(568e) Spherical Composite Powders As Feedstock for Additive Manufacturing

Our recent work showed that mechanical milling of powders of different materials in presence of two immiscible fluids as process control agent may yield composite spherical particles. It is hypothesized the fluids form a suspension so that spherical composite powders form after emulsified droplets capture and retain suspended particles. Because of their excellent flowability, such composite spheres are attractive as feedstock material for additive manufacturing. This effort is aimed to develop spherical powders with morphology and composition suitable for additive manufacturing of reactive materials. In one approach, metal powders are milled in presence of molten tin and wax as two immiscible fluids. The experiment is aimed to encapsulate metal particles inside tin droplets and recover solidified tin-bound spheres containing densely packed reactive metal particles. An experimental setup is developed including a miniature attritor mill combined with a heater and an enclosure to perform the milling in an inert gas environment. The inert gas is needed to prevent the possibility of ignition of evaporating wax. The experiments are performed with different metal powders, varying the milling time and milling intensity adjusted selecting different ball to powder mass ratios and rotation rate of the impeller. In a different approach, core-shell spheres are desired, with the core being a reactive material and shell being a low-melting metal. An example could be Ti-core, Al-shell particles. Preparing core-shell spheres relies on a staged milling in presence of two immiscible fluids, hexane and acetonitrile. The core powder is milled first and is expected to be encapsulated in emulsified acetonitrile droplets. The shell material is then added and milling continues. Initially, conditions are explored yielding spherical particles containing core material spheres. In follow-up experiments, preparation of core-shell spheres is targeted. This talk will present methodologies and results of the described effort.