Powders for powder bed fusion: a review

Abstract

The quality of powder used in powder bed-based additive manufacturing plays a key role concerning process performance and end part properties. Even though this is a generally accepted fact, there is still a lack of a comprehensive understanding of the powder property-part property relationship. However, numerous investigations focusing on selected powder properties and their corresponding influence on process aspects or final part properties have been published in recent years. Still, generalized statements on powder requirements for a defined process performance are not available. This can be attributed to the fact that the community has not yet come to an agreement which characterization techniques are most suitable for powder characterization in the additive manufacturing context and in most cases only selected aspects have been investigated for special powder materials. The aim of this review is to assess these building blocks of knowledge and to provide an overview on the current state of the art.

Material Reuse in Laser Powder Bed Fusion: Side Effects of the Laser—Metal Powder Interaction

“…The literature shows that powder recycling, when referring to the LPBF process, can be done in a variety of ways [23,77], ranging from the reintroduction of sieved powder after each build and adding the used and sieved powder together with the virgin one with or without mixing, to the mixing of used powder with powder of the same age after each cycle (defined as the number of jobs after which the amount of feedstock in not enough to perform further jobs). According to literature, the first two procedures seem to be the most used [19,[78][79][80][81].…”

“…What is most striking from the results performed on many different alloys (stainless steels, Ti-6Al-4V, Alsi10Mg, IN718 and IN625, Co-Cr, Scalmalloy) [19,30,37,58,[82][83][84][85][86][87][88], in terms of reused powder characterization and, most importantly, of the microstructural and mechanical properties of the final parts, is that, while the former are quite similar for the same alloy, the latter are characterized by very scattered results [23]. Mechanical properties could be improved, decreased, or unaffected by the reuse of feedstock material, as shown by the results reported in Table 1.…”

“…The laser powder bed fusion process is always performed under inert atmosphere, in order to avoid any possible interaction between the metal particles (very reactive with a high specific surface area) and impurities such as humidity and light elements (i.e., oxygen, carbon oxides), which might affect the local chemical composition and the resulting mechanical properties of the manufactured parts [18,23,58]. Furthermore, a continuous flow of inert gas is essential in order to limit the redeposition on the powder bed of by-products during the process; this is crucial because should the removal of by-products by the shielding gas flow not be effective, there is a high risk of laser attenuation [97][98][99].…”

“…However, process parameters are, in general, quite different in terms of laser power and scan speed, and the laser-matter interaction is much more complicated in LPBF processes, since the powder feedstock is inherently unstable and the solidified material undergoes multiple thermal cycles corresponding to the fusion of subsequent layers during the additive process [19][20][21][22]. Furthermore, owing to the similarities with welding and to the complicated interaction between laser and metal particles, when comparing laser powder bed fusion with other metal forming processes, it is evident that the range of processable alloys is very limited and the number of high-productivity commercially available alloys is even smaller [23]. One of the reasons behind this is that the level of metal powder sensitivity to the laser action during LPBF is not yet fully understood, despite the efforts of the scientific community to uncover it [24][25][26][27], and the same applies to the final mechanical properties of the built parts.…”

Accelerating Fuel Cell Development with Additive Manufacturing Technologies: State of the Art, Opportunities and Challenges

“…Afterward, it gradually expanded to metals and alloys, which is known as direct metal laser sintering (DMLS) or selective laser melting (SLM). The minimum thickness achieved by PBF is 60–100 μm for sintered polymers and 30–60 μm for metals .…”