determines the quality of the powder bed and, consequently, affects the quality of the manufactured
part. However, powder spreading behavior under additive manufacturing condition is still not clear. Here, we studied particle-scale powder
dynamics during the powder spreading process by using in-situ high-speed high-energy x-ray imaging.
Evolution of the repose angle, slope surface speed, slope surface roughness, and the dynamics of
powder clusters at the powder front were revealed and quantified. Interactions of the individual metal
powders, with boundaries (substrate and container wall), were characterized, and coefficients of friction
between the powders and boundaries were calculated. The effects of particle size on powder flow
dynamics were revealed. The particle-scale powder spreading dynamics, reported here, are important
for understanding of powder spreading behavior, and for the development and validation of models that can
accurately predict powder spreading behavior.