Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing

Yuze Huang; Tristan G. Fleming; Samuel J. Clark; Sebastian Marussi; Kamel Fezzaa; Jeyan Thiyagalingam; Chu Lun Alex Leung; Peter D Lee

doi:10.1038/s41467-022-28694-x

Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing

Yuze Huang, Tristan G. Fleming, Samuel J. Clark, Sebastian Marussi, Kamel Fezzaa, Jeyan Thiyagalingam, Chu Lun Alex Leung, Peter D Lee

Research output: Contribution to journal › Article › peer-review

334 Citations (Scopus)

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Abstract

Keyhole porosity is a key concern in laser powder-bed fusion (LPBF), potentially impacting component fatigue life. However, some keyhole porosity formation mechanisms, e.g., keyhole fluctuation, collapse and bubble growth and shrinkage, remain unclear. Using synchrotron X-ray imaging we reveal keyhole and bubble behaviour, quantifying their formation dynamics. The findings support the hypotheses that: (i) keyhole porosity can initiate not only in unstable, but also in the transition keyhole regimes created by high laser power-velocity conditions, causing fast radial keyhole fluctuations (2.5–10 kHz); (ii) transition regime collapse tends to occur part way up the rear-wall; and (iii) immediately after keyhole collapse, bubbles undergo rapid growth due to pressure equilibration, then shrink due to metal-vapour condensation. Concurrent with condensation, hydrogen diffusion into the bubble slows the shrinkage and stabilises the bubble size. The keyhole fluctuation and bubble evolution mechanisms revealed here may guide the development of control systems for minimising porosity.

Original language	English
Article number	1170
Number of pages	11
Journal	Nature Communications
Volume	13
DOIs	https://doi.org/10.1038/s41467-022-28694-x
Publication status	Published - 4 Mar 2022
Externally published	Yes

Bibliographical note

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

Funding

This research is supported by the Office of Naval Research (ONR) Grant N62909-19-1-2109 to P.D.L., Y.H. and S.J.C., the Engineering and Physical Sciences Research Council (EPSRC) grants (EP/R511638/1 and EP/V061798/1) for P.D.L. and C.L.A.L., EPSRC grant (EP/N509577/1) for C.L.A.L., EPSRC grant (EP/T001569/1) via the Alan Turing Institute for J.T., the UK-EPSRC via MAPP: EPSRC Future Manufacturing Hub in Manufacture using Advanced Powder Processes (EP/P006566/1) for P.D.L., C.L.A.L., Y.H., T.G.F., S.J.C. and S.M., and the Royal Academy of Engineering (CiET1819/10) for P.D.L. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility, operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We also acknowledge the use of facilities and support provided by the Research Complex at Harwell, and the Advanced Photon Source for providing the beam-time (213874). We are grateful for HRL laboratory for providing the Al7A77 powder for this study. The authors also acknowledge the beamline experiment support from Yunhui Chen, Lorna Sinclair, David Rees, Niranjan Parab and other staff at the 32-ID beamline for their assistance, and sample preparation support from Elena Ruckh and Saurabh Shah for tomographic scans. This research is supported by the Office of Naval Research (ONR) Grant N62909-19-1-2109 to P.D.L., Y.H. and S.J.C., the Engineering and Physical Sciences Research Council (EPSRC) grants (EP/R511638/1 and EP/V061798/1) for P.D.L. and C.L.A.L., EPSRC grant (EP/N509577/1) for C.L.A.L., EPSRC grant (EP/T001569/1) via the Alan Turing Institute for J.T.,?the UK-EPSRC via MAPP: EPSRC Future Manufacturing Hub in Manufacture using Advanced Powder Processes (EP/P006566/1) for P.D.L., C.L.A.L., Y.H., T.G.F., S.J.C. and S.M., and the Royal Academy of Engineering (CiET1819/10) for P.D.L. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility, operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We also acknowledge the use of facilities and support provided by the Research Complex at Harwell, and the Advanced Photon Source for providing the beam-time (213874). We are grateful for HRL laboratory for providing the Al7A77 powder for this study. The authors also acknowledge the beamline experiment support from Yunhui Chen, Lorna Sinclair, David Rees, Niranjan Parab and other staff at the 32-ID beamline for their assistance, and sample preparation support from Elena Ruckh and Saurabh Shah for tomographic scans.

Funders	Funder number
Engineering and Physical Sciences Research Council
U.S. Department of Energy
Office of Science
Royal Academy of Engineering, The	CiET1819/10
Argonne National Laboratory	DE-AC02-06CH11357, 213874
Engineering and Physical Sciences Research Council	EP/N509577/1, EP/V061798/1, EP/T001569/1, EP/P006566/1, EP/R511638/1
Office of Naval Research	N62909-19-1-2109

ASJC Scopus subject areas

General Chemistry
General Biochemistry,Genetics and Molecular Biology
General Physics and Astronomy

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PublishedFinal published version, 3.26 MBLicence: CC BY

Cite this

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abstract = "Keyhole porosity is a key concern in laser powder-bed fusion (LPBF), potentially impacting component fatigue life. However, some keyhole porosity formation mechanisms, e.g., keyhole fluctuation, collapse and bubble growth and shrinkage, remain unclear. Using synchrotron X-ray imaging we reveal keyhole and bubble behaviour, quantifying their formation dynamics. The findings support the hypotheses that: (i) keyhole porosity can initiate not only in unstable, but also in the transition keyhole regimes created by high laser power-velocity conditions, causing fast radial keyhole fluctuations (2.5–10 kHz); (ii) transition regime collapse tends to occur part way up the rear-wall; and (iii) immediately after keyhole collapse, bubbles undergo rapid growth due to pressure equilibration, then shrink due to metal-vapour condensation. Concurrent with condensation, hydrogen diffusion into the bubble slows the shrinkage and stabilises the bubble size. The keyhole fluctuation and bubble evolution mechanisms revealed here may guide the development of control systems for minimising porosity.",

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N2 - Keyhole porosity is a key concern in laser powder-bed fusion (LPBF), potentially impacting component fatigue life. However, some keyhole porosity formation mechanisms, e.g., keyhole fluctuation, collapse and bubble growth and shrinkage, remain unclear. Using synchrotron X-ray imaging we reveal keyhole and bubble behaviour, quantifying their formation dynamics. The findings support the hypotheses that: (i) keyhole porosity can initiate not only in unstable, but also in the transition keyhole regimes created by high laser power-velocity conditions, causing fast radial keyhole fluctuations (2.5–10 kHz); (ii) transition regime collapse tends to occur part way up the rear-wall; and (iii) immediately after keyhole collapse, bubbles undergo rapid growth due to pressure equilibration, then shrink due to metal-vapour condensation. Concurrent with condensation, hydrogen diffusion into the bubble slows the shrinkage and stabilises the bubble size. The keyhole fluctuation and bubble evolution mechanisms revealed here may guide the development of control systems for minimising porosity.

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Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing

Abstract

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