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Transcript of Summary: Processing Options - Materialsmatclass/101/pdffiles/Lecture_16.pdf · Summary: Processing...

  • Summary: Processing Options

    Austenite ()

    Bainite ( + Fe3C plates/needles)

    Pearlite ( + Fe3C layers + a proeutectoid phase)

    Martensite (BCT phase diffusionless

    transformation)

    Tempered Martensite ( + very fine

    Fe3C particles)

    slow cool

    moderate cool

    rapid quench

    reheat

    Str

    en

    gth

    Du

    cti

    lity

    Martensite T Martensite

    bainite fine pearlite

    coarse pearlite spheroidite

    General Trends

    Adapted from Fig. 10.27, Callister 6e.

  • Chapter 11: Metal AlloysApplications and Processing

    ISSUES TO ADDRESS...

    How are metal alloys classified and how are they used?

    What are some of the common fabrication techniques?

    How do properties vary throughout a piece of materialthat has been quenched, for example?

    How can properties be modified by post heat treatment?

  • Taxonomy of Metals

    Adapted from Fig. 9.21,Callister 6e. (Fig. 9.21 adapted from Binary Alloy Phase Diagrams, 2nd ed.,Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.)

    Adapted from Fig. 11.1, Callister 6e.

    Fe3C

    cementite

    Metal Alloys

    Steels

    Ferrous Nonferrous

    Cast Irons Cu Al Mg Ti

  • Steels

    Low Alloy High Alloy

    low carbon

  • Basic Ideas in Alloying Steels:1. Phase Partitioning at Austenite/Pearlite Interface

    Carbide FormersV, Ti, Nb

    Ferrite Formers (solid solution)Ni, Si, Mn

    Paritioning at the Austenite/Pearlite InterfaceSlows transformationAllows Bainite or Martensite to form on cooling

  • Basic Ideas in Alloying Steels:2. Alloying to Control the Eutectoid Transformation

    AlloyingControl Nose in TTT DiagramControl Eutectoid Temperature and C Composition

    Cr: added (~8 12wt %) to make steel stainlessNi: High concentrations to stabilize austenite austenitic steels

  • Hardenability of Steels

    Ability to form martensite Jominy end quench test to measure hardenability.

    Hardness versus distance from the quenched end.

    24C water

    specimen (heated to phase field)

    flat ground

    4

    1

    Ha

    rdn

    ess

    , HR

    C

    Distance from quenched end

    Adapted from Fig. 11.10, Callister 6e. (Fig. 11.10 adapted from A.G. Guy, Essentials of Materials Science, McGraw-Hill Book Company, New York, 1978.)

    Adapted from Fig. 11.11, Callister 6e.

  • Why Hardness Changes with Position

    The cooling rate varies with position.

    Adapted from Fig. 11.12, Callister 6e. (Fig. 11.12 adapted from H. Boyer (Ed.) Atlas of Isothermal Transformation and Cooling Transformation Diagrams, American Society for Metals, 1977, p. 376.)

    distance from quenched end (in)Ha

    rdn

    ess

    , HR

    C

    20

    40

    60

    0 1 2 3

    600

    400

    200A M

    A P

    Martensite

    Martensite + Pearlite

    Fine Pearlite

    Pearlite

    0.1 1 10 100 1000

    T(C)

    M(start)

    Time (s)

    0

    0%100%

    M(finish)

  • Hardenability vs. Alloy Content

    Jominy end quenchresults, 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. 11.13, Callister 6e. (Fig. 11.13 adapted from figure furnished courtesy Republic Steel Corporation.)

    T(C)

    10-1 10 103 1050

    200

    400

    600

    800

    Time (s)

    M(start)M(90%)

    TE

    A Bshift from A to B due to alloying

    Cooling rate (C/s)

    Ha

    rdn

    ess

    , HR

    C

    20

    40

    60

    100 20 30 40 50Distance from quenched end (mm)

    210100 3

    4140

    8640

    5140

    1040

    50

    80

    100

    %M4340

  • Quenching Medium and Geometry

    Effect of quenching medium:

    Mediumairoil

    water

    Hardnesssmall

    moderatelarge

    Severity of Quenchsmall

    moderatelarge

    Effect of geometry:When surface-to-volume ratio increases:

    --cooling rate increases--hardness increases

    Positioncenter

    surface

    Cooling ratesmalllarge

    Hardnesssmalllarge

  • Nonferrous Alloys

    NonFerrous Alloys

    Cu AlloysBrass: Zn is subst. impurity (costume jewelry, coins, corrosion resistant)Bronze: Sn, Al, Si, Ni are subst. impurity (bushings, landing gear)Cu-Be: precip. hardened for strength

