In situ absorptivity measurements of metallic powders during laser powder-bed fusion additive manufacturing

By J. Trapp, A. Rubenchik, Gabe Guss, Manyalibo Matthews. 2017

448 citations recorded by the source corpus.

Abstract The effective absorptivity of continuous wave 1070 nm laser light has been studied for bare and metal powder-coated discs of 316L stainless steel as well as for aluminum alloy 1100 and tungsten by use of direct calorimetric measurements. After carefully validating the applicability of the method, the effective absorptivity is plotted as a function of incident laser power from 30 up to ≈540 W for scanning speeds of 100, 500 and 1500 mm s −1 . The effective absorptivity versus power curves of the bulk materials typically show a slight change in effective absorptivity from 30 W until the onset of the formation of a recoil pressure-induced surface depression. As observed using high-speed video, this change in surface morphology leads to an increase in absorption of the laser light. At the higher powers beyond the keyhole transition, a saturation value is reached for both bare discs and powder-coated disks. For ≈100 μm thick powder layers, the measured absorptivity was found to be two times that of the bare polished discs for low-laser power. There is a sharp decrease when full melting of the powder tracks is achieved, followed by a keyhole-driven increase at higher powers, similar to the bare disc case. It is shown that, under conditions associated with laser powder-bed fusion additive manufacturing, absorptivity values can vary greatly, and differ from both powder-layer measurements and liquid metal estimates from the literature.

Subfields: Automotive Engineering, Mechanical Engineering

View Paper: https://www.semanticscholar.org/paper/f36189122103e49ba123a31aa4c6d6bca0b557cb

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Citations in the corpus

Material-structure-performance integrated laser-metal additive manufacturing (2021, background): “Absorptivity varies in a complicated way as a function of particle morphology beforemelting (138),melt poolmorphology aftermelting, and real-time processing temperature (136, 139).”
Finite interface dissipation phase field modeling of Ni–Nb under additive manufacturing conditions (2019, background): “[51] which shows experimental evidence for low effective absorptivity of the solid/liquid phases and high effective absorptivity upon vaporization and keyhole formation.”
3D printing of Aluminium alloys: Additive Manufacturing of Aluminium alloys using selective laser melting (2019, background): “The absorptivity of a material changes with the process parameters employed during SLM [43].”
Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF) of Ti6Al4V: High-fidelity modelling and experimental validation (2019, background): “To shed more light on this matter, the nominal absorptivity is determined for all six cases [50]:”
Effect of Laser-Matter Interaction on Molten Pool Flow and Keyhole Dynamics (2019, methodology): “The measurements using calorimetry [18, 19] or the integrated sphere method [20] have clearly revealed that the total laser absorption is noticeably increased when a keyhole is formed and that the increment in absorptivity”