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The cohesive interactions between fine metal powder particles cruciallyinfluence their flow behavior, which is in turn important to many powder-basedmanufacturing processes including emerging methods for powder-based metaladditive manufacturing (AM). The present work proposes a novel modeling andcharacterization approach for micron-scale metal powders, with a special focuson characteristics of importance to powder-bed AM. The model is based on thediscrete element method (DEM), and the considered particle-to-particle andparticle-to-wall interactions involve frictional contact, rolling resistanceand cohesive forces. Special emphasis lies on the modeling of cohesion. Theproposed adhesion force law is defined by the pull-off force resulting from thesurface energy of powder particles in combination with a van-der-Waals forcecurve regularization. The model is applied to predict the angle of repose (AOR)of exemplary spherical Ti-6Al-4V powders, and the surface energy valueunderlying the adhesion force law is calibrated by fitting the correspondingangle of repose values from numerical and experimental funnel tests. To thebest of the authors' knowledge, this is the first work providing anexperimental estimate for the effective surface energy of the considered classof metal powders. By this approach, an effective surface energy of $0.1mJ/m^2$is found for the investigated Ti-6Al-4V powder. This value is considerablylower than typical experimental values for flat metal contact surfaces in therange of $30-50 mJ/m^2$, indicating the crucial influence of factors such assurface roughness and chemical surface contamination on fine metal powders.More importantly, the present study demonstrates that a neglect of the relatedcohesive forces leads to a drastical underestimation of the AOR and,consequently, to an insufficient representation of the bulk powder behavior.

Modeling and Characterization of Cohesion in Fine Metal Powders with a Focus on Additive Manufacturing Process Simulations