| 1. |
- Deckers, Tobias, et al.
(författare)
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Einfluss heliumhaltiger Prozess-gase auf den Laser-Strahlschmelz-prozess
- 2022
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Ingår i: Zeitschrift Kunststofftechnik. - : Walter de Gruyter GmbH. - 1864-2217. ; 117:7-8, s. 452-455
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Tidskriftsartikel (refereegranskat)abstract
- Influence of Process Gases Containing Helium on the Laser Beam Melting Process. Can the process gas play a key role in optimizing the PBF-LB/M process (layer thickness, scan speed, processability of new materials, etc.)? This article provide insights into the current state of research at Linde GmbH regarding he-lium-containing process gases and presenting the novel process gas ADDvance® Laser230. Due to its composition, the gas mixture allows to significantly improve process productivity and stability.
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| 2. |
- Deckers, Tobias, et al.
(författare)
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Impact of processing gas composition on process stability and properties of PBF-LB/M processed alloy 718
- 2024
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Ingår i: Journal of Manufacturing Processes. - 1526-6125. ; 120, s. 712-718
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Tidskriftsartikel (refereegranskat)abstract
- The almost unlimited design freedom of the laser-based powder bed fusion of metals (PBF-LB/M) makes this technology very attractive for industry. However, as a developing technology, it still faces some challenges when it comes to productivity and robustness, to name some. Whereas numerous studies covered the impact of laser-based parameters on material properties and robustness, the effect of the processing gas received limited attention. The objective of this study was to evaluate the effect of processing gas composition, containing helium (He) and hydrogen (H2), compared to conventionally used argon (Ar), during PBF-LB/M processing of virgin alloy 718 powder, on printing behavior and part properties. The four gases studied were Ar, Ar +30%He, Ar +30%He +2%H2, and Ar +70%He. Optical Tomography (OT) was used to monitor process stability, which unveiled a significant decrease in process-by products (spatters) between 51 % and 89 % using He and H2-containing gases. It was also found that the process gas decreased the bulk porosity from an average value of 0.08 % when processed with Ar to 0.04 % when using Ar + 70%He. The oxygen pickup by the spatter particles was reduced from 630 ppm (Ar) to 331 ppm (Ar +70%He). EBSD analysis revealed that there were no evident changes in microstructure with the processing gas. The samples processed also had similar tensile properties with yield and ultimate tensile strength of 1180 MPa and 1395 MPa, respectively. However, there was a slight increase in ductility from 16.5 % to 17.2 %, when processed with pure Ar and Ar + 70%He, respectively. This study shows that utilizing standard Ar processing atmosphere with He addition leads to a more stable process with reduced spatter, porosity and a marginal increase in ductility for Alloy 718.
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| 3. |
- Mellin, P., et al.
(författare)
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Environmental and safety aspects of AM metal powder recycling
- 2019
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Ingår i: Euro PM 2019 Congress and Exhibition.
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Konferensbidrag (refereegranskat)abstract
- Repeated recirculation of powder in AM processes ultimately results in a powder with degraded properties. We firstly discuss this topic and describe an experiment designed to understand the mechanisms behind the degradation. Secondly, we perform yield analysis for build jobs on a SLM 125 at RISE IVF. Further on, we consider the required resources and estimate the emitted carbon dioxide equivalents (kgCO2eq) during production of the PBF-LB fraction of two gas atomized powders. The first powder is a tool steel alloy that emits 3.1 kgCO2eq/kg; the second powder is Hastelloy X (HX) that emits 24.2 kgCO2eq/kg. The HX powder, if degraded, is hence very desirable to recycle. Producing 1 kg of PBF-LB fraction from recycled HX material causes 5.7 kgCO2eq vs 24.2 from virgin sources. Finally, we review the health and safety aspects of recirculation and recycling of powder.
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| 4. |
- Pauzon, Camille Nicole Géraldine, 1994, et al.
(författare)
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Argon-helium mixtures as Laser-Powder Bed Fusion atmospheres: Towards increased build rate of Ti-6Al-4V
- 2020
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136. ; 279
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the gas thermal properties and density on the laser powder bed fusion (L-PBF) process was investigated by using inert argon, characterized by high density, and helium, characterized by high thermal conductivity and heat capacity, and their gas mixtures. The results highlighted that for L-PBF of Ti-6Al-4V, the effect of residual impurities such as oxygen and nitrogen on the process stability and defect generation is prevailing the type of the process gas. However, by monitoring the residual oxygen level in the process atmosphere, the results showed that using the argon-helium mixtures allows to increase the produced material density upon higher build rates. High density, greater than 99.98 % is indeed achieved using a mixture of 50 % argon and 50 % helium, allowing for a build rate increase of 44 % in comparison to the standard build rate. The analysis of the produced material revealed the presence of thermal residual stresses attributed to an enhanced energy input when using the gas mixtures. The latter offer a positive balance of density and thermal properties, and in turn, probably reduce the accumulation of process by-products at the melt pool that interfere with and attenuate the laser radiation. The possible detrimental effect of the introduced residual stresses is efficiently eliminated by the conventional stress relieving treatment leading to the decomposition of α´martensite into a fine (α + β) microstructure. This study opens the perspective on the development of the gas recipes for improved process stability and increased productivity of L-PBF process.
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| 5. |
- Pauzon, Camille Nicole Géraldine, 1994, et al.
