Pore metamorphosis during liquid phase sintering in microgravity


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Abstract

Liquid Phase Sintering (LPS) experiments have been conducted on several sounding rocket flights, Space Shuttle missions and aboard Mir Station, where more than 100 samples were processed for various times. Analysis of those samples revealed considerable pore formation and metamorphosis. Pore filling and coarsening was 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 different diffusion patterns (surface diffusion and volume diffusion) that associated with interfacial energy differences, instabilities, and grain coarsening along the interface between phases. Low liquid volume fraction and the presence of the agglomeration, which results in high local solid volume fraction, enhances the volume diffusion during the process which causes the pore breakup. This paper attempts to show pore bifurcation behavior, which produces either smaller pore by a breakup mechanism or coarsened pore of large size. 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 are presented.

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