Morphological development of solidification structures under forced fluid flow: experimental observation

Morphological evolution of solidification structures in stirred Sn - 15Pb (wt-%) alloy has been investigated using various stirrer geometries and stirring intensities. A serial sectioning experiment was carried out to evaluate the actual morphology of the solid formed in three dimensions, and illustrated that microstructural observation from a single two-dimensional section may be inconclusive in many cases. Based on experimental observation it is proposed that the morphological evolution can be explained as a growth phenomenon. Different solidification structures observed under melt stirring conditions can be explained on the basis of the effect of fluid flow characteristics on diffusion geometry around the growing solid. It has been shown that a low intensity laminar flow produces a dendritic structure; particle rotation under shear flow produces a rosette morphology, and intense turbulent flow produces fine and compact solidification structures.