Chapter 10 – Phase Diagrams
Definitions and Basic Concepts
Equilibrium phase diagrams
•
binary isomorphous diagrams
•
reading phases present, compositions and amounts
•
binary eutectic diagrams
•
diagrams with intermediate phases or compounds
•
eutectoid and peritectic reactions
•
ceramic phase diagrams
•
iron - iron carbide diagram
•
developing iron - iron carbide microstructures
Chapter 10 (continued)
Closed-Book Questions
54 Describe the changes in the equilibrium structure (atomic
and microscopic scale) of a liquid mixture of nickel and
copper as it's cooled and solidified. Other binary
isomorphous systems could be substituted. The phase
diagram will be provided.
55 Describe the possibilities for the solid atomic structure
present when two dissimilar metals are mixed. Consider
binary eutectic diagrams only.
56 Describe what happens (in terms of atomic and microscopic
scale structure) to a liquid mixture of 20 wt% Ag in Cu as it
is cooled to below 779 C. The phase diagram will be
provided. Other materials and compositions could be
substituted.
1
Chapter 10 (continued)
Closed-Book Questions
57 Describe what happens in an invariant reaction other than
the eutectic reaction.
58 What do horizontal and vertical straight lines indicate on a
two-component phase diagram?
59 Describe the origin and equilibrium microstructure of
hypereutectoid and hypoeutectoid steel.
Chapter 10 (continued)
Open-Book Questions
17 Be able to read a pure component phase diagram
18 Be able to use a binary isomorphous phase diagram
19 Be able to determine the phases present, the
compositions and amounts of each phase present at a
given temperature and overall composition (application
of the lever rule)
20 Be able to calculate the amount of proeutectic and
eutectic material for a given phase
2
Chapter 10 (continued)
Open-Book Questions
21 Be able to write a eutectoid, peritectic and monotectic
reaction
22 Be able to identify the phases present on the Fe-C phase
diagram and their structure
23 Be able to apply the lever rule on the Fe-C phase diagram
24 Be able to calculate the amount of proeutectoid versus
eutectoid material for both hypoeutectoid and
hypereutectoid steels
25 Be able to identify the invariant reactions on the Fe-C
phase diagrams
Chapter 10 (continued)
Definitions and Basic Concepts
Definitions:
______ - The element or compound present in the ________
________. Defines the _______________.
_______ - The element or compound present in the _______
__________
component - Element and/or compound of which an _______
__________.
3
Chapter 10 (continued)
Definitions and Basic Concepts
Definitions:
(cont.)
(cont.)
___________ - The ___________________ of solute atoms
that may _________________. Addition in
excess of the solubility limit results in the
formation of another _________________
that has a _________________________.
_____ - A ___________ portion of a system that has uniform
________________________________.
Chapter 10 (continued)
Definitions and Basic Concepts
(cont.)
•
_______________ are a phase
•
All ___________ (solid, liquid, gas) are a phase
•
Each phase has its own properties and a boundary
•
Only a single difference is needed. The change can be
either ___________________
example - water and ice are separate phases
4
Chapter 10 (continued)
Definitions and Basic Concepts
(cont.)
•
A single-phase system is termed homogeneous.
•
A system with 2 or more phases is termed a ________, and
is also termed a heterogeneous system.
•
Most materials are multiphase. The phases interact such
that the overall properties are better than either individual
phase.
Chapter 10 (continued)
Definitions and Basic Concepts
(cont.)
Figure 10.5 - Strength increase and ductility decrease as a
function of composition
5
Chapter 10 (continued)
Definitions and Basic Concepts
(cont.)
Microstructure - What can be seen by microscopic examination
•
Characterized by:
_______________________
_______________________
_______________________
Chapter 10 (continued)
Definitions and Basic Concepts
Microstructure
•
(cont.)
(cont.)
These factors are affected by:
__________________
__________________
__________________
(see Ch. 11)
6
Chapter 10 (continued)
Definitions and Basic Concepts
(cont.)
Phase equilibria
____________ - A system where _____________________
for a given composition, temperature, and
pressure.
•
It is the condition that the system is trying to achieve.
Chapter 10 (continued)
Definitions and Basic Concepts
Phase equilibria
(cont.)
(cont.)
•
The practical meaning is that at equilibrium there will be
no _______________________________________.
•
metastable phases - Not a ____________________, but
may it persist indefinitely with
imperceptible changes with time.
•
(remember thermodynamics. vs. kinetics)
7
Chapter 10 (continued)
Equilibrium Phase Diagram
•
A concise representation of the ________________ and
________________ in an equilibrium mixture.
•
Pure component diagrams:
•
example:
pressure vs. temperature
water
Figure 10.38
Chapter 10 (continued)
binary phase diagrams:
temperature vs. composition
(at constant pressure)
8
Chapter 10 (continued)
Binary Isomorphous Diagrams
•
The simplest binary systems are the binary ___________
systems.
•
Isomophous means there is a ______________ in the solid
phase as composition changes, or in other words there is
only a _____________________ ever present.
Chapter 10 (continued)
Binary Isomorphous
Diagrams (cont.)
example:
Cu - Ni
Pure components melt
at a _____________
Alloys melt over a______
________________. This
creates a _____________.
Figure 10.2
9
Chapter 10 (continued)
Binary Isomorphous Diagrams
(cont.)
As a liquid is cooled the solid
begins to form at point (b).
The material continues to cool
as solid is formed, until it is all
solid at point (d).
The liquid and solid in the
______________ do not have
the same ______________.
