Pore metamorphosis during liquid phase sintering in microgravity

This dissertation documents the pore metamorphosis in microgravity liquid phase sintered Co-Cu and Fe-Cu samples that have been successfully conducted on several sounding rocket flights, Space Shuttle missions and aboard the Mir Station. Pore filling and coarsening were found in most samples while pore breakup was also found in low liquid volume samples. Pores showed bifurcated behaviors based on their liquid volume fractions. These behaviors resulted from particle rearrangement, particle growth and volume diffusion that associated with interfacial energy differences, instabilities, and grain coarsening along the interface between phases. The mechanisms for pore breakup, pore coarsening and pore filling are discussed. An initiation mechanism induced by grain growth, capillary force and other weak forces is proposed and the results from theoretical analysis and CFD numerical simulation for pore breakup are presented. The microstructure evolutions of Co-Cu and Fe-Cu samples and the grain growth measurements that associated with pore morphological changes are also documented in this dissertation.