Page 40 - ESAM-1-2

Engineering Science in
Additive Manufacturing Multi-material additive manufacturing of metals

reactive chemical compounds, and contact with mechanical Ti-6Al-4V, and IN718 confirm that surface roughness
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components present in the build chamber (i.e., recoater). 110 worsens with powder reuse, potentially compromising
Powder degradation occurs due to thermal, fatigue resistance and overall component performance.
chemical, and mechanical effects, including but not Given this detailed understanding of powder
limited to dealloying, sintering, oxidation, deformation, degradation and its consequences, it is essential to explore
contamination, oxide deposition, particle fragmentation, the current state-of-the-art recycling techniques. These
and wear. The mechanisms are exacerbated by the intense range from mechanical to advanced approaches. For a more
heat input inherent in beam-based AM. LPBF and EB-PBF in-depth understanding, the authors recommend reviewing
techniques typically operate under vacuum or inert gas the articles by Lanzutti and Marin and Powell et al. A
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conditions, mitigating oxidation and cross-contamination range of powder recycling and rejuvenation techniques has
risks. LDED is more susceptible to such degradation as a been explored; conventional strategies include mechanical
result of relatively less controlled atmospheres. methods (e.g., sieving and centrifugal separation), thermal
treatment (e.g., vacuum degassing, re-sintering, and
The key contributing factor to powder degradation in
powder-based metal AM is its direct interaction with the conventional remelting), and chemical approaches (e.g.,
melt pool. The dynamic flow within the melt pool can lead acid and electrochemical etching). Emerging technologies
to the ejection of molten metals, resulting in the formation such as plasma cleaning and plasma spheroidization offer
promising methods as well. Plasma cleaning uses ionized
of metal jets, droplets, and powder spatter. These spatters, gas to remove surface contaminants (e.g., moisture and
rich in partially fused and oxidized particles, can further trapped gases), whereas plasma spheroidization reshapes
contaminate the powder bed, compounding degradation irregular powder particles to improve flowability and
across build layers. This understanding of degradation packing density.
mechanisms is crucial, as the degraded powder significantly
impacts the mechanical behavior of printed components. While most current research focuses on single-alloy
powder reuse, MM powder recyclability in MMAM
The use of degraded powder affects key mechanical
properties, including chemical composition, density, remains underexplored. A detailed discussion of future
research direction in MMAM powder reuse is presented
porosity, tensile strength, and surface roughness. In single in Section 6.1.
alloy materials, the use of recycled powder can lead to a
gradual change in chemical composition, particularly in 2.7. In-process monitoring
critical alloys such as IN718 and Ti-48Al-2Cr-2Nb, In-process monitoring has emerged as a critical enabler
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which in turn influences the mechanical properties. Studies for ensuring process stability, defect mitigation, and
on density and porosity have shown that reused powder quality assurance in MAM, particularly when fabricating
can lead to lower or less predictable part densities, driven MM components. In-process monitoring in PBF, LDED,
by uneven particle size distributions, increased spatter
presence, and incomplete melting. and WAAM processes benefits from in-situ monitoring
techniques aimed at detecting defects and ensuring part
Beyond the chemical composition, density, and quality during fabrication. In PBF, monitoring focuses on
porosity, the use of recycled powder has been shown to powder spreading uniformity, laser-powder interactions,
have a significant effect on the material’s tensile properties. melt pool characteristics (size, shape, and temperature),
Properties such as ultimate tensile strength (UTS), yield scan path accuracy, and layer geometry. Optical imaging,
strength (YS), Young’s modulus, and elongation have seen pyrometry, infrared (IR) cameras, and data-driven
the most change, though the extent varies with the alloy. methods such as computer vision and neural networks
Tang et al. observed that the use of recycled Ti-6Al-4V are commonly used to identify defects such as porosity or
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powder alloy resulted in an increase in strength due to incomplete fusion. 119,120 Real-time monitoring facilitates
high oxygen content, whereas SS316 and AlSi10Mg process parameter adjustments to reduce defects and
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typically exhibit reduced strength and stiffness, mainly due improve part consistency.
to higher porosity and coarser particle sizes. Similarly, in LDED, monitoring methods include
Finally, surface roughness is another critical factor that pyrometry, IR imaging, and acoustic emission (AE)
is affected by powder reuse. Recycled powders often contain sensors to track melt pool temperature, build height, and
larger particles that do not fully melt, leading to a rougher crack formation. These sensors enable closed-loop control
surface finish. This not only degrades the build quality but strategies to maintain stable thermal conditions and
also increases the need for post-processing, which is both geometry, improving material uniformity and reducing
costly and time-consuming. Studies involving SS316, defects. 120,121 WAAM uses comparable optical and thermal
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Volume 1 Issue 2 (2025) 8 doi: 10.36922/ESAM025180010