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Towards sustainability in additive manufacturing: material and process aspects
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.ORCID iD: 0000-0003-4443-3097
2023 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Mot hållbarhet i additiv tillverkning: material- och processaspekter (Swedish)
Abstract [en]

The acceptance of additive manufacturing (AM) depends on the quality of final parts and process repeatability. Recently, many studies have been dedicated to the establishment of the relationship between the process behavior and material performance. Phenomena such as laser-material interaction, melt pool dynamics, ejecta formation and particle movement behavior on a powder bed are of a particular interest for the AM community as these events directly influence the outcome of the process. Another aspect, which hinders the adoption of AM, is the need for cost-efficient powder materials, their sustainable processing and recycling. 

The research work presented in this thesis explores scientific aspects related to the above-mentioned topics, with a particular focus on the material and process behavior phenomena in powder bed fusion-laser melting (PBF-LM) and directed energy deposition (DED) processes. 

Paper A shows a comparative study of dissimilarly shaped gas and water atomized low alloy steel powders regarding their processability, packing capacities, particle movement behavior and powder performance in PBF-LM. The impact of chemical composition and morphology of the powders on the process behavior was revealed. Powder spattering and melt pool instabilities were discussed in detail. 

Paper B contains research on the particle movement and denudation behavior on a powder bed when using near-spherical and non-spherical steel powders. The influence of particle morphology on the dynamics of arbitrary-shaped powder particles was studied by applying an analytical correlation formula to calculate the drag force exerted on powder particles of various shape. Particle entrainment of gas and water atomized powders in front of the laser beam was measured, revealing a significant difference in the powder transfer towards the melt pool.

Paper C explains the role of ejecta in the recycled powder and the changing behavior of the material due to ejecta pick-up. The impact of multiple powder recycling steps on the degradation of low alloy steel powder in laser powder bed fusion was studied. Oxygen content, particle size and ejecta occurrence gradually increased after each recycling step and were identified as the main contributors to the property alterations observed in the powder during recycling. In addition, a direct correlation between the increase in oxygen and more frequent spatter ejection with repeated recycling was established. 

Paper D focuses on the impact of powder aging on the degradation of AlSi10Mg powder during processing in PBF-LM. The analysis of the powder properties, affected by laser exposure and the aging procedure, showed a change of chemical and morphological characteristics of the powders in virgin and aged conditions. The oxygen content in the powders appeared to have a significant effect on the powders' surface appearance and light absorbance, gradually deteriorating the processability of the powders with the increase of oxygen level. Porosity occurrence and its influence on the mechanical properties of the powders was also studied, demonstrating a rapid decrease of ultimate tensile strength and elongation from virgin condition to aged.

Papers E and F investigate the possibilities of iron ore waste reduction using Al powder as a reducing agent and a laser beam as a heat source. Paper E focuses on the Fe2O3-Al interaction behavior and extent of the iron ore reduction, whereas Paper F reports on the high-speed imaging investigation possibilities of laser beam-material surface interaction when processing Fe2O3-Al powders and an Fe2O3 powder-AlSI5 wire combination in DED. In-situ observation of various melt pool phenomena and exothermic reaction behavior of the material combinations using high-speed imaging was carried out. In addition to that, the influence of feed materials and laser power on the thermite reaction time was discussed in detail, showing their dissimilar behavior.

All six papers include research on laser additive manufacturing using powder feedstocks. The papers discuss various phenomena regarding powder processability, recycling and laser beam-material interaction behavior in both PBF-LM and DED. High-speed imaging was used as the main tool to observe and study the above listed topics.  

