| 1. |
- Leicht, Alexander, 1987, et al.
(författare)
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Effect of part thickness on the microstructure and tensile properties of 316L parts produced by laser powder bed fusion
- 2021
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Ingår i: Advances in Industrial and Manufacturing Engineering. - : Elsevier BV. - 2666-9129. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing provides a unique possibility to manufacture parts with advanced design and thin-walled structures. To explore thin-wall capacity, laser powder bed fusion was employed to fabricate 316L samples with different section thicknesses. A detailed microstructure characterization was then carried out, and tensile properties were assessed. It was found that reducing the part thickness did not affect the microstructure but did reduce the tensile properties. Samples with 1 mm thickness exhibited the lowest yield strength of 457 ± 11 MPa and elongation to fracture of 49 ± 20%, while the tensile properties improved when the sample thickness was increased to 3 mm. The 3 mm thick samples generated tensile properties comparable to those of standard dimensions. The results emphasize that part thickness must be considered when assessing mechanical properties and must be adjusted when performing design optimization and simulations of samples produced with laser powder bed fusion.
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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
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| 6. |
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| 7. |
- Pauzon, Camille Nicole Géraldine, 1994, et al.
(författare)
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Effect of helium as process gas on laser powder bed fusion of Ti-6Al-4V studied with operando diffraction and radiography
- 2022
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Ingår i: European Journal of Materials. - : Informa UK Limited. - 2688-9277. ; 2:1, s. 422-435
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Tidskriftsartikel (refereegranskat)abstract
- The utilisation of helium as process gas in laser powder bed fusion limits the generation of Ti-6Al-4V hot and incandescent spatters and enhances their cooling rate. In the present study, operando X-ray diffraction using synchrotron X-rays permits to verify that the cooling rates experienced by the deposited material are not significantly affected by the process gas unlike spatters. Topography measurements of the top printed surface reveal lower roughness of He-produced samples, attributed to the previously observed reduction of spatters with He and thus a reduction of redepositions on the powder bed and printed surfaces. Operando radiography provides with insights on the spatter formation mechanisms namely particle entrainment, agglomeration, melting and spheroidization.Highlights The top surface average roughness of samples produced with He is lower than that of Ar equivalent Deposited Ti-6Al-4V cooling rates during LPBF are not significantly affected by the use of He Grain size and orientation of Ti-6Al-4V is similar when processing under Ar, He, and a mixture of both Operando radiography permits to identify the mechanisms of Ti-6Al-4V spatter formation.
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| 8. |
- 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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| 9. |
- Pauzon, Camille Nicole Géraldine, 1994, et al.
(författare)
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Effect of the process atmosphere composition on alloy 718 produced by laser powder bed fusion
- 2021
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Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 11:8
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Tidskriftsartikel (refereegranskat)abstract
- The detrimental effect of nitrogen and oxygen when it comes to the precipitation of the strengthening γ’’ and γ’ phases in Alloy 718 is well-known from traditional manufacturing. Hence, the influence of the two processing atmospheres, namely argon and nitrogen, during the laser powder bed fusion (L-PBF) of Alloy 718 parts was studied. Regardless of the gas type, considerable losses of both oxygen of about 150 ppm O2 (≈30%) and nitrogen on the level of around 400 ppm N2 (≈25%) were measured in comparison to the feedstock powder. The utilization of nitrogen as processing atmosphere led to a slightly higher nitrogen content in the as-built material—about 50 ppm—compared to the argon atmosphere. The presence of the stable nitrides and Al-rich oxides observed in the as-built material was related to the transfer of these inclusions from the nitrogen atomized powder feedstock to the components. This was confirmed by dedicated analysis of the powder feedstock and supported by thermodynamic and kinetic calculations. Rapid cooling rates were held responsible for the limited nitrogen pick-up. Oxide dissociation during laser–powder interaction, metal vaporization followed by oxidation and spatter generation, and their removal by processing atmosphere are the factors describing an important oxygen loss during L-PBF. In addi-tion, the reduction of the oxygen level in the process atmosphere from 500 to 50 ppm resulted in the reduction in the oxygen level in as-built component by about 5%.
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| 10. |
- 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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| 11. |
- Pauzon, Camille Nicole Géraldine, 1994, et al.
