Chapter 9site.iugaza.edu.ps/mhaiba/files/2010/02/CH9-phase-diagrams-2015.pdf · Given composition...
Transcript of Chapter 9site.iugaza.edu.ps/mhaiba/files/2010/02/CH9-phase-diagrams-2015.pdf · Given composition...
Chapter 9
Phase
Diagrams
12/12/2015 11:23 AM
Mohammad Suliman Abuhaiba, Ph.D., PE1
Assignment1, 6, 11, 16, 21, 27, 39, 44,
49, 54, 59, 65
Due Tuesday 01/12/2015Exam #5 on Ch9: Tuesday 8/12/2015
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Learning Objectives
1. Isomorphous and eutectic phase
diagrams:
a. label various phase regions
b. Label liquidus, solidus, and solvus lines
2. Given a binary phase diagram at
equilibrium, composition of an alloy, its
temperature, determine:
a. phases present
b. compositions of phases
c. mass fractions of phase
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Learning Objectives
3. For some given binary phase
diagram upon heating or cooling,
locate temperatures & compositions
and write reactions of:
Eutectic
Eutectoid
Peritectic
congruent phase transformations
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Learning Objectives
4. Given composition of an Fe–C alloy
containing between 0.022 & 2.14 wt% C:
a. Is alloy hypoeutectoid or
hypereutectoid?
b.name proeutectoid phase
c.compute mass fractions of
proeutectoid phase and pearlite
d.schematic diagram of microstructure at
a temperature just below eutectoid
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Why Study Phase Diagrams?
Design & control of HT procedures
Strong correlation between
microstructure & mechanical properties
Development of microstructure of an
alloy is related to char of its phase
diagram
Phase Diagram (PD) provides valuable
info about melting, casting, crystallization,
and other phenomena
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9.2 Solubility LimitFigure 9.1: Solubility of Sugar (C12H22O11 in a
sugar-water syrup
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9.3 Phases
A phase: physically distinct &
homogenous portion in a
material.
Each phase is a homogenous part
of total mass & has its own
characteristics and properties.
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9.3 Phases
Phase Characteristics:
Same structure or atomic arrangement
Same composition & properties
Definite interface between phase and
any surrounding or adjoining phases
Two types of alloys:
single phase
multiple phases
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9.3 Phases
Alloying consists of two basic forms:
1. Solid solutions
2. Inter-metallic compounds
Solid Solutions (SS): solid material in
which atoms or ions of elements
constituting it are dispersed
uniformly.
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9.3 Phases
A SS is not a mixture
A mixture contains more than one
type of phase whose char are
retained when mixture is formed.
Components of SS completely
dissolve in one another and do
not retain their individual char.
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9.3 Phases
Properties are controlled by creating
point defects such as substititional &
interstitial atoms.
Solute: minor element that is added
to solvent (major element)
When crystal structure of solvent is
maintained during allying, alloy is
called a Solid Solution.
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9.6 One Component (Unary) Phase Diagrams
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9.7 Binary Isomorphous Systems
A phase diagram (PD) shows
relationships among temperature,
composition, and phases present in a
particular alloy system under
equilibrium conditions
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9.7 Binary Isomorphous Systems
From PD, we can predict:
how a material will solidify under
equilibrium conditions
phases for diff temp and comp.
Equilibrium means that state of a
system remains constant over an
indefinite period of time.
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9.7 Binary
IsomorphousSystems
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9.7 Binary Isomorphous Systems
Only one solid phase forms, the two
components in the system display
complete solid solubility
Liquidus temperature
Solidus temperature
Freezing range: pure metals & alloys
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9.7 Binary Isomorphous Systems
When temperature of molten metal
is reduced to freezing point:
Energy of latent heat of solidification is
given off while temperature remains
constant.
Eventually, solidification is complete
and solid metal continues cooling to RT.
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9.7 Binary Isomorphous Systems
Cooling curve for
solidification of pure
metals
Alloys solidify over a
range of temperatures
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9.7 Binary Isomorphous Systems
9.8 Interpretation of Phase Diagrams
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% 100
opposite arm of leverPhase
total length of tie line
Example Problem 9.1
Derive the lever rule
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9.8 Interpretation of Phase Diagrams
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Volume & mass fractions
9.9 Development of Microstructure in Isomorphous Alloys
The completely solidified alloy in the phase
diagram shown is a solid solution because:
Alloying element (Cu, solute) is
completely dissolved in host metal (Ni,
solvent)
Each grain has same composition
Atomic radius of Cu is 0.128nm & that of
Ni is 0.125nm,
Both elements are FCC; HRRs are obeyed.
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9.9 Development of Microstructure in Isomorphous Alloys
Two conditions required for growth of solid a:
1. Latent heat of fusion (DHf), which evolves
as liquid solidifies, be removed from solid
liquid interface.
2. Diffusion must occur so that compositions
of solid and liquid phases follow solidus
and liquidus curves during cooling.
