Effect of cyclic pressure consolidation on the uniformity of metal matrix composites

Abstract

The cold compaction of ceramic-metal powder blends by the cyclic application of pressure improves compacted density. This enhanced densification has been attributed to a repeated generation of mismatch strain between the matrix and reinforcement phases, in a process similar to that seen in the thermal cycling of fully dense composites. It was postulated that cyclic compression may also reduce density gradients and improve overall uniformity. To test this hypothesis, aluminum and alumina powders were mixed and consolidated under both monotonic and cyclic loading at room temperature. Three aspect ratios were used and double-action compaction was included. X-ray computed tomography (CT) shows that the spatial density of uniformity improved during cyclic compaction. The distribution of ceramic particles was found to be more uniform following pressure cycling, especially for compacts having lower aspect ratios. A composite with 40 pct reinforcement achieved nearly uniform full density following double-action cyclic compaction. Cyclic compaction improves overall density as well as density uniformity and reinforcement distribution uniformity.