Abstract
The influence of convection on the morphology of primary dendrites and on the distribution of germanium in primary crystals of hypoeutectic Ag–Ge alloy was studied. The experiment in microgravity provided conditions for the suppression of melt flow. Both the morphology of the primary dendrites and their chemical composition profiles were found to vary considerably depending on the intensity of convection. Primary crystals in specimens solidified in the space laboratory exhibited strong supersaturation with germanium. This supersaturation is associated with a decrease of solute in the eutectic. The overall segregation of germanium between crystals and the melt during the growth of primary dendrites is strongly promoted by convection. The influence of convection on the non-equilibrium primary crystallisation, particularly on the solute trapping process, the occurrence of which is likely in the initial stage of primary crystallisation (solute rich core), is discussed. A higher solute gradient close to the core in the space sample implies a higher melt stability below the liquidus when convection is suppressed.
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