| Abstract: | Results of a study on primary crystallization in hypoeutectic and hypereutectic alloys under different convection conditions during solidification are presented. The conditions of suppressed buoyancy driven convection are assumed in the microgravity samples. The intensity of convection was shown to affect the resulting microstructures significantly. The number and the size of primary dendrites in both hypoeutectic samples was found to be comparable. In the microgravity processed hypoeutectic sample the primary dendrites exhibit a greater tendency to branch compared with the ground-based sample. In eutectic samples, a small amount of primary solid solution, due to the existence of an asymmetric coupled zone, was observed. In hypereutectic samples the number of primary germanium crystals is higher in the space sample. The influence of convection on the nucleation of primary crystals thus depends on the composition of such samples. In the case of the primary solid solution the effect of convection on the growth stage of crystallization appears. On the other hand, in the case of primary germanium the intensity of convection affects mainly the nucleation stage of crystallization. The influence of convection on the growth is only secondary. The reasons for such a difference are based on the transport requirements during the nucleation stage. |
