Page 150 - MSAM-4-2

Materials Science in Additive Manufacturing Bi-modal powder spreading behavior of ceramics

and printing parameters were kept constant to isolate the
effect of powder properties themselves. Subsequently, the
powder bed density was measured using a density cup, and
the relative density of the green parts was evaluated based
on the printed samples. Some of the major findings from
this study are given below:
(i) Smaller powders (1 µm and 5 µm) exhibited
markedly improved flow characteristics when used
at elevated temperatures, reducing moisture-induced
agglomeration. On the other hand, coarser powders
(10 µm and 20 µm) displayed excellent flowability
across both room and higher temperatures.
(ii) Discrete element simulations and experiments
revealed that, for the bimodal powder (5 µm and
20 µm), finer particles settled at the start of the
spreading direction. In comparison, larger particles
migrated toward the trailing edge, inducing a spatial
gradient in powder size distribution.
(iii) The powder bed packing density also dropped in the
Figure 7. Comparison of packing density and part relative density along spreading direction. Particularly, regions dominated
the X- and Y-axes at different axis positions. Packing density and part by smaller particles showed denser packing, whereas
relative density along the X-axis show a decreasing trend in the spreading
direction, indicating non-uniform powder spreading and part density the larger particle-dominated regions showed lower
packing density, resulting in a packing density gradient
the amount of powder ejection was larger than the binder along the spreading direction.
residue after curing. Previous studies also showed that (iv) Local fluctuations in powder bed packing density
smaller powders lead to higher green density. 7,81,82 were reflected in spatial variations of green part
density, mirroring the same pattern of packing density
These results demonstrate that PSD directly affects the observed in the powder bed.
green part properties. Finer particles contribute to higher
local packing density and, thus, yield higher relative density These findings highlight the critical influence of
in the printed part, while coarser regions exhibit lower PSD, temperature, flow behavior, and powder spreading
density. This spatial variation can be strategically used to behavior on powder bed uniformity, packing density, and
design parts with location-specific properties. This graded green part density. The observed preferential deposition
density can potentially optimize mechanical properties, for of smaller powders, coupled with differential packing
instance, densifying certain regions for superior strength densities, signifies the importance of addressing spatial
while maintaining lower density in others for lightweight inhomogeneities in powder bed-based AM. Furthermore,
design or thermal management. this phenomenon opens up the possibility of fabricating
parts with functionally graded densities.
4. Conclusion Acknowledgments

AM processing physics in powder bed processes like BJT
are readily affected by the powder bed spreading process The authors would like to acknowledge Denka Chemicals
and characteristics. This study systematically investigated GmbH, Tokyo, Japan, for their support in supplying all the
the flowability of unimodal alumina powders (1 µm, 5 µm, powders used in this study.
10 µm, and 20 µm) to choose a bimodal powder that shows Funding
the highest packing density. The 5 µm and 20 µm powders
with a 4:1 volume-to-percentage ratio were chosen based This work was partially supported by NSF CMMI Award
on the DEM simulation to formulate the bimodal powder. #1944120 and partially funded by Applied Research Laboratory,
This bimodal powder was used for further powder bed Penn State, through the Walker Student Fellowship.
formation and printing experiments. Powder samples were
collected from a powder bed deposited in a BJT machine Conflict of interest
that uses an overhead feed system and a roller-based Guha Manogharan serves as the Editorial Board Member
powder spreading mechanism, where all the spreading of the journal, but was not in any way involved in the

Volume 4 Issue 2 (2025) 11 doi: 10.36922/MSAM02510016