Reducing cohesion of metal powders for additive manufacturing by nanoparticle dry-coating

Additive manufacturing processes, such as laser powder bed fusion, require steady powder processing but often exhibit poor flowability and low powder bed densities. Reducing the attractive Van-der-Waals force through nanoparticle coating can enhance initially poor flowability. We investigated the effect of dry-coating nanosized SiO2 on gas-atomized CoCrFeNi powders containing different amounts of particles < 20 μm with respect to nanoparticle concentration and mixing time. The dynamic angle of repose of a 0–90 μm powder reduced 50% and bulk powder density increased 30% with nanoparticle concentrations up to 0.153 wt.-%. The granular Bond-number was correlated with the powder flowability and porosity. The effect of mixing time was investigated with mixing two fractions 20–90 μm and 0–90 μm at a constant nominal nanoparticle surface area coverage of 128% for 2 to 1440 min. Short mixing times improved the flowability, while extensive mixing resulted in nanoparticle reagglomeration and deteriorated flow.