Muddiest Points Phase Diagrams II: Eutec6c Microstructures
Muddiest Points: • “How do I determine what microstructure looks like?”
• “How does size of area in the microstructure diagram relate to its phase frac6on?”
• “When is the microstructure alterna6ng platelets of alpha and beta vs. blobs of alpha or beta?
• “Why is maximum strength at the eutec6c composi6on?
Pb-Sn Phase Diagram: Effect of Composition on Strength
0
100
200
300
20%Sn 80%Sn60%Sn40%Sn0%Sn 100%Sn
Composition, wt%
T, Co
327
18319.2 61.9 97.5
232
o
o
o
0%Pb100%PbStrength (M
pa) 40
30
20
10
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Single-‐Phase Region Microstructures
L L
α β β
1. T= 325°, Co = 10% Sn
2. T= 182°, Co = 10% Sn
3. T= 325°, Co = 99% Sn
4. T=182°, Co = 99% Sn
Phases: Chem. Comp: Phase wt. Fract.:
Phases: Chem. Comp: Phase wt. Fract.:
Phases: Chem. Comp: Phase wt. Fract.:
Phases: Chem. Comp: Phase wt. Fract.:
α
Co Co
X
X
X
X
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Eutec6c Microstructure 61.9 wt. % Sn
L
EutecAc α+ β
αβαβα
L
1. T= 184 °C, Co=61.9% Sn
Phases: Chem. Comp: Phase wt. Fract.:
2. T= 182°C, Co= 61.9% Sn Phases: Chem. Comp: Phase wt. Fract.:
R S
S R+S
Wα= Wβ= 1- Wα
X X
α β
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Hypoeutec6c Microstructure: 40 wt. % Sn
L
1. T= 300 °C, Co= 40 % Sn
2. T= 225°C, Co= 40 % Sn
3. T= 184°C, Co= 40 %
4. T= 182°C, Co= 40 %
Phases: Chem. Comp: Phase wt. Fract.:
α
α
α
α
α
Phases: Chem. Comp: Phase wt. Fract.:
Phases: Chem. Comp: Phase wt. Fract.:
Phases: Chem. Comp:
Phase wt. Fract.:
α
T U
U T+U
Wα= WL= 1- Wα
C D
WL= 1- Wα
F E
α
α
α F E+F
Wα= Wβ= 1 - Wα
Co
L
L
D C+D
Wα=
X
X X X
17 46
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Hypereutec6c Microstructure: 85 wt. % Sn 1. T= 300 °C, Co= 85 % Sn Phases: Chem. Comp: Phase wt. Fract.:
L
2. T= 210°C, Co= 85 % Sn Phases: Chem. Comp: Phase wt. Fract.:
3. T= 184°C, Co= 85 % Sn
4. T= 182°C, Co= 85 % Sn
Phases: Chem. Comp: Phase wt. Fract.:
Phases: Chem. Comp: Phase wt. Fract.:
β β
β
β
β
β β
β
Co
β β β
L
L
G H
G G+H
Wβ=
J K
J J+K
Wβ=
WL= 1- Wβ X X+Y Wβ=
X Y
β + L
X
X
XX
WL= 1- Wβ
Wα= 1 - Wβ
80 98
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Summary of Eutec6c Microstructures
α
α
α β
β β
T= 182°C, Co = 40% Sn T= 182°C, Ceu = 61.9 % Sn T= 182°C, Co = 85% Sn
α
T= 182°C, Co = 10% Sn
X β β
T= 182°C, Co = 99% Sn
X X X X
Pb-Sn Phase Diagram: Effect of Composition on Strength
0
100
200
300
20%Sn 80%Sn60%Sn40%Sn0%Sn 100%Sn
Composition, wt%
T, Co
327
18319.2 61.9 97.5
232
o
o
o
0%Pb100%Pb
Strength (M
pa) 40
30
20
10
α
α
α β
β β
Co = 40% Sn Ceu = 61.9 % Sn Co = 85% Sn
Homework 12. Problem 5. Focused reading: Ch. 9, sec 9.12, pp. 305 – 309Quiz the Wiz- Eutectic Microstructures
Muddiest Points Phase Diagrams II: Eutec6c Microstructures
Muddiest Points: • “How do I determine what microstructure looks like?”
• “How does size of area in the microstructure diagram relate to its phase frac6on?”
• “When is the microstructure alterna6ng platelets of alpha and beta vs. blobs of alpha or beta?
• “Why is maximum strength at the eutec6c composi6on?
