Effect of compaction density on foamability of Al–TiH₂ powder compacts

Abstract

Al-TiH₂ powder mixtures have been cold compacted into precursors for foaming using single action, uniaxial pressing. After heat treatment, at 800°C for 5 min, foaming was only observed for precursors with a theoretical density above 94%. This density limit corresponds to the transition from interconnected to closed porosity, confirming that isolating porosity and enveloping the foaming agent in the matrix are vital to successful foaming. Although the variation in foam density for similar samples was small, the cell structures were different indicating that a low variation in foam density is not necessarily a good indication of achieving reproducible foam structures. The orientation of the sample had little effect on the foaming response for compacts with a length to diameter ratio below 1:2. For longer samples the foaming response was not uniform along the length of the sample indicating that in complex pressings the variation in local pressure must be understood in order to avoid regions being compacted below the critical density for foaming.