(författare)
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Control of residual oxygen of the process atmosphere during laser-powder bed fusion processing of Ti-6Al-4V
- 2021
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Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604. ; 38
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the residual oxygen concentration in the process atmosphere during laser-powder bed fusion (L-PBF) of Ti-6Al-4V was investigated, using an external oxygen monitoring system equipped with two types of oxygen sensors typically used in L-PBF hardware: a lambda probe and an electrochemical oxygen sensor. The recordings of the oxygen variations during L-PBF highlighted that the electrochemical sensor is more reliable than the lambda probe, whose signal showed a maximum deviation of about 700 ppm O2 after 7 h, attributed to its sensitivity to hydrogen present in the system. The study revealed that proper monitoring of the oxygen in the laboratory scale L-PBF system used is necessary to limit oxygen and nitrogen pick-ups by the built material. Concentrations as high as 2200 ppm O2 and 500 ppm N2 in the Ti-6Al-4V part built under standard conditions were measured, compared to maximum levels of 1800 ppm O2 and 250 ppm N2 with the external oxygen control. In addition, the findings underline the critical effect of the component design, such as the high aspect ratio columns or the lattice structures, on the heat accumulation in case of Ti-6Al-4V, leading to enhanced oxygen and nitrogen pick-up, as high as 600 ppm O2 and 150 ppm N2 difference between the bottom and top of the cylindrical samples of 70 mm height used in this study. The determination of tensile properties of samples built at different heights put in evidence the detrimental effect of the oxygen increase with build height on the ductility, which decreased from 12% to below 6% between the bottom and top positions. This work highlights that the possible presence of impurities in the L-PBF atmosphere can have harmful impact on the properties of Ti-6Al-4V components, which can be mitigated adjusting the oxygen control system.
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| 6. |
- Pauzon, Camille Nicole Géraldine, 1994, et al.
(författare)
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Effect of argon and nitrogen atmospheres on the properties of stainless steel 316 L parts produced by laser-powder bed fusion
- 2019
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Ingår i: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 179
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Tidskriftsartikel (refereegranskat)abstract
- The role of the inert gas during laser powder bed fusion (L-PBF) is to remove the process by-products and the air that is initially present in the process chamber. On this purpose, different gas supply options are available. The effect of the process gas and its purity, using argon and nitrogen, on the properties of the 316 L stainless steel produced by L-PBF was studied. The results obtained showed that utilization of argon and nitrogen result in residual oxygen levels that vary over the course of the process sequence in the process chamber. It can be concluded that 316 L stainless steel is a robust alloy to process by L-PBF. A limited effect of the residual oxygen or the gas type (argon or nitrogen) on the tensile properties of the 316 L stainless steel parts was registered. The oxygen and nitrogen pick-up within the produced parts are limited. However, when processing 316 L stainless steel with lower purity gas supply such as a nitrogen generator, risks related to powder degradation arise. Out of the available gas options, the findings highlighted that processing with high purity argon ensures limited powder degradation and high toughness of the produced parts.
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| 7. |
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| 8. |
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| 9. |
- Pauzon, Camille Nicole Géraldine, 1994, et al.
(författare)
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Effect of the process gas and scan speed on the properties and productivity of thin 316L structures produced by Laser-Powder Bed Fusion
- 2020
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Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 51:10, s. 5339-5350
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Tidskriftsartikel (refereegranskat)abstract
- The development of the laser powder bed fusion (L-PBF) process to increase its robustness and productivity is challenged by ambitious design optimizations, such as thin wall structures. In this study, in addition to the effect of commonly used gases as Ar and N2, increased laser scanning speed and new process gases, such as helium, were successfully implemented. This implementation allowed to build 316L stainless steel components with thin walls of 1 mm thickness with an enhanced build rate of 37 pct. The sample size effect and the surface roughness were held responsible for the reduction in strength (YS > 430 MPa) and elongation (EAB > 30 pct) for the 1 mm samples studied. Similar strength was achieved for all process gases. The increased scanning speed was accompanied by a more random texture, smaller cell size, and grain size factor along the building direction when compared to the material built with the standard laser parameters. Stronger preferential orientation 〈101〉 along the building direction was observed for material built with standard parameters. Finally, the use of helium as a process gas was successful and resulted in reduced cell size. This finding is promising for the future development of high strength 316L stainless steel built with high build rates.
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| 10. |
- Pauzon, Camille Nicole Géraldine, 1994, et al.
(författare)
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Mitigating oxygen pick-up during laser powder bed fusion of Ti-6Al-4V by limiting heat accumulation
- 2021
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Ingår i: Materials Letters. - : Elsevier BV. - 1873-4979 .- 0167-577X. ; 288
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Tidskriftsartikel (refereegranskat)abstract
- The dissolution of oxygen in Ti-6Al-4V during laser powder bed fusion (L-PBF) is a limitation for the final ductility of the produced components and a challenge for the end-users. In the present work, the effect of the residual oxygen in the process atmosphere of a laboratory scale L-PBF machine, as well as the role of heat accumulation, are studied. It was shown that oxygen content in the as-built Ti-6Al-4V is determined by the size of the scanned area and build time. The heat accumulation aspect was investigated by adjusting the inter-layer time (ILT), by increasing the recoating time or the number of produced parts. The results showed that oxygen pick-up could be limited by reducing residual oxygen level in the atmosphere or heat accumulation. A 400 ppm O2 reduction measured at the top of a 70 mm column was achieved by increasing the ILT manually by 4.5s, and a 1200 ppm O2 reduction by increasing the scanned area by 7 times. By doing so, the hardness at full height was reduced by approximately 30 HV10. It is shown that design features characterised by high aspect ratio can absorb significant amount of oxygen resulting in increased brittleness.
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