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Engineering Science in
Additive Manufacturing Reusability of Ti6Al4V powder in LPBF

different study, where several different shapes were all three stages of the powder, with an increasing number
printed; however, the overall volume of the printed area of defects in the higher stages of use, despite the use of
was approximately the same. The Ti6Al4V (Ti64) powder sieving on the recollected powder. Hand counting of the
was procured from AP&C (GE Additive, Cincinnati, Ohio, particles revealed a rapidly increasing number of defects
USA) with a size range of 15 μm to 45 μm. Powders were in the powder that made it through the sieve, as the size of
collected after each print and weighed before sieving. The the defects was still small enough to pass through the sieve.
powder was then sieved and weighed again to determine These defective particles are displayed in Figure 1A-C,
the amount that could be reused in the next print. The mesh even in the new powder supplied by the manufacturer.
size used for sieving was a 230 mesh in a 200 mm round This can be due to the difficulty during the manufacturing
sieve. The sieving process was done by placing ~500 g of process in achieving completely spherical particles. During
powder in the sieve and then sieving for 10 min. This was the manufacturing process, as the molten spheres of metal
done after every print, with the used powder being passed are being cooled, collisions can occur, leading to defects
through the sieve once before using the powder to print in the new powder. Most of the defects would be caught
again. This sieving process could have been adjusted with if they end up being larger than the mesh size of the sieve.
a 325 mesh size to maintain the large particles at 45 μm as However, the defective particles that are smaller than the
they were received from the manufacturer, instead of letting upper bound of the mesh could cause flowability issues.
the larger particles through with the 230 mesh. Five prints In Figure 1A, the displayed powder contains some small
were run, and three states of the powder were examined. defects with an average of the percentage of the particles
From the prints, two sets of parts were examined, and the that are defective from a relatively spherical shape, and
microhardness of the parts was determined, as no print no welded particles gave a value of 8.8 ± 0.9% defective
ran for the final powder state. From the powder, samples particles over four SEM scans. This strategy for determining
were taken from the as-purchased fresh, 3-use, and 5-use the percentage of defects was applied to the other two sets
powders, with only the as-purchased powder for the new of powder, with all values for the percentage of defective
sample being examined. Imaging of the used and virgin particles in all three batches listed in the second column of
powder was performed using a field-emission scanning Table 1. In the new powder, most defects originate from tiny
electron microscope (FESEM; FEI Siron, Portland, USA) particles that are welded onto larger particles, with fewer
for both the >63 μm and <63 μm powder collected after defects being caused by larger particles that are welded or
each print. The images were then used to evaluate the misshapen during the manufacturing process. The 3-use
percentage of defects in the <63 μm and virgin powder. The powder in Figure 1B contains less of the much smaller
defective particles were separated into two groups, with particles welded to larger particles and instead is primarily
one being the misshapen particles and the other being the composed of misshapen particles with a higher proportion
particles that were welded together. Misshapen particles of particles that are of the same size being conjoined to
were determined by whether the particles were no longer each other, with the average amount of defects in the 3-use
spherical. For the welded particles, they were determined by powder being approximately 6.4% higher than that of the
whether the particles were two or more conjoined particles new powder. The five powders in Figure 1C contain an
with a minimum size of 5 μm. Hardness was measured even higher amount of the conjoined particles, with the
using a Phase II Plus Micro Vickers Hardness Tester (Phase average size of the particles being larger than the prior sets
II Plus, USA) on a ground and polished section of a part of powder. The percentage of particles with defects in the
from the four prints. Imaging of the microstructure for 5-use powder set was 10.6% higher than that of the new
examining the porosity of printed samples was performed powder. This increase in defects could have been reduced
using a Keyence 6000 series optical microscope (Keyence, by using a sieve size of approximately 45 μm, which is the
Itasca, IL, USA) on the ground and polished surface of the high end of the initial distribution from the factory. These
samples. MATLAB was used for analyzing the scanning
electron microscopy (SEM) imaging of the <63 μm powder Table 1. Characterization of powder samples and part
size distribution. A piece of equipment with a metal funnel, hardness
platform, and a mounted protractor was used to determine Sample Percentage Percentage of Powder’s Printed
the angle of repose of the powder. of powder recollected distribution part’s
defects powder values D10, hardness
3. Results and discussion (%) <63 μm (%) D50, D90 (μm) (HV0.2)

3.1. Ti64 powder analysis New 8.8±0.9 100 13.5, 24.2, 38.9 396±41
Defect characterization, conducted using SEM, MATLAB, 3-Use 15.2±1.8 96.9±1.3 16.2, 26.7, 39.6 385±27
and manual counting, revealed the presence of defects in 5-Use 19.4±3.3 <95 15.9, 31.3, 45

Volume 1 Issue 4 (2025) 3 doi: 10.36922/ESAM025420028