ch09_lecture note

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1
Chapter 9 - 1
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?
Chapter 9: Phase Diagrams
Phase BPhase A
Nickel atom
Copper atom
Chapter 9 - 2
Phase Equilibria: Solubility Limit
Introduction
– Solutions – solid solutions, single phase
– Mixtures – more than one phase
• Solubility Limit:
Max concentration for
which only a single phase 
solution occurs.
Question: What is the
solubility limit at 20°C?
Answer: 65 wt% sugar.
If Co < 65 wt% sugar: syrup
If Co > 65 wt% sugar: syrup + sugar.
65
Sucrose/Water Phase Diagram
Pu
re
 
Su
ga
r
Te
m
pe
ra
tu
re
 (°
C
)
0 20 40 60 80 100
Co =Composition (wt% sugar)
L
(liquid solution 
i.e., syrup)
Solubility 
Limit L
(liquid) 
+ 
S
(solid 
sugar)20
40
60
80
100
Pu
re
 
W
at
er
Adapted from Fig. 9.1, 
Callister 7e.
2
Chapter 9 - 3
• Components:
The elements or compounds which are present in the mixture
(e.g., Al and Cu)
• Phases:
The physically and chemically distinct material regions
that result (e.g., α and β).
Aluminum-
Copper
Alloy
Components and Phases
α (darker 
phase)
β (lighter 
phase)
Adapted from 
chapter-opening 
photograph, 
Chapter 9, 
Callister 3e. 
Chapter 9 - 4
Effect of T & Composition (Co)
• Changing T can change # of phases: 
Adapted from 
Fig. 9.1, 
Callister 7e.
D (100°C,90)
2 phases 
B (100°C,70)
1 phase 
path A to B.
• Changing Co can change # of phases: path B to D.
A (20°C,70)
2 phases
70 80 1006040200
Te
m
pe
ra
tu
re
 (°
C
)
Co =Composition (wt% sugar)
L
(liquid solution 
i.e., syrup)
20
100
40
60
80
0
L
(liquid) 
+ 
S
(solid 
sugar)
water-
sugar
system
3
Chapter 9 - 5
Phase Equilibria
0.12781.8FCCCu
0.12461.9FCCNi
r (nm)electronegCrystal
Structure
• Both have the same crystal structure (FCC) and have 
similar electronegativities and atomic radii (W. Hume –
Rothery rules) suggesting high mutual solubility. 
Simple solution system (e.g., Ni-Cu solution)
• Ni and Cu are totally miscible in all proportions.
Chapter 9 - 6
Phase Diagrams
• Indicate phases as function of T, Co, and P. 
• For this course:
-binary systems: just 2 components.
-independent variables: T and Co (P = 1 atm is almost always used).
• Phase
Diagram
for Cu-Ni
system
Adapted from Fig. 9.3(a), Callister 7e.
(Fig. 9.3(a) is adapted from Phase 
Diagrams of Binary Nickel Alloys, P. Nash 
(Ed.), ASM International, Materials Park, 
OH (1991).
• 2 phases:
L (liquid)
α (FCC solid solution)
• 3 phase fields: 
L
L + α
α
wt% Ni20 40 60 80 10001000
1100
1200
1300
1400
1500
1600
T(°C)
L (liquid)
α
(FCC solid 
solution)
L +
 αliquidu
s
sol
idu
s
4
Chapter 9 - 7
• Note:The Ni-Cu alloy system shown in the 
previous slide is a binary isomorphous
system;
• Note: Isomorphous : Having the same 
structure. In the phase diagram sense, 
isomorphicity means having the same crystal 
structure or complete solid solubility for all 
compositions. 
Chapter 9 - 8
wt% Ni20 40 60 80 10001000
1100
1200
1300
1400
1500
1600
T(°C)
L (liquid)
α
(FCC solid 
solution)
L +
 α
liqu
idu
s
sol
idu
s
Cu-Ni
phase
diagram
Phase Diagrams:
# and types of phases
• Rule 1: If we know T and Co, then we know:
--the # and types of phases present.
• Examples:
A(1100°C, 60): 
1 phase: α
B(1250°C, 35): 
2 phases: L + α
Adapted from Fig. 9.3(a), Callister 7e.
(Fig. 9.3(a) is adapted from Phase 
Diagrams of Binary Nickel Alloys, P. Nash 
(Ed.), ASM International, Materials Park, 
OH, 1991).
