Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 1

Pb-Sn Eutectic System

L + a L + b

a + b

200

T(ºC)

18.3

C, wt% Sn

20 60 80 100 0

300

100

L (liquid)

a 183ºC

61.9 97.8

b

40

Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 2

• For alloys for which

C0 < 2 wt% Sn

• Result: at room temperature -- polycrystalline with grains of

a phase having

composition C0

Microstructural Developments

in Eutectic Systems I

0

L + a

200

T(ºC)

C , wt% Sn 10

2

20 C0

300

100

L

a

30

a + b

400

(room T solubility limit)

TE

(Pb-Sn System)

a L

L: C0 wt% Sn

a: C0 wt% Sn

Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 3

• For alloys for which

2 wt% Sn < C0 < 18.3 wt% Sn

• Result:

at temperatures in a + b range

-- polycrystalline with a grains

and small b-phase particles

Microstructural Developments

in Eutectic Systems II

Pb-Sn

system

L + a

200

T(ºC)

C , wt% Sn 10

18.3

20 0 C0

300

100

L

a

30

a + b

400

(sol. limit at TE)

TE

2 (sol. limit at T room )

L

a

L: C0 wt% Sn

a b

a: C0 wt% Sn

Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 4

• For alloy of composition C0 = CE

• Result: Eutectic microstructure (lamellar structure)

-- alternating layers (lamellae) of a and b phases.

Microstructural Developments

in Eutectic Systems III

160 m

Micrograph of Pb-Sn eutectic microstructure

Pb-Sn

system

L b

a b

200

T(ºC)

C, wt% Sn

20 60 80 100 0

300

100

L

a b

L + a

183ºC

40

TE

18.3

a: 18.3 wt%Sn

97.8

b: 97.8 wt% Sn

CE 61.9

L: C0 wt% Sn

Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 5

Lamellar Eutectic Structure

Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 6

• For alloys for which 18.3 wt% Sn < C0 < 61.9 wt% Sn

• Result: a phase particles and a eutectic microconstituent

Microstructural Developments

in Eutectic Systems IV

18.3 61.9

S R

97.8

S R

primary a

eutectic a

eutectic b

WL = (1- W a ) = 0.50

Ca = 18.3 wt% Sn

CL = 61.9 wt% Sn S

R + S Wa = = 0.50

• Just above TE :

• Just below TE :

C a = 18.3 wt% Sn

C b = 97.8 wt% Sn S

R + S W a = = 0.73

W b = 0.27

Pb-Sn

system L +

b 200

T(ºC)

C, wt% Sn

20 60 80 100 0

300

100

L

a b

L + a

40

a + b

TE

L: C0 wt% Sn L a L

a

Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 7

L + a L + b

a + b

200

C, wt% Sn 20 60 80 100 0

300

100

L

a b

TE

40

(Pb-Sn System)

Hypoeutectic & Hypereutectic

160 m

eutectic micro-constituent

hypereutectic: (illustration only)

b

b b

b b

b

175 m

a

a

a

a a

a

hypoeutectic: C0 = 50 wt% Sn

T(ºC)

61.9

eutectic

eutectic: C0 = 61.9 wt% Sn

Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 8

Intermetallic Compounds

Mg2Pb

Note: intermetallic compound exists as a line on the diagram - not an

area - because of stoichiometry (i.e. composition of a compound

is a fixed value).

Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 9

• Eutectoid – one solid phase transforms to two other

solid phases

S2 S1+S3

a + Fe3C (For Fe-C, 727ºC, 0.76 wt% C)

intermetallic compound - cementite

cool

heat

Eutectic, Eutectoid, & Peritectic

• Eutectic - liquid transforms to two solid phases

L a + b (For Pb-Sn, 183ºC, 61.9 wt% Sn)

cool

heat

cool

heat

• Peritectic - liquid and one solid phase transform to a

second solid phase

S1 + L S2

+ L (For Fe-C, 1493ºC, 0.16 wt% C)

Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 10

Eutectoid & Peritectic

Cu-Zn Phase diagram

Eutectoid transformation +

Peritectic transformation + L

Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 11

Congruent & Incongruent

Transformation

• Congruent transformation – no compositional alteration during transformation

ex) allotropic transformation, melting of pure materials, melting of intermetallic compounds

• Incongruent transformation – compositional alteration

during transformation

ex) eutectic, eutectoid, and peritectic reactions

Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 12

Congruent Incongruent

Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 13

• Phase diagrams are useful tools to determine:

-- the number and types of phases present,

-- the composition of each phase,

-- and the weight fraction of each phase

given the temperature and composition of the system.

• The microstructure of an alloy depends on

-- its composition, and

-- whether or not cooling rate allows for maintenance of

equilibrium.

• Important phase diagram phase transformations include

eutectic, eutectoid, and peritectic.

Summary

Prof. Yo-Sep Min Fusion Technology of Chemical & Materials Engineering Lecture 14, Chapter 9 - 14

Problem set (due to May 11): 9.11; 9.15; 9.20

ANNOUNCEMENTS

Reading: pp. 344~356