Effect of powder size distribution on densification and microstructural evolution of binder-jet 3D-printed alloy 625

Binder-jet 3D-printing is a powder bed additive manufacturing process that selectively deposits binder on a powder bed layer-by-layer to fabricate a green part followed by a sintering step for densification. Gas-atomized alloy 625 powders of three different powder size distributions including 16-63 pm (full), 16-25 pm (fine) and 53-63 jim (coarse) powders were 3D-printed with green relative bulk densities of about 52%, 45% and 48%, respectively, followed by vacuum-sintering at temperatures between 1225 and 1300 degrees C for 4 h. For the fine and coarse powders with narrow size distribution, printing defects with high pore coordination numbers may form during the binder jetting process which cannot be removed during the final sintering stage even during supersolidus liquid phase sintering. However, the full particle size distribution gave higher green density with fewer large, highly coordinated pores so supersolidus liquid phase sintering was able to reach near-full density. Additionally, the fine powders gave non-uniform, anisotropic linear shrinkage during sintering which is unfavorable for designing complex structures. The results suggest that particle size distribution is a determining factor for supersolidus liquid phase sintering, pore removal and final microstructure, if printing parameters such as layer thickness, binder saturation, printhead binder droplet size and drying time are similar. (C) 2018 Published by Elsevier Ltd.