DESIGN, ASSEMBLY AND CHARACTERIZATION OF COMPOSITE ...

2.5.4.2 Rearrangement
With the formation of a wetting liquid, particles may pack to a higher density
rapidly, releasing liquid to fill pores between grains. The solid-liquid surface energy is
lower than the solid-vapor surface energy, resulting in reduced system energy. During
rearrangement the compact exhibits viscous response to the capillary action. The apparent
viscosity of the compact increases due to elimination of porosity; as a consequence, the
densification rate decreases continuously. Full density by rearrangement is possible if
enough liquid is formed. Rearrangement may be inhibited, if rigid particle contacts
formed through compaction or solid-state diffusion are present.
2.5.4.3 Dissolution-Precipitation
As densification by rearrangement slows, solubility and diffusivity effects become
dominant. The solubility of a grain in its surrounding liquid varies inversely with the
grain size: small grains have a higher solubility than large ones. The difference in
solubility establishes a concentration gradient in the liquid. Material is transported from
the small grains to the large grains by diffusion through the liquid. The net result is a
progressive growth of the larger grains at the expense of the smaller grains, giving fewer
grains with a larger average size. This allows the growing grains to better fill in space.
2.5.4.4 Final densification
In the final stage, liquid-phase sintering is controlled by the slow densification of
the rigid solid structure. Processes dominant in this stage have been active earlier, but
only become significant late in the cycle. Microstructural coarsening continues and the
residual pores enlarge if they contain trapped gas, giving compact swelling. In general,
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