(صورة توضيحية فقط)
A eutectic system is a mixture of two or more components that solidifies at a single, sharp temperature that is lower than the melting point of any of the individual components. This specific composition is the eutectic point. Upon cooling, a eutectic liquid transforms into a fine mixture of solid phases, often with a characteristic lamellar (layered) microstructure.
The concept of a eutectic system is best visualized using a binary phase diagram, which plots temperature against composition. The eutectic point is the specific composition and temperature at which the liquid phase is in equilibrium with two solid phases. For a binary system of components A and B, the eutectic reaction is represented as [latex]L \rightleftharpoons \alpha + \beta[/latex], where L is the liquid phase, and [latex]\alpha[/latex] and [latex]\beta[/latex] are two different solid phases (rich in A and B, respectively). This invariant reaction occurs at a constant temperature, the eutectic temperature.
The low melting point of eutectic alloys is highly advantageous for casting, as it reduces the energy required and minimizes thermal stress on molds. The microstructure formed during eutectic solidification is typically a fine, intimate mixture of the solid phases, such as alternating layers (lamellae) of [latex]\alpha[/latex] and [latex]\beta[/latex]. This fine microstructure can impart unique mechanical properties, such as high strength and wear resistance, as seen in cast iron where the eutectic structure consists of ferrite and cementite. Compositions other than the eutectic are termed hypoeutectic or hypereutectic, and they begin to solidify by precipitating one of the primary solid phases before reaching the eutectic temperature, where the remaining liquid then undergoes the eutectic transformation.
Eutectic System
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