    Al Alloys-lower : 2.7g/cm3 -Cu, Mg, Si, Mn, Zn additions -solid sol. or precip. strengthened (struct.

    aircraft parts & packaging)

    Mg Alloys-very low : 1.7g/cm3 -ignites easily -aircraft, missles

    Refractory metals-high melting T -Nb, Mo, W, Ta Noble metals

    -Ag, Au, Pt -oxid./corr. resistant

    Ti Alloys-lower : 4.5g/cm3

    vs 7.9 for steel -reactive at high T -space applic.

    Based on discussion and data provided in Section 11.3, Callister 6e.

  • Metal Fabrication Methods (1)

    CASTING JOININGFORMING

    Ao Ad

    force

    dieblank

    force

    Forging(wrenches, crankshafts)

    Rolling(I-beams, rails)

    Extrusion(rods, tubing)

    Adapted from Fig. 11.7, Callister 6e.

    ram billet

    container

    containerforce

    die holder

    die

    Ao

    Adextrusion

    roll

    AoAd

    roll

    Drawing(rods, wire, tubing)

    often atelev. T

    tensile force

    AoAddie

    die

  • Forming Temperature

    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., 1996. (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. 10.10, p. 415 (Orig. source: A.J. McEvily, Jr.and R.H. Bush, Trans. ASM 55, 1962, p. 654.)

    (a) (b) (c)

    --Swaged

  • Metal Fabrication Methods (2)

    plasterdie formedaround waxprototype

    FORMING JOININGCASTING Sand Casting

    (large parts, e.g.,auto engine blocks)

    Sand Sand

    molten metal

    Investment Casting(low volume, complex shapese.g., jewelry, turbine blades)

    wax

    Die Casting(high volume, low T alloys)

    Continuous Casting(simple slab shapes)

    molten

    solidified

  • Metal Fabrication Methods (3)

    CASTINGFORMING JOINING Powder Processing

    (materials w/low ductility)

    pressure

    heat

    point contact at low T

    densification by diffusion at higher T

    area contact

    densify

    Welding(when one large part isimpractical)

    Heat affected zone:(region in which themicrostructure has beenchanged).

    Adapted from Fig. 11.8, Callister 6e.(Fig. 11.8 from Iron Castings Handbook, C.F. Walton and T.J. Opar (Ed.), 1981.)

    piece 1 piece 2

    fused base metal

    filler metal (melted)base metal (melted)

    unaffectedunaffectedheat affected zone

  • Thermal Processing of Metals

    Annealing: Heat to Tanneal, then cool slowly.

    Types of Annealing

    Process Anneal: Negate effect of cold working by (recovery/ recrystallization)

    Stress Relief: Reduce stress caused by:

    -plastic deformation -nonuniform cooling -phase transform.

    Normalize (steels): Deform steel with large grains, then normalize to make grains small.

    Full Anneal (steels): Make soft steels for good forming by heating to get , then cool in furnace to get coarse P.

    Spheroidize (steels): Make very soft steels for good machining. Heat just below TE & hold for

    15-25h.

    Based on discussion in Section 11.7, Callister 6e.

  • Precipitation Hardening

    Particles impede dislocations. Ex: Al-Cu system Procedure:

    --Pt A: solution heat treat(get solid solution)

    --Pt B: quench to room temp.--Pt C: reheat to nucleate

    small crystals within crystals.

    Other precipitationsystems: Cu-Be Cu-Sn Mg-Al

    Pt A (soln heat treat)

    Pt B

    Pt C (precipitate )

    Temp.

    Time

    Adapted from Fig. 11.22, Callister 6e. (Fig. 11.22 adapted from J.L. Murray, International Metals Review 30, p.5, 1985.)

    Adapted from Fig. 11.20, Callister 6e.

    300

    400

    500

    600

    700

    0 10 20 30 40 50wt%Cu(Al)

    L+L

    +

    +L

    T(C)

    A

    B

    C

    composition range needed for precipitation hardening

    CuAl2

  • Precipitate Effect on TS, %El

    2014 Al Alloy:

    TS peaks withprecipitation time.

    Increasing T acceleratesprocess.

