1. Single solid phase binary alloy -1
Phase rule predicts that solid lines on one component systems become areas on a binary.
Results in region where solid and liquid are in equilibrium, instead of a line.

2. Single solid phase binary alloy - 2
As cool from the melt and cross the liquidus line, crystals begin to form and then grow as cooling proceeds.
The composition of the crystal follows the solidus line, ideally, and the composition of all crystals adjusts continuously, not just simply the crystal being formed at a particular temperature.

3. Single solid phase binary alloy - 3
In reality the diffusion rate of atoms inside a crystal is very slow.
The composition of the crystals is unable to change at the rate indicated by the diagram.
The composition of each crystal varies from the center outwards - known as coring

4. BINARY ALLOY WITH EUTECTIC
Solubility limits
 and  are the solid solutions
Solubility limits are given by triple points
Eutectic is given by central triple point

5. Line that crosses into solid solution phase
FIRST EXAMPLE
Line that crosses into solid solution phase
Cross liquidus - a crystals begin to form
Cross into single phase region - a crystals fill material
Cross into two phase region - b crystals from inside a crystals
Precipitation hardening

6. SECOND EXAMPLE
Eutectic Alloy
Alloy has the eutectic composition
Converts directly from liquid to two solid phases

7. THIRD EXAMPLE
Complex Phases
Cross liquidus
a crystals begin
Grow as T drops
Cross eutectic line
Remaining liquid converts into a + b forming eutectic grains
Final state consists of a grains and eutectic grains

8. Cu - Ag System
Same general shape as Pb-Sn
Melting points different
Solubility limits different
Eutectic different
General features of behavior are the same

9. COMPOUND FORMATION
Forms Mg2Pb
Treat as two phase diagrams fused together
One is phase diagram of Mg with Mg2Pb
Other is phase diagram of Pb with Mg2Pb
Vertical line means Mg2Pb does not form solid solutions

10. Phase diagram of Fe and Fe3C
IRON CARBON DIAGRAM
Phase diagram of Fe and Fe3C
Would be a simple eutectic if not for fcc - bcc change
Left hand axis shows changes in Fe crystal structure
At high T bcc - fcc transition
At lower T fcc - bcc transition
Generates two additional horizontal lines
Higher one is called peritectic
Lower one is called eutectoid

12. THE EUTECTOID REGION

13. HYPO-EUTECTOID
STEEL
Carbon content less than eutectoid composition
Soft steel used for plates and pressing operations

14. HYPER – EUTECTOID STEEL
Carbon content more than eutectoid composition
Used for machine tools, knives, etc

15. TIME-TEMPERATURE-TRANSFORMATION DIAGRAM
FOR EUTECTOID STEEL

16. MARTENSITE – not on phase diagram
Bct crystal structure
“stretched” bcc
Hardest of the phases
Hardness increases with carbon content

17. HARDNESS OF PEARLITE DEPENDS ON MICROSTRUCTURE

18. HEAT TREATMENTS
Conventional
Martempering
austempering