introduction tdf rev gasal13 14

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Transformasi Diagram Fasa:

INTRODUCTION



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



Transformasi AllotropicThe Solid phases are crystalline, but difference in composition, crystall

structure/dimensions



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.



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



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.



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



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!



Looking at a simple “Phase Diagram” for Sugar –

Water (or milk)



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



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



Solidification(cooling) curves

L

S

L

S

Pure metal Alloy

Tm L S L + S

Solidification

complete

Soldification

begins

TL

TS



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



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)



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



• 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



• 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



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



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



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



Microstructural changes during solidification

L

S

L S

T

t

Tm

L

S

Pure metal

S



Microstructural changes during solidification

L

S

Alloy

L + S

TL

TS

L

S

T

t



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



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



• 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 :

introduction tdf rev gasal13 14

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