Dendrite growth velocity measurements in undercooled Ni and Ni-C melts in space

Under terrestrial processing conditions, convection in the melt shows a major impact on metallic solidification, especially at small crystal growth velocities. Previous studies of dendrite growth in undercooled Ni melts on earth show systematic deviations of experimental data and predictions of dendrite growth theory at small undercoolings. The discrepancy is partly reduced if convection is taken into consideration. The present experimental studies in space aim to test, under the conditions of reduced convection in microgravity, the predictions of dendrite growth models by measurements of the growth velocities in pure Ni and dilute Ni-0.6 at.% C alloy melts. A comparison of velocity data of the pure metal and the dilute alloy is used to investigate the prediction of marginal stability theory that for growing dendrites, the addition of a strongly partitioning element may lead to an enhancement of the growth velocity. The experiments were performed during the MSL-1-R mission in July 1997 using the electromagnetic levitation facility TEMPUS.