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2023.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Research subject
Manufacturing Systems Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-95789ISBN: 978-91-8048-278-3 (print)ISBN: 978-91-8048-279-0 (electronic)OAI: oai:DiVA.org:ltu-95789DiVA, id: diva2:1741016
Public defence
2023-04-27, E632, Luleå tekniska universitet, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2023-03-02 Created: 2023-03-02 Last updated: 2023-04-06Bibliographically approved
List of papers
1. A comparative study of water and gas atomized low alloy steel powders for additive manufacturing
Open this publication in new window or tab >>A comparative study of water and gas atomized low alloy steel powders for additive manufacturing
2020 (English)In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 36, article id 101675Article in journal (Refereed) Published
Abstract [en]

This work reports a study of the differences between laser processing of water and gas atomized low alloy steel powders with a focus on powder behavior and performance in additive manufacturing. Material packing densities were measured to establish a relationship between powder packing and track formation. The results showed that the track height when using water atomized powder was 15% lower than the value achieved for the gas atomized powder. High-speed imaging was utilized to observe the material behavior and analyze the powder particle movement under laser irradiation. It was found that water atomized powder has less particle entrainment due to its tendency towards mechanical interlocking. The occurrence of powder spattering and melt pool instabilities was also studied. More frequent spatter ejection is believed to be due to the higher amount of oxygen in the water atomized powder.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Additive manufacturing, Laser powder bed fusion, Water atomized powder, Packing density, Low alloy steel, High-speed imaging
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-81523 (URN)10.1016/j.addma.2020.101675 (DOI)000600807800194 ()2-s2.0-85095580581 (Scopus ID)
Funder
Interreg Nord, 304–7463-2018
Note

Validerad;2021;Nivå 2;2021-01-04 (alebob);

Finansiär: EIT Raw Materials Knowledge and Innovation Community, Europe (17070)

Available from: 2020-11-23 Created: 2020-11-23 Last updated: 2023-09-06Bibliographically approved
2. The role of powder morphology in particle movement behavior in laser powder bed fusion with an emphasis on fluid drag
Open this publication in new window or tab >>The role of powder morphology in particle movement behavior in laser powder bed fusion with an emphasis on fluid drag
2022 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 395, p. 720-731Article in journal (Refereed) Published
Abstract [en]

This study investigates the movement behavior of particles of dissimilar morphology in the powder bed in Laser Powder Bed Fusion. Gas atomized (GA) and water atomized (WA) low alloy steel powders were employed to study their motion around the laser scan path. Particle velocities, entrainment distances and denudation zones were measured for both powders using high-speed imaging. The entrainment of GA powder particles in front of the laser beam towards the process area was initiated 1.6 mm from the edge of the melt pool, whereas the distance was 0.6–0.8 mm for the WA powder. The differences in observed behavior were related to the variations in particle shape of the two types of powder. The processing of WA powder resulted in a 16% narrower denudation zone (for a low volumetric energy density) compared to GA powder. However, the denudation width difference decreased with increasing volumetric energy density, most likely due to a steeper pressure gradient in the process area which diminishes the impact of powder shape. X-ray computed microtomography was utilized to estimate the drag force acting on the powder particles of various morphologies. The results showed that the radial drag force exerted on GA powder was 64% greater than when using WA powder. Moreover, if the WA powder particles were of elongated shape the drag force decreased by almost an order of magnitude, demonstrating the importance of the particle's morphology in the process dynamics.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Water atomized powder, Particle movement, Dissimilar morphology, Drag force, Laser powder bed fusion, Additive manufacturing
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-87583 (URN)10.1016/j.powtec.2021.10.020 (DOI)000718001100004 ()2-s2.0-85117723002 (Scopus ID)
Funder
Interreg Nord, 304-7463-2018
Note

Validerad;2021;Nivå 2;2021-10-25 (beamah);

Funder: EIT Raw Materials (No.17070)

2022-03-02: Dubblettpost PID: 1554744 har raderats. (sofila)

Available from: 2021-10-21 Created: 2021-10-21 Last updated: 2023-03-02Bibliographically approved
3. Spattering and oxidation phenomena during recycling of low alloy steel powder in Laser Powder Bed Fusion
Open this publication in new window or tab >>Spattering and oxidation phenomena during recycling of low alloy steel powder in Laser Powder Bed Fusion
2021 (English)In: Materials Today Communications, ISSN 2352-4928, Vol. 27, article id 102241Article in journal (Refereed) Published
Abstract [en]

