fully miscible solution
DESCRIPTION
Fully Miscible Solution. Simple solution system (e.g., Ni-Cu solution). Both have the same crystal structure (FCC) and have similar electronegativities and atomic radii ( W. Hume – Rothery rules ) suggesting high mutual solubility. - PowerPoint PPT PresentationTRANSCRIPT
Fully Miscible Solution
CrystalStructure
electroneg r (nm)
Ni FCC 1.9 0.1246
Cu FCC 1.8 0.1278
• Both have the same crystal structure (FCC) and have similar electronegativities and atomic radii (W. Hume – Rothery rules) suggesting high mutual solubility.
Simple solution system (e.g., Ni-Cu solution)
• Ni and Cu are totally miscible at all mixture compositions – isomorphous
Copper-Nickel Binary Equilibrium Phase Diagram
• Solid solutions are typically designated by lower case Greek letters: etc.
• Liquidus line separates liquid from two phase field
• Solidus line separates two phase field from a solid solution
• Pure metals have melting points
• Alloys have melting ranges
What do we have? What’s the composition?
• Draw Tie line – connects the phases in equilibrium with each other - essentially an isotherm
The Lever Rule
L
L
LL
LL CC
CC
SR
RW
CC
CC
SR
S
MM
MW
00
wt% Ni
20
1200
1300
T(°C)
L (liquid)
(solid)L +
liquidus
solidus
30 40 50
L + B
TB
tie line
CoCL C
SR
Adapted from Fig. 9.3(b), Callister 7e.
Derived from Conservation of Mass:
(1) W + WL = 1
(2) WC + WLCL = Co
Let W = mass fraction (amount of phase)
Co = 35 wt% Ni
Example Calculation
wt% Ni
20
1200
1300
T(°C)
L (liquid)
(solid)L +
liquidus
solidus
3 0 4 0 5 0
L +
Cu-Ni system
35Co
32CL
BTB
tie line
4C3
R S
At TB: Both and L
% 733243
3543wt
= 27 wt%
WL S
R +S
W R
R +S
• Phase diagram: Cu-Ni system.
• System is: --binary i.e., 2 components: Cu and Ni. --isomorphous i.e., complete solubility of one component in another; phase field extends from 0 to 100 wt% Ni.
• Consider Co = 35 wt%Ni.
Equilibrium Cooling in a Cu-Ni Binary
• C changes as we solidify.• Cu-Ni case:
• Fast rate of cooling: Cored structure
• Slow rate of cooling: Equilibrium structure
First to solidify has C = 46 wt% Ni.
Last to solidify has C = 35 wt% Ni.
Cored vs Equilibrium Phases
First to solidify: 46 wt% Ni
Uniform C:
35 wt% Ni
Last to solidify: < 35 wt% Ni
Mechanical Properties: Cu-Ni System
• Effect of solid solution strengthening on:
--Tensile strength (TS) --Ductility (%EL,%AR)
--Peak as a function of Co --Min. as a function of Co
Te
nsile
Str
en
gth
(M
Pa
)
Composition, wt% NiCu Ni0 20 40 60 80 100
200
300
400
TS for pure Ni
TS for pure Cu
Elo
ng
atio
n (
%E
L)
Composition, wt% NiCu Ni0 20 40 60 80 10020
30
40
50
60
%EL for pure Ni
%EL for pure Cu
Consider Pb-Sn System
CrystalStructure
electroneg r (nm)
Pb FCC 1.8 0.175
Sn Tetragonal 1.8 0.151
W. Hume – Rothery Rules:• Atomic size is within 15%• Same electronegativity• Do not have same crystal structure
Simple solution system (e.g., Pb-Sn solution)
13.7%
Will have some miscibility, but will not have complete miscibility
From Greek eut ktos, easily melted
Binary-Eutectic System
Eutectic Reaction:
L(CE) (CE) + (CE)
Eutectic Point
Solidus
Liquidus
Solvus
Consider (1): Co < 2 wt% Sn Result: --at extreme ends --polycrystal of grains i.e., only one solid phase.
Microstructural Evolution in Eutectic
0
L + 200
T(°C)
Co , wt% Sn10
2
20Co
300
100
L
30
+
400
(room T solubility limit)
TE
(Pb-SnSystem)
L
L: Co wt% Sn
: Co wt% Sn
Consider (2):2 wt% Sn < Co < 18.3 wt% Sn
Result: Initially liquid + then alonefinally two phases
polycrystal fine -phase inclusions
Microstructural Evolution in Eutectic
Pb-Snsystem
L +
200
T(°C)
Co , wt% Sn10
18.3
200Co
300
100
L
30
+
400
(sol. limit at TE)
TE
2(sol. limit at Troom)
L
L: Co wt% Sn
: Co wt% Sn
Consider (3): Co = CE • Result: Eutectic microstructure (lamellar structure) --alternating layers (lamellae) of and crystals.
Microstructural Evolution in Eutectic
160 m
Micrograph of Pb-Sn eutectic microstructure
Pb-Snsystem
L
200
T(°C)
C, wt% Sn
20 60 80 1000
300
100
L
L+ 183°C
40
TE
18.3
: 18.3 wt%Sn
97.8
: 97.8 wt% Sn
CE61.9
L: Co wt% Sn
Lamellar Eutectic Structure
Consider (4): 18.3 wt% Sn < Co < 61.9 wt% Sn
Microstructural Evolution in Eutectic
18.3 61.9
SR
97.8
SR
primary eutectic
eutectic
Pb-Snsystem
L+200
T(°C)
Co, wt% Sn
20 60 80 1000
300
100
L
L+
40
+
TE
L: Co wt% Sn LL
Result: crystals and a eutectic microstructure
Hypoeutectic vs Hypereutectic
175 m
hypoeutectic: Co = 50 wt% Sn
L+L+
+
200
Co, wt% Sn20 60 80 1000
300
100
L
TE
40
(Pb-Sn System)
160 m
eutectic micro-constituent
hypereutectic: (illustration only)
T(°C)
61.9eutectic
eutectic: Co = 61.9 wt% Sn