B
(1
25
0°
C
,3
5)
A(1100°C,60)
5
Chapter 9 - 9
wt% Ni
20
1200
1300
T(°C)
L (liquid)
α
(solid)L +
 α
liqui
dus
solid
us
30 40 50
L + 
α
Cu-Ni 
system
Phase Diagrams:
composition of phases
• Rule 2: If we know T and Co, then we know:
--the composition of each phase.
• Examples:
TA A
35
Co
32
CL
At TA = 1320°C: 
Only Liquid (L) 
CL = Co ( = 35 wt% Ni)
At TB = 1250°C: 
Both α and L
CL = C liquidus ( = 32 wt% Ni here) 
Cα = Csolidus ( = 43 wt% Ni here)
At TD = 1190°C: 
Only Solid ( α) 
Cα = Co ( = 35 wt% Ni)
Co = 35 wt% Ni
Adapted from Fig. 9.3(b), Callister 7e.
(Fig. 9.3(b) is adapted from Phase Diagrams
of Binary Nickel Alloys, P. Nash (Ed.), ASM 
International, Materials Park, OH, 1991.)
B
TB
DTD
tie line
4
Cα3
Chapter 9 - 10
• Rule 3: If we know T and Co, then we know:
--the amount of each phase (given in wt%).
• Examples:
At TA: Only Liquid (L) 
WL = 100 wt%, Wα = 0
At TD: Only Solid ( α) 
WL = 0, Wα = 100 wt%
Co = 35 wt% Ni
Adapted from Fig. 9.3(b), Callister 7e.
(Fig. 9.3(b) is adapted from Phase Diagrams of 
Binary Nickel Alloys, P. Nash (Ed.), ASM 
International, Materials Park, OH, 1991.)
Phase Diagrams:
weight fractions of phases
wt% Ni
20
1200
1300
T(°C)
L (liquid)
α
(solid)L +
 α
liqui
dus
solid
us
30 40 50
L + 
α
Cu-Ni 
system
TA A
35
Co
32
CL
B
TB
DTD
tie line
4
Cα3
R S
At TB: Both α and L
% 73
3243
3543 wt=−
−=
= 27 wt%
WL = SR +S
Wα = RR +S
6
Chapter 9 - 11
• Tie line – connects the phases in equilibrium with 
each other - essentially an isotherm
The Lever Rule
How much of each phase?
Think of it as a lever (teeter-totter)
ML Mα
R S
RMSM L ⋅=⋅α 
L
L
LL
L
L CC
CC
SR
RW
CC
CC
SR
S
MM
MW −
−=+=−
−=+=+= ααα
α
α
00 
wt% Ni
20
1200
1300
T(°C)
L (liquid)
α
(solid)L +
 α
liqui
dus
solid
us
30 40 50
L + 
α
B
TB
tie line
CoCL Cα
SR
Adapted from Fig. 9.3(b), 
Callister 7e.
Chapter 9 - 12
wt% Ni
20
1200
1300
30 40 50
1100
L (liquid)
α
(solid)
L +
 α
L +
 α
T(°C)
A
35
Co
L: 35wt%Ni
Cu-Ni
system
• Phase diagram:
Cu-Ni system.
• System is:
--binary
i.e., 2 components:
Cu and Ni.
--isomorphous
i.e., complete
solubility of one
component in
another; α phase
field extends from
0 to 100 wt% Ni.
Adapted from Fig. 9.4, 
Callister 7e.
• Consider
Co = 35 wt%Ni.
Ex: Cooling in a Cu-Ni Binary
4635
4332
α: 43 wt% Ni
L: 32 wt% Ni
L: 24 wt% Ni
α: 36 wt% Ni
Bα: 46 wt% Ni
L: 35 wt% Ni
C
D
E
24 36
7
Chapter 9 - 13
• Cα changes as we solidify.
• Cu-Ni case:
• Fast rate of cooling:
Cored structure
• Slow rate of cooling:
Equilibrium structure
First α to solidify has Cα = 46 wt% Ni.
Last α to solidify has Cα = 35 wt% Ni.
Cored vs Equilibrium Phases
First α to solidify: 
46 wt% Ni
Uniform Cα:
35 wt% Ni
Last α to solidify: 
< 35 wt% Ni
Chapter 9 - 14
Mechanical Properties: Cu-Ni System
• Effect of solid solution strengthening on:
--Tensile strength (TS) --Ductility (%EL,%AR)
--Peak as a function of Co --Min. as a function of Co
Adapted from Fig. 9.6(a), Callister 7e. Adapted from Fig. 9.6(b), Callister 7e.
