Evaluation of Kinetics and Microstructural Development in Pure, Composite, and Alloyed Silver Spheres Processed in the MSFC Drop Tube

Solidification phenomena in silverbased spherical samples was investigated by utilizing the approximate 4.5 seconds of "containerless" time afforded by the 105m drop tube facility at the Marshall Space Flight Center. The microstructure and extent of solidification was found to strongly depend on sample diameter, sample temperature above the melting point upon release, and the drop tube atmosphere. The experimental observations were found to be in agreement with a numerical model developed that includes fully time dependent heat equations, consideration of local equilibrium at the solid - liquid interface(s), couples the heat transfer coefficient, and allows radiative and/or fluid layer heat transfer at the outer boundary. Discrepancies between the experiment and model are discussed and some novel aspects to be implemented are presented.