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 mu m with respect to nano particle concentration and mixing time. The dynamic angle of repose of a 0-90 mu m 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 pm and 0-90 mu m 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. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Adding nanosized SiO2 to gas-atomized CoCrFeNi powders can improve flowability and bulk density, with a reduction in dynamic angle of repose and an increase in powder density observed. However, the effect of nanoparticle concentration, mixing time, and Bond-number on powder flowability and porosity should be carefully considered in the additive manufacturing process.