(författare)
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Impact of contour scanning and helium-rich process gas on performances of Alloy 718 lattices produced by laser powder bed fusion
- 2022
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Ingår i: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 215
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Tidskriftsartikel (refereegranskat)abstract
- Contour scanning and process gas type are process parameters typically considered achieving second order effects compared to first order factors such as laser power and scanning speed. The present work highlights that contour scanning is crucial to ensure geometrical accuracy and thereby the high performance under uniaxial compression of complex Alloy 718 lattice structures. Studies of X-ray computed tomography visualizations of as-built and compression-strained structures reveal the continuous and smooth bending and compression of the walls, and the earlier onset of internal contact appearance in the denser lattices printed with contour. In contrast, the effect of addition of He to the Ar process gas appears to have limited influence on the mechanical response of the lattices and their microstructure as characterized by electron backscattered diffraction. However, the addition of He proved to significantly enhance the cooling rate and to reduce the amount of the generated spatters as evidenced by in situ monitoring of the process emissions, which is very promising for the process stability and powder reusability during laser powder bed fusion.
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| 12. |
- 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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| 13. |
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| 14. |
- Pauzon, Camille Nicole Géraldine, 1994, et al.
(författare)
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Reduction of incandescent spatter with helium addition to the process gas during laser powder bed fusion of Ti-6Al-4V
- 2021
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Ingår i: CIRP Journal of Manufacturing Science and Technology. - : Elsevier BV. - 1755-5817 .- 1878-0016. ; 35, s. 371-378
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the process gas during laser powder bed fusion (L-PBF) was investigated using high-speed shadowgraphy while melting Ti-6Al-4V powder under high purity argon, helium, and a mixture of both, on a laboratory-scale machine. These recordings reveal that the generation of incandescent spatters can be reduced by at least 60% using pure helium and by ∼30% using addition of helium to argon in comparison to the use of traditional argon. The quantity of colder spatters appeared unaffected by the change of process gas. Different configurations of gas flow versus laser scanning direction were investigated and revealed that fumes and spatters are less accumulated at the laser spot with helium addition. Furthermore, the use of the argon–helium mixture proved to be as efficient as pure argon in the dragging and extraction of the fumes. Shadowgraphs revealed the more rapid expansion of fumes in helium-rich atmospheres, limiting the accumulation of scattering objects close to the laser spot and thus melt pool instability. These results were correlated to process snapshots on an industrial-scale system, confirming the reduction of hot spatter generation. Finally, the findings put in evidence the more rapid cooling of spatters with helium addition to the process gas – a promising aspect to limit powder bed degradation during L-PBF. In addition, the use of mixtures of helium and argon would be economically interesting compared to pure helium, typically more expensive than the traditionally used argon.
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| 15. |
- Pauzon, Camille Nicole Géraldine, 1994, et al.
(författare)
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Residual stresses and porosity in Ti-6Al-4V produced by laser powder bed fusion as a function of process atmosphere and component design
- 2021
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Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604. ; 47
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the process gas, laser scan speed, and sample thickness on the build-up of residual stresses and porosity in Ti-6Al-4V produced by laser powder bed fusion was studied. Pure argon and helium, as well as a mixture of those (30% helium), were employed to establish process atmospheres with a low residual oxygen content of 100 ppm O-2. The results highlight that the subsurface residual stresses measured by X-ray diffraction were significantly lower in the thin samples (220 MPa) than in the cuboid samples (645 MPa). This difference was attributed to the shorter laser vector length, resulting in heat accumulation and thus in-situ stress relief. The addition of helium to the process gas did not introduce additional subsurface residual stresses in the simple geometries, even for the increased scanning speed. Finally, larger deflection was found in the cantilever built under helium (after removal from the baseplate), than in those produced under argon and an argon-helium mixture. This result demonstrates that complex designs involving large scanned areas could be subjected to higher residual stress when manufactured under helium due to the gas's high thermal conductivity, heat capacity, and thermal diffusivity.
