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Transformasi Diagram Fasa:
INTRODUCTION
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Transfromasi Fasa
Solid
Liquid
solid
solid
LiquidPeleburan
Pembekuan
solid
GasLiquid
Melting
Boiling
Sublimation
•Change from one phase to another
•Occurs because energy change is negative/goes from high to low energy state
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Transformasi AllotropicThe Solid phases are crystalline, but difference in composition, crystall
structure/dimensions
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Beberapa definisi
System: A body of engineering material under investigation. e.g. Ag – Cu
system, NiO-MgO system (or even sugar-milk system)
Component of a system: Pure metals and or compounds of which an
alloy is composed, e.g. Cu and Ag or Fe and Fe3C. They are thesolute(s) and solvent
Solubility Limit: The maximum concentration of solute atoms that may
dissolve in the Solvent to form a “solid solution” at some temperature.
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DefinisiPhases: A homogenous portion of a system that has uniform physical and
chemical characteristics, e.g. pure material, solid solution, liquid solution,
and gaseous solution, ice and water, syrup and sugar. Single phase system = Homogeneous system
Multi phase system = Heterogeneous system or mixtures
Microstructure: A system’s microstructure is characterized by the number
of phases present, their proportions, and the manner in which they are
distributed or arranged. Factors affecting microstructure are: alloying
elements present, their concentrations, and the heat treatment of the alloy.
Phase boundary :
- Boundary between phases in a phase diagram
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Definisi
Phase Equilibrium: A stable configuration with lowest free-energy (internal energy of
a system, and also randomness or disorder of the atoms or molecules (entropy).
Any change in Temperature, Composition, and Pressure causes an increase in free
energy and away from Equilibrium thus forcing a move to another ‘state’
Equilibrium Phase Diagram: It is a “map” of the information about the control of
microstructure or phase structure of a particular material system. The relationships
between temperature and the compositions and the quantities of phases present at
equilibrium are represented.
Definition that focus on “Binary Systems”
Binary Isomorphous Systems: An alloy system that contains two components that attain
complete liquid and solid solubility of the components, e.g. Cu and Ni alloy. It is thesimplest binary system.
Binary Eutectic Systems: An alloy system that contains two components that has a
special composition with a minimum melting temperature.
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With these definitions in mind:
ISSUES TO ADDRESS...
• When we combine two elements... what “equilibrium state” would we expect to get?
• In particular, if we specify...
--a composition (e.g., wt% Cu - wt% Ni), and
--a temperature (T
) and/or a Pressure (P)then...
How many phases do we get?
What is the composition of each phase?
How much of each phase do we get?
Phase BPhase A
Nickel atom Copper atom
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Gibb’s Phase Rule: a tool to define the number of phases and/or
degrees of phase changes that can be found in a system at equilibrium
where:
F is # degrees of freedom of the system (independent parameters)
C is # components (elements) in system
P is # phases at equil. N is # "noncompostional" parameters in system (temp &/or Press
F C P N
ure)
• For any system under study the rule determines if the system is at equilibrium
• For a given system, we can use it to predict how many phases can be expected
• Using this rule, for a given phase field, we can predict how many independent parameters(degrees of freedom) we can specify
• Typically, N = 1 in most condensed systems – pressure is fixed!
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Looking at a simple “Phase Diagram” for Sugar –
Water (or milk)
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Effect of Temperature (T) & Composition (C o)
• Changing T can change # of phases:
D (100 C,90)
2 phases
B (100 C,70)
1 phase
See path A to B.
• Changing C o can change # of phases: See path B to D.
Adapted from Fig.
9.1,
Callister 7e.
A (20 C,70)
2 phases
70 80 1006040200
T e m p e r a t u r e ( ° C )
C o =Composition (wt% sugar)
L(liquid solution
i.e, syrup)
20
100
40
60
80
0
L (liquid)
+
S (solid
sugar)
water-
sugar
system
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A simple phase diagram
Temperature
Triple point
(Invariant point)
Solid
Liquid
Vapor
Pressure
Phase boundary
System: H2O
At triple point, P=3, C=1, F=0
i.e. this is an invariant pointAt phase boundary, P=2, C=1, F=1
In each phase, P=1, C=1, F=2
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Solidification(cooling) curves
L
S
L
S
Pure metal Alloy
Tm L S L + S
Solidification
complete
Soldification
begins
TL
TS
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Phase Diagram: A Map based on a System’s Free Energy indicating “equilibuim”
system structures – as predicted by Gibbs Rule
• Indicate ‘stable’ phases as function of T , P & C omposition,
• We will focus on: -binary systems: just 2 components.
-independent variables: T and C o (P = 1 atm is almost always used).
