1. Phase
Any physically distinct, chemically homogeneous and mechanically separable portion of a substance
Can be continuous or discontinuous
Can be solid, liquid or gas
Can be a pure substance or a solution

2. Multiple Solid Phases Multiple solid phases are common in metals
Phases defined by composition (not by state – solid, liquid, gas)
Example – two phases shown to the right, dark phase and then the lighter phase

3. Single Phase vs. Multiple Phases

4. Solubility Unlimited Solubility Limited Solubility
Hume Rothery’s Conditions
Similar Size
Same Crystal Structure
Same Valance
Similar Electronegativity
Implies single phase
Limited Solubility
Implies multiple phases
No Solubility (oil and water region)

5. Solid Solutions
Just like we have liquid solutions (ex mixing alcohol and water => liquid solution), we can have solid solutions.
Solid solution is mixed as a liquid and then allowed to solidify
May mix two metal elements together then allow to solidify => solid solution

6. Two Types of Solid Solutions
Interstitial Solid Solution
Substitutional Solid Solution

7. Equilibrium Phase Diagram Cooling Curve
DT/D t
Superheat
Thermal Arrest
Temperature
Local
Solidification
Time
Total
Solidification
Time
REMEMBER THIS?
Time

8. Cooling Curves and the Phase Diagram
In your groups, work on problem in your book

9. You just made a phase diagram!
Comp.
(wt % V)
temp
( C )
2625 20
2500
2300 40
2350
2150 60
2225
2050 80
2100
1975
100
1910

10. Equilibrium Phase Diagram
Equilibrium: state of a system remains constant over an indefinite period of time
Binary phase diagram: diagram for alloy composed of two elements
Shows relationship in a metal among
temperature
pressure
composition
Gibb’s Phase Rule

11. Types of Phase diagrams
Number of Constituents
Number of phases
Unary (like the water one shown at the beginning) – one constituent
Binary - two constituents , like an alloy (we will focus on these)
Ternary - three constituents; requires 3-D diagram
Isomorphous – one solid phase
Polymorphous – multiple solid phases

12. Utilization of Phase Diagrams
For each point of temperature and composition, three pieces of information can be obtained
Phase present
The amount of each phase present ( how many ice cubes are in the glass)
lever law
Composition of each phase (chem make-up of phases)
tie line

13. Liquidus and Solidus Temperature
Liquidus – The temperature at which the first solid forms during solidification
Solidus – The temperature below which the liquid has completely solidified.
liquidus
solidus
Wt % MgO

14. Tie Line –Composition of Phases
Draw a vertical line at the composition of the “alloy” of interest ex – 40 wt % MgO see purple line
For a given temperature draw an isotherm (horizontal line) ex at 2400 C red line
Where line crosses “phase boundary” (in this case the liquidus line or solidus line), draw a vertical line
Ex – composition of liquid phase is ~32% MgO; Composition of solid phase is ~ 60 % MgO
liquidus
solidus
Wt % MgO

15. Lever Law – Amount of each phase
Using the compositions of the phases determined from the tie line, calculate the amount of each phase as this:
Opposite lever arm/total length of lever * 100%
Therefore:
Amt L = (60-40)/(60-32) * 100 = 71%
Amt S = (40-32)/(60-32)*100 = 29%
Solid
C = 60 %MgO
Liquid
C = 32 %MgO
**Notice the composition
of the phases does not have to add up to 100% but the amount does!!*****
Alloy
C = 40 %MgO

16. What’s the difference between Amount and Composition????
Composition is the chemical make-up of the phase (if we had a glass of coke with ice in it, our liquid phase would have one chemical make-up – won’t begin to think what it might be, the liquid phase would have a chemical make-up of ~ H2O. The composition of the “alloy” would be the total chemical make-up of the ice and coke combined (which would be watery coke?)

17. What’s the difference between Amount and Composition????
Amount is the quantity of the phase (if we had a glass of coke with ice in it, we could take the ice cubes out and weigh them and then weigh the coke to figure out the amount of the solid and liquid phase or use the lever law)

18. Phase Diagram and Microstructure
Can you relate this to nucleation and growth?
Where does nucleation occur?
Where does growth occur?

19. Solidification of Alloy, x

20. Three-Phase Reactions
Involves 3 distinct phases
Occurs at a single “point”
Often times is associated with special properties or characteristics for that material
Eutectic L => S1 + S2
Eutectoid S1 => S2+ S3
Peritectic L + S1 => S2
Peritectoid S1 + S2 => S3
Monotectic L1 => S1 + L2
Miscibility gap; Oil and water region, where two liquid phases coexist

21. Intermetallic
A compound formed of two or more metals that has its own unique composition, structure and properties.
Exists as a single phase region where you would expect a two phase region
Typically hard, brittle and strong
Stoichiometric – single composition
Non Stoichiometric – range of compositions

22. Solvus
Indicates solubility limit

23. ID all of the three phase reactions by name and “reaction”
Group Work
ID all of the three phase reactions by name and “reaction”

24. Hypo- and Hyper-Eutectic

25. Hyper-Eutectic vs. Hypo-Eutectic Microstructural Differences

26. Composition and the Microstructure of Lead Tin

27. Lead-Tin Eutectic Microstructure
Temperature

28. Iron- Carbon Equilibrium Diagram
Phases
d - delta ferrite
g - austenite
a - alpha ferrite (ferrite)
Fe3C - cementite
Reactions
Peritectic (L+ S1 > S2)
Eutectic ( L > S1 + S2)
Eutectoid (S1 > S2 + S3)

29. Steels and the Simplified Iron- Carbon Diagram

30. Ternary Phase Diagram