    %EL reaches minimumwith precipitation time.

    precipitation heat treat time (h)

    ten

    sile

    str

    en

    gth

    (M

    Pa

    )

    300

    400

    500

    2001min 1h 1day 1mo 1yr

    204C

    149C

    non-

    equi

    l. so

    lid s

    olut

    ion

    man

    y sm

    all

    prec

    ipita

    tes

    ag

    ed

    fe

    wer

    larg

    e

    pre

    cipi

    tate

    s

    ove

    rage

    d%

    EL

    (2

    in s

    am

    ple

    )10

    20

    30

    0 1min 1h 1day 1mo 1yr

    204C 149C

    precipitation heat treat time (h)

    Adapted from Fig. 11.25 (a) and (b), Callister 6e. (Fig. 11.25 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.)

  • Summary

    Steels: increase TS, Hardness (and cost) by adding--C (low alloy steels)--Cr, V, Ni, Mo, W (high alloy steels)--ductility usually decreases w/additions.

    Non-ferrous:--Cu, Al, Ti, Mg, Refractory, and noble metals.

    Fabrication techniques:--forming, casting, joining.

    Hardenability--increases with alloy content.

    Precipitation hardening--effective means to increase strength in

    Al, Cu, and Mg alloys.

  • Chapter 8: Mechanical Failure

    ISSUES TO ADDRESS... How do flaws in a material initiate failure? How is fracture resistance quantified; how do different

    material classes compare? How do we estimate the stress to fracture? How do loading rate, loading history, and temperature

    affect the failure stress?

    Ship-cyclic loadingfrom waves.

    Computer chip-cyclicthermal loading.

    Hip implant-cyclicloading from walking.

    Adapted from Fig. 8.0, Callister 6e.(Fig. 8.0 is by Neil Boenzi, The New York Times.)

    Adapted from Fig. 18.11W(b), Callister 6e. (Fig. 18.11W(b) is courtesy of National Semiconductor Corporation.)

    Adapted from Fig. 17.19(b), Callister 6e.

  • Ductile vs. Brittle Failure

    Highly Ductile Moderately Ductile Brittle

    Ductile:Warning before

    fracture

    Brittle:Little

    warning

  • Example: Pipe Failure

    Ductile failure:--one piece--large deformation

    Brittle failure:--many pieces--small deformation

    Figures from V.J. Colangelo and F.A. Heiser, Analysis of Metallurgical Failures (2nd ed.), Fig. 4.1(a) and (b), p. 66 John Wiley and Sons, Inc., 1987. Used with permission.

  • Moderately Ductile Failure

    Evolution to failure:

    necking void nucleation

    void growth and linkage

    shearing at surface

    fracture

    Resultingfracturesurfaces(steel)

    50 m

    particlesserve as voidnucleationsites.

    50 m

    100 m

    From V.J. Colangelo and F.A. Heiser, Analysis of Metallurgical Failures(2nd ed.), Fig. 11.28, p. 294, John Wiley and Sons, Inc., 1987. (Orig. source: P. Thornton, J. Mater. Sci., Vol. 6, 1971, pp. 347-56.)

    Fracture surface of tire cord wire loaded in tension. Courtesy of F. Roehrig, CC Technologies, Dublin, OH. Used with permission.

  • Cup-and-Cone Fracture and Brittle Fracture

    Cup-and-cone fracture in Al

    Dimpling (Center) Dimpling (Edge)

  • Brittle Fracture Surfaces

    Intergranular(between grains)

    Intragranular(within grains)

    Al Oxide(ceramic)

    Reprinted w/ permission from

    "Failure Analysis of Brittle Materials", p. 78.

    Copyright 1990, The American Ceramic

    Society, Westerville, OH. (Micrograph by R.M. Gruver and H.

    Kirchner.)

    316 S. Steel (metal)

    Reprinted w/ permission from

    "Metals Handbook", 9th ed, Fig. 650, p. 357.

    Copyright 1985, ASM International, Materials Park, OH. (Micrograph

    by D.R. Diercks, Argonne National Lab.)

    304 S. Steel (metal)Reprinted w/permission from "Metals Handbook", 9th ed, Fig. 633, p. 650. Copyright 1985, ASM International, Materials Park, OH. (Micrograph by J.R. Keiser and A.R. Olsen, Oak Ridge National Lab.)

    Polypropylene(polymer)Reprinted w/ permission from R.W. Hertzberg, "Defor-mation and Fracture Mechanics of Engineering Materials", (4th ed.) Fig. 7.35(d), p. 303, John Wiley and Sons, Inc., 1996.

