Denudation of metal powder layers in laser powder bed fusion processes
TL;DR: In this paper, the authors study the denudation of metal powders that is observed near the laser scan path as a function of laser parameters and ambient gas pressure and show that the observed depletion of metal powder particles in the zone immediately surrounding the solidified track is due to a competition between outward metal vapor flux directed away from the laser spot and entrainment of powder particles.
About: This article is published in Acta Materialia.The article was published on 2016-08-01 and is currently open access. It has received 587 citations till now. The article focuses on the topics: Metal powder & Selective laser melting.
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TL;DR: A review of the emerging research on additive manufacturing of metallic materials is provided in this article, which provides a comprehensive overview of the physical processes and the underlying science of metallurgical structure and properties of the deposited parts.
4,192 citations
Cites background from "Denudation of metal powder layers i..."
...Other than a few reported cases in which a keyhole is formed during AM [34,176], the melting process typically remains in conduction mode as the penetration into the previously deposited layer only needs to be a small fraction of the layer height to ensure interlayer bonding....
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TL;DR: A comprehensive understanding of the interrelation between the various aspects of the subject, as this is essential to demonstrate credibility for industrial needs, is presented in this paper, which highlights some key topics requiring attention for further progression.
761 citations
TL;DR: In this paper, a review of the literature and the commercial tools for insitu monitoring of powder bed fusion (PBF) processes is presented, focusing on the development of automated defect detection rules and the study of process control strategies.
Abstract: Despite continuous technological enhancements of metal Additive Manufacturing (AM) systems, the lack of process repeatability and stability still represents a barrier for the industrial breakthrough. The most relevant metal AM applications currently involve industrial sectors (e.g., aerospace and bio-medical) where defects avoidance is fundamental. Because of this, there is the need to develop novel in-situ monitoring tools able to keep under control the stability of the process on a layer-by-layer basis, and to detect the onset of defects as soon as possible. On the one hand, AM systems must be equipped with in-situ sensing devices able to measure relevant quantities during the process, a.k.a. process signatures. On the other hand, in-process data analytics and statistical monitoring techniques are required to detect and localize the defects in an automated way. This paper reviews the literature and the commercial tools for insitu monitoring of Powder Bed Fusion (PBF) processes. It explores the different categories of defects and their main causes, the most relevant process signatures and the in-situ sensing approaches proposed so far. Particular attention is devoted to the development of automated defect detection rules and the study of process control strategies, which represent two critical fields for the development of future smart PBF systems.
505 citations
Cites background from "Denudation of metal powder layers i..."
...In particular, improper hatch spacing may produce linear void structures associated with the powder denudation effect, i.e., the apparent clearing of powder around a single track bead (Matthews et al., 2016)....
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..., the apparent clearing of powder around a single track bead (Matthews et al., 2016)....
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TL;DR: The high-speed synchrotron hard X-ray imaging and diffraction techniques used to monitor the laser powder bed fusion (LPBF) process of Ti-6Al-4V in situ and in real time demonstrate that many scientifically and technologically significant phenomena in LPBF, including melt pool dynamics, powder ejection, rapid solidification, and phase transformation, can be probed with unprecedented spatial and temporal resolutions.
Abstract: We employ the high-speed synchrotron hard X-ray imaging and diffraction techniques to monitor the laser powder bed fusion (LPBF) process of Ti-6Al-4V in situ and in real time. We demonstrate that many scientifically and technologically significant phenomena in LPBF, including melt pool dynamics, powder ejection, rapid solidification, and phase transformation, can be probed with unprecedented spatial and temporal resolutions. In particular, the keyhole pore formation is experimentally revealed with high spatial and temporal resolutions. The solidification rate is quantitatively measured, and the slowly decrease in solidification rate during the relatively steady state could be a manifestation of the recalescence phenomenon. The high-speed diffraction enables a reasonable estimation of the cooling rate and phase transformation rate, and the diffusionless transformation from β to α
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phase is evident. The data present here will facilitate the understanding of dynamics and kinetics in metal LPBF process, and the experiment platform established will undoubtedly become a new paradigm for future research and development of metal additive manufacturing.
490 citations
TL;DR: A mechanism map for predicting the evolution of melt features, changes in melt track morphology from a continuous hemi-cylindrical track to disconnected beads with decreasing linear energy density and improved molten pool wetting with increasing laser power is developed.
Abstract: The laser–matter interaction and solidification phenomena associated with laser additive manufacturing (LAM) remain unclear, slowing its process development and optimisation. Here, through in situ and operando high-speed synchrotron X-ray imaging, we reveal the underlying physical phenomena during the deposition of the first and second layer melt tracks. We show that the laser-induced gas/vapour jet promotes the formation of melt tracks and denuded zones via spattering (at a velocity of 1 m s−1). We also uncover mechanisms of pore migration by Marangoni-driven flow (recirculating at a velocity of 0.4 m s−1), pore dissolution and dispersion by laser re-melting. We develop a mechanism map for predicting the evolution of melt features, changes in melt track morphology from a continuous hemi-cylindrical track to disconnected beads with decreasing linear energy density and improved molten pool wetting with increasing laser power. Our results clarify aspects of the physics behind LAM, which are critical for its development. Additive manufacturing of metals is now widely available, but the interaction of the metal powder with the laser remains unclear. Here, the authors use X-rays to image melt features and pore behaviour during laser melting of powders.
