Improved Densification and Uniformity of Composite Powder Compacts due to Pressure Cycling

The effects of pressure cycling on the densification of composite powder compacts have been investigated. Mixed powders of lead (Pb) and various amounts of alumina (Al2O3) were consolidated under static and cyclic loading at room temperature in constrained uniaxial consolidation experiments. The experiments show that the fractional density dramatically decreases with increasing volume fraction of alumina in static compaction. In contrast, the compacts subjected to a large number of loading cycles where the pressure varied from zero to a constant maximum value show that similar results are obtained at low volume fraction of alumina, however, much higher fractional densities are obtained at high alumina contents. Additionally, increasing the amplitude of the compaction pressure cycle and the number of cycles significantly increases the compacted fractional density, but changes in the frequency have relatively little effect at the same number of cycles. Green composites fabricated under cyclic pressure also have significantly increased hardness and green strength relative to those produced in static compaction. Cyclic application of pressure also leads to more uniform density distributions.