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The decomposition of supersaturated solid solution of numerous alloys during aging occurs throughout discontinuous cellular reaction resulting in the formation of the alternating structure α and β phases. The discontinuous precipitation is characterized by the presence of sharp reaction front which separates the initial state from the reaction product.

In this contribution, the morphology of cellular precipitation in an Cu-4.5 at. % In alloy has been investigated by optical microscopy and electron microscopy ( TEM and SEM ). The lamellar precipitates develop from the grain boundary into the grain by discontinuous reaction during aging at 673 K. The discontinuous precipitation clearly revealed by optical and scanning electron micrographs was observed to decompose into lamellar structure. It has been observed different orientations of lamellae in the same cell and the discontinuous reaction is more developed in certain sites of matrix, like grain boundaries and interphases of matrix. On the other hand, the shape of reaction front is analyzed by transmission electron microscopy.