Properties of reactive Al:Ni compacts fabricated by radial forging of elemental and alloy powders

We explore rotary swaging of powders into solid compacts as an inexpensive means of producing reactive materials with refined microstructures and improved properties. Rotary swaging is a cold forging process that reduces the diameter of tubes, and in this study the tubes are packed with reactive combinations of elemental and alloy powders. The diameter reductions create a nearly fully dense compact from the powders and also reduce the average reactant spacing through plastic deformation. The extent of diameter reduction controls the microstructural refinement, observed through cross-sectional imaging. We correlate the observed changes in microstructure with reaction properties that are characterized using differential scanning calorimetry (DSC), hot-plate ignition studies, and velocity measurements. Exothermic peaks in DSC scans all shift to lower onset temperatures; hot plate ignition temperatures decrease; and reaction velocities rise as the degree of swaging is increased. We vary the shape of the initial reactants by substituting Ni flakes for Ni powders and find no improvement in microstructure or reaction properties, due to clumping of the Ni flakes during the initial compaction steps. We also vary chemistry by substituting Al-Mg alloy powders for Al powders and find that the alloy powders yield lower DSC exothermic peak temperatures, lower ignition temperatures, and higher reaction velocities compared to similar compacts with pure Al powders. This combination of results suggests that rotary swaging is an effective technique for producing reactive materials at low cost.