eutektische

Eutektische, or eutectic, refers to a class of invariant reactions and compositions in alloy systems in which a liquid of a particular composition solidifies into two or more solid phases at a single temperature, known as the eutectic temperature. In a binary phase diagram, the eutectic point marks the lowest melting temperature that a mixture of the two components can achieve. The characteristic reaction is L → α + β, occurring at the eutectic composition.

During solidification, the two solid phases grow simultaneously from the melt and form a fine, interleaved microstructure. The common morphologies are lamellar or rod-like arrangements of the phases embedded in one another, resulting from diffusion and rapid coupled growth. This microstructure imparts a combination of properties that differ from the individual constituents.

Common examples include the lead–tin eutectic (about 61.9 weight percent tin and 183°C) used in solders; the iron–carbon eutectic (about 4.3 percent carbon at 1147°C), which forms ledeburite in cast iron; and the aluminum–silicon eutectic (about 12.6 percent silicon at about 577°C), significant in casting alloys.

Eutectic systems are contrasted with eutectoids and peritectics, and with solid-state reactions. In practice, eutectic compositions provide predictable melting temperatures and fine microstructures that are advantageous for casting, soldering, and alloy design, where a low and sharply defined melting point is desirable.