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8/17/2019 ES 67 Phase Diagrams (2)
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PHASE DIAGRAMS
Illustrates the stable phase/s present ina system at a given condition (pressure,temperature and composition)
Provides a correlation between themicrostructure of materials and itsmechanical properties
Used in the design and control of heattreatment procedures, especially formetals
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BASIC TERMS AND CONCEPTS
1. System # speci$c body of material underconsideration
2.Phase # homogeneous portion of a system that
has uniform physical and chemicalcharacteristics
3.Component # pure substances or compounds
of which a system is composed
4.So!"##ty $#m#t # ma%imum concentration ofsolute atoms that may dissolve in the solvent to
form a solid solution jdlgamutan2!"
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System& S%GAR&'ATER S(STEM
Phases& $#)!#* So!t#on Phase an* So#* S!+a, Phas
Components& 'ate, an* S!+a,
Solubility Limit & -a,#es #th T as #n*#/ate* #n the +,ap
stration of the Basic Concepts
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One&Component o, %NAR( Phase D#a+,am
'implest and easiest type of phase diagram omposition is held constant, diagram is that of apure substance
Phase Bo!n*a,#es
# at any point on thesecurves, phases on eitherside of the curve coe%istwith one another
T,#pe0Ina,#antPo#nt # all three phasesof a substance (solid,liuid, gas) are
simultaneously ine uilibrium jdlgamutan2!"
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o&Component o, B#na,y Phase D#a+,a
Pressure is held constant, temperatureand composition are variable
*%tremely common and applicable tobinary alloys
pes of Binary Phase Diagrams:
1.B#na,y Isomo,pho!s System
2.B#na,y E!te/t#/ System
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o,pho!s System COPPER&NICE$ S(STEM
$#)!#* Phase #+omogeneous liuid solutionof u and i
&Phase # 'ubstitutionalsolid solution of u and i
**Cu and Ni are completely soluble in the solid
state due to the fact that both metals possess thesame FCC cr stal structure
-elting .emperatures&
TC! 5 16789C
TN# 5 14839C
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Inte,p,etat#on o: Phase D#a+,ams
PHASES PRESENTLocate the temperaturecomposition point on
the dia!ram and note the phases present" aslabeled.
COMPOSITIONS O; THE PHASES
RE$ATI-E AMO%NTS O; PHASES
PRESENT
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PHASES PRESENT
COMPOSITIONS O; THE PHASES(in terms of component concentration)
For sin!le phase re!ions" the composition of this phase
is simply the same as the alloy composition
For t#ophase re!ions"1. Construct a tie line at the !i$en temperature
2. Note the intersection of the tie line and the
phase boundaries 3. From these points of intersection" identify thecomposition of the phase by droppin! a perpendicularline to the compositiona%is
RE$ATI-E AMO%NTS O; PHASES
Inte,p,etat#on o: Phase D#a+,ams
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PHASES PRESENT
COMPOSITIONS O; THE PHASES
RE$ATI-E AMO%NTS O; PHASESPRESENT
For sin!le phase re!ions" alloy is composed entirelyof that phase
For t#ophase re!ions" use the in$erse le$er rule asfollo#s& 1. Construct a tie line at the !i$en temperature 2. 'easure the len!th of the entire le$er" the
!i$en temperaturecomposition point bein! thefulcrum
Inte,p,etat#on o: Phase D#a+,ams
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Illustration
< Po#nt A
Phase/s Present&
&So#* So!t#on
omposition of the Phase&
=6>N#&46>C!
elative 0mount of the Phas
166>
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Illustration
< Po#nt B
Phase/s Present&
&So#* So!t#on$#)!#* Phase
omposition of the Phases&
42.8>N#&8?.8>C!
$ 31.8>N#&=7.8>C!
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Illustration
< Po#nt B
elative 0mount of the Phas
'$ 5 =7> $
' 5 32>
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e/t#/ System COPPER&SI$-ER S(STEM
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tant :eat!,es o: a E!te/t#/ B#na,y Phase D#a+,am
h,ee s#n+e&phase ,e+#ons @ an* $#)!#* solid solution of u with 0g as solute solid solution of 0g with u as solute
#m#te* so!"##ty #n the so#* phase
h,ee to&phase ,e+#ons $@ $@
na,#ant o, E!te/t#/ po#nt :oo#n+ the ,ea/t
$ 5
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n&I,on Ca,"#*e Phase D#a+,am
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G#""s Phase R!e
4ictate the construction of Phase 4iagrams
Proposed by the !5th century physicist 67 8illard9ibbs
epresents a criterion for the number of phasesthat coe%ist within a system at euilibrium
P number of phases present; number of degrees of freedom or e%ternally
controlled variables that can be changedindependently without altering the number of phasesthat coe%ist at euilibrium
C number of components in a system
N number of non:compositional variables (eg7, . jdlgamutan2!"