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

Author:

Huang YuzeORCID,Fleming Tristan G.ORCID,Clark Samuel J.ORCID,Marussi Sebastian,Fezzaa Kamel,Thiyagalingam JeyanORCID,Leung Chu Lun AlexORCID,Lee Peter D.ORCID

Abstract

AbstractKeyhole 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.

Funder

United States Department of Defense | United States Navy | ONR | Office of Naval Research Global

RCUK | Engineering and Physical Sciences Research Council

Royal Academy of Engineering

Publisher

Springer Science and Business Media LLC

Subject

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

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