Phase Diagram --
for Cu-Ni system
• 2 phases are possible: L (liquid)
(FCC solid solution) • 3 ‘phase fields’ are observed:
L L +
wt% Ni 20 40 60 80 100 0 1000
1100 1200 1300 1400 1500 1600 T (°C)
L (liquid)
(FCC solid
solution) An “Isomorphic”
Phase System
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wt% Ni 20 40 60 80 100 0 1000 1100 1200
1300 1400 1500 1600 T (°C)
L (liquid)
(FCC solid
solution)
Cu-Niphase
diagram
Phase Diagrams:
• Rule 1: If we know T and C o then we know the # and types of all phases
present.
• Examples:
A(1100 C, 60):
1 phase:B (1250 C, 35):
2 phases: L +
B (
1 2 5 0
C ,
3 5
)
A(1100 C,60)
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wt% Ni 20
1200
1300
T (°C) L (liquid)
(solid) 30 40 50
Cu-Ni
system
Phase Diagrams:
• Examples: T A A
35 C o 32 C L
At T A = 1320 C:
Only Liquid (L)C L = C o ( = 35 wt% Ni)
At T B = 1250 C:
Both and L
C L = C liquidus ( = 32 wt% Ni)
C = C solidus ( = 43 wt% Ni)
At T D = 1190 C:
Only Solid ( )
C = C o ( = 35 wt% Ni )
C o = 35 wt% Ni
adapted from Phase Diagrams
of Binary Nickel Alloys, P. Nash (Ed.), ASM
International, Materials Park, OH, 1991.
B T B D
T D
tie line
4 C 3
• Rule 2: If we know T and C o we know the composition of each phase
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• Tie line – a line connecting the phases in equilibrium with each other
– at a fixed temperature (a so-called Isotherm)
The Lever Rule
How much of each phase?
We can Think of it as a lever! So to balance:
ML M
R S
R M S M L
L
L
LL
L
LC C
C C
S R
R W
C C
C C
S R
S
M M
M W
00
wt% Ni 20
1200
1300 T (°C)
L (liquid)
(solid) 3 0 4 0 5 0
B T B
tie line
C o C
L C
S R
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• Rule 3: If we know T and C o then we know the amount of each phase
(given in wt%)
• Examples:
At T A : Only Liquid (L)
W L = 100 wt%, W = 0 At T D : Only Solid ( )
W L = 0, W = 100 wt%
C o = 35 wt% Ni
Therefore we define….
wt% Ni 20
1200
1300
T (°C) L (liquid)
(solid) 3 0 4 0 5 0
Cu-Ni
system
T A A
35 C o 32
C L
B T B
D T D
tie line
4 C 3
R S At T B : Both and L
%733243
3543 wt
= 27 wt%
W L S
R + S
W R
R + S
Notice: as in a lever “the opposite leg” controls with a balance
(fulcrum) at the ‘base composition’ and R+S = tie line length =
difference in composition limiting phase boundary, at the temp of
interest
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Pembuatan diagram Fasa: Biner/ dua
komponen
• Conduct an experiment
• Take 10 metal samples(pure Cu, Cu-10%Ni,
Cu-20%Ni, Cu-30%Ni………, pure Ni)
• Melt each sample and then let it solidify
• Record the cooling curves
•
Note temperatures at which phasetransformations occur
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Hasil grafik pembekuan masin-masin komposisi
L
S
L S
t
T
L
L + S
TL
TS S
L
L + S
TL
TS
Pure Cu
Cu-10%Ni
Cu-20%Ni
LL S
Pure Ni
S
TNi
TCu
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Binary isomorphous phase diagram
x x
x
x
x
x
xx
x
xx
x
x x x x
x x x x
L+S
L
S
Composition
Temp
TCu
TNi
10 60 70 80 9030 40 50200 100
Cu Ni%Ni
Cu
Ni
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Microstructural changes during solidification
L
S
L S
T
t
Tm
L
S
Pure metal
S
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Microstructural changes during solidification
L
S
Alloy
L + S
TL
TS
L
S
T
t
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L
Binary isomorphous phase diagram
L+S
L
S
Composition
T
10 60 70 80 9030 40 50200 100
A B%B
L
L
S
T1
T2
T3
T4
CL C0 CS
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Catatan :
• Diagram fasa tersebut adalah diagram fasa dalam
kesetimbangan (slow cooling)
• The phase boundary which separates the L fromthe L+S region is called LIQUIDUS
• The phase boundary which separates the S fromthe L+S region is called SOLIDUS
• The horizontal (isothermal) line drawn at aspecific temperature is called the TIE LINE
•
The tie line can be meaningfully drawn only in atwo-phase region
• The average composition of the alloy is CO
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• The intersection of the tie line with the liquidus givesthe composition of the liquid, CL
• The intersection of the tie line with the solidus gives
the composition of the solid, CS
• By simple mass balance,
CO = f S CS + f L CL
and f S + f L = 1
CO = f S CS + (1- f S) CL
S f 0C LC
S C LC S f OC LC
S C LC L f S C OC
S C LC Lever
Rule
Catatan :
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