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| 16. |
- Pauzon, Camille Nicole Géraldine, 1994
(författare)
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Tailored process gases for laser powder bed fusion
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Metal laser powder bed fusion (L-PBF) allows for production of complex components using the energy from a laser to locally melt micron-sized powder following a layer-wise approach. Considerable scientific efforts are focused on addressing the influence of the process parameters on the melting stability and the control of material properties, while developing necessary monitoring and characterization tools. The importance of the process atmosphere has largely been undermined in favour of first order parameters connected to the laser scanning. The role of the atmosphere has been limited to the reduction of the operating residual oxygen level down to typically 1000 ppm. This thesis focuses on providing knowledge on the influence of the process atmosphere on the laser – metal powder interaction during L-PBF and the resulting properties of the built material in terms of generated defects, microstructure and mechanical properties. Different purities and compositions of generated atmospheres have been investigated to manufacture the most used materials in the field, namely 316L stainless steel, Alloy 718 and Ti-6Al-4V. The scope of process gases was extended from the traditionally employed argon to also include nitrogen, helium and mixtures of argon and helium. Purities from the typical 1000 ppm O2 threshold down to a few ppm were achieved using external monitoring of the atmosphere on both industrial- and laboratory-scale production machines. The investigated materials displayed different sensitivities to the atmosphere composition. 316L stainless steel had limited differences in terms of composition and strength when processed with high purity argon or nitrogen. Only processing with a built-in nitrogen generator, with which the process starts as soon as 10000 ppm residual O2 is reached, led to the increased oxidation of spatter particles and the appearance of large lack-of-fusion defects. A reduction in residual oxygen down to few ppm allowed to significantly hinder the development of thick Cr- and Al-rich particulate oxides on the surface of Alloy 718 spatter particles exposed to the L-PBF environment. In addition, Ti-6Al-4V had the highest sensitivity to the presence of impurities with significant oxygen and nitrogen pick-ups leading to embrittlement. This could be partially mitigated by limiting heat accumulation with longer interlayer time at the expense of productivity or by decreasing the oxygen level in the build chamber to below 100 ppm. Finally, helium was introduced as a new process gas that allowed to reduce the generation of spatter particles, favouring a stable melt pool, without significantly disrupting the residual stress state of the built part, which is critical for the productivity of L-PBF.
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| 17. |
- Pauzon, Camille Nicole Géraldine, 1994
(författare)
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The process atmosphere as a parameter in the Laser-Powder Bed Fusion process
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Laser-Powder Bed Fusion (L-PBF) is an Additive Manufacturing (AM) technique that allows to produce near-net shape components of complex design. Applied to metallic materials, L-PBF allows to consolidate subsequent layers of powder using the heat from laser radiation. The powder particles are typically micron-sized and have a high specific surface area, making them prone to surface oxidation. As several layers are consolidated, the powder feedstock and solidified material are exposed to repeated thermal cycles, involving high peak temperatures and high heating/cooling rates. This heat input is likely to trigger oxidation by enhancing the reaction of the heated material with the residual oxygen present in the process atmosphere. To limit the extent of oxidation, protective atmospheres are used. These atmospheres are typically established by blanketing the powder bed using an inert gas, which permits the dilution of the present oxygen, and to some extent other impurities such as nitrogen and humidity. The gas will also drag away possible process by-products that are likely to introduce defects within the material upon their re-deposition. Although the gas is necessary for the L-PBF process, its role has mainly been disregarded until now as focus has been placed on other process parameters such as laser related ones (e.g. laser power and scanning speed). As a result, the available gases for L-PBF are limited to the noble argon and the relatively inert nitrogen, leading to the L-PBF machines being designed only for the use of these gases. The present study aims to raise awareness of the significant role of the gas properties and control for the L-PBF process. The effect of the residual oxygen and processing gas properties are addressed. The results highlight that the residual oxygen guidelines should be proposed based on the sensitivity of the material to the oxygen and nitrogen exposure. While Ti-6Al-4V shows a difference in density at 1000 ppm O2 compared to 100 ppm O2, 316L stainless steel exhibits consistent mechanical properties for any oxygen level below 1000 ppm O2. Upon higher oxygen partial pressure (e.g. 2000 ppm O2), the 316L stainless steel powder particles develop oxide features on the surface. These features are consistent with an increased oxygen pick-up by the material, and the further reduction of its impact toughness, reflecting an increase in oxide inclusions content within the built material. Furthermore, the work conducted in this thesis gives an insight on the effect of the gas density and thermal properties on the produced Ti-6Al-4V material. Helium gas, which is significantly lighter than argon and nitrogen, was successfully implemented in the L-PBF process of Ti-6Al-4V. Helium and argon-helium gas mixtures enable a reduction in the porosity upon higher build rates. This is attributed to the positive balance of density and thermal properties offered by these mixtures. The obtained results could be used to initiate the development of new gas mixtures aiming at increasing the L-PBF productivity and process robustness.
