| 1. |
- Chen, Zhuoer, 1989, et al.
(författare)
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Influence of part geometry on spatter formation in laser powder bed fusion of Inconel 718 alloy revealed by optical tomography
- 2022
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Ingår i: Journal of Manufacturing Processes. - : Elsevier BV. - 1526-6125. ; 81, s. 680-695
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Tidskriftsartikel (refereegranskat)abstract
- The metal powder used during the Laser Powder Bed Fusion (L-PBF) process is usually cycled for reuse in subsequent build jobs for cost-effectiveness and sustainability. Qualification guidelines are being established based on testing results of powder properties in terms of flowability, chemistry and rheological behaviors, etc. for making decisions on whether a batch of reused powder is suitable for producing parts that meet certain requirements. The current paper aims to develop experimental strategies for tracking powder history using novel design of specimens and on-line monitoring. Powder-capturing containers designed with internal lattice structures of varied beam lengths and diameters were manufactured by the L-PBF process using an Inconel 718 powder to investigate the influence of part geometry on the degradation of reused powder. The L-PBF experiment was monitored by a commercial Optical Tomography (OT) system which records the thermal emissions from the build area. Data were extracted from the OT images to evaluate the emissions of spatter particles introduced to the powder bed, which is influenced by the local layer profiles of the lattices and the overall geometries of the container. The collected powder samples were tested by combustion analysis for oxygen content and characterized by Scanning Electron Microscopy (SEM). Surface chemistry analyses of the powders were performed by X-ray Photoelectron Spectroscopy (XPS). Depending on the lattice structure geometry, the oxygen uptake in the powder collected from the containers was increasing by 10 ppm in case of empty container and up to as high as 118 ppm in case of container with larger areas of overhangs and higher surface-to-volume ratio. XPS results revealed the presences of Al-rich and Cr-rich oxides on the surface of powder samples collected from the container filled with lattices of high surface-to-volume ratio and the container filled with lattices of large overhangs, which agrees with the analyses of OT data.
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| 2. |
- Cordova Gonzalez, Laura, 1989, et al.
(författare)
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Rheological Behavior of Inconel 718 Powder for Electron-Beam Melting
- 2022
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Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 12:7
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the impact of powder reuse in powder-bed-fusion electron beams (PBF-EB) is key to maintain the processability and yield. Powder oxidation, due to exposure to high temperatures for a prolonged period of time, can lead to a decrease in electrical conductivity of the powder and, hence, electrostatic forces that originate during interaction with the electron beam. The effect of oxidation on physical properties as powder rheological properties, apparent/tap density and charging are studied in this work. The analysis using Scanning Electron Microscopy (SEM) shows thermodynamically stable Al-rich oxide particulates (sized 100–200 nm) covering the surface of the reused powder particles, with an increase of 20% in bulk oxygen in comparison to the virgin powder and, measured by X-ray Photoelectron Spectroscopy (XPS), average oxide thickness of circa 13 nm in the reused powder. On the one hand, reusing the powder positively impacted the flowability studied using the Revolution Powder Analyzer (RPA), in which the avalanche angle was decreased from 37 deg to 30 deg, for virgin and reused powder, respectively. The volume fraction of loose powder was similar for both virgin and reused powder, 57% and 56%, respectively, while the packed volume fraction was measured lower in the reused (57%) than the virgin powder (60%). On the other hand, the charging behavior, studied using the ION Charge Module of the powder, worsened; this almost doubled in the reuse powder (−9.18 V/g) compared to the virgin powder (−5.84 V/g). The observation of ejected particles from the build volume is attributed to the charging behavior and lower packing volume fraction in the reused powder
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| 3. |
- de Andrade Schwerz, Claudia, 1992, et al.
