1. Intermetallic Compounds
Antifluorite Structure:
FCC Unit cell with Anions occupying FCC sites
Cations occupying 8 octahedral interstitial sites
Mg2Pb
Intermetallic compounds form lines - not areas - because stoichiometry (i.e. composition) is exact.

2. Intermetallic Compounds
Source: Reed-Hill, Abbaschian, Physical Metallurgy Principles, 3rd Edition, PWS Publishing Company, 1994.

3. Monotectic Monotectic Reaction: L L1 + Solid Cu + L1 26.8%
cool
heat
Monotectic Reaction: L L1 + Solid
Pb and Zn do not mix in solid state:
RT: Cu in Pb < 0.007%
RT: Pb in Cu ~ – 0.005%
Cu + L1
26.8%
Source: Reed-Hill, Abbaschian, Physical Metallurgy Principles, 3rd Edition, PWS Publishing Company, 1994.

4. Eutectoid & Peritectic
Eutectoid Reaction: 1 solid phase  2 solid phases
  + Fe3C (727ºC)
cool
heat
intermetallic compound - cementite
Peritectic Reaction: liquid + solid 1  solid 2
 + L  (1493ºC)
cool
heat

5. Eutectoid and Peritectic
Copper-Zinc Binary Equilibrium Phase Diagram:

6. Eutectoid & Peritectic
Peritectic transition  + L 
Cu-Zn Phase diagram
d + L e
Eutectoid transition   + 

7. Congruent vs Incongruent
Congruent phase transformation: no compositional change associated with transformation
Examples:
Allotropic phase transformations
Melting points of pure metals
Congruent Melting Point
Incongruent phase transformation: at least one phase will experience change in composition
Examples:
Melting in isomorphous alloys
Eutectic reactions
Pertectic Reactions
Eutectoid reactions Ni Ti

8. Iron-Carbon System Diagram is not ever plotted past 12 wt% Cementite
Hägg carbide
Source: Reed-Hill, Abbaschian, Physical Metallurgy Principles, 3rd Edition, PWS Publishing Company, 1994.

9. Iron Carbon Phase Diagram
d ferrite,
BCC
Formation of Ledeburite
FCC A3
ACM
A1 (Eutectoid Temperature)
Formation of Pearlite
a ferrite
BCC
Steel
Cast Irons
Source: Reed-Hill, Abbaschian, Physical Metallurgy Principles, 3rd Edition, PWS Publishing Company, 1994.

10. Cementite – What is it?
Iron Carbide – Ceramic Compound
Purple: Carbon atoms
Orange: Iron atoms
Cementite has an orthorhombic lattice with approximate parameters , and nm.
There are twelve iron atoms and four carbon atoms per unit cell, corresponding to the formula Fe3C.
Source:
H. K. D. H. Bhadeshia

11. Pearlite: What is it? The eutectoid transformation:
g (0.77% C) a (0.02%C) + Fe3C (6.67%C)
Alternate lamellae of ferrite and cementite w/ ferrite as the continuous phase
Diffusional Transformation
“Pearlite” name is related to the regular array of the lamellae in colonies. Etching attacks the ferrite phase more than the cementite. The raised and regularly spaced cementite lamellae act as diffraction gratings and a pearl-like luster is produced by the diffraction of light of various wavelengths from different colonies [1]

12. Pearlite Two phases appear in definite ratio by the lever rule:
Since the densities are same (7.86 and 7.4) lamellae widths are 7:1
Heterogeneous nucleation and growth of pearlite colonies – but typically grows into only 1 grain
Reed-Hill, Abbaschian, 1994, [5]

13. Lamellae Nucleation Reed-Hill, Abbaschian, 1994

14. Interlamellar Spacing
Interlamellar spacing l is almost constant in pearlite formed from g at a fixed T
Temperature has a strong effect on spacing – lower T promotes smaller l
Pearlite formed at 700oC has l ~ 1 mm and Rockwell C - 15
Pearlite formed at 600oC has l ~ 0.1 mm and Rockwell C - 40
Zener and Hillert Eq. for spacing [1]:
sa/Fe3C = Interfacial energy per unit area of a/Fe3C boundary
TE = The equilibrium temperature (Ae1)
DHV = The change in enthalpy per unit volume b/t g and a/Fe3C
DT = The undercooling below Ae1

15. Effect of Undercooling on l
Krauss, Steels, 1995

16. Effect of Interlamellar Spacing
Stone et al, 1975

17. Iron-Carbon (Fe-C) Phase Diagram
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
3 invariant points: C
-Peritectic (C) [0.17%C]:
L + d Þ g A S R
4.30
-Eutectoid (B) [0.77 %C]: g Þ a +
Fe3C g
-Eutectic (A) [4.32 %C]: L Þ g +
Fe3C
0.76 C
eutectoid B R S
Fe3C (cementite-hard) a
(ferrite-soft)

18. 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 C0
0.76 g g r s w a = /( + ) g
(1-
proeutectoid ferrite
pearlite
100 mm R S a w = /( + )
Fe3C
(1- g

19. Proeuctectoid Ferrite – Pearlite
0.38 wt% C: Plain Carbon – Medium Carbon Steel