Enhanced near-infrared absorption for laser powder bed fusion using reduced graphene oxide

Abstract

Laser powder bed fusion (LPBF) is a revolutionary manufacturing technology that fabricates parts with unparalleled complexity, layer-by-layer. However, there are limited choices of commercial powders for LPBF, constrained partly by the laser absorbance, an area that is not well investigated. Carbon additives are commonly used to promote near infra-red (NIR) absorbance of the powders but their efficiency is limited. Here, we combine operando synchrotron X-ray imaging with chemical characterisation techniques to elucidate the role of additives on NIR absorption, melt track and defect evolution mechanisms during LPBF. We employ a reduced graphene oxide (rGO) additive to enable LPBF of low NIR absorbance powder, SiO 2 , under systematic build conditions. This work successfully manufactured glass tracks with a high relative density (99.6%) and overhang features ( > 5 mm long) without pre/post heat treatment. Compared to conventional carbon additives, the rGO increases the powder's NIR absorbance by ca. 3 times and decreases the warpage and porosity in LPBF glass tracks. Our approach will dramatically widen the palette of materials for laser processing and enable existing LPBF machines to process low absorbance powder, such as SiO 2 , using a NIR beam.

Quantification of Interdependent Dynamics during Laser Additive Manufacturing Using X‐Ray Imaging Informed Multi‐Physics and Multiphase Simulation

“…These mechanisms include pore formation due to a gas release of hydrogen [ 30 ] or nitrogen from the powder composition, argon or nitrogen from gas atomized powders [ 50 ] (Supporting Information), or a release of CO 2 from the decomposition of adventitious carbon at the powder surface during LPBF. [ 26 , 53 ]…”

Advances and challenges in direct additive manufacturing of dense ceramic oxides

“…The limited laser-material interaction is another critical challenge in dAM when dealing with ceramic oxides. Most commercial L-PBF/L-DED devices are tailored for processing metallic materials, typically employing NIR lasers with wavelengths (λ) between 1 030 nm and 1 070 nm [169]. Unfortunately, at this λ range, the energy absorption rate of ceramic oxides is remarkably low with high temperaturesensitivity.…”

“…The enhanced absorption rate of the feedstock resulted in a more stable molten pool and a denser structure in dAMed ceramics. Recently, Leung et al [169] demonstrated a significant advancement in laser absorptance by utilizing reduced graphene oxide (rGO) as the absorbing material. Compared to conventional carbon additives, rGO achieved a remarkable threefold improvement in absorptance.…”

“…Additionally, high energy input was found to effectively suppress LOF defects but simultaneously increased the occurrence of gas pores. Similarly, Leung et al [169] utilized synchrotron x-ray imaging device to illuminate the transient dynamic behavior of SiO 2 melt doped with absorption additives (figure 16(h)). Their in-situ observations revealed a sequence of physical phenomena in melted tracks, including cavity formation, plume generation, particle splattering, and the formation and collapse of bubbles.…”

“…Figure 16. In-situ monitoring of dAMed ceramic oxides: (a) thermal image depicting the preheating area in L-PBF of Al 2 O 3 -ZrO 2 ceramic [196]; (b) average temperature evolution over time in L-PBF of ZrO 2 ceramic [97]; (c) evolution of signal with different laser powers in L-PBF of Al 2 O 3 ceramic [199]; (d) high-speed video image illustrating the phenomenon of melt flowing out in L-PBF of Al 2 O 3 -ZrO 2 ceramic[16]; (e) high-speed video image demonstrating the evolution of crack defects in L-PBFed Al 2 O 3 ceramic[198]; (f) high-speed video image in two adjacent Al 2 O 3 scan tracks, revealing powder denudation zones[26]; (g) 3D visualization of Al 2 O 3 molten pool using operando x-ray computed tomography[190]; (h) time-series radiographs acquired in L-PBF for absorber-doped SiO 2 ceramic using different scan speeds[169]. (a) Reprinted from[196], Copyright © 2010 Published by Elsevier B.V. (b) Reprinted from[97], Copyright © 2015 Elsevier B.V. All rights reserved.…”