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    5.1 DEFINITIONS AND BASIC CONCEPTS

    5.2 PHASE DIAGRAM

    5.3 MICROSTRUCTURE

    CHAPTER 5CHAPTER 5

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    har/jkbr/fkmp/2013 Materials Science 2

    What can you explain about the map shown in the above figure?

    Showing the region of sea (liquid phase) and land (solid phase) Showing boundaries lines between sea and land; and between countries (such

    as Malaysia !hailand "ndonesia etc#)

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    har/jkbr/fkmp/2013 Materials Science 3

    ISSUES TO ADDRESS...

    When we combine two elements... what equilibrium state do we get?

    In particular, if we specify...

    a composition (e.g., wt%Cu - wt%Ni), and a temperature (T)

    then...

    How many phases do we get?

    What is the composition of each phase?

    How much of each phase do we get?

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    har/jkbr/fkmp/2013 Materials Science 4

    Example of metal alloy system phase diagram (Figure 5.1), showing theregion of liquid phase, solid phase and the mixture of the two phases.

    Figure 5.1 : inary phase diagram

    ! " liquid phase

    and " solid phase

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    5.1 DEFINITIONS AND BASIC CONCEPTS

    It is funda!nta" t# at!$ia"s s%i!n%! and !n&in!!$in& t'at

    ($#(!$ti!s #f at!$ia"s $!f"!%ts t'!i$ i%$#st$u%tu$!.

    Mi%$#st$u%tu$!s a$! %#nt$#""!d )* t'! %#(#siti#n#f t'!at!$ia"s and '#+ it is($#%!ss!d.

    Manufa%tu$in& , s'a(in& - ass!)"in& !n&in!!$in&

    ($#du%t d!/i%!s - ($#/id!s t'! at!$ia"s ($#(!$ti!s

    $!0ui$!d.

    M#st at!$ia"s ($#%!ssin& in/#"/!s t'!$a" 'ist#$*.

    I(#$tant t# und!$stand '#+ ($#%!ssin& 'ist#$*

    (a$ti%u"a$"* t!(!$atu$! %#nt$#" i%$#st$u%tu$! and($#(!$ti!s.

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    S$M% %SS%&!"'( )%*"&"!"$&S +

    P'as! Dia&$aMAP #f at!$ia"s ('as!s#$ a dia&$a +it' t!(!$atu$! and %#(#siti#n as a4!s

    ($#/id! s#! funda!nta" n#+"!d&! #f +'at t'!!0ui"i)$iu st$u%tu$! #f a !ta""i% #$ %!$ai% a""#*.

    M!ta""i% A""#* a i4tu$! #f !ta"s +it' #t'!$ !ta"s #$ n#n6

    !ta"s.E4a("! 7 B$ass , a i4tu$! #f %#((!$ Cu and 8in% 9n

    C#(#n!nts t'! %'!i%a" !"!!nts #$ %#(#unds +'i%'

    a! u( a""#*s.E4a("! 7 in )$ass t'! ain %#(#n!nts a$! Cu and 9n.

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    har/jkbr/fkmp/2013 Materials Science 7

    Bina$* a""#* %#ntains t+# 2 %#(#n!nts.

    T!$na$* a""#* %#ntains t'$!! 3 %#(#n!nts.:ua$t!$na$* a""#* %#ntains f#u$ ; %#(#n!nts.

    P'as! a"" (a$ts #f an a""#* i%$#st$u%tu$! +'i%' 'as a'##&!n!#us at#i% st$u%tu$! and t'! sa! %#(#siti#n.

    F#$ !4a("!< in a )ina$* a""#* s#"id stat! t'!i%$#st$u%tu$! %an ta! #n! #f f#u$ f#$s=

    a a sin&"! s#"id s#"uti#n=

    ) t+# s!(a$at!d (u$! %#(#n!nts=

    % t+# s!(a$at!d s#"id s#"uti#ns=

    d %'!i%a" %#(#unds< t#&!t'!$ +it' s#"id s#"uti#n.

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    #olid solution" a solid in whi$h an element is %dissol&es' in another sothat it is homogeneously dispersed, at an atomi$ s$ale.

    A""#* a$! d!s%$i)!d )* statin& t'! %#(#n!nts and t'!i$

    %#n%!nt$ati#ns< in +!i&'t #$ at# >.

    T'! +!i&'t > #f %#(#n!nt A 7

    T'! at# #$ #" > #f %#(#n!nt A 7

    N#. #f #"s ? +!i&'t in &[email protected]#i% #$ #"!%u"a$ +t in &[email protected]#"

    t in &$as ? N#. #f #"s 4 at#i% #$ #"!%u"a$ +t in &[email protected]#"

    %100componentsallofweight

    Acomponentofweight=

    A

    W

    %100componentsallofmols)(oratomsofnumber

    Acomponentofmols)(oratomsofnumber=

    A

    X

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    C#nstituti#n t'! %#nstituti#n #f an a""#* is d!s%$i)!d )* 7

    a t'! ('as!s ($!s!nt

    ) t'! +!i&'t f$a%ti#n #f !a%' ('as!

