At what point does an alloy change from liquid to solid without passing through a liquid/solid state?

The eutectic point is significant because it represents a unique composition of an alloy where it can transition from liquid to solid at a constant temperature without passing through the solid-liquid intermediate state. At the eutectic composition, the mixture of phases coexists in thermodynamic equilibrium, allowing for a simultaneous crystallization of two different solid phases when the alloy cools. This results in a more uniform microstructure and specific mechanical properties.

Understanding the eutectic point is crucial for materials engineers as it informs decisions regarding phase transformations and the resulting characteristics of the alloy. It stands out from other points like the solidus and liquidus, which indicate phase boundaries but don't reflect the simultaneous phase change experienced at the eutectic point. The solidus point marks where the material is entirely solid, while the liquidus point indicates the temperature above which the material is completely liquid. The fusion point generally refers to the melting of pure metals rather than alloys, making the eutectic point the most relevant for this specific transition in alloys.