Pressure sintering by power law creep

During the pressure sintering of a powder compact, one of the more important contributions to densification is that of power-law creep. We calculate first the contribution of power-law creep to final stage densification; it is modelled by considering the voids as spherical holes surrounded by thick spherical shells of solid material which flow by power-law creep. The result gives a plausible explanation of the experimental observations of Urick and Notis on the densification of CoO, and in the limit of Newtonian viscosity, becomes identical with certain other published densification equations.At a rather earlier stage of sintering the voidage may be better described by connected cylindrical holes than by spheres. We calculate the densification-rate during this intermediate stage of sintering by-considering a thick cylindrical shell which undergoes power-law creep.Finally, we calculate the densification-rate (and the density itself) during the initial stage of sintering, when powder particles in the compact are still discrete and touch their neighbours over small areas of contact. Again we consider only the contribution of power-law creep, and modify a result due to Johnson (which has been successful in interpreting hot hardness tests) to calculate how creep allows the particles to press into each other, and causes the compact to densify.Throughout the text, a steady-state creep law has been used. An appendix lists the results when this is replaced by a time-hardening creep law.