Although metal foams -produced by the powder compaction technique- have been a subject of research for a long time, the influence of the compaction of powder mixtures on the evolution of a foam only played a minor role in previous investigations.
In this work foamable precursors are produced in four different ways: (i) by uniaxial hot pressing, (ii) by hot extrusion, (iii) via a combination of uniaxial compaction and rolling and (iv) by (newly adapted to foamable precursors) current-activated, pressure-assisted densification (CAPAD). In all cases, the quality of compaction is evaluated by measuring the density of the produced precursor, its electrical resistance and by evaluating its microstructure. Furthermore, the foaming behaviour is assessed by heating samples and observing foam evolution and expansion by means of X-ray radioscopy. Also pore formation and evolution were investigated by time-resolved X ray tomography.
We found that it is possible to reduce the required pressure by a factor of 6 to still yield a foamable precursor by using the CAPAD compaction compared to uniaxial hot pressing, but obtaining a slightly wider pore size distribution of the resulting pores. We assume an improved particle bonding thanks to an internal generated and locally concentrated heat at the particle contact points. The increased pore size may be generated by a partially activated blowing agent particles. But for the high required current density of about 4 A/mm², this technique has the potential to enable production of larger size precursors by uniaxial compaction.