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

The effect of pressure cycling on the densification and ejection of Pb-Al2O 3 powder mixtures is investigated and compared to static loading. The volum e fraction of Al2O3 is varied between 0 and 80%. The density of all mixture s increases with time under constant pressure even at room temperature. Thi s mechanical behavior is the result of the creep of lead. This effect dimin ishes with increasing volume fraction of Al2O3 Pressure cycling does not ha ve any influence on the final density of lead samples in the absence of Al2 O3 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 t he same dwell time. This effect is enhanced with increasing Al2O3 percentag e. A static pressure approximately 50-80% larger than the cyclic one is req uired 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. (C) 2000 Acta M etallurgica inc. Published by Elsevier Science Ltd. All rights reserved.