eutectic science definition

1. The proportion of constituents in an alloy or other mixture that yields the lowest possible complete melting point. In all other proportions, the mixture will not have a uniform melting point; some of the mixture will remain solid and some liquid. At the eutectic, the solidus  and liquidus  temperatures are the same.
2. An alloy or other mixture with constituents in the proportions of the eutectic.
3. The melting point of the eutectic.

eutectic

Substance X consists of two components, A and B (approximately 80% A and 20% B). Above the liquidus (the temperature at which the first solid begins to form) both components are liquid. As the temperature drops to the liquidus, component A starts to solidify, and the remaining liquid becomes less rich in component A and more rich in component B.

When the temperature has dropped to the solidus, which is the same as the eutectic temperature, solid B starts to form as well.

Below the solidus, the entire mixture is solid. A liquid of composition Y (consisting of approximately 80% B and 20% A) would cool in a similar manner, but with solid B forming first. A mixture of eutectic proportions is always either entirely solid or entirely liquid.