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In situ radiographic and ex situ tomographic analysis of pore interactions during multilayer builds in laser powder bed fusion

Sinclair, L; Leung, CLA; Marussi, S; Clark, SJ; Chen, Y; Olbinado, MP; Rack, A; ... Lee, PD; + view all (2020) In situ radiographic and ex situ tomographic analysis of pore interactions during multilayer builds in laser powder bed fusion. Additive Manufacturing , 36 , Article 101512. 10.1016/j.addma.2020.101512.

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Abstract

Porosity and high surface roughness can be detrimental to the mechanical performance of laser powder bed fusion (LPBF) additive manufactured components, potentially resulting in reduced component life. However, the link between powder layer thickness on pore formation and surface undulations in the LPBF parts remains unclear. In this paper, the influence of processing parameters on Ti-6Al-4 V additive manufactured thin-wall components are investigated for multilayer builds, using a custom-built process replicator and in situ high-speed synchrotron X-ray imaging. In addition to the formation of initial keyhole pores, the results reveal three pore phenomena in multilayer builds resulting from keyhole melting: (i) healing of the previous layers' pores via liquid filling during remelting; (ii) insufficient laser penetration depth to remelt and heal pores; and (iii) pores formed by keyholing which merge with existing pores, increasing the pore size. The results also show that the variation of powder layer thickness influences which pore formation mechanisms take place in multilayer builds. High-resolution microcomputed tomography images reveal that clusters of pores form at the ends of tracks, and variations in the layer thickness and melt flow cause irregular remelting and track height undulations. Extreme variations in height were found to lead to lack of fusion pores in the trough regions. It is hypothesised that the end of track pores were augmented by soluble gas which is partitioned into the melt pool and swept to track ends, supersaturating during end of track solidification and diffusing into pores increasing their size.

Type: Article
Title: In situ radiographic and ex situ tomographic analysis of pore interactions during multilayer builds in laser powder bed fusion
DOI: 10.1016/j.addma.2020.101512
Publisher version: https://doi.org/10.1016/j.addma.2020.101512
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher's terms and conditions.
Keywords: Additive manufacturing, laser powder bed fusion, in situ X-ray imaging, Ti-6Al-4V, porosity
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Mechanical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/10111279
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