    3m

    4 mm160m

    1 mm(Orig. source: K. Friedrick, Fracture 1977, Vol. 3, ICF4, Waterloo, CA, 1977, p. 1119.)

  • Brittle Fracture Surfaces

    Transgranular fracture(ductile cast iron)

    Intergranular fracture

    Fractography study of fracture surfaces (usually SEM)

  • Brittle Fracture Surfaces

    Brittle fracture surfaces

    Arrows indicate origin

    Fracture surface structure:Crack OriginCrack path

  • Ideal vs. Real Materials

    Stress-strain behavior (Room T):

    E/10

    E/100

    0.1

    perfect matl-no flaws

    carefully produced glass fiber

    typical ceramic typical strengthened metaltypical polymer

    TS

  • Flaws are Stress Concentrators!

    Elliptical hole ina plate:

    Stress distrib. in front of a hole:

    Stress conc. factor:

    BAD! Kt>>3NOT SO BAD

    Kt=3

    max

    t

    2oa + 1

    t

    o

    2a

    Kt = max /o

    Large Kt promotes failure:

    o = average stressT = radius of crack tip2a = crack length

  • Engineering Fracture Design

    Avoid sharp corners!

    r/h

    sharper fillet radius

    increasing w/h

    0 0.5 1.01.0

    1.5

    2.0

    2.5

    Stress Conc. Factor, Ktmax

    o=

    Adapted from Fig. 8.2W(c), Callister 6e.(Fig. 8.2W(c) is from G.H. Neugebauer, Prod. Eng. (NY), Vol. 14, pp. 82-87 1943.)

    r , fillet

    radius

    w

    h

    o

    max

  • When Does a Crack Propagate?

    t at a cracktip is verysmall!

    Result: crack tipstress is very large.

    Crack propagates when:the tip stress is largeenough to make:

    distance, x, from crack tip

    tip =K2 xtip

    increasing K

    K Kc

  • Geometry, Load, & Material

    Condition for crack propagation:

    Values of K for some standard loads & geometries:

    2a2a

    aa

    K = a K = 1.1 a

    K KcStress Intensity Factor:--Depends on load &

    geometry.

    Fracture Toughness:--Depends on the material,

    temperature, environment, &rate of loading.

    units of K :MPa mor ksi in

    Adapted from Fig. 8.8, Callister 6e.

  • Fracture Toughness

    Kc = Y c (a)

    Kc Fracture toughnessY Geometric factor (crack geometry)c Critical stress for crack propagationa Crack length (depends on crack geometry)

    Mode I (Tensile)

    Mode II (Sliding)

    Mode III (Tearing)

    Crack Mode Designations

  • Graphite/ Ceramics/ Semicond

    Metals/ Alloys

    Composites/ fibersPolymers

    5

    KIc

    (MP

    a

    m0

    .5)

    1

    Mg alloysAl alloys

    Ti alloys

    Steels

    Si crystalGlass-soda

    Concrete

    Si carbide

    PC

    Glass6

    0.5

    0.7

    2

    4

    3

    10

    20

    30

    Diamond

    PVC

    PP

    Polyester

    PS

    PET

    C-C(|| fibers)1

    0.6

    67

    40506070

    100

    Al oxideSi nitride

    C/C( fibers)1

    Al/Al oxide(sf)2

    Al oxid/SiC(w)3

    Al oxid/ZrO2(p)4Si nitr/SiC(w)5

    Glass/SiC(w)6

    Y2O3/ZrO2(p)4

    Kcmetals

    Kccomp

    Kccer Kc

    poly

    inc

    rea

    sin

    g

    Based on data in Table B5,Callister 6e.Composite reinforcement geometry is: f = fibers; sf = short fibers; w = whiskers; p = particles. Addition data as noted (vol. fraction of reinforcement):1. (55vol%) ASM Handbook, Vol. 21, ASM Int., Materials Park, OH (2001) p. 606.2. (55 vol%) Courtesy J. Cornie, MMC, Inc., Waltham, MA.3. (30 vol%) P.F. Becher et al., Fracture Mechanics of Ceramics, Vol. 7, Plenum Press (1986). pp. 61-73.4. Courtesy CoorsTek, Golden, CO.5. (30 vol%) S.T. Buljan et al., "Development of Ceramic Matrix Composites for Application in Technology for Advanced Engines Program", ORNL/Sub/85-22011/2, ORNL, 1992.6. (20vol%) F.D. Gace et al., Ceram. Eng. Sci. Proc., Vol. 7 (1986) pp. 978-82.

    Fracture Toughness