Answer:

When solid solubility is limited and the melting points of the components are not vastly different, a Eutectic Phase diagram usually results.

Explanation:

For example, the Pb-Sn phase diagram . As there is complete liquid solubility, the liquid phase extends over all compositions above the melting temperatures of the components. The solid phase at the left end is lead-rich which dissolves only a limited amount of tin. The solubility decreases with decreasing temperature. This limit of the solid solubility is indicated by the  phase BOUNDARY between α and α + β, called solvus. The solid solution phase at  the right end is the tin-rich β, with only a very small quantity of lead dissolved  in it. The phase boundaries on this diagram are as follows:

Liquidus I: boundary between L and L + α regions

Liquidus II: boundary between L and L + β regions

Solidus I: boundary between α and L + α regions

Solidus II: boundary between β and L + β regions

Solvus I: boundary between α and α + β regions

Solvus II: boundary between β and α + β regions

The THREE two-phase regions are separated by a horizontal line

corresponding to the temperature Te called the eutectic temperature. Below the

eutectic temperature, the material is fully solid for all compositions. The

composition which remains fully liquid up to the eutectic temperature during

cooling is called the eutectic composition ce. At the eutectic temperature, the

following eutectic reaction takes place:

                 cooling------->

                 L↔α+β

                  <------ heating