The growth and planar to cellular and cellular to dendritic transition of crystals in Fe-C alloy melts have been successfully observed 'in-situ' by use of a confocal laser microscope combined with an infrared image furnace. The observations clearly indicated that an increase in the growth rate of planar crystals in an Fe-0.83%C alloy melt, which solidifies as the γ-phase, induced the formation of perturbations at the melt/crystal interface. The perturbation subsequently developed into cells followed by preferred growth of some cells which overgrew over the adjacent cell. Perturbations were also formed on the cell, yielding dendrite cells with secondary arms. The spacing between the secondary arms was also coarsened by the overgrowth. Similarly, planar to cellular transition and coarsening of the cell took place in Fe-0.2%C alloy melt which solidifies as σ-phase. Cell tip stability has been discussed on the basis of these observations. In addition, the engulfment of non-metallic inclusions into solidifying and growing cellular crystals upon cooling was observed.
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