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Paper: Laser-matter interactions in additive manufacturing of stainless steel SS316L and 13-93 bioactive glass revealed by in situ X-ray imaging

Publication: Additive Manufacturing

Authors: Leung, C.L.A., Marussi, S., Towrie, M., Val Garcia, J., Atwood, R.C.,  Bodey, A.J., Jones, J.R., Withers, P.J., Lee, P.D.

MAPP researchers are using the UK’s national synchrotron, the Diamond Light Source, to shed more light on laser additive manufacturing (LAM) technologies.

Previously the in-situ real-time measurements used to learn more about LAM, including Schlieren imaging, have captured the temperature field and/or images at above the molten pool surface. But they cannot study the changes inside the melt zone.

Advances in third-generation synchrotron radiation sources allow the use of a high flux X-ray beam to capture LAM radiographically at a high spatial and temporal resolution.

This paper details the use of a custom built LAM process replicator (LAMPR) with in-situ and operando synchrotron X-ray real-time radiography to study laser-matter interactions and powder consolidation phenomena during LAM of stainless steel SS316L and 13-93 bioactive glass.

The paper states the LAMPR is: "Designed to mimic the major features of a typical LPBF system while permitting in situ and operando imaging of the laser-matter interaction and powder consolidation phenomena with synchrotron X-rays. It is a compact, lightweight (ca.15 kg) and portable device that can be integrated into different synchrotron X-ray imaging and diffraction beamlines." (Leung et al. 2018, p649)

Two powders with large differences in chemical, optical and thermophysical properties were chosen for the study. This was to better understand the effects of powder properties on laser absorption mechanisms, melt flow behaviour and the evolution of the melt track and defects.

The study revealed the very different melt behaviours of the two powders during LAM.

The work is useful in understanding the mechanisms behind the formation of defects and other technical challenges.

This understanding will help control technical challenges that can affect the use of LAM technologies for high-performance structural applications.

The paper can be viewed here. 

Schematic of the LAMPR mounted on a synchrotron beam line - Schematic of the LAMPR mounted on a synchrotron beam line. It comprises three sub-assemblies: One a stainless steel environmental build chamber, Two a laser system, and three a laser enclosure. A three-quarter section view of the environmental chamber. The purple arrows indicate the directions of the incoming X-ray beam and the attenuated X-ray beam. The red arrow indicates the scan direction of the laser beam, which moves parallel along the length of the powder bed. The blue arrow indicates the argon flow direction which is perpendicular to the X-ray beam and parallel to the laser beam.
Schematic of the LAMPR mounted on a synchrotron beam line. It comprises 3 sub-assemblies: 1) a stainless steel environmental build chamber (blue), 2) a laser system (green), & 3) a laser enclosure (black).b A 3/4 section view of the environmental chamber