Cooling Curve
 A cooling curve is a
graphical plot of the
changes in temperature
with time for a material
over the entire
temperature range through
which it cools.
Cooling Curve for Pure Metals
Cooling Curve
 This is by far the most widely used experimental method.
 It relies on the information obtained from the cooling
process.
 In this method, alloys with different compositions are melted
and then the temperature of the mixture is measured at a
certain time interval while cooling back to room
temperature.
 A cooling curve for each mixture is constructed and the
initial and final phase change temperatures are determined.
Then these temperatures are used for the construction of the
phase diagrams.
Cooling curve for the solidification of a
pure metal
Under equilibrium
conditions, all
metals exhibit a
definite melting or
freezing point. If a
cooling curve is
plotted for a pure
metal. It will show a
horizontal line at
the melting or
freezing
temperature.
Cooling curve for Binary allloy forming solid solution.
Liquid Soln. Liquid + Solid Soln.
Cooling curve for Binary alloy forming solid solution with
eutectic reaction
U
TEMPERATURE
V
ISOTHERM
W
Liquid
Soln.
X
Liquid + Solid 1+ Solid2
Soln.
TIME
Y
Non Equilibrium Cooling
•If the liquid cools too fast for it to stabilize as it cools, we develop a cored structure. The
structure does not have uniform composition.
Consider Fig. At point b’, the solid for a 35%Ni-65%Cu mixture forms with 46% Ni.
•With rapid cooling, this solid remains with this composition while successive solids with
gradually reduced amounts of Ni form around this center core. This produces a shift in the
solidus line (the liquid has a higher percentage of Cu) and results in less than optimal
properties.
•This can be a problem in castings. The coring can be resolved by heat-treating at a
temperature just below the solidus line to produce atomic diffusion leading to a more
homogeneous composition.
THATS ALL!