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

and advanced. These technologies allow us to produce powder . The mechanical deformation of particle shape
[15]
innovative components that were previously impossible to is largely caused by laser heat exposure that welds satellites
make. In the biomedical sector, surgeons currently replace to particles . This result has also been confirmed by Park
[16]
various human body components with 3D parts [1,2] . et al. Furthermore, Popov et al. claimed that satellites
[17]
[16]
Laser powder bed fusion (L-PBF) and electron beam exist in virgin powder, but that the bonding of satellites
melting (EBM) are the most commonly used metallic AM with particles, which produces agglomerations, is induced
technologies, and both use the same printing process . by the sieving process.
[1]
They begin by spreading a fine layer of powder across the Rock et al. also investigated the impact of spatters
[18]
build plate. Then, either a laser or an electron beam melts on PSD and particle morphology. They concluded that the
the powder. Next, the build platform descends to allow the particle morphology of virgin powder differs significantly
next layer of powder to be spread and melted, and this cycle from that of powder recycled 10 times. They also
repeats until the 3D part is complete. The difference between discovered that, despite the fact that the sieving process
these two technologies is the energy source: L-PBF uses a removes the majority of spatters, some do infiltrate the
laser to melt the powder, whereas EBM requires an electron feedstock powder. Consequently, the spatters are extremely
beam . The main methods used to produce AM powders are likely to affect the powder and the mechanical properties
[1]
gas atomization, induction melted bar atomization, plasma of the manufactured part. Rock et al. and Anwar and
[18]
atomized wire, plasma rotating electrode atomization Pham both claimed that despite the gas flow effect,
[14]
and water atomization, among others. Each process has spatters are candidates for melting and incorporation into
advantages and disadvantages in terms of powder properties. a component if ejected into a laser pattern.
For example, water atomization produces particles with [10]
irregular shapes and wetness [3-5] . Herzog et al. also reported Moreover, according to Sutton et al., laser spatters
[6]
an increase in oxygen content associated with powder and solidified particles, also known as ejecta or heat-
produced by water atomization, whereas the gas atomization affected powder, are responsible for compromising the
process reduces the risk of oxidation and contamination [6-8] . morphological and chemical properties of reused powder.
Plasma atomized wire produces a high-quality powder with Spatters not only contaminate the powder bed when they
a high ratio of spherical particles, high powder density, and are ejected, but also affect the mechanical properties
low porosity [3,9] . of the next part printed when they are deposited over
its laser pattern. Furthermore, the very small spatters
The printing process itself has a significant impact on traveling through the sieve device can influence the
powder features, particularly the particle-size distribution morphology of recycled powder and increase its oxygen
(PSD), chemical composition, and morphology. When concentration. In addition, Tan et al. explained a defect
[5]
a laser melts the powder, it produces spatters and heat- called the balling effect that occurs in the L-PBF printing
affected particles, which deposit on the powder bed, process when laser power is not properly adjusted. Balling
affecting the nearby portion of the powder bed [10,11] . This is affects melt pool formation and produces partially melted
especially the case when printing lattice parts, which offer powder. Consequently, it enhances porosity inside parts
the multiple advantages of energy absorption, lightweight and affects their surface roughness. Furthermore, Powell
construction, excellent mechanical and thermal properties, et al. showed that the handling and removal procedure
[19]
and reduction of material consumption . However, it has can impact powder properties. The unfused powder
[12]
been argued that printing this type of structure accelerates can be easily polluted by impurities such as fibers, dust,
powder bed contamination and degradation by producing and other pollutants transported by ambient air during
a considerable number of spatters . the handling, cleaning, and sieving processes. Thus,
[13]
Anwar and Pham studied the effects of inert gas when sieve devices and procedures are not effective,
[14]
flow velocity and scanning direction on the formation and the sieved powder can be polluted. Contamination can
accumulation of spattered powder. Their research showed also be caused by the presence of foreign material in the
that flow velocity affects the accumulation of spatters dispenser. For example, after a material change, some
on the build plate. They also underline that scanning in particles of the previous material can be mixed with
the direction of the gas flow significantly decreases the the newly loaded material. Soundarapandiyan et al.
[20]
accumulation of spatters over the powder bed. The presence reported a severe contamination scenario caused by the
of spatters on the powder bed must be minimized as much presence of Inconel 625 particles in the aluminum powder
as possible since it not only increases the percentage sample, which resulted in mechanical component failure.
of porosity within the printed component, but is also Storage techniques are also critical for preserving powder
responsible for modifying the morphology of recycled quality. When a reactive powder is not stored in an inert

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