ABSTRACT
This chapter considers several important issues that are not taken into account in the simple sintering models. Rayleigh instability effects can arise and influence the morphological stability of continuous second phases in microstructures produced by solid-state and liquid-phase sintering. A common feature of such inhomogeneities is that they become exaggerated during sintering, often leading to a reduction of the densification rate and to the development of large pores or cracklike voids during sintering. When the sintering data for ceramic matrices with controlled amounts of rigid inclusions are compared with the predictions of the rule of mixtures, drastic deviations are found, particularly for polycrystalline powder matrices. The effect of percolation on the rigidity of the composite is an important factor since this will influence the sintering kinetics. When the effects of transient stresses and network formation between the inclusions are taken into account, the models appear to provide a reasonably good description of viscous sintering with rigid inclusions.
