I want to know about the reason leading to a particular composition of a metal mixture to form a eutectic alloy. I know that Gibbs free energy plays a very role and I can figure out the thermodynamic explanation through it. But, I need to know and understand this phenomenon by other perspectives as well.Thanks in advance for helping.
We get eutectic microstructures because of the preferential segregation of the two different phase elements (i.e the diffusion of the atoms during the solidification of the alloys. Solute rejection happens during the liquid to solid transformation during cooling with the alpha phase rejecting beta atoms and vice versa, leading to the mutual growth of alpha-beta phases). As you have pointed out, this is driven by the Gibbs free energy.
Another main reason for the eutectic formation is the surface energy of the phases (solid-liquid interface energy). In the eutectic composition, the interface surface energy of the alpha-beta phase gets balanced with that of the surface energy of the liquid and this results in the perfect lamellar growth of the the eutectics.
Also, as you would have noticed, the eutectic microstructure is not restricted to a single alloy composition (although the phase diagram says so) and they form in a much broader composition range. During solidification, the composition of an alloy varies at each point (since the solute concentration varies) and because of this you will get eutectic phase formation at many different points even though your alloy composition is not eutectic.
A study on the solidification of binary alloys will help you to understand the eutectic formation in a much better way.
Hope you find this answer suitable.
regards,
Raghav.
Hi
An eutectic structure usually forms by simply mixing (alloying) at least two chemical elements, i.e., iron and graphite, in which that the eutectic point(eutectic temperature, eutectic composition) at the phase diagram, for instance of Iron-graphite, illustrates a specific composition of Iron & Graphite and a melting point of the mixture of Iron & graphite. The melting point of the mixture is much lower than the melting point of the pure Iron and the melting point of the pure Graphite. In other words, the transformation of the molten mixture to solid phases occurs at a sub-cooling temperature, i.e., lower than the melting temperature of pure Iron & pure graphite, in a thermodynamic favorable condition.
hi
it needs to be noted that eutectic alloys are a mix of two alloying element such as A & B which are completely soluble in molten phase when the molten alloy reaches the eutectic temp the first amount of solid from first phase(alpha) forms.assume that alpha is a phase rich of (A) with forming this phase the concentration of B in the neighboring melt will increase so the beta phase which is rich of B will form to remain the melt in the eutectic concentration this will continue till the last melt transforms to the solid phase. this concentration controlled phenomena will lead to a layered micro-structure called eutectic.
dear doctor
A eutectic system (/juːˈtɛktɪk/ yew-TEK-tik)[1] from the Greek "ευ" (eu = easy) and "Τήξις" (teksis = melting) describes a homogeneous solid mix of atomic and/or chemical species, forming a joint super-lattice, by striking a unique atomic percentage ratio between the components — as each pure component has its own distinct bulk lattice arrangement. It is only in this atomic/molecular ratio that the eutectic system melts as a whole, at a specific temperature (the eutectic temperature) the super-lattice releasing at once all its components into a liquid mixture. The eutectic temperature is the lowest possible melting temperature over all of the mixing ratios for the involved component species.
Upon heating any other mixture ratio, and reaching the eutectic temperature — see the adjacent phase diagram — one component's lattice will melt first, while the temperature of the mixture has to further increase for (all) the other component lattice(s) to melt. Conversely, as a non-eutectic mixture cools down, each mixture's component will solidify (form its lattice) at a distinct temperature, until all material is solid.
regards
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