Formation of the Microstructure in Eutectics

A generic eutectic phase diagram used as an example of the evolving microstructure when the starting compositing intersects the solvus line. 

If the starting composition Q happens to be the eutectic composition Ce, the system will remain molten imtil the eutectic temperature is reached. At this point the melt transforms into a with composition Q and 3 with composition Cz- The relative amoimt of the two phases is determined by the lever rule. Using one end of the tie-line as the pivot point, e.g.. Cl and balancing the torque from N atoms acting on lever arm (Ce — Ci) agaiirst Np acting on (C2 — Ci) we obtain 

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