050

Title:

Spherical composite powders of metals and alloys for additive manufacturing of reactive structural materials

Discipline: Energetic Materials

Presenter:

Daniel Hastings

Abstract:

Our recent work showed that mechanical milling of powders of different materials in the presence of two immiscible fluids as process control agents may yield composite spherical particles. Because of their excellent flowability, such composite spheres are attractive feedstock materials for additive manufacturing. Spherical powders are less prone to clogging nozzles in extrusion/ink printers and spread in controllable layers for laser sintering. This effort is aimed to produce spherical aluminum and aluminum-titanium composite powders that serve as AM feedstock. Aluminum spheres were prepared and examined by scanning electron microscopy, nitrogen porosimetry and laser diffraction based particle size analysis. The spheres comprised porous agglomerates of flakes of different dimensions. Thermogravimetric analysis demonstrated that in dry oxygenated environments, reactivity of spherical composites approaches that of nano-aluminum. At the same time, it was observed that, unlike nano-aluminum, composite spheres contain a high fraction of active aluminum leading to a much greater degree of their oxidation when heated to 1100 °C. Isothermal microcalorimetry performed at 80% relative humidity suggests spherical aglomerates age less rapidly than micron-sized aluminum powder. The high reactivity at elevated temperatures and stability at lower temperatures, make these new powders attractive for energetic formulations. Initial experiments additionally showed that the prepared composite powders can be ignited and burn readily in air without aerosolization. The reactivity of the spheres increased for samples prepared with longer milling times while commercial powders cannot be ignited in the same experiments. Composite spheres of aluminum and titanium have also been prepared; presently, they are being characterized.

Author(s):

Daniel Hastings, Mirko Schoenitz, Edward Dreizin

Funding Acknowledgements:

Air Force Office of Scientific Research