Gravitational effects on grain coarsening during liquid-phase sintering

Grain growth in liquid-phase sintering (LPS) is often treated as an extension of Ostwald ripening. However, the inherent grain contact at high solid contents leads to coalescence and other conflicts with most coarsening theories. Consequently, grain growth rates during LPS significantly deviate from the predictions of most coarsening theories. This study compares grain sizes of tungsten heavy alloys sintered on Earth and under microgravity conditions. The microgravity samples consistently produced a smaller grain size. A case is made for a gravity contribution to coarsening during LPS. Such a concept provides a rationalization for previously reported differences in sintered grain size with location in compacts sintered on Earth.