Page 126 - MSAM-2-3

Materials Science in Additive Manufacturing Powder alteration caused by L-PBF process

atmosphere, particles are more likely to come into contact while a powder with a narrower PSD has better flowability
with the ambient air. As a result, the powder is exposed and produces components with optimal tensile properties
to corrosion, oxidation, and contamination . Aside from and hardness. Moreover, it has been demonstrated
[19]
these factors, the chemical properties of the powder change that powder properties are not uniform throughout all
significantly after multiple reuse cycles. Tang et al. regions of the powder bed. Pal et al. investigated the
[21]
[28]
observed an increase in oxygen content while aluminum evolution of L-PBF Ti-6Al-4V and Co-Cr-W-Mo powder
and vanadium percentages remained stable in Ti-6Al-4V characteristics and mechanical properties of specimens
powder after 21 printing cycles on an EBM machine. Popov printed in two different locations over the build plate. For
et al. also observed oxygen pickup in titanium powder, both materials, powder near the dispenser (position 1)
[16]
which exceeded the maximum ASTM F2924-14 (2014a) had more fine particles and a better spherical shape than
standard after 69 prints in an EBM process. Park et al. powder near the collecting bin (position 2). Parts printed
[17]
validated prior findings for the same material in a selective in position 1 showed greater density and smaller pores,
laser melting process across 38 cycles, with an increase in resulting in higher tensile properties than specimens
oxygen and nitrogen content exceeding titanium Grade 23 printed in position 2.
standards. It is also worth noting the change in powder The condition and properties of the powder have
particle size that occurs due to reusing powder. O’Leary a significant impact on the quality of the printed part.
et al. noticed a significant drop in the proportion of According to recent studies [1,29] , the spherical particle
[22]
fine particles <15 µm in diameter and an increase in the shape is ideal for metal AM because it improves powder
number of larger particles over 45 µm in diameter after flowability. Mechanical properties such as tensile strength,
recycling Ti-6Al-4V powder 5 times in an L-PBF process. yield strength, surface roughness, and dimensional
They also observed that powder surfaces became rougher accuracy are also improved by the spherical shape. Liu
and less spherical. Similar results were achieved with AISI [27]
304L stainless steel powder by Sutton et al. who revealed et al. found that powder with a wide PSD improved
[23]
an increase in particle diameters after 5 reuse cycles. powder bed density, part density, and surface finish, while
powder with a narrower PSD produced parts with higher
Continuous refreshing or collective aging are two tensile properties and hardness. Zhang et al. reported
[30]
recycling techniques used in AM. In powder refreshing, that Er (erbium)-modified 7075 aluminum alloy powders
the quality of recycled powder is determined by the prepared by ball milling reduced crack failure. However,
percentages of virgin and reused powder utilized in the the Er particles present in the melt pool drastically affected
mix. Tan et al. showed that combining 75% virgin the flowability and increased the porosity of the part.
[5]
powder with 25% reused powder results in an excellent The aforementioned studies revealed changes in powder
flowability that is comparable to 100% virgin powder. In characteristics and mechanical qualities of manufactured
the collective aging technique, the depositing and mixing components caused by the AM process itself, particularly
methodologies for combining dispenser powder with powder degradation induced by laser heat exposure and
reused powder have a substantial impact on the quality of powder reuse cycles [11,13,31-36] .
printed components. [24]
However, in the literature published to date, the
It is crucial to emphasize that changes in physical powder influence of the geometry of printed parts as well as their
characteristics, specifically PSD and morphology, have an positions over the build plate on the evolution of powder
impact on both the rheological powder characteristics and characteristics remains unclear and sparsely discussed.
the mechanical performances of completed parts [21,25,26] . Therefore, this study investigated the influence of part
Brika et al. investigated the impact of geometrical geometry, part location and proximity of the printed
[9]
particle characteristics on both rheological properties and parts on the contamination of the powder bed and on
mechanical performances of printed parts, and showed that the recycled powder. The study also examined the extent
using extremely spherical powders substantially improved to which lattice structures speed up powder degradation.
powder flowability, powder density, and part density. It also Maraging steel powder was mainly used in the experiments
increased mechanical properties, namely ultimate tensile because very few studies had been conducted to investigate
strength, and yield strength, as well as surface roughness the contamination and recycling of this material.
and dimension accuracy. Furthermore, Liu et al.
[27]
reported that variation in powder PSD was responsible for 2. Materials and methods
differences in powder quality and mechanical properties.
Powder with a wide PSD provides better powder bed 2.1. Materials
density, higher density parts under low laser energy The powder used was EOS Maraging Steel MS1 (18%
intensity, and smoother surface finishing on components, Ni Maraging 300). The material data concerning its

Volume 2 Issue 3 (2023) 3 https://doi.org/10.36922/msam.1781