(författare)
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In-situ detection of redeposited spatter and its influence on the formation of internal flaws in laser powder bed fusion
- 2021
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Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604. ; 47
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Tidskriftsartikel (refereegranskat)abstract
- The pervasive adoption of laser powder bed fusion (LPBF) as an industrial manufacturing technique relies on the improvement of its repeatability, currently limited by the stochastic formation of flaws. Considering that large flaws can form randomly and despite the optimization of process parameters, an in-situ monitoring technique suitable for detecting deviations that originate these critical flaws is paramount. The redeposition of spatters on the build area has previously been identified as one of the factors responsible for the rise of internal flaws, but so far limited are the efforts towards their detection. This study aims to detect spatter redeposits via in-situ monitoring and to couple the detections to lack of fusion. For that, long-exposure near-infrared in-situ monitoring associated with image analysis is employed to determine the exact locations and quantify the incidence of spatter redeposits across three full builds performed at varying layer thicknesses. The existence and distribution of internal flaws is verified ex-situ by means of ultrasonic inspection and metallography. The formation of internal flaws is attributed to spatter redeposits after detailed characterization of size, particle and surface morphology of spatter and identification of particles with identical characteristics on the fracture surface in the adjacencies of lack of fusion. It is found that spatters preferentially redeposit on the adjacencies of the gas outlet, but that the affected portion of the build area and the prevalence of detections is heavily dependent on the powder layer thickness employed in the manufacturing process. The monitoring system setup preferentially acquires signal from spatters redeposited on print regions, making it particularly suitable for flaw detection.
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| 4. |
- Fiegl, Tobias, et al.
(författare)
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Effect of AlSi10Mg0.4 long-term reused powder in PBF-LB/M on the mechanical properties
- 2021
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Ingår i: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 212
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Tidskriftsartikel (refereegranskat)abstract
- Laser-based powder bed fusion (PBF-LB/M) is a well-established additive manufacturing (AM) process capable of producing high quality parts with excellent mechanical properties. Industrial applications of additively manufactured parts require the usage of fresh powder which makes the process expensive, especially in case of AM machines with enlarged build envelopes. Processing long-term reused powder fits to economic yields with the drawback of increased porosity and incorporated oxides. In this study, a detailed analysis of components made of virgin and long-term reused AlSi10Mg0.4 powder is provided. The experiments reveal that process parameters qualified for the virgin powder are not working offhand for the reused powder, as an increase of porosity from less than 1 % up to 3 % and a decline of tensile strength as well as yield strength of about 15 % are observed. The results indicate that powder degradation, which is based on the formation of hydroxides and oxides, has a significant impact on as-built microstructure as well as mechanical properties of additively manufactured parts. The amount of hydrogen and oxygen is measured for different powder conditions and the powder ageing process of AlSi10Mg0.4 is discussed in detail.
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| 5. |
- Hearn, William, 1992, et al.
(författare)
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Impact of powder properties on deoxidation and densification of carbon steels during powder bed fusion – Laser beam
- 2024
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Ingår i: Powder Technology. - : Elsevier B.V.. - 1873-328X .- 0032-5910. ; 431
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Tidskriftsartikel (refereegranskat)abstract
- This work examined the influence of powder properties on deoxidation and densification of carbon steels during powder bed fusion-laser beam (PBF-LB) at compositions between 0.06 and 1.1 wt% C. Analysis revealed that deoxidation was greatest in alloys with high carbon content, reaching losses of up to 440–600 ppm at compositions of 0.75 and 1.1 wt% C. This behavior was not due to enhanced oxygen removal by spatter, as spatter in high carbon alloys had less oxygen pickup (∼4% vs. ∼27%) and formed smaller oxide layers (∼42 nm vs. ∼82 nm). Instead, it was due to the high oxygen affinity of carbon at elevated temperature, which resulted in formation of gaseous carbon oxides that were subsequently removed by the process atmosphere. Regarding densification, powders with high avalanche energy (>7.75 mJ/kg), break energy (>4.75 mJ/kg), and particle size distribution (D10 > 25 μm) were more likely to form lack of fusion porosity at low energy input.
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| 6. |
- Pauzon, Camille Nicole Géraldine, 1994, et al.
(författare)
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Effect of layer thickness on spatter properties during laser powder bed fusion of Ti–6Al–4V
- 2023
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Ingår i: Powder Metallurgy. - : Informa UK Limited. - 0032-5899 .- 1743-2901. ; 66:4, s. 333-342
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Tidskriftsartikel (refereegranskat)abstract
- High layer thicknesses for laser powder bed fusion are promising for productivity increase. However, these are associated with increased process instability, spatter generation and powder degradation, crucial for alloys sensitive to oxygen. The effect of increasing layer thickness from 30 to 60 µm is studied focusing on Ti-6Al-4V spatter formation during LPBF and its characterisation, with scanning and transmission electron microscopy, combustion analysis and X-ray photoelectron spectroscopy. Results indicate that spatters are covered with a uniform Ti-Al-based oxide layer and Al-rich oxide particulates, the thickness of which is about twice that present on virgin powder. The oxygen content was about 60% higher in spatters compared to the virgin powder. The study highlights that increasing the layer thickness to 60 µm permits to reduce the total generation of spatters by ∼40%, while maintaining similar spatter characteristics and static tensile properties. Hence, this allows to increase build rate without compromising process robustness.