    % t'! %#(#siti#n #f !a%' ('as!

    E0ui"i)$iu %#nstituti#n t'!$! is n# fu$t'!$ t!nd!n%* f#$t'! %#nstituti#n #f a sa("! #f &i/!n %#(#siti#n t# %'an&!

    +it' ti! at a %#nstant t!(!$atu$! T and($!ssu$! (.

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    5.2 PHASE DIAGRAM

    P$#%!ssin& #f !n&in!!$in& at!$ia"s a"+a*s in/#"/!s at!$ia"sin "i0uid #$ s#"id stat!.

    In t'!s! stat!s< ($!ssu$! ( #n"* 'as a sa"" inf"u!n%! #n t'!!0ui"i)$iu %#nstituti#n< and %an )! n!&"!%t!d.

    In ('as! dia&$a< +! +i"" #n"* )! %#n%!$n!d +it' at!$ia"stat!s +'i%' a$! %#nt$#""!d )* t'! $!ainin& t+# stat!

    /a$ia)"!s 7 t!(!$atu$! and %#(#siti#n.

    T'! ('as! dia&$a #f t'! %#(#n!nts A and B is d!t!$in!dat a standa$d ($!ssu$! #f 1 at )* t'! t!(!$atu$! T and t'!%#(#siti#n B #$ B #$ A #$ A.

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    S#! #f t'! i(#$tant inf#$ati#n #)taina)"! f$# ('as!

    dia&$as is 7

    1. T# s'#+ +'at ('as!s a$! ($!s!nt at diff!$!nt

    %#(#siti#ns and t!(!$atu$!s und!$ s"#+ %##"in&!0ui"i)$iu %#nditi#ns.

    2. T# indi%at! t'! !0ui"i)$iu s#"id s#"u)i"it* #f #n!

    !"!!nt #$ %#(#und in an#t'!$.3. T# indi%at! t'! t!(!$atu$! at +'i%' an a""#* %##"!d

    und!$ !0ui"i)$iu %#nditi#ns sta$ts t# s#"idif* and t'!

    t!(!$atu$! $an&! #/!$ +'i%' s#"idifi%ati#n #%%u$s.

    ;. T# indi%at! t'! t!(!$atu$! at +'i%' diff!$!nt ('as!s

    sta$t t# !"t.

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    -

    Liquidus line

    Solidus lineSolidus line

    Solvus lineSolvus line

    *igure ,#- +!he 'g./u equilibrium system showing types of linesin the binary phase diagram#

    -rich solid () -rich solid ()

    '*(#!ut!%ti% '*(!$!ut!%ti%

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    Fi&u$! 5. s'#+s t'! t*(!s #f "in! in t'! ('as! dia&$a 7

    i0uidus "in! t'! ('as! )#unda$* +'i%' "iits t'! )#tt#

    #f t'! "i0uidfi!"d

    S#"idus "in! t'! "in! &i/in& t'! u((!$ "iit #f t'! sin&"!

    ('as! s#"id fi!"d.

    S#"/us "in! t'! "in! +'i%' s!(a$at!s t'! t+# ('as! fi!"d

    +it' t'! sin&"! ('as! s#"id fi!"d.

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    !01%S $* "&2'3"'&! 3%'/!"$&S +

    Eut!%t#id a ('as! t$ansf#$ati#n in +'i%' a s#"id ('as!t$ansf#$s #n %##"in& int# t+# s#"id ('as!s is#t'!$a""*.

    , -

    Eut!%ti% a ('as! t$ansf#$ati#n in +'i%' a"" t'! "i0uid ('as!t$ansf#$s #n %##"in& int# t+# s#"id ('as!s is#t'!$a""*.

    , -

    P!$it!%ti% a ('as! t$ansf#$ati#n in +'i%'< u(#n %##"in&< a"i0uid ('as! %#)in!s +it' a s#"id ('as! t# ($#du%! a n!+

    s#"id ('as!. - ,

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    har/jkbr/fkmp/2013 Materials Science 15

    ale 5.1 : ypes of hree*+hase n&ariant -ea$tions $$urring in inary

    +hase /iagrams

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    5.2.1 R!adin& a ('as! dia&$a

    A T'! %#nstituti#n (#int

    T'! stat! /a$ia)"!s< t!(!$atu$! and %#(#siti#n Sn and P)62

    +t> Sn a""#*s at 25C.

    'at d#!s t'! a""#* %#nsist #f in !a%' %as!

