Multiple grain growth events in liquid phase sintering

Sintered tungsten heavy alloys consist of a solidified liquid alloy matrix phase which interpenetrates a solid tungsten skeletal structure. A consequence of liquid phase sintering is considerable grain growth while the compact densifies. The driving force for grain growth is a decrease in the interfacial surface energy, and the process itself is the combined result of liquid diffusion, solid diffusion, and vapor diffusion if porosity is present. In this study, we utilized microgravity sintered samples to avoid solid-liquid segregation to study the multiple diffusion processes. Coupled with the diffusion event through the liquid phase, there is simultaneous solid-state sintering such as coalescence. The dihedral angle determines the contiguity and the grain growth rate. The liquid diffusion grain growth rate constant is at least one order of magnitude larger than the solid diffusion grain growth rate constant. As composition changes, the ratio of grain growth contributions from these three components also changes, which, in turn, causes grain size, grain size distribution, and contiguity variations.