Under terrestrial processing conditions,convection in the melt shows a major impact on metallicsolidification, especially at small crystal growth velocities.Previous studies of dendrite growth in undercooled Ni melts onearth show systematic deviations of experimental data andpredictions of dendrite growth theory at small undercooling. Thediscrepancy is partly reduced if convection is taken intoconsideration. The present experimental studies in space aim totest, under the conditions of reduced convection in microgravity,the predictions of dendrite growth models by measurements ofthe growth velocities in pure Ni and dilute Ni-0.6 at. percent Calloy melts. A comparison of velocity data of the pure metal andthe dilute alloy is used to investigate the prediction of marginalstability theory that for growing dendrites, the addition of astrongly partitioning element may lead to an enhancement of thegrowth velocity. The experiments were performed during theMSL- 1-R mission in July 1997 using the electromagneticlevitation facility TEMPUS.
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