    P)6 +t> Sn 7 .

    P)62 +t> Sn 7 .

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    3. T'! a""#* %#$$!s(#ndin& initia""* t# t'! %#nstituti#n (#int 1 is%##"!d /!$* s"#+"* t# $## t!(!$atu$!.

    At +'i%' t!(!$atu$!s d# %'an&!s in t'! nu)!$ #$ t*(! #f('as!s #%%u$

    'at ('as!s a$! ($!s!nt at (#int 2.......

    'at ('as!s a$! ($!s!nt at (#int 3...

    ;. Sii"a$"*< t'! a""#* %#$$!s(#ndin& t# t'! %#nstituti#n (#int ;is %##"!d t# $## t!(!$atu$!. Id!ntif* t'! f#""#+in& 7

    Initia" %#(#siti#n t!(!$atu$! 7 ..

    Initia" ('as!s 7

    T!(!$atu$! at +'i%' %'an&! t'! ('as! #%%u$s 7

    Fina" ('as!s 7 .

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    B C#(#siti#n #f t'! ('as!s

    In a sin&"!6('as! $!&i#n< t'! ('as! %#(#siti#n anda""#* %#(#siti#n %#in%id!.

    In a t+#6('as! $!&i#n< t'! %#(#siti#ns #f t'! ('as!s

    a$! f#und at t'! !nds #f t'! is#t'!$a" "in! s(annin&

    t'! fi!"d t'$#u&' t'! %#nstituti#n (#int. T'is "in! is

    %a""!d t'! ti!6"in!.

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    56%S!"$&S 8 ;

    Us! t'! P)6Sn dia&$a )!"#+ t# ans+!$ t'! f#""#+in& 0u!sti#n.

    (Pb) + (Sn)

    L + (Pb)

    L+ (Sn)(Pb)

    (Sn)

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    1. T'! %#nstituti#n (#int f#$ a Sn6 +t> P) a""#* at 25C "i!s

    in a t+#6('as! fi!"d. C#nst$u%t a ti!6"in! #n t'! fi&u$! and$!ad #ff t'! t+# ('as!s and t'!i$ %#(#siti#ns.

    P'as!s 7 ..

    C#(#siti#n #f ('as! 1 7 C#(#siti#n #f ('as! 2 7

    2. T'! a""#* is s"#+"* %##"!d t# 2C. At t'is t!(!$atu$! .

    a H#+ an* ('as!s a$! ($!s!nt) Gi/! t'! a(($#4iat! %#(#siti#n #f t'! ('as!s.

    % 'i%' is t'! d#inant ('as!

    d 'at a$! t'! ($#(#$ti#ns )* +!i&'t #f !a%' ('as!

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    MICROSTRUCTURES IN EUTECTIC SKSTEMS 6 III

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    MICROSTRUCTURES IN EUTECTIC SKSTEMS 6 I

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    +rolemsC#nsid!$ t'! P)6Sn dia&$a< a! a ('as! ana"*sis f#$ t'!

    ("u)u a""#* !0ui"i)$iu s#"idifi%ati#n f#$ !a%' %#(#siti#n

    )!"#+ =

    i P#int d +it' ;> Sn at 1J3C - T.

    ii P#int ! +it' ;> Sn at 1J3C 6T.

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    P'as! "i0uid P$#!ut!%ti%6

    P'as!%#(#siti#n

    L1.> Sn in "i0uid 1.2> Sn in ($#!ut!%ti%6

    A#unt #f

    ('as!

    ; 1.2 1>? ;>

    L1. 1.2

    L1. ; 1>?51>.

    L1. 1.2

    P'as! T#ta" B!ta

    P'as!

    %#(#siti#n 1.2> Sn in

    .5> Sn in

    A#unt #f

    ('as!

    .5 ; 1> ? 3>

    .5 1.2

    ; 1.2 1> ? 2>

    .5 1.2

    i

    ii

    > !ut!%ti% ? > t#ta" > ($#!ut!%ti%

    ? 3 > 6 51> ? 22>

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    !!! )iagram eans ime*emperature*ransformation

    6lso 7nown as an sothermal ransformation/iagram

    i$rostru$ture and property $hanges in Fe*2

    alloys is an example of a real appli$ation of phasetransformation 7nowledge.

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    #tudy a eute$toid steel annealed 8ust elow theeute$toid temperature

    Experiment for following the mi$rostru$tural$hanges whi$h o$$ur during the isothermaltransformation of an eute$toid plain*$aron steelat 95o2

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    sothermaltransformation

    mi$rostru$ture

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    alid only for eute$toid steels, and $onstanttemperature transformations

    wo solid line : start and end of transformation /ashed line : 53 transformation

    Eute$toid temperature a hori;ontal line (ao&ewhi$h is austenite)

    ransformation rate in$reases with de$reasingtemperature

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    6ustenite ransformation

    Possible transformation involving the decomposition of austenite.