Figure 10.3
Chapter 10 (continued)
Information from phase diagrams
Given temperature and composition we can determine
•
the _______________
• the ___________ of those phases
• the ______________ phase
10
Chapter 10 (continued)
Information from phase diagrams
(cont.)
Phases present
read directly from the
diagram.
For two-phase mixtures the
phases are located at the
end of the _______________,
at the specified temperature.
Chapter 10 (continued)
Information from phase diagrams
(cont.)
Composition of phases
•
In single-phase regions the composition is read directly
from the x-axis. The _________ composition and ______
composition are one and the same.
•
In a two-phase region, the compositions are read from the
_________________________.
•
Both phases are at their _______________.
11
Chapter 10 (continued)
Information from phase diagrams
(cont.)
Quantity of phases present
•
Found by the __________
(sometimes called the inverse lever rule)
•
In the two-phase region locate the overall composition and
the compositions of the two-phases present.
Chapter 10 (continued)
Information from phase diagrams
Quantity of phases present
•
(cont.)
(cont.)
nomenclature used here - Components 1 and 2
Phases α and L
Cα = wt fraction Component 1 in α phase
CL = wt fraction Component 1 in the liquid phase
C0 = wt fraction Component 1 overall
Wα = fraction of the total alloy in the α phase
WL = fraction of the total alloy in the liquid phase
12
Chapter 10 (continued)
Information from phase diagrams
Quantity of phases present
(cont.)
(cont.)
to calculate the fractions of the overall alloy in each phase
or use the actual length of the line segments
Chapter 10 (continued)
Microstructure development - Equilibrium cooling
•
In almost all cases in this chapter we will assume sufficient
time has been allowed to reach equilibrium.
Microstructure development - Non-equilibrium cooling
•
In many practical cases, diffusion rates are too low
(cooling rates are too high) too high to allow diffusion
completely occur. ____________________________.
•
A cored structure results in which the solid phase has a
varying composition. The average composition is the
same, but it is not uniform.
13
Chapter 10 (continued)
Microstructure development - Non-equilibrium cooling
The first solid formed
is at 46 % Ni.
Later solids are at a
lower composition.
Given sufficient time
it will all even out
Figure 10.4
Chapter 10 (continued)
Binary eutectic diagrams
Can be seen in Figures 10.6 (Cu-Ag) and 10.7 (Pb-Sn)
3 single-phase regions:
3 two-phase regions:
•
•
______
_____
______
_____
______
_____
solidus line = the below which everything is solid = ABEGF
liquidus line = line above which everything is liquid = AEF
14
Chapter 10 (continued)
Binary eutectic diagrams
(cont.)
Cu - Ag
Figure 10.6
Chapter 10 (continued)
Binary eutectic diagrams
(cont.)
Pb - Sn
Figure 10.7
15
Chapter 10 (continued)
Binary eutectic diagrams
(cont.)
α-solid is a ____________
________ as the solvent
________ as the solute
max. solubility of Ag in Cu occurs at 779°C.
(8.0 wt% Ag, 92.0 wt% Cu)
β-solid is a solid solution
________ as the solvent
________ as the solute
max. solubility of Cu in Ag also occurs at 779°C.
(8.8 wt% Cu, 91.2 wt% Ag)
Chapter 10 (continued)
Binary eutectic diagrams
(cont.)
•
Adding Ag to Cu decreases the melting point of Cu
line AE
•
Adding Cu to Ag decreases the melting point of Ag
line EF
•
point E is called an ____________ (____________)
L, α, and β can exist simultaneously, but only at 779°C
16
Chapter 10 (continued)
Binary eutectic diagrams
(cont.)
•
Note: Examples switch to lead-tin
•
A material with an overall composition of CE (61.9% Sn)
while cooling undergoes the ___________________
L (61.9 w% Sn) ---> α (18.3 w% Sn) + β (97.8 w% Sn)
•
The quantities and compositions of the α and β which
result from the eutectic reaction are read as before, and
are distributed in a layered structure.
Chapter 10 (continued)
Binary eutectic diagrams
(cont.)
Eutectic
reaction
Figure 10.11
17
Chapter 10 (continued)
Binary eutectic diagrams
(cont.)
Eutectic
reaction
Figure 10.12
Chapter 10 (continued)
Binary eutectic diagrams
(cont.)
Sample microstructures
approximately 2 wt % tin (Sn)
Figure 10.9
18
Chapter 10 (continued)
Binary eutectic diagrams
(cont.)
Sample microstructures
approximately 15 wt % Sn
Figure 10.10
Chapter 10 (continued)
Binary eutectic diagrams
•
(cont.)
The other reaction of interest is __________ compositions
that cross the ___________ temperature.
Example:
Overall composition of 40 wt % Sn.
•
At T just above eutectic T you have α (18.3% Sn) +
L (61.9% Sn)
•
As the material cools to just below the eutectic T, the ____
portion of the mixture transforms by the ______________.
19
Chapter 10 (continued)
Binary eutectic diagrams
Example:
(cont.)
Overall composition of 40 wt % Sn.
Figure 10.14
Chapter 10 (continued)
Binary eutectic diagrams
Example:
(cont.)
Overall composition of 40 wt % Sn
(cont.).
•
The lever rule gives the quantities of ____________.
•
But we need to distinguish between the α produced above
the eutectic T (____________) and that produced by the
eutectic reaction.
•
This is done by applying the lever __________ the eutectic
temperature.
20
Chapter 10 (continued)
Binary eutectic diagrams
(cont.)
Shows proeutectic
(primary) α and
the layered eutectic
structure.
There is α in two
places.
Figure 10.15
21