Research of 316L Metallic Powder for Use in SLM 3D Printing

Abstract

Abstract3D metal printing is an increasingly popular production of steel parts. The most widespread and most accurate method is SLM (Selective Laser Melting), which uses metallic powder as the input material. The article is dedicated to researching the supplied powder from Renishaw. The powder is made by gas atomization and 3 phases of powder (virgin, sift and waste) that are present in the SLM process are examined. Powder morphology by SEM electron microscopy is investigated and the porosity of the powder is measured by optical method. Next, the powder grain size fraction is examined. In conclusion, there are recommendations and other directions of possible research. The main quantitative result from research is that, in general, small particles are reduced in the sift powder and the number of larger particles is increased, but the powder is still usable for further use.

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

“…The surfaces of the recycled powders also appear rougher compared to the initially smooth virgin powders. In addition, fine particles called satellites (<5 µm) are attached to the surface of the virgin 316L SS and AlSi10Mg powders (e.g., dashed arrows of the zoomed areas in Figure 1a,d), which is common in virgin metallic powders produced by the gas atomization process [37,42,68]. However, fewer satellites are observed in both recycled powders as shown in Figure 1b,d, often attributed to their detachment from the surface of unmelted powder particles when they are being blown off from the as-built AM parts [27,55,67].…”

“…In addition, the agglomeration of small powder particles on the larger ones could be observed for the recycled 316L SS, as shown in Figure 1b. Such agglomerates are typically caused by the spattering of unmelted powders (powder spatter) from the powder bed upon contact with the laser heat source during SLM fabrication, which are then attached to other unconsolidated or semi-consolidated powder particles [36][37][38]47]. Similarly, other studies have shown that such agglomerates could also arise from melted powder particles that are ejected from the powder bed (droplet spatter), which eventually solidify during the flight and then either adhere to the as-fabricated part or impinge on other powder particles [69][70][71][72].…”

“…Nevertheless, for L-PBF AM, high packing density and high flowability are desired to ensure optimal powder melting and homogeneous deposition of the powder bed layers [36]. Thus, in terms of morphology, smooth, spherical particles with as little satellites/defects as possible are desirable [29,[37][38][39]. In addition, Hajnys et al [37], Liu et al [40], and Benson et al [41] explained that a wide PSD with a mix of large and fine particle sizes can improve the packing density of the powder bed through the accumulation of the fine powders within the interstitial spaces that exist around the larger powder particles.…”

“…Thus, in terms of morphology, smooth, spherical particles with as little satellites/defects as possible are desirable [29,[37][38][39]. In addition, Hajnys et al [37], Liu et al [40], and Benson et al [41] explained that a wide PSD with a mix of large and fine particle sizes can improve the packing density of the powder bed through the accumulation of the fine powders within the interstitial spaces that exist around the larger powder particles. However, some studies have also shown slightly reduced flowability when a wide PSD is used for AM fabrication due to increased inter-particle friction, thereby suggesting that some compromise is needed when selecting the particle sizes to attain the highest possible packing density while maximizing flowability [42][43][44].…”

“…Nevertheless, any increased oxygen absorption and oxide formation need to be taken into consideration before reusing the recycled powders as they may adversely affect the performance of the eventual as-built parts during service [28,29]. On the other hand, Hajnys et al [37] observed an increase in the PSD of recycled 316L SS powder but considered further reuse to be acceptable. Similarly, although Nezhadfar et al [64] observed more of satellites and porosity on the surface of recycled 316L SS powder after 12 times of reuse, they reported an inconclusive trend in the ductility and mechanical strength in the solidified parts.…”