Thermal Equilibrium Diagram

Thermal Equilibrium Diagrams

The cooling curve for a combination of metals highlights the start and end of solidification for that particular alloy. These points are then transferred to the thermal equilibrium diagram, as shown.

If the information from a range of cooling curves for different combinations of the alloy is collected on one chart, a thermal equilibrium diagram is formed.

The given table shows the solidification temperatures for various alloys of metal A and metal B. The melting point of metal A is 270°C and metal B is 630°C.

Draw The Diagram

Label the Diagram and describe its main features

Liquidus line:  for the alloy system this line represents the boundary between the fully liquid state and the beginning of solidification.

Solidus line:  the boundary line that determines the end of solidification. Below this line, the alloy is completely solid.

Liquid region:  the two metals are soluble in a liquid state.

Solid region:  the two metals are soluble in a solid state.

Pasty region:  between the liquidus and solidus lines, the alloy system is in a partly liquid and a partly solid state.

For the alloy of 50% B determine, from the diagram, the ratio of phases at 400°C.

How to calculate ratio of solid and liquid and composition of phases for the same temperature (not based on the table above).