Te
ns
ile
 S
tre
ng
th
 (M
P
a)
Composition, wt% Ni
Cu Ni
0 20 40 60 80 100
200
300
400
TS for 
pure Ni
TS for pure Cu
E
lo
ng
at
io
n 
(%
E
L)
Composition, wt% Ni
Cu Ni
0 20 40 60 80 10020
30
40
50
60
%EL for 
pure Ni
%EL for pure Cu
8
Chapter 9 - 15
: Min. melting TE
2 components
has a special composition
with a min. melting T.
Adapted from Fig. 9.7, 
Callister 7e.
Binary-EutecticSystems
• Eutectic transition
L(CE) α(CαE) + β(CβE)
• 3 single phase regions 
(L, α, β) 
• Limited solubility: 
α: mostly Cu 
β: mostly Ag 
• TE : No liquid below TE
• CE
composition
Ex.: Cu-Ag system
Cu-Ag
system
L (liquid)
α L + α L+β β
α + β
Co , wt% Ag
20 40 60 80 1000
200
1200
T(°C)
400
600
800
1000
CE
TE 8.0 71.9 91.2
779°C
Chapter 9 - 16
L+α
L+β
α + β
200
T(°C)
18.3
C, wt% Sn
20 60 80 1000
300
100
L (liquid)
α 183°C
61.9 97.8
β
• For a 40 wt% Sn-60 wt% Pb alloy at 150°C, find...
--the phases present: Pb-Sn
system
EX: Pb-Sn Eutectic System (1)
α + β
--compositions of phases:
CO = 40 wt% Sn
--the relative amount
of each phase:
150
40
Co
11
Cα
99
Cβ
SR
Cα = 11 wt% Sn
Cβ = 99 wt% Sn
Wα= Cβ - COCβ - Cα
= 99 - 4099 - 11 =
59
88 = 67 wt%
S
R+S =
Wβ = CO - CαCβ - Cα=
R
R+S
= 29
88
= 33 wt%= 40 - 11
99 - 11
Adapted from Fig. 9.8, 
Callister 7e.
9
Chapter 9 - 17
L+β
α + β
200
T(°C)
C, wt% Sn
20 60 80 1000
300
100
L (liquid)
α β
L+α
183°C
• For a 40 wt% Sn-60 wt% Pb alloy at 200°C, find...
--the phases present: Pb-Sn
system
Adapted from Fig. 9.8, 
Callister 7e.
EX: Pb-Sn Eutectic System (2)
α + L
--compositions of phases:
CO = 40 wt% Sn
--the relative amount
of each phase:
Wα =
CL - CO
CL - Cα
=
46 - 40
46 - 17
=
6
29 = 21 wt%
WL =
CO - Cα
CL - Cα
=
23
29 = 79 wt%
40
Co
46
CL
17
Cα
220
SR
Cα = 17 wt% Sn
CL = 46 wt% Sn
Chapter 9 - 18
• Co < 2 wt% Sn
• Result:
--at extreme ends
--polycrystal of α grains
i.e., only one solid phase.
Adapted from Fig. 9.11, 
Callister 7e.
Microstructures 
in Eutectic Systems: I
0
L+ α
200
T(°C)
Co, wt% Sn
10
2
20
Co
300
100
L
α
30
α+β
400
(room T solubility limit)
TE
(Pb-Sn
System)
α
L
L: Co wt% Sn
α: Co wt% Sn
10
Chapter 9 - 19
• 2 wt% Sn < Co < 18.3 wt% Sn
• Result:
ƒ Initially liquid + α
ƒ then α alone
ƒ finally two phases
¾ α polycrystal
¾ fine β-phase inclusions
Adapted from Fig. 9.12, 
Callister 7e.
Microstructures 
in Eutectic Systems: II
Pb-Sn
system
L + α
200
T(°C)
Co , wt% Sn
10
18.3
200
Co
300
100
L
α
30
α+ β
400
(sol. limit at TE)
TE
2
(sol. limit at Troom)
L
α
L: Co wt% Sn
αβ
α: Co wt% Sn
Chapter 9 - 20
• Co = CE
• Result: Eutectic microstructure (lamellar structure)
--alternating layers (lamellae) of α and β crystals.
Adapted from Fig. 9.13, 
Callister 7e.
Microstructures 
in Eutectic Systems: III
Adapted from Fig. 9.14, Callister 7e.
160μm
Micrograph of Pb-Sn
eutectic 
microstructure
Pb-Sn
system
L + β
α + β
200
T(°C)
C, wt% Sn
20 60 80 1000
300
100
L
α β
L+α
183°C
40
TE
18.3
α: 18.3 wt%Sn
97.8
β: 97.8 wt% Sn
CE
61.9
L: Co wt% Sn
11
Chapter 9 - 21
Lamellar Eutectic Structure
Adapted from Figs. 9.14 & 9.15, Callister 
7e.
