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
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
Single Phase vs. Multiple Phases
Solubility
• Unlimited 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)
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
Two Types of Solid Solutions
Interstitial Solid Solution
Substitutional Solid Solution
Equilibrium Phase Diagram
Cooling Curve
Temperature
DT/D t
Superheat
Thermal Arrest
Local
Solidification
Time
Total
Solidification
Time
Time
Cooling Curves and the Phase Diagram
In your groups, work on problem
10-57 in your book
You just made a phase diagram!
temp
(C)
2625
2500
2300
2350
2150
2225
2050
2100
1975
1910
2700
2500
Temperature [C]
Comp.
(wt % V)
0
20
20
40
40
60
60
80
80
100
2300
2100
1900
1700
1500
0
20
40
60
Compostion (wt % V)
80
100
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
Types of Phase diagrams
Number of Constituents
• 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
Number of phases
• Isomorphous – one solid
phase
• Polymorphous – multiple
solid phases
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
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.
Wt % MgO
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
Wt % MgO
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%
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
Solid
C = 60 %MgO
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?)
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)
http://michellegeller.typepad.com/michelle_geller_w
eblog/images/2007/03/28/gluttony.jpg
Phase Diagram and Microstructure
• Can you relate this
to nucleation and
growth?
• Where does
nucleation occur?
• Where does growth
occur?
Solidification of Alloy, x
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
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
Solvus
• Indicates
solubility
limit
Group Work
ID all of the three phase reactions by name and “reaction”
Hypo- and Hyper-Eutectic
Hyper-Eutectic vs. Hypo-Eutectic
Microstructural Differences
Composition and the
Microstructure of Lead Tin
Lead-Tin Eutectic Microstructure
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)
Steels and the Simplified Iron- Carbon Diagram
Ternary Phase Diagram