24 Metal Fabrication Methods (v) FORMING CASTING • Die Casting -- high volume -- for alloys having low melting temperatures MISCELLANEOUS • Continuous Casting -- simple shapes (e.g., rectangular slabs, cylinders) molten solidified Chapter 11 - 25 Metal Fabrication Methods (vi) FORMING CASTING • Powder Metallurgy (metals w/low ductilities) MISCELLANEOUS • Welding (when fabrication of one large part is impractical) pressure filler metal (melted) base metal (melted) fused base metal heat area contact densify unaffected piece 1 heat-affected zone unaffected Fig. 11.10, Callister piece 2 & Rethwisch 10e. • Heat-affected zone: point contact at low T densification by diffusion at higher T (region in which the microstructure has been changed). [From Iron Castings Handbook, C.F. Walton and T.J. Opar (Ed.), Iron Castings Society, Des Plaines, IL,1981.] Chapter 11 - 26 Thermal Processing of Metals Annealing: Heat to Tanneal, then cool slowly. • Stress Relief: Reduce • Spheroidize (steels): stresses resulting from: - plastic deformation - nonuniform cooling - phase transform. Make very soft steels for good machining. Heat just below Teutectoid & hold for 15-25 h. Types of Annealing • Process Anneal: Negate effects of cold working by (recovery/ recrystallization) • Full Anneal (steels): Make soft steels for good forming. Heat to get γ, then furnace-cool to obtain coarse pearlite. • Normalize (steels): Deform steel with large grains. Then heat treat to allow recrystallization and formation of smaller grains. Based on discussion in Section 11.8, Callister & Rethwisch 10e. Chapter 11 - 27 Heat Treatment Temperature-Time Paths a) Full Annealing A b) Quenching c) Tempering (Tempered Martensite) P A B Fig. 10.25, Callister & Rethwisch 10e. [Adapted from H. Boyer (Editor), Atlas of Isothermal Transformation and Cooling Transformation Diagrams, 1977. Reproduced by permission of ASM International, Materials Park, OH.] b) a) c) Chapter 11 - 28 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. Chapter 11 - 29 ANNOUNCEMENTS Reading: Core Problems: Self-help Problems: Chapter 11 - 30