A new method for assessing the recyclability of powders within Powder Bed Fusion process

Gorji, Nima E. and Saxena, Prateek and Corfield, Martin and Clare, Adam and Rueff, Jean Pascal and Bogan, Justin and González, Pierre G.M. and Snelgrove, Matthew and Hughes, Greg and O'Connor, Robert and Raghavendra, Ramesh and Brabazon, Dermot (2020) A new method for assessing the recyclability of powders within Powder Bed Fusion process. Materials Characterization, 161. ISSN 1044-5803

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Recycling metallic powders used in the additive manufacturing (AM) process is essential for reducing the process cost, manufacturing time, energy consumption, and metallic waste. In this paper, the focus is on pore formation in recycled powder particles of stainless steel 316L during the selective laser melting process. We have introduced the concept of optimizing the powder bed's printing area in order to see the extent of the affected powders during the 3D-printing process. X-ray Computed Tomography (XCT) is used to characterize the pores inside the particles. The results from image processing of the tomography (rendered in 3D format) indicate a broader pore size distribution and a higher pore density in recycled powders compared to their virgin counterparts. To elucidate on this, the Electron Dispersion spectroscopy (EDX) analysis and Synchrotron-based Hard X-ray Photoelectron Spectroscopy (HAXPES) were performed to reveal the chemical composition distribution across the pore area and bulk of the recycled powder particles. Higher concentrations of Fe, Cr, and Ni were recorded on the interior wall of the pore in recycled particles and higher Mn, S and Si concentrations were recorded in the outer layer around the pore area and on the surface of the recycled particle. The pore formation in recycled powder is attributed to out-diffusion of Mn, S and Si to the outer surface as a result of the incident laser heat during the AM process due to higher electron affinity of such metallic elements to oxygenation. HAXPES analysis shows a higher MnO concentration around the pore area which impedes the in-diffusion of other elements into the bulk and thereby helps to creates a void. The inside wall of the pore area (dendrites), has a higher concentration of Fe and Cr oxide. We believe the higher pore density in recycled powders is due, at least in part to composition redistribution, promoted by laser heat during the AM process. Nanoindentation analyses on both virgin and recycled powder particles shows a lower hardness and higher effective modulus in the recycled powder particles attributed to the higher porosity in recycled powders.

Item Type: Article
Additional Information: Funding Information: This research is supported by a research grant from Science Foundation Ireland (SFI) under grant number 16/RC/3872 and is co-funded under the European Regional Development Fund . We acknowledge Dr. B. O'Connell for his valuable assistance in running the characterization and measurements. N.E. Gorji Acknowledges the New Foundation Award (No. P60687) received from Irish Research Council (2019) and also the ECIU Research Mobility (No. P60617) grant (2018). The authors would like to thank SOLEIL Synchrotron for using their HAXPES measurement facilities as well as the support given by the beamline scientists (SOLEIL proposal No. 20180106). Publisher Copyright: © 2020 Elsevier Inc.
Uncontrolled Keywords: /dk/atira/pure/subjectarea/asjc/2500
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Depositing User: Admin SSL
Date Deposited: 19 Oct 2022 23:04
Last Modified: 16 Aug 2023 03:25
URI: http://repository-testing.wit.ie/id/eprint/3878

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