Gibbs Phase Rule P + F = C + 2 P: # of phases F: Degrees of freedom C: # of components Normally, pressure = 1 atm P + F = C + 1 or F = C - P + 1 Apply to eutectic phase diagram 1 phase field: F = 2 – 1 + 1 = 2 Change T and C independently in phase field 2 phase field: F = 2 – 2 + 1 = 1 C depends on T – not independent 3 phase point: F = 2 – 3 +1 = 0 C and T defined only at one point (Eutectic point) (no degrees of freedom)
25
Embed
Gibbs Phase Rule - Materials - UC Santa Barbara |matclass/101/pdffiles/Lecture_13.pdfIron-Carbon (Fe-C) Phase Diagram Adapted from Fig. 9.21,Callister 6e. (Fig. 9.21 adapted from Binary
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Gibbs Phase RuleP + F = C + 2
P: # of phasesF: Degrees of freedomC: # of components
Normally, pressure = 1 atm
P + F = C + 1
or
F = C - P + 1Apply to eutectic phase diagram
1 phase field: F = 2 – 1 + 1 = 2 Change T and C independently in phase field
2 phase field: F = 2 – 2 + 1 = 1 C depends on T – not independent
3 phase point: F = 2 – 3 +1 = 0 C and T defined only at one point(Eutectic point) (no degrees of freedom)
Ex: Pb-Sn Eutectic System (1)
• For a 40wt%Sn-60wt%Pb alloy at 150 °C, find...--the phases present:
Adapted from Fig. 9.12, Callister 6e.(Fig. 9.12 from Metals Handbook, Vol. 9, 9th ed., Metallography and Microstructures, American Society for Metals, Materials Park, OH, 1985.)
Microstructures in Eutectic Systems (4)
• 18.3wt%Sn < Co < 61.9wt%Sn• Result: α crystals and a eutectic microstructure
L + α200
T(°C)
Co, wt% Sn
20 400
300
100
L
α
60
L: Cowt%Sn
α + β
TEβ
080 100
L + β
Co18.3 61.9
Lα
Lα
primary α
97.8
S
S
RR
eutectic αeutectic β
Pb-Snsystem
• Just above TE:
WL = (1-Wα) =50wt%
Cα = 18.3wt%Sn
CL = 61.9wt%SnS
R + SWα = =50wt%
• Just below TE:Cα = 18.3wt%Sn
Cβ = 97.8wt%SnS
R + SWα = =73wt%
Wβ = 27wt%Adapted from Fig. 9.14, Callister 6e.
Microstructure in Eutectic Systems (4')
Hypoeutectic Microstructure
Microstructure50% Pb – 50% Sn alloyExpain the phases
Hypoeutectic & Hypereutectic
T(°C)
(Pb-Sn System)
L + α200
Co, wt% Sn20 400
300
100
L
α
60
α + β
TE β
080 100
L + β
18.361.9
97.8
Cohypoeutectic
Cohypereutectic
eutectic
hypereutectic: (illustration only)
160µm
eutectic: Co=61.9wt%Sn
175µm
β
ββ
ββ
β
α
α
α
αα
α
hypoeutectic: Co=50wt%Sn
eutectic micro-constituent
Adapted from Fig. 9.7, Callister 6e. (Fig. 9.7 adapted from Binary Phase Diagrams, 2nd ed., Vol. 3, T.B. Massalski (Editor-in-Chief), ASM International, Materials Park, OH, 1990.)
(Figs. 9.12 and 9.15 from Metals Handbook, 9th ed.,Vol. 9, Metallography and Microstructures, American Society for Metals, Materials Park, OH, 1985.)
Adapted from Fig. 9.15, Callister 6e. Adapted from Fig. 9.12,
Callister 6e.
Adapted from Fig. 9.15, Callister 6e. (Illustration only)
Composition changefor at least one phasefor phase transformation
Section of Ni-Ti Phase Diagram
Fe-C Phase Diagram (Steel!)
Iron-Carbon (Fe-C) Phase Diagram
Adapted from Fig. 9.21,Callister 6e. (Fig. 9.21 adapted from Binary Alloy Phase Diagrams, 2nd ed.,Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.)
(Adapted from Fig. 9.24, Callister 6e. (Fig. 9.24 from Metals Handbook, 9th ed., Vol. 9, Metallography and Microstructures, American Society for Metals, Materials Park, OH, 1985.)
Result: Pearlite = alternating layers of α and Fe3C phases.
120µm
• 2 important points
-Eutectic (A):
-Eutectoid (B): L ⇒ γ + Fe3C
γ ⇒ α +Fe3C
Fe
3C
(c
em
en
tite
)
1600
1400
1200
1000
800
600
4000 1 2 3 4 5 6 6.7
L
γ (austenite)
γ+L
γ+Fe3C
α+Fe3C
α+γ
L+Fe3C
δ
(Fe) Co, wt% C0.77 4.30
727°C = Teutectoid
1148°C
T(°C)
A
B
SR
R S
γ γγγ
Fe3C (cementite-hard)α (ferrite-soft)
αC
eu
tec
toid
Hypoeutectoid Steel
Adapted from Figs. 9.21 and 9.26,Callister 6e. (Fig. 9.21 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.)
Adapted from Figs. 9.21 and 9.29,Callister 6e. (Fig. 9.21 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.)
Adapted fromFig. 9.30,Callister6e. (Fig. 9.30copyright 1971 by United States Steel Corporation.)
Pearlite Microstructure
Partitioning of carbon (to Fe3C)
Alloying Steel With More ElementsT
Eu
tec
toid
(°C
)
wt. % of alloying elements
Ti
Ni600
800
1000
1200
0 4 8 12
Mo SiW
Cr
Mn
wt. % of alloying elements
Ce
ute
cto
id (
wt%
C)
Ni
Ti
0 4 8 120
0.2
0.4
0.6
0.8
Cr
SiMnW
Mo
• Teutectoid changes: • Ceutectoid changes:
Adapted from Fig. 9.31,Callister 6e. (Fig. 9.31 from Edgar C. Bain, Functions of the Alloying Elements in Steel, American Society for Metals, 1939, p. 127.)
Adapted from Fig. 9.32,Callister 6e. (Fig. 9.32 from Edgar C. Bain, Functions of the Alloying Elements in Steel, American Society for Metals, 1939, p. 127.)