Chapter 9 - 22
• 18.3 wt% Sn < Co < 61.9 wt% Sn
• Result: α crystals and a eutectic microstructure
Microstructures 
in Eutectic Systems: IV
18.3 61.9
SR
97.8
SR
primary α
eutectic α
eutectic β
WL = (1-Wα) = 50 wt%
Cα = 18.3 wt% Sn
CL = 61.9 wt% Sn
S
R + S
Wα= = 50 wt%
• Just above TE :
• Just below TE :
Cα = 18.3 wt% Sn
Cβ = 97.8 wt% Sn
S
R + S
Wα= = 73 wt%
Wβ = 27 wt%
Adapted from Fig. 9.16, 
Callister 7e.
Pb-Sn
system
L+β200
T(°C)
Co, wt% Sn
20 60 80 1000
300
100
L
α β
L+α
40
α+β
TE
L: Co wt% Sn Lα
Lα
12
Chapter 9 - 23
L+α
L+β
α + β
200
Co, wt% Sn20 60 80 1000
300
100
L
α β
TE
40
(Pb-Sn
System)
Hypoeutectic & Hypereutectic
Adapted from Fig. 9.8, 
Callister 7e. (Fig. 9.8 
adapted from Binary Phase 
Diagrams, 2nd ed., Vol. 3, 
T.B. Massalski (Editor-in-
Chief), ASM International, 
Materials Park, OH, 1990.)
160 μm
eutectic micro-constituent
Adapted from Fig. 9.14, 
Callister 7e.
hypereutectic: (illustration only)
β
ββ
β
β
β
Adapted from Fig. 9.17, 
Callister 7e. (Illustration 
only)
(Figs. 9.14 and 9.17 
from Metals 
Handbook, 9th ed.,
Vol. 9, 
Metallography and 
Microstructures, 
American Society for 
Metals, Materials 
Park, OH, 1985.)
175 μm 
α
α
α
ααα
hypoeutectic: Co = 50 wt% Sn
Adapted from 
Fig. 9.17, Callister 7e.
T(°C)
61.9
eutectic
eutectic: Co =61.9wt% Sn
Chapter 9 - 24
Intermetallic Compounds
Mg2Pb
Note: intermetallic compound forms a line - not an area -
because stoichiometry (i.e. composition) is exact.
Adapted from 
Fig. 9.20, Callister 7e.
13
Chapter 9 - 25
Eutectoid & Peritectic
• Eutectic(共晶) - liquid in equilibrium with two solids
L α + βcool
heat
intermetallic compound 
- cementite
cool
heat
• Eutectoid(共析) - solid phase in equation with two 
solid phases
S2 S1+S3
γ α + Fe3C (727ºC)
cool
heat
• Peritectic(包晶) - liquid + solid 1 Æ solid 2 (Fig 9.21)
S1 + L S2
δ + L γ (1493ºC)
Chapter 9 - 26
Eutectoid & Peritectic
Cu-Zn Phase diagram
Adapted from 
Fig. 9.21, Callister 7e.
Eutectoid transition δ γ + ε
Peritectic transition γ + L δ
14
Chapter 9 - 27
Iron-Carbon (Fe-C) Phase Diagram
• 2 important 
points
-Eutectoid (B):
γ ⇒ α +Fe3C
-Eutectic (A):
L ⇒ γ +Fe3C
Adapted from Fig. 9.24,Callister 7e. 
Fe
3C
 (c
em
en
tit
e)
1600
1400
1200
1000
800
600
400
0 1 2 3 4 5 6 6.7
L
γ 
(austenite)
γ+L
γ+Fe3C
α+Fe3C
α+γ
L+Fe3C
δ
(Fe) Co, wt% C
1148°C
T(°C)
α 727°C = T eutectoid
A
SR
4.30
Result: Pearlite = 
alternating layers of 
α and Fe3C phases
120 μm
(Adapted from Fig. 9.27, Callister 7e.)
γ γ
γγ
R S
0.76
C
eu
te
ct
oi
d
B
Fe3C (cementite-hard)
α (ferrite-soft)
Chapter 9 - 28
Hypoeutectoid Steel
Adapted from Figs. 9.24 
and 9.29,Callister 7e. 
(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.)
Fe
3C
 (c
em
en
tit
e)
1600
1400
1200
1000
800
600
4000 1 2 3 4 5 6 6.7
L
γ 
(austenite)
γ+L
γ + Fe3C
α+ Fe3C
L+Fe3C
δ
(Fe) Co, wt% C
1148°C
T(°C)
α
727°C
(Fe-C 
System)
C0
0.
