Dynamic powder compaction of some rapidly solidified crystalline and amorphous powders: Compaction characteristics

Abstract

A range of powders was quantitatively studied using two dynamic compaction machines with different loading rates. One used shock wave reflections to achieve high pressures, the other used a single shock to maximize interparticle melting. Quantitative compaction parameters were determined for both dynamic techniques and for static compaction. Such data is essential if good quality dynamic compactions are to be economically produced. The powders investigated include planar flow cast aluminium and iron as well as sponge iron and a fine tungsten powder. In the case of iron, the soft sponge powder showed a similar final density, irrespective of the compaction technique, while the hard amorphous powder showed a large dependence on the technique used. This was slightly reduced when this powder was softened by crystallization. For all the powders at a given pressure, dynamic compaction resulted in a much higher density than static compaction, especially for the amorphous iron. For the hard powders, higher densities were obtained by the single, rather than by the reflected shock machine. Complete densification and interparticle melting was achieved for several of the powders, others achieved densification, but the impact energy was insufficient for interparticle melting. Shock hardening occurred in most cases. For the sponge iron and tungsten the hardness was doubled compared with the starting powder. No increase was found for the hard amorphous iron, which previously has been shown not to work harden. The hardness of copper powder doubled when compacted by the reflected shock technique, but not for the single shock compaction, which produced a sufficiently high average temperature rise to anneal out any hardening.