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Eutectic Solidification

  Anomalous Eutectics     9 of 9

Most eutectic systems grow with uniform lamellar spacings which correspond to extremum conditions. However, some eutectics do not do this but show a wide range of spacings within each specimen and an average spacing which is considerably higher than that corresponding to extremum growth. This is due to at least one of the two phases having preferred crystallographic growth directions (and tending to exhibit facets ). Such systems cannot readily adjust their interlamellar spacings in response to changing growth conditions. Observed spacings tend to vary locally, typically between a lower limit close to the extremum value and an upper limit of lb at which the facetted phase branches - usually via an offshoot in an equivalent crystallographic direction.

A well-known example of an anomalous eutectic is Al-Si. Such systems can often be modified by melt additions, so as to promote solidification like a regular eutectic. Such additions usually poison the preferred atomic addition sites on the facetted phase, so that growth occurs more readily in different directions.

  Kinetics | Redistribution | Cell, dendrite and grain structure | Eutectic

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