The influence of an increasing particle coordination on the densification of spherical powders

Abstract

The densification of spherical powders by cold compaction, hot-isostatic pressing and sintering can be described in terms of the shrinkage of the Voronoi cells associated lith the initial packing of the powder particles. The shape of the average cell is determined by the radial distribution function of a "random dense" packing of spheres. The advantage of this approach lies in its ability to explain luantitatively the continuous formation of new neighbours (increase in particle coordination'). Using simple constitutive relations for low temperature plasticity, diffusion, and power-lal creep, the effects of an increasing coordination on densification by these mechanisms are assessed. The results show that in pressing operations, with negligible contribution from diffusion, densification becomes increasingly more difficult than would be expected on the basis of constant coordination; that in sintering, on the other hand, densification rates are underestimated by two-sphere models.