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.
Eutectic System
1884
- Frederick Guthrie
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 [\beta] 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.
UNESCO Nomenclature: 3308
– Metallurgy
类型
物理现象
中断
实质性
使用方法
广泛使用
前体
- studies on freezing-point depression in aqueous solutions
- development of thermal analysis techniques like calorimetry
- josiah willard gibbs’ work on phase equilibria and the phase rule
- early metallography for observing microstructures
应用
- lead-tin and lead-free solders for joining electronic components
- casting of complex shapes using cast iron, which is a near-eutectic iron-carbon alloy
- brazing alloys for joining dissimilar metals at high temperatures
- 用于热能存储的相变材料
- production of galinstan, a non-toxic liquid metal alloy at room temperature
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