    Solid arrow : transformation involving diffusion

    Dashed arrow : diffusionless transformation

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    #low $ooling, $oarse pearlite formed with thi$7

    ferrite and $ementite layers n$reased $ooling rate, lamellar thi$7nessde$reases

    n$reased $ooling rate still allows formation ofainite

    Faster $ooling rate allow formation of martensite

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    Properties of phases

    Properties of pearlite

    Fairly tough

    Fairly ductileDepends on size of lamellae

    Properties of bainite

    Tough

    Structure between pearliteand martensite ( + Fe3C)

    Properties of martensite

    Very hard HRC 45-55

    Brittle

    bc tetragonal structure

    Supersaturated solution of C in FeHigh residual stresses

    Metastable

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    +earlite mi$rostru$ture

    6lternate

    plates of$aride andferrite.

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    ainite i$rostru$ture

    =pper ainite

    Formed from >5o2 to 55o2

    2ementite in form of rod

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    !ower ainite Formed from ?5o2 to >5o2 !ow diffusion rate produ$ed iron $aride

    pre$ipitate within ferrite plates " predominantly

    along single orientation (55o to longitudinal axis offerrite)

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    Formation of martensite

    @igh $ooling rates * quen$hing

    " -apid $ooling with water or oil /iffusion of $aron inhiited"

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    i$rostru$ture of martensite

    artensite is $reatedwhen austenite transforms

    y a shear me$hanisminstead of y nu$leationand growth.

    he shear transformationprodu$ts are a$i$ular.

    n this $ase, e$ause of

    high $aron (1.?3) there isretained austenite.

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    eat treatment

    /efinition of heat treatment is a $ontrolled

    heating and $ooling $y$les intended to ad8ust themi$rostru$ture and me$hani$al properties of amaterial for a spe$ifi$ purpose.

    Examples: annealing, normali;ing, quen$hing andtempering

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    'nnealing

    aterial exposed to ele&ated temperature forextended period of time, and then slowly $ooled.

    =sed to relie&e stresses, in$rease softness,du$tility and toughness, or to

    produ$e spe$ifi$ mi$rostru$ture

    Full annealing : ransformation to austenite, thenfurna$e $ooled to $oarse pearlite (relati&ely softand du$tile material)

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    &ormali

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    g-ates

    A: Slow cooling in furnace

    -- lamellar coarse pearlite

    B: Cooling in still air-- fine pearlite

    C: Split transformation

    -- fine pearlite and martensite

    D: Rapid cooling

    -- martensite

    E: Critical cooling rate-- slowest rate to produce nopearlite (full martensite)

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    !empering

    @eating martensite to etween 1 A BC2

    #oftens A toughens martensite Effe$ts dependent on temperature and in$lude" #tress relief

    " Epsilon $aride pre$ipitates from martensite" 2ementite pre$ipitates from martensite

    " Epsilon $aride $on&erts to $ementite

    " -etained austenite transforms to ainite

    Eff t f t i

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    Effe$t of tempering

    n$reases du$tility and toughness -edu$es hardness and strength

    #olid solution elements ha&e little effe$t ontempering

    "

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    artempering (arquen$hing)

    Modified quench to minimize distortion of heat treated steel:

    1) austenitize steel2) quench in hot oil or molten saltjust above martensite

    start temperature

    3) hold in quenching medium until uniform temperature in

    steel (but before austenite to bainite transformationbegins)

    4) cool at moderate rate to prevent thermal gradients

    ! usuall"# parts are later tempered to toughen steel

    t m i ( hi )

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    artempering (arquen$hing)

    6ustempering

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    6ustempering

    1) 6usteniti;e steel?) Duen$h in hot salt

    ath8ust ao&emartensiti$temperature

    >) sothermal hold) 2ooled to room

    temperature in air

    6ustempering

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    sothermal heat treatment pro$ess to produ$e ainite

    6lternati&e to quen$hing and tempering

    mpro&ed du$tility and impa$t strength for parti$ularhardness

    /e$reased $ra$7ing and distortion quen$hing

    +arti$ularly ad&antageous for thin se$tions (>G0H)

    Ithi$7er se$tions ha&e non*uniform properties due todifferent $ooling ratesJ

    6ustempering

    SUMMARY

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    SUMMARY

    Phase diagrams are useful tools to determine:

    --the number and types of phases,

    --the wt% of each phase,

    --and the composition of each phase

    for a given T and composition of the system.

    Alloying to produce a solid solution usually

    --increases the tensile strength T!"

    --decreases the ductility.

    #inary eutectics and binary eutectoids allow fora range of microstructures.