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

Abstract

a b s t r a c tWe 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.

SHS in Ni/Al Nanofoils: A Review of Experiments and Molecular Dynamics Simulations

“…In addition to magnetron sputtering, mechanical processing of the thermite‐type RMNFs are developing, including Al–Cu 2 O–Cu or Al–NiO, Al–CuO, and Al–Cu 2 O systems . Some new mechanical approaches, like radial forges, have been applied to the Ni–Al system in order to produce dense reactive materials . In the field of systems with elemental components (reactions of synthesis from elements), research also continues.…”

Exothermic Reaction Kinetics in High Energy Density Al-Ni with Nanoscale Multilayers Synthesized by Cryomilling

“…The thermodynamic modification is therefore necessary to improve its usability and reliability. Several reactive Al-Ni systems have been produced by methods like combustion synthesis [8], mixing and pressing of powders [9,10], welding [11,12], forging [13], rolling [14,15], vacuum deposition [11,15], cladding [16], and high energy ball milling [17][18][19]. It is well-known fact that the reactivity of these composites depends strongly on their corresponding microstructures.…”

Reactive Structural Materials: Preparation and Characterization

“…Perhaps the most studied composition is based on nickel and aluminum with the TMD of 6.95 g cm −3 for the stoichiometric composition containing 31.5 wt% of Al and 68.5 wt% of Ni. The composites were prepared by cold pressing, with densities in the mid to low of 90% of TMD, radial forging, and by cold spray, although the powders were ball‐milled prior to spraying . A combination of hot isostatic pressing (HIP) with monitoring heat release in the consolidated sample was used to prepare low‐porosity, RSM components, while retaining their micro‐structure and reactivity in the consolidated shapes.…”

“…Fully dense composites suitable for RSM applications have been prepared by mechanical processing bulk metals or packed powders using swaging, a cold forging process reducing diameter of tubes . The scale of mixing achieved in such a processing and the structure of the layered system are illustrated in Figure for a composite prepared from nickel flakes with powders of aluminum and magnesium.…”

“…Minor porosity is observed. Most of pores appear between Ni flakes and at boundaries between Ni and Al …”