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| 18. |
- Pauzon, Camille Nicole Géraldine, 1994, et al.
(författare)
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Thermally Induced Porosity within HIPed Ti64 Parts: Effect of Entrapped Argon versus Helium in L-PBF
- 2019
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Ingår i: Euro PM 2019 Congress and Exhibition.
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Konferensbidrag (refereegranskat)abstract
- For Laser-Powder Bed Fusion (L-PBF), gas porosity is likely to be introduced by gas entrapment within the rapidly solidifying melt pool. Under standard argon processing conditions, argon is likely to be within these pores. It is believed that porosity can be efficiently removed by Hot Isostatic Pressing (HIP). However, when Ti-6Al-4V parts are HIPed and further subjected to high temperatures, there is a risk for thermally induced porosity (TIP) to occur. The latter is formed by the previously pressurized argon gas, not eliminated during the HIP because of the limited diffusion of atomic argon within the metal matrix. Helium, because of its smaller atomic radius, is suspected to diffuse faster. In this study, effect of helium on process induced porosity and its elimination during HIP in comparison to Ar is investigated. This is done through the X-ray computed tomography study of the porosity evolution through the AM process chain.
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| 19. |
- 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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| 20. |
- Raza, Ahmad, 1993, et al.
(författare)
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Effect of processing gas on spatter generation and oxidation of TiAl6V4 alloy in laser powder bed fusion process
- 2023
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 613
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Tidskriftsartikel (refereegranskat)abstract
- The atmosphere is a vital factor influencing powder degradation during laser powder bed fusion. Particularly, its purity, density, and thermal conductivity, can strongly affect spatter generation, thermal history, and oxidation. It is critical to understand the atmosphere-spatter properties relationship to enhance powder recyclability and overall process sustainability. Herein, the effect of processing gases, among pure Ar, (Ar+He), and He, on spatter generation and oxidation during TiAl6V4 processing is investigated. To evaluate their influence on impurity pickup and morphology of spatters, bulk chemical analysis and scanning electron microscopy were conducted. The nature and thickness of surface oxides on spatters were comprehensively examined using surface analysis tools including X-ray photoelectron spectroscopy, Auger electron spectroscopy, and nano secondary ion mass spectroscopy. The bulk chemical analysis showed a 70% increase in oxygen content and a 3-fold increase in nitrogen content from virgin to spatter collected in standard argon atmosphere. The increase of impurities was substantially lower for the spatters generated in He and the mixture of (Ar+He). The surface analysis showed that the spatter surface was covered with a uniform Ti- and Al-rich oxide layer along with Al-based oxide particulates. Finally, this study discusses the nature of oxide on TiAl6V4 spatters.
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| 21. |
- Raza, Ahmad, 1993, et al.
(författare)
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Spatter oxidation during laser powder bed fusion of Alloy 718: Dependence on oxygen content in the process atmosphere
- 2021
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Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604. ; 48
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Tidskriftsartikel (refereegranskat)abstract
- In laser powder bed fusion (L-PBF), powder degradation is mainly driven by the accumulation of highly oxidized spatter particles in the powder bed. Although the amount of spattering can be controlled by the melt pool stability, spatter formation is an unavoidable characteristic of PBF processes. Oxidized spatter risks defect formation in the printed components. However, the factors influencing the level of spatter oxidation during L-PBF processing are not yet fully understood. Herein, the residual oxygen in the process atmosphere was reduced from the traditionally applied 1000–20 ppm using an oxygen partial pressure control system to process Alloy 718 powder. Spatter particles accumulated on the gas inlet were further analyzed to reveal the effect of the oxygen content in the process atmosphere on the spatter oxidation by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Increasing the residual oxygen in the process atmosphere increased surface coverage by oxide phases rich in Al and Cr. The XPS analysis confirmed that the surface of Alloy 718 spatter particles were covered with Al- and Cr-based oxides, whose thickness increased with the oxygen content in the process atmosphere. The bulk oxygen content in the spatter powder showed the same trend with approximately thrice the oxygen content in spatters generated at 1000 ppm O2 (608 ppm O in the sample) compared to spatters generated with oxygen at 20 ppm (206 ppm O in the sample). Thermodynamic simulations demonstrate a transition from thick Al- and Cr-based mixed corundum and spinel-type oxides to Al-based corundum oxide with decreasing oxygen partial pressure, consistent with the XPS findings.
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