Download - phase equilibria and phase transformation

7/25/2019 phase equilibria and phase transformation

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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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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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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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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 &$as@at#i% #$ #"!%u"a$ +t in &$as@#"

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

%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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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.