Densification of powder mixtures containing soft and hard components under static and cyclic pressure

Abstract

The effect of pressure cycling on the densification and ejection of Pb-Al2O3 powder mixtures is investigated and compared to static loading. The volume fraction of Al2O3 is varied between 0 and 80%. The density of all mixtures increases with time under constant pressure even at room temperature. This mechanical behavior is the result of the creep of lead. This effect diminishes with increasing volume fraction of Al2O3. Pressure cycling does not have any influence on the final density of lead samples in the absence of Al2O3. The influence of cycling becomes, however, noticeable in the presence of Al2O3 in the mixture. In this case, the density and strength of specimens are higher than the corresponding ones obtained after static pressing for the same dwell time. This effect is enhanced with increasing Al2O3 percentage. A static pressure approximately 50-80% larger than the cyclic one is required to achieve the same density. Moreover, the strength of compacts with high Al2O3 content is substantially higher after cyclic pressing than under static pressing. The ejection force is higher after cyclic compaction at a given pressure level owing to the higher density achieved.