The document describes slow cooling and rapid cooling of an isomorphous alloy using a Cu-Ni system. For slow cooling, the alloy solidifies completely with a uniform composition along the solidus line. For rapid cooling, solidification takes longer and is incomplete, resulting in segregation of grains with non-uniform composition. The document also describes a binary eutectic system using Cu-Ag, which has three single-phase regions (α, β, liquid), limited solid solubility, and a eutectic reaction that occurs at a single temperature and composition.

1. CHAPTER 2 (CONTD.)
 Slow Cooling of an Isomorphous Alloy
 Rapid Cooling of an Isomorphous Alloy
 Binary Eutectic System
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2. SLOW COOLING OF AN ISOMORPHOUS ALLOY
 Also, called as Equilibrium Cooling.
 Let us consider Cu-Ni system 35 wt% Ni–65 wt%
Cu.
 At 1300° C; point a, the alloy is completely liquid.
 As cooling begins, no microstructural or
compositional changes will be realized until we
reach the liquidus line.
 At 1260°C; point b, the first solid α begins to form,
which has a composition dictated by the tie line
drawn at this temperature i.e., 46 wt% Ni–54 wt%
Cu.
 With continued cooling, both compositions and
relative amounts of each of the phases will change.
 The fraction of α phase will increase.MTE/III SEMESTER/MSE/MTE 2101 2
Pic Courtesy: Material Science and Engineering, Callister.

3.  At 1250°C, point c, the compositions of the liquid
and α phases are 32 wt% Ni–68 wt% Cu [L(32 Ni)]
and 43 wt% Ni–57 wt% Cu [ (43 Ni)].
 The solidification process is virtually complete
at1220°C about point d; the composition of the
solid is approximately 35 wt% Ni–65 wt% Cu.
 Upon crossing the solidus line, this remaining
liquid solidifies; the final product then is a
polycrystalline -phase solid solution that has a
uniform 35 wt% Ni–65 wt% Cu composition at
point e.
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Pic Courtesy: Material Science and Engineering, Callister.

4. RAPID COOLING OF AN ISOMORPHOUS ALLOY
 Also, called as Non Equilibrium Cooling.
 Let us consider Cu-Ni system 35 wt% Ni–65
wt% Cu.
 At 1300° C; point a´, the alloy is completely
liquid.
 As cooling begins, no microstructural or
compositional changes will be realized until we
reach the liquidus line.
 At point b´, (approximately 1260°C), α-phase
particles begin to form, which, from the tie line
constructed, have a composition of 46 wt% Ni–
54 wt% Cu [ (46 Ni)].
MTE/III SEMESTER/MSE/MTE 2101 4Pic Courtesy: Material Science and Engineering, Callister.

5.  Upon further cooling to point c´ (about 1260°C
), the liquid composition has shifted to 29 wt%
Ni–71 wt% Cu; furthermore, at this temperature
the composition of the αphase that solidified is
40 wt% Ni–60 wt% Cu [ (40 Ni)].
 Because of the rapid cooling, the solidus line
shifted (indicated in dashed line) and solid
composition has increased.
 At point d´ (temperature 1220°C), the
solidification should complete but there is still
little amount of liquid is left.
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Pic Courtesy: Material Science and Engineering, Callister.

6.  The solidification should be completed at point
e´ in comparison to slow cooling but since there
is a shift in the solidus line, solidification process
takes longer time than usual.
 It completes at point e´ (temperature 1205°C).
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Pic Courtesy: Material Science and Engineering, Callister.

7. PHENOMENA OF SEGREGATION TAKES PLACE WHICH IS NOTHING BUT NON-
UNIFORM DISTRIBUTION OF GRAINS.
Slow Cooling Rapid Cooling
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8. BINARY EUTECTIC
SYSTEMS
 Another type of common
and relatively simple phase
diagram found for binary
alloys for the copper–silver
system; this is known as a
binary eutectic phase
diagram.
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Pic Courtesy: Material Science and Engineering, Callister

9. Features of Phase Diagram
 Three single-phase regions are found on the
diagram: α,β and liquid.
 α phase: Cu rich solid solution, solute is Ag,
FCC structure.
 β phase: Ag rich solid solution, solute is Cu,
FCC structure.
 Pure copper and pure silver are also
to be α and β phases.
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10. Features of Phase Diagram (Contd.)
 The solubility in each of these solid phases is
limited, in that at any temperature below line
BEG only a limited concentration of silver will
dissolve in copper (for the α phase) similarly
copper in silver (for the β phase).
 The solubility limit for the α phase
to the boundary line, labelled CBA, between
the α/(α+β) and α/(α+L) phase regions; it
increases with temperature to a maximum [8.0
wt% Ag at 779°C] at point B and decreases
back to zero at the melting temperature of
pure copper, point A 1085°C.
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11. Features of Phase Diagram (Contd.)
 The solid solubility limit line separating the α
and (α+β) phase regions is termed a solvus
line; the boundary AB between the α and
(α+L) fields is the solidus line.
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12. Features of Phase Diagram (Contd.)
 There are also three two-phase regions found for
the copper–silver system: α + L, β+L, α+β.
 As silver is added to copper, the temperature at
which the alloys become totally liquid decreases
along the liquidus line, line AE; thus, the melting
temperature of copper is lowered by silver
additions.
 The same can be said for silver, as copper is added
to silver, the temperature of copper reduces
complete melting along the other liquidus line, FE..
 These liquidus lines meet at the point E on the
phase diagram, through which also passes the
horizontal isotherm line BEG.
 Point E is called an invariant point.
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13. Features of Phase Diagram (Contd.)
 An important reaction occurs for an alloy of
composition CE as it changes temperature TE; in
passing through this reaction may be written as
follows:
 The reaction occurring at Point E along line BEG is
called as “Eutectic Reaction”.
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