DHf is removed over a range of
temperatures so that cooling curves shows
a change in slope
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9.9 Development of Microstructure in
Isomorphous Alloys
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Figure 9.4: Development of
microstructure
during equilibrium
solidification of a 35
wt % Ni–65 wt % Cu
alloy
9.9 Development of Microstructure in Isomorphous Alloys
On cooling from liquidus to 1250 oC,
some Ni atoms must diffuse from 1st solid
to new solid, reducing Ni in 1st solid.
Additional Ni atoms diffuse from
solidifying liquid to new solid.
Meanwhile, Cu atoms have
concentrated – by diffusion – into
remaining liquid.
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9.9 Development of Microstructure in Isomorphous Alloys
The process must continue until we
reach solidus temperature, where
last liquid to freeze, which contains
Cu-28%Ni, solidifies and forms a solid
containing Cu-35 %Ni.
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9.9 Development of
Microstructure in Isomorphous Alloys
Figure 9.5: Development of
microstructure
during non-
equilibrium
solidification of a
35 wt% Ni–65 wt%
Cu alloy
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9.10 Mechanical Properties of Isomorphous Alloys
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9.11 Binary Eutectic Systems
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Composition (wt % Ag)
Tem
pe
ratu
re (
°C
)
AgCu
9.11 Binary Eutectic Systems
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Example Problem 9.2For a 40 wt% Sn–60 wt% Pb alloy at 150°C,
a. what phase(s) is (are) present?
b. What is (are) composition(s) of phase(s)?
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Example Problem 9.3
For lead–tin alloy in Example Problem 9.2,
calculate relative amount of each phase
present in terms of
a. mass fraction
b. volume fraction. At 150°C take densities
of Pb & Sn to be 11.23 & 7.24 g/cm3,
respectively.
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9.12 Development
of Microstructure in Eutectic Alloys
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9.12 Development
of Microstructure in
Eutectic Alloys
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9.12 Development
of Microstructure in Eutectic Alloys
9.12 Development of Microstructure in
Eutectic Alloys
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9.12 Development of Microstructure in
Eutectic Alloys
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Figure 9.14: microstructure of a
Pb–Sn alloy of eutectic
composition.
Alternating layers of a
lead-rich a-phase solid solution (dark layers),
and a tin-rich b-phase solid solution (light
layers)
Source: Metals Handbook, 9th edition, Vol. 9,
Metallography and Microstructures, 1985.
Reproduced by permission of ASM International,
Materials Park, OH.
9.12 Development of Microstructure in
Eutectic Alloys
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Figure 9.15:Schematic
representation of
formation of eutectic
structure for lead–tin
system. Directions of
diffusion of tin & lead
atoms are indicated
by blue & red arrows
9.12 Development of Microstructure in Eutectic Alloys
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9.12 Development of Microstructure in Eutectic Alloys
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9.13 Equilibrium Diagrams Having Intermediate Phases or Compounds
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9.13 Equilibrium Diagrams Having Intermediate Phases or Compounds
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9.14 Eutectoid and Peritectic Reactions
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9.15 Congruent Phase Transformations
Congruent
transformations:
no compositional
alterations
allotropic
transformations
melting of pure
materials
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9.15 Congruent Phase Transformations
Incongruent
transformations: at least one of the
phases will
experience a change
in composition
Eutectic &
eutectoid reactions
melting of an alloy
that belongs to an
isomorphous system
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9.18 The IRON–IRON Carbide(Fe–Fe3C) Phase Diagram
Mohammad Suliman Abuhaiba, Ph.D., PE
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9.18 The IRON–IRON Carbide(Fe–Fe3C) Phase Diagram
Mohammad Suliman Abuhaiba, Ph.D., PE
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9.18 The IRON–IRON Carbide(Fe–Fe3C) Phase Diagram
Mohammad Suliman Abuhaiba, Ph.D., PE
9.19 Development
of Microstructure in Iron Carbon Alloys
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9.19 Development of Microstructure in Iron Carbon Alloys
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Figure 9.28; Schematic
representation of the
formation of pearlite from
austenite; direction of
carbon diffusion
indicated by arrows.
9.19 Development of Microstructure
in Iron Carbon AlloysHypo-eutectoid Alloys
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Development of
Microstructure
in Iron Carbon
AlloysHypo-eutectoid
Alloys
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9.19 Development of Microstructure in Iron Carbon
Alloys - Hypo-eutectoid Alloys
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9.19 Development of Microstructure in Iron Carbon
Alloys - Hyper-eutectoid Alloys
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EXAMPLE PROBLEM 9.4
For a 99.65 wt% Fe–0.35 wt% C alloy at a
temperature just below the eutectoid,
determine the following:
a. Fractions of total ferrite & cementite
phases
b. Fractions of pro-eutectoid ferrite &
pearlite
c. Fraction of eutectoid ferrite
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Influence of Other Alloying Elements
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