Initiation of metamorphosis of porosity during liquid-phase sintering in microgravity

In microgravity liquid-phase sintering (LPS), the reduction of sedimentation-driven convection permits the study of pore formation and metamorphosis otherwise obscured by gravity. These motions result from interfacial energy differences, instabilities, and grain coarsening along the interface between phases. A theoretical model is presented to monitor the trends of shape changes of a pore in microgravity. LPS experiments were conducted on four suborbital sounding rockets, six experiments on five different Space Shuttle missions, and on a mission to the Mir Station where 67 samples were processed in the Russian Optizone furnace for various times. Results from these flight experiments were used to investigate pore metamorphosis and grain coarsening for various copper and silver based systems at different liquid volume fractions. Results for pore formation in the Fe-Cu system processed under argon are presented, along with an analysis of the microstructures in the region near the bubble.