A modified Bridgman technique was used to grow a nickel-alloyed gray cast iron. During the experiments, morphological modifications (MMs) were induced by the change in chemical composition of the melt in front of the solid/liquid interface. This was achieved by means of an "in-situ" addition of commercial modifiers, maintaining the thermal-gradient-to-growth-rate ratio. Optical and scanning electron microscopy (SEM) and X-ray diffraction were used to characterize the resulting microstructures. From the analysis of the evolution of the microstructures during our unidirectional experiments, correlated with results of other researchers, a new explanation for MMs observed in cast iron is proposed; it covers the whole range of morphologies from flake to nodular graphite. The explanation emphasizes the following points.(1) Graphite always grows like sheet crystals. (2) The MM of flake cast iron starts when the triple-contact line between austenite-graphite-liquid disappears, provoking the separation of austenite from graphite during eutectic growth. (3) Vermicular and nodular morphologies arise from the compacting action of solid austenite and liquid, respectively, exerted upon sheet crystals.

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Experimental evidence of transient self-dewetting of metallic surfaces is presented. Steel surfaces are melted by a pulsed electron gun, and the subsequent fast cooling against its substrate gives rise to the formation of characteristic patterns that we attribute to the dewetting of the liquid film. The patterns formed are similar to those obtained by spinodal dewetting, that is, when the dewetting action develops from a nonlinear instability on the liquid surface, and not from holes nucleation. High-purity iron does not show a similar behavior, indicating that the origin of the instability is due to the influence of the sulfur in the temperature dependence of the surface tension of the melt, which gives rise to a Be’nard-Marangoni instability.

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A new unidirectional solidification (US) method to study gray cast iron was developed. It is based on the combination of the classical Bridgman-type technique and the directional casting technique. By means of this method, it is possible to achieve, among others, the following aims: (a) changes in chemical composition of the melt during the experiment without modifying G/R (G: thermal gradient and R: solidification rate); (b) US of modified (compacted/vermicular) gray-cast iron, avoiding equiaxal nucleation in front of the solid/liquid (S/L) interface; and (c) quenching of the S/L interface retaining the microstructure of the growing solid.