Speaker
Description
Laser powder bed fusion (L-PBF) is associated with the generation of spatters in the vicinity and from the melt pool, which are precursors for the formation of defects in the produced components. The main mechanisms for spatter formation were identified as direct melt pool spatters and entrained ones. Direct melt pool spatters are caused by important convection forces within the melt pool, caused by the Marangoni flow and the recoil pressure, which overcome the surface tension and lead to liquid break-up. Entrained spatters are powder bed particles dragged upwards by a local lateral flow, induced by vaporization of species above the melt pool and the rapid expansion of the resulting fumes. In general, spatter particles experience elevated temperatures promoting their oxidation, and eventually redeposit on the powder bed. Their incorporation in the powder feedstock carries risk for oxygen pick-up, oxide inclusions incorporation and lack-of-fusion defects formation. Besides reducing the oxygen partial pressure in the build chamber to limit oxidation of the hot metal particles and deposited material, the process atmosphere has the role to convey these spatters and fumes, acting as scattering objects for the laser, away from the melt pool formation region.
The presented work shows evidence that helium and its mixtures with argon allow to not only remove but also limit the generation of spatters during L-PBF by up to 60% compared to standard argon, while fulfilling its shielding role. In situ monitoring of the process as well as in depth characterization of the generated spatter morphology by high resolution scanning electron microscopy and chemical analysis by combustion analysis provide new insights on the effect of the process gas properties on the L-PBF stability and the properties of the most commonly used alloys by the additive manufacturing community, namely 316L stainless steel, Alloy 718 and Ti-6Al-4V.
| Speaker Country | France |
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