1. Microstructures in Eutectic Systems: I
• Co < 2 wt% Sn
• Result:
--at extreme ends
--polycrystal of a grains
i.e., only one solid phase. L + a
200
T(°C) Co ,
wt% Sn 10 2 20
300
100 30 b
400
(room T solubility limit) TE
(Pb-Sn
System)
L: Co wt% Sn a L
a: Co wt% Sn

2. Microstructures in Eutectic Systems: II
L: Co wt% Sn
• 2 wt% Sn < Co < 18.3 wt% Sn
• Result:
Initially liquid + 
then  alone
finally two phases
a polycrystal
fine -phase inclusions
Pb-Sn
system L + a
200
T(°C) Co ,
wt% Sn 10
18.3 20
300
100 30 b
400
(sol. limit at TE) TE 2
(sol. limit at T
room ) L a
a: Co wt% Sn a b

3. Microstructures in Eutectic Systems: III
• Co = CE
• Result: Eutectic microstructure (lamellar structure)
--alternating layers (lamellae) of a and b crystals.
Adapted from Fig. 9.14, Callister 7e.
160 m
Micrograph of Pb-Sn
eutectic
microstructure
Pb-Sn
system
L
a
200
T(°C)
C, wt% Sn 20 60 80
100
300 L a b +
183°C 40 TE
L: Co wt% Sn CE
61.9
18.3
: 18.3 wt%Sn
97.8
: 97.8 wt% Sn

4. Microstructures in Eutectic Systems: IV
• wt% Sn < Co < 61.9 wt% Sn
• Result: a crystals and a eutectic microstructure
primary a
eutectic b
Pb-Sn
system L +
200
T(°C)
Co, wt% Sn 20 60 80
100
300 40 TE
L: Co
wt% Sn L a
18.3
61.9 S R
97.8 S R

5. Hypoeutectic & Hypereutectic
300 L
T(°C) L + a a
200 L + b b
(Pb-Sn TE
System) a + b
100
175 mm a
hypoeutectic: Co = 50 wt% Sn
hypereutectic: (illustration only) b
Co, wt% Sn 20 40 60 80
100
eutectic
61.9
eutectic: Co = 61.9 wt% Sn
160 mm
eutectic micro-constituent

6. Intermetallic Compounds
Mg2Pb
Note: intermetallic compound forms a line - not an area - because stoichiometry (i.e. composition) is exact.

7. Cu-Zn Phase diagram

8. Iron-Carbon Phase Diagram Extract
Fe3C (cementite)
1600
1400
1200
1000
800
600
400 1 2 3 4 5 6
6.7 L g
(austenite) +L
+Fe3C a +
L+Fe3C d
(Fe)
Co, wt% C
1148°C
T(°C)
727°C = T
eutectoid A S R
4.30
0.76 C
eutectoid B

9. Pearlite Result: Pearlite = alternating layers of a
and Fe3C phases
120 mm
Fe3C (cementite-hard) a
(ferrite-soft)

10. Hypoeutectoid Steel T(°C) d L +L g (austenite) Fe3C (cementite) a
1600
1400
1200
1000
800
600
400 1 2 3 4 5 6
6.7 L g
(austenite) +L
+ Fe3C a
L+Fe3C d
(Fe)
Co , wt% C
1148°C
T(°C)
727°C
(Fe-C
System) C0
0.76 g

11. Hypoeutectoid Steel 100 mm pearlite Proeutectoid ferrite a w = S /( R+ )
Fe3C
(1-
pearlite g
100 mm
pearlite
Proeutectoid ferrite

12. Hypereutectoid Steel T(°C) d L +L g g (austenite) Fe3C (cementite) a
1600
1400
1200
1000
800
600
400 1 2 3 4 5 6
6.7 L g
(austenite) +L
+Fe3C a
L+Fe3C d
(Fe)
Co , wt%C
1148°C
T(°C)
(Fe-C
System) g Co
0.76

13. Hypereutectoid Steel proeutectoid Fe3C pearlite 60 mm w a = S /( R + )
(1-
pearlite g
60 mm
proeutectoid Fe3C
pearlite

14. Alloying Steel with More Elements
• Teutectoid changes: T
Eutectoid
(°C)
wt. % of alloying elements Ti Ni Mo Si W Cr Mn
• Ceutectoid changes:
wt. % of alloying elements C
eutectoid
(wt%C) Ni Ti Cr Si Mn W Mo

15. Taxonomy of Metals Steels Cast Irons <1.4 wt% C 3-4.5 wt% C
Alloys
Ferrous
Nonferrous
Steels
<1.4 wt% C
Cast Irons
3-4.5 wt% C Cu Al Mg Ti
microstructure:
ferrite, graphite
cementite Fe 3 C
cementite
1600
1400
1200
1000
800
600
400 1 2 4 5 6
6.7 L g
austenite +L
+Fe3C a
ferrite +
L+Fe3C d
(Fe)
Co , wt% C
Eutectic:
Eutectoid:
0.76
4.30
727°C
1148°C
T(°C)

16. Steels