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

Abstract

Metal additive manufacturing is changing the way in which engineers and designers model the production of three-dimensional (3D) objects, with rapid growth seen in recent years. Laser powder bed fusion (LPBF) is the most used metal additive manufacturing technique, and it is based on the efficient interaction between a high-energy laser and a metal powder feedstock. To make LPBF more cost-efficient and environmentally friendly, it is of paramount importance to recycle (reuse) the unfused powder from a build job. However, since the laser-powder interaction involves complex physics phenomena and generates by-products which might affect the integrity of the feedstock and the final build part, a better understanding of the overall process should be attained. The present review paper is focused on the clarification of the interaction between laser and metal powder, with a strong focus on its side effects. Figure 1. Schematics of the laser powder bed fusion (LPBF) equipment. Adapted from Reference [9] with permission from Elsevier.While the market and the applications of laser powder bed fusion continuously and impressively grew in recent years, there is a common view across users and researchers concerning the repeatability of the process in terms of chemical composition and mechanical properties of the final parts, which are of paramount importance when challenging environmental or testing conditions are considered [10][11][12][13][14][15][16].The most typical approach to study the microstructural and mechanical properties of parts built by LPBF is to compare them with castings of the same alloy or, rather, the corresponding alloy since the starting material is metal powder rather than a fuse. However, in some existing alloys designed for cast and wrought parts, laser additive manufacturing processing results in cracking or other microstructure deficiencies [11,12,16,17]. It is worth noting that LPBF has more similarities with laser welding rather than casting, since the two laser-based techniques have some common features (i.e., melt-pool formation, moving heat source) [18]. 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 ...

Reuse of Ti6Al4V Powder and Its Impact on Surface Tension, Melt Pool Behavior and Mechanical Properties of Additively Manufactured Components

“…According to Santecchia et al [ 40 ], when the time of flight of a spatter particle is long enough, its surface can experience strong oxidation. It was observed mostly in the case of highly reactive powders (i.e., Ti6Al4V) due to their chemical composition characterized by the high presence of elements with a high oxidation potential.…”

Comparison between Virgin and Recycled 316L SS and AlSi10Mg Powders Used for Laser Powder Bed Fusion Additive Manufacturing

“…In addition, the inclusion of fine powder particles (fines) also contributes to high packing density due to the fine particles filling the interstitial spaces that exist among the larger particles [40,44,90]. However, these fine particles tend to result in wider PSD and have been found to reduce powder flowability [30,36,55,67]. Therefore, as a compromise, it is suggested that smooth, spherical particles with as minimum defects as possible with narrower PSD should be used for AM fabrication to attain optimized flowability with relatively high packing density [29,37,42].…”

“…While research into the process-microstructure-property relationship of AM metallic parts is certainly important, another equally essential aspect that has been given less attention is the properties of the metal powder used for AM processing, i.e., the feedstock materials. So far, available studies in the literature have revealed that the quality of these feedstock materials play a major role in determining the quality of the as-built AM parts, particularly densification levels and porosity contents [28][29][30]. In fact, the quality of metal powders used for AM is often assessed through their physical properties such as particle size, particle size distribution (PSD), morphology, packing density and flowability, as well as their chemical composition.…”

Reuse of Grade 23 Ti6Al4V Powder during the Laser-Based Powder Bed Fusion Process

“…A practical way to reduce costs associated with the use of powder feedstock is to recycle powder from previous part builds. Without the inclusion of a recycling regime the cost of the powder in the finished part can double [1]. Typically, during the laser-based powder bed fusion (L-PBF) process, only 10-50% of the of the powder within the build volume is utilised [1].…”

“…Without the inclusion of a recycling regime the cost of the powder in the finished part can double [1]. Typically, during the laser-based powder bed fusion (L-PBF) process, only 10-50% of the of the powder within the build volume is utilised [1]. Within this additive manufacturing (AM) process, the powder is consolidated into the final part and the remainder is available for reuse.…”