1. Material Science & Metallurgy Non Equilibrium Cooling
Cooling Curves
Non Equilibrium Cooling
Mohit Patel

2. 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

3. 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.

4. 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.

5. Cooling curve for Binary allloy forming solid solution.
Liquid Soln.
Liquid + Solid Soln.

6. Cooling curve for Binary alloy forming solid solution with eutectic reaction
ISOTHERM
TEMPERATURE W X Y
Liquid Soln.
Liquid + Solid 1+ Solid2 Soln.
TIME

7. 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.

9. THATS ALL!