Page 58 - ESAM-1-4

Engineering Science in
Additive Manufacturing Reusability of Ti6Al4V powder in LPBF

to flow off the edge of the platform. The new powder had the representative defects are displayed in Figure 4. These
the highest angle of repose at 27.8 ± 1°, while the two used parts displayed lack-of-fusion pores in all samples with
powders had lower angles of repose at 24.6 ± 1° and 25.6 ± the new powder, resulting in very few defects. In contrast,
0.4° for 3-use and 5-use powders, respectively, as displayed the 3-use powder resulted in a greater lack of fusion pores,
in Figure 3A. These values show that the new powder has as indicated by the dark pores in Figure 4B. For the new
slightly less flowability than the used powder. This could powder parts, there were very few pores across the entire
be due to the change in particle size, primarily the increase polished surface, whereas the parts printed with the 3-use
in all sizes across the powder distribution range, and the powder had more lack-of-fusion porosity. These are due to
disappearance of very small particles in the used powders. the increasing particle size and the lack of small powders
This disappearance of the small particles in the used (<10 μm) in the used powder, leading to a lower packing
powders could be the cause of the lower angle of repose, density and, ultimately, an increase in the lack-of-fusion
with the lack of small particles to fill the voids between the defects. Although it has been demonstrated by Alamos
larger particles, thus leaving gaps between particles that et al., that there is no noticeable change in the fatigue
39
allow the larger particles to continue to move and flow life of reused Ti64 powder, our results do not support
better while having a lower packing density. This does end such conclusions and need more careful studies to fully
up with better flowability, but it could be speculated that understand the influence of these porosities on the static
the powder will have a worse packing density, leading to and dynamic mechanical properties of AM-processed Ti64
higher amounts of defects in the finished part. parts. 40,41
3.2. Printed part quality and microhardness The hardness of the parts was also tested. The values

The part quality was determined by examining the for the two parts tested, as shown in the fifth column
ground and polished sections of a part from each print. of Table 1, reveal no noticeable differences between the
These sections were examined for defects in the parts; parts despite the change in color of the used powders,
which is due to a slightly higher number of oxidized

A B particles resulting from the increase in defects. Although
this increase in the number of oxidized particles did not
affect the hardness, it has been shown that the increased
oxidation does have an effect on the embrittlement, as
demonstrated by Meier et al., though it could be another
42
reason for the increased number of lack-of-fusion pores in
the printed parts.
Figure 2. New Ti64 powder and the rejected powder from the 3-use
powder were imaged with an SEM at 200× magnification. (A) New Our results indicate that standard tests like hardness
as-purchased powder. (B) Rejected 3-use powder. measurements may not be appropriate to measure the part

A B

Figure 3. Angle of repose data and testing equipment used for Ti64 powder. (A) Angle of repose for the three powder conditions (n=5). (B) The overall
setup for the testing, with an inset showing a measurement being taken at 60° on the protractor, resulting in an angle of repose of 30°.

Volume 1 Issue 4 (2025) 5 doi: 10.36922/ESAM025420028