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Objectives
1. Define “phase”
2. Fully characterize the state of a
material at a point on a phase
diagram.
3. Identify the invariant points on a
given phase diagram.
4. Utilize the Fe-C diagram todescribe the microstructure of a
given alloy.
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Solubility Limit
Maximum fraction of a substance which willdissolve in another under a given condition.
Example: Sugar in Water
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Phase:
Homogeneous volume with uniformphysical and chemical characteristics
Phase Diagram A map of the solubility limits for thedifferent phases in an alloy as a
function of composition andtemperature.
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Which of the following constitute phases and what is
the basis for defining or not defining them as a phase?
1. Magnesium dissolved in seawater
2. Tramp impurities collected at the grain
boundaries in cast iron
3. Copper poor grains in Brass (Cu-Zn alloy)
4. Amorphous regions in largely crystalline
polyethylene polymer
5. Carbon atoms in iron crystals
6. Water vapor in air
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Phase:
Homogeneous volume with uniformphysical and chemical characteristics
Phase Diagram A map of the solubility limits for thedifferent phases in an alloy as a
function of composition andtemperature.
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Terms:Greek = solid phases
Liquid phases = L
Two phase regions notalways labeled
Combination of neighboring
(horizontal) single phase
regions
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- alpha
-beta
-gamma
-delta-zeta
-eta
-theta
-epsilon
Greek Alphabet
(lower case)-iota
-kappa
-lambda
-mu-nu
-omicron
-pi
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Equilibrium
The transformation temperatures change with
different heating/cooling rates
To avoid an infinity of phase diagrams, all
diagrams are Equilibrium diagrams.
Equilibrium implies extremely slow processes.
Thus these diagrams are the behavior as thecooling/heating rate approaches zero.
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Isomorphous
One phase due tocomplete solid
solution solubility
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What happens if you have poor Solid
Solution Solubility?
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Composition of Component Phases
The Tie Line
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Proportion of Phases Present: The
Reverse Lever Law
43-35 8
43-32 11PL = =
Pa = =35-32 3
43-32 11
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The Composition of the Al3Ni2 is most
nearly:
A. 43 % Ni B. 50% Ni C. 57 % Ni
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The Proportion of Al3Ni2 is most nearly:
A. 5/7 B. 8/14 C. 6/14
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RXN NAME
Peritectic
Eutectoid
Peritectoid
Eutectic
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Pearlite:
Ferrite (white)
Cementite (dark)
Eutectoid Equilibrium Structure
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What’s Up with Al3Ni?
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Intermediate Compound
A compound which forms at a single ratio of
constituents.
Phase region for IC is a vertical line
IC will be bordered by two phase regions
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A State is Characterized by 4 Things:
1. Composition and Temperature
2. Number and Names of phases
3. Composition of phases
4. Proportion of phases