Eutektik

Eutektik, or eutectic, is a term used in materials science and metallurgy to describe a specific composition in a multicomponent system that solidifies from a liquid into two or more solid phases at a single temperature, known as the eutectic temperature. This composition has the lowest melting point for that system and tends to produce distinctive microstructures upon solidification.

In a binary phase diagram, the eutectic point marks the invariant reaction L → α + β at Te, where a liquid transforms into two solid phases simultaneously. The resulting microstructure typically consists of finely intermixed lamellae or rod-like colonies of the two solids, a pattern that depends on cooling rate and diffusion during solidification. The overall phase proportions follow the lever rule.

Common eutectic systems include the tin–lead solder Sn-Pb, which is about 61.9% tin and 38.1% lead with a melting point of 183°C, and the iron–carbon system near 4.3 wt% C at roughly 1147°C, forming ledeburite (austenite plus cementite) in cast iron. Eutectic alloys are valued for their sharp, single melting point and good castability, making them useful in solders, brazing alloys, and certain casting applications. Eutectic microstructures can exhibit excellent machinability and tailored mechanical properties.

Related concepts include eutectoid reactions (solid-state analogs) and peritectic reactions (transformations between solid and liquid phases). The study of eutectics employs phase diagrams, thermal analysis and microscopy to understand solidification kinetics and the resulting material properties.