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| 7. |
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| 8. |
- Raza, Ahmad, 1993, et al.
(författare)
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Characterization of spatter and sublimation in alloy 718 during electron beam melting
- 2021
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 14:20
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Tidskriftsartikel (refereegranskat)abstract
- Due to elevated temperatures and high vacuum levels in electron beam melting (EBM), spatter formation and accumulation in the feedstock powder, and sublimation of alloying elements from the base feedstock powder can affect the feedstock powder’s reusability and change the alloy composition of fabricated parts. This study focused on the experimental and thermodynamic analysis of spatter particles generated in EBM, and analyzed sublimating alloying elements from Alloy 718 during EBM. Heat shields obtained after processing Alloy 718 in an Arcam A2X plus machine were analyzed to evaluate the spatters and metal condensate. Comprehensive morphological, microstructural, and chemical analyses were performed using scanning electron microscopy (SEM), focused ion beam (FIB), and energy dispersive spectroscopy (EDS). The morphological analysis showed that the area coverage of heat shields by spatter increased from top (<1%) to bottom (>25%), indicating that the spatter particles had projectile trajectories. Similarly, the metal condensate had a higher thickness of ~50 µm toward the bottom of the heat shield, indicating more significant condensation of metal vapors at the bottom. Microstructural analysis of spatters highlighted that the surfaces of spatter particles sampled from the heat shields were also covered with condensate, and the thickness of the deposited condensate depended on the time of landing of spatter particles on the heat shield during the build. The chemical analysis showed that the spatter particles had 17-fold higher oxygen content than virgin powder used in the build. Analysis of the metalized layer indicated that it was formed by oxidized metal condensate and was significantly enriched with Cr due to its higher vapor pressure under EBM conditions.
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| 9. |
- Raza, Ahmad, 1993, et al.
(författare)
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Degradation of AlSi10Mg powder during laser based powder bed fusion processing
- 2021
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Ingår i: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 198
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge concerning powder degradation during additive manufacturing (AM) processing is essential to improve the reusability of the powder in AM and hence maximize feedstock powder reuse and economy of the process. AlSi10Mg powder degradation in Concept Laser XLINE 2000R machine over the total period of 30 months was analyzed in order to understand the extent and mechanism affecting powder aging. Thereby, detailed analysis of the powder morphology, microstructure and surface chemistry was performed by SEM, TEM and XPS. The results show an increase in volume fraction of heavily oxidized spatter particles up to 3% in 30 months. XPS analysis of the powder surface chemistry indicates that powder particles are covered by uniform oxide layer, formed by Mg- and Al-based oxides, average thickness of which increased from ~4 nm in case of the virgin powder up to about 38 nm in case of the reused for about 30 month powder, established by XPS. Analysis of the oxide characteristics were consistent with the observed oxygen content in the sampled powder. Columnar oxide scale formation on spatter particles was revealed as well, reaching up to 125 nm in thickness measured using STEM. Results of the XPS and STEM-EDX analysis of oxide composition are shown to be in agreement with the thermodynamic calculations confirming that oxide scale on sputter particles is formed by MgAl2O4 spinel and Al2O3 (corundum) oxides.
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| 10. |
- Raza, Ahmad, 1993, et al.
(författare)
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Effect of layer thickness on spatters oxidation of Hastelloy X alloy during powder bed fusion-laser beam processing
- 2023
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 422
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the impact of powder layer thickness on spatter generation and oxidation behavior during the processing of Hastelloy X. In-situ monitoring using optical tomography reveals that thicker powder layers result in a higher number of hot spatters generated during laser-melt-powder interaction. Scanning electron microscopy and Auger electron spectroscopy analysis demonstrate the presence of different types of spatters that oxidize differently depending on their origin. X-ray photoelectron spectroscopy analysis further shows that the surface enrichment of oxide-forming elements such as Al, Ti, Cr, and Fe varies with the type of spatter particle. Additionally, depth profile analysis using X-ray photoelectron spectroscopy indicates that the average oxide layer thickness increases from ∼2.5 nm in virgin to ∼68 nm in spatters generated at 150 μm powder layer thickness. The findings suggest that powder layer thickness is a crucial factor in controlling spatter generation and oxidation behavior during powder bed fusion-laser beam processing.
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