468 citations
References
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TL;DR: Additive manufacturing implies layer by layer shaping and consolidation of powder feedstock to arbitrary configurations, normally using a computer controlled laser as discussed by the authors, which is based on a novel materials incremental manufacturing philosophy.
Abstract: Unlike conventional materials removal methods, additive manufacturing (AM) is based on a novel materials incremental manufacturing philosophy. Additive manufacturing implies layer by layer shaping and consolidation of powder feedstock to arbitrary configurations, normally using a computer controlled laser. The current development focus of AM is to produce complex shaped functional metallic components, including metals, alloys and metal matrix composites (MMCs), to meet demanding requirements from aerospace, defence, automotive and biomedical industries. Laser sintering (LS), laser melting (LM) and laser metal deposition (LMD) are presently regarded as the three most versatile AM processes. Laser based AM processes generally have a complex non-equilibrium physical and chemical metallurgical nature, which is material and process dependent. The influence of material characteristics and processing conditions on metallurgical mechanisms and resultant microstructural and mechanical properties of AM proc...
2,402 citations
Book•
01 Jan 1996
TL;DR: In this paper, the authors provide an overview and fundamentals of Lasers in Medicine, Biotechnology and Arts: Lasers In Medicine and Biotechnology, Restoration and Conservation of Artworks.
Abstract: Part I Overview and Fundamentals: Introduction.- Thermal, Photophysical, and Photochemical Processes.- Reaction Kinetics and Transport of Species.- Nucleation and Cluster Formation.- Lasers, Experimental Aspects, Spatial Confinement.- Part II Temperature Distributions and Surface Melting: General Solutions of the Heat Equations.- Semi-infinite Substrates.- Infinite Slabs.- Non-uniform Media.- Surface Melting.- Part III Material Removal: Vaporization, Plasma Formation.- Nanosecond-Laser Ablation.- Ultrashort-Pulse Laser Ablation.- Etching of Metals and Insulators.- Etching of Semiconductors.- Part IV Material Deposition: Laser-CVD of Microstructures.- Growth of Fibers.- Direct Writing.- Thin-Film Formation by Laser-CVD.- Adsorbed Layers, Laser-MBE.- Liquid-Phase Deposition, Electroplating.- Thin-Film Formation by Pulsed-Laser Deposition and Laser-Induced Evaporation.- Part V Material Transformations, Synthesis and Structure Formation: Material Transformations, Laser Cleaning.- Doping.- Cladding, Alloying, and Synthesis.- Oxidation, Nitridation, and Reduction.- Transformation and Functionalization of Organic Materials.- Instabilities and Structure Formation.- Part VI Diagnostic Techniques, Plasmas: Diagnostic Techniques.- Analysis of Species and Plasmas,- Part VII Lasers in Medicine, Biotechnology and Arts: Lasers in Medicine and Biotechnology.- Restoration and Conservation of Artworks.
2,359 citations
TL;DR: In this article, the development of the microstructure of the Ti-6Al-4V alloy processed by selective laser melting (SLM) was studied by light optical microscopy.
2,201 citations
"Denudation of metal powder layers i..." refers background in this paper
...5b of [7]) which they attributed to powder denudation and accumulation of surface roughness between layers....
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...The effect of denudation on the deposition pattern produced by multiple, overlapping tracks has been studied in the past [7,15] and is relevant when considering a complete additive manufacturing process....
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TL;DR: In this paper, a comparative study of selective laser melting (SLM) and electron beam melting (EBM) is presented for the fabrication of complex, multi-functional metal or alloy monoliths by CAD-directed, selective melting of precursor powder beds.
1,144 citations
"Denudation of metal powder layers i..." refers background in this paper
...While the new design freedoms afforded by additive manufacturing of components directly from digital files has impacted multiple areas of industry, the resulting properties of the material in the printed part generally do not match those of wrought or cast metal [1,2]....
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01 Jan 2012
TL;DR: In this paper, a comparative study of selective laser melting (SLM) and electron beam melting (EBM) is presented for the fabrication of complex, multi-functional metal or alloy monoliths by CAD-directed, selective melting of precursor powder beds.
Abstract: Selective laser melting (SLM) and electron beam melting (EBM) are relatively new rapid, additive manufacturing technologies which can allow for the fabrication of complex, multi-functional metal or alloy monoliths by CAD-directed, selective melting of precursor powder beds. By altering the beam parameters and scan strategies, new and unusual, even non-equilibrium microstructures can be produced; including controlled microstructural architectures which ideally extend the contemporary materials science and engineering paradigm relating structure-properties-processing-performance. In this study, comparative examples for SLM and EBM fabricated components from pre-alloyed, atomized precursor powders are presented. These include Cu, Ti-6Al-4V, alloy 625 (a Ni-base superalloy), a Co-base superalloy, and 17-4 PH stainless steel. These systems are characterized by optical metallography, scanning and transmission electron microscopy, and X-ray diffraction.
922 citations