76
Adapted from Fig. 9.30,Callister 7e.
proeutectoid ferritepearlite
100 μm Hypoeutectoidsteel
R S
α
wα =S/(R+S)
wFe3C =(1-wα)
wpearlite = wγ
pearlite
r s
wα =s/(r+s)
wγ =(1- wα)
γ
γ γ
γα
αα
γγ
γ γ
γ γ
γγ
15
Chapter 9 - 29
Hypereutectoid Steel
Fe
3C
 (c
em
en
tit
e)
1600
1400
1200
1000
800
600
4000 1 2 3 4 5 6 6.7
L
γ 
(austenite)
γ+L
γ +Fe3C
α +Fe3C
L+Fe3C
δ
(Fe) Co, wt%C
1148°C
T(°C)
α
Adapted from Figs. 9.24 
and 9.32,Callister 7e. 
(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.)
(Fe-C 
System)
0.
76 Co
Adapted from Fig. 9.33,Callister 7e. 
proeutectoid Fe3C
60 μmHypereutectoid 
steel
pearlite
R S
wα =S/(R+S)
wFe3C =(1-w α)
wpearlite = wγ
pearlite
sr
wFe3C =r/(r+s)
wγ =(1-w Fe3C)
Fe3C
γγ
γ γ
γγ
γ γ
γγ
γ γ
Chapter 9 - 30
Example: Phase Equilibria
For a 99.6 wt% Fe-0.40 wt% C at a temperature 
just below the eutectoid, determine the 
following
a) composition of Fe3C and ferrite (α)
b) the amount of carbide (cementite) in grams 
that forms per 100 g of steel
c) the amount of pearlite and proeutectoid 
ferrite (α)
16Chapter 9 - 31
Chapter 9 – Phase Equilibria
Solution:
g 3.94
g 5.7 CFe
g7.5100 
022.07.6
022.04.0 
100x
CFe
CFe
3
CFe3
3
3
=α
=
=−
−=
−
−=α+ α
α
x
CC
CCo
b) the amount of carbide 
(cementite) in grams that 
forms per 100 g of steel
a) composition of Fe3C and ferrite (α)
CO = 0.40 wt% C
Cα = 0.022 wt% C
CFe C = 6.70 wt% C3
Fe
3C
 (c
em
en
tit
e)
1600
1400
1200
1000
800
600
4000 1 2 3 4 5 6 6.7
L
γ 
(austenite)
γ+L
γ + Fe3C
α + Fe3C
L+Fe3C
δ
Co, wt% C
1148°C
T(°C)
727°C
CO
R S
CFe C3Cα
Chapter 9 - 32
Chapter 9 – Phase Equilibria
c. the amount of pearlite and proeutectoid ferrite (α) 
note: amount of pearlite = amount of γ just above TE
Co = 0.40 wt% C
Cα = 0.022 wt% C
Cpearlite = Cγ = 0.76 wt% C
 
γ
γ + α =
Co −Cα
Cγ −Cα
x 100 = 51.2 g
pearlite = 51.2 g
proeutectoid α = 48.8 g F
e 3
C
 (c
em
en
tit
e)
1600
1400
1200
1000
800
600
4000 1 2 3 4 5 6 6.7
L
γ 
(austenite)
γ+L
γ + Fe3C
α + Fe3C
L+Fe3C
δ
Co, wt% C
1148°C
T(°C)
727°C
CO
R S
CγCα
17
Chapter 9 - 33
Alloying Steel with More Elements
• Teutectoid changes: • Ceutectoid changes: 
Adapted from Fig. 9.34,Callister 7e. (Fig. 9.34 
from Edgar C. Bain, Functions of the Alloying 
Elements in Steel, American Society for Metals, 
1939, p. 127.)
Adapted from Fig. 9.35,Callister 7e. (Fig. 9.35 
from Edgar C. Bain, Functions of the Alloying 
Elements in Steel, American Society for Metals, 
1939, p. 127.)
T E
ut
ec
to
id
(°C
)
wt. % of alloying elements
Ti
Ni
Mo Si W
Cr
Mn
wt. % of alloying elements
C
eu
te
ct
oi
d
(w
t%
C
)
Ni
Ti
Cr
Si
MnWMo
Chapter 9 - 34
• 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 (TS)
--decreases the ductility.
• Binary eutectics and binary eutectoids allow for
a range of microstructures.
Summary
18
Chapter 9 - 35
Core Problems:
Self-help Problems:
ANNOUNCEMENTS
Reading: