Sintering of bimodal alumina powder mixtures with a nanocrystalline component

Packing characteristics and sintering behavior of the bimodal mixtures of nanocrystalline (75 nm) and conventional (1 mu m) alumina powders were investigated. Green density of the pure nanocrystalline compact was lower than that of the pure coarse particles. Increase in the packing density was observed at 70% coarse particle composition. The powders shrinkage characteristics were determined by dilatometry. The cold pressed compacts were sintered within the temperature range of 1300 degrees C to 1600 degrees C. The green density followed the packing rules giving rise to higher packings in the bimodal compacts. At temperatures below 1400 degrees C, the relative density kept this pattern. Above 1400 degrees C, this advantageous densification was lost. The changes in densification of the compacts versus powder composition and sintering temperature were discussed with respect to phase transition and sintering in the compacts. (C) 1999 Acta Metallurgica Inc.