This study reports on the impact of repeated powder recycling on the degradation of low alloy steel powder in Laser Powder Bed Fusion. The average powder particle size increased slightly upon recycling due to powder agglomeration and the presence of spatters and other ejecta from the process zone. The oxygen content showed a continuous growth after each recycle, while the other chemical elements of the recycled powder remained largely unchanged. A map of ejecta classification is presented, featuring various ejecta types formed during laser processing. Ejecta of increased diameter and different shapes were observed in the recycled powder, using high-speed imaging and Scanning Electron Microscopy. The ejecta were collected after each powder recycle to enable the calculation of the ejecta mass generated during the process. The result showed a direct correlation between oxygen content in the powder and spatter/ejecta formation with the number of recycling events. It is likely that the increase in oxygen contributes to powder spattering.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Low alloy steel, Spattering, Powder degradation, Recycling, Laser Powder Bed Fusion, Additive manufacturing
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-83247 (URN)10.1016/j.mtcomm.2021.102241 (DOI)000683034600006 ()2-s2.0-85102510106 (Scopus ID)
Funder
Interreg Nord, 304-7463-2018
Note

Validerad;2021;Nivå 2;2021-03-23 (johcin);

Finansiär: EIT Raw Materials Knowledge and Innovation Community (17070)

Available from: 2021-03-12 Created: 2021-03-12 Last updated: 2023-03-02Bibliographically approved
4. Influence of AlSi10Mg powder aging on the material degradation and its processing in laser powder bed fusion
Open this publication in new window or tab >>Influence of AlSi10Mg powder aging on the material degradation and its processing in laser powder bed fusion
Show others...
2022 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 412, article id 118024Article in journal (Refereed) Published
Abstract [en]

This study investigates the impact of powder aging on the degradation of AlSi10Mg powder during processing in laser powder bed fusion. Powder aging as result of handling, continuous storage and recycling is a fundamental concern for aluminum alloys as it introduces oxygen to the feedstock material. In this work, the analysis of the powder properties, affected by laser exposure and the aging procedure, showed a change of chemical and morphological characteristics of the powders in virgin and aged conditions. The oxygen content in the powders appeared to have a significant effect on the powders' surface appearance and light absorbance, gradually deteriorating the processability of the powders with the increase of oxygen level. Optical microscopy and X-ray computed tomography were used to analyze the porosity distribution in the printed part samples, identifying the origin, size and location of the pores. A direct relationship between the pore occurrence in final parts and the oxygen content in the powders was observed, revealing a higher degree of porosity in the aged powder sample (6.5%) in comparison with the virgin state (3.16%). The evolution of mechanical properties in the part samples after laser processing and powder aging was also studied, demonstrating a rapid decrease of ultimate tensile strength and elongation from virgin condition to aged.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Additive manufacturing, Aging, Aluminum, Laser powder bed fusion, Powder absorbance, Powder condition
National Category
Manufacturing, Surface and Joining Technology Materials Chemistry
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-93764 (URN)10.1016/j.powtec.2022.118024 (DOI)000929653800004 ()2-s2.0-85140083469 (Scopus ID)
Note

Validerad;2022;Nivå 2;2022-10-31 (hanlid);

Funder: EIT Raw Materials (18079 SAMOA)

Available from: 2022-10-31 Created: 2022-10-31 Last updated: 2024-03-07Bibliographically approved
5. Laser-assisted reduction of iron ore using aluminum powder
Open this publication in new window or tab >>Laser-assisted reduction of iron ore using aluminum powder
2023 (English)In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 35, no 2, article id 022007Article in journal (Refereed) Published
Abstract [en]

This study reports on the laser-assisted reduction of iron ore waste using Al powder as areducing agent. Due to climate change and the global warming situation, it has become ofparamount importance to search for and/or develop green and sustainable processes for ironand steel production. In this regard, a new method for iron ore utilization is proposed in thiswork, investigating the possibility of iron ore waste reduction via metallothermic reaction withAl powder. Laser processing of iron ore fines was performed, focusing on the Fe2O3-Alinteraction behavior and extent of the iron ore reduction. The reaction between the materialsproceeded in a rather intense uncontrolled manner which led to a formation of Fe-rich domainsand alumina as two separate phases. In addition, a combination of Al2O3 and Fe2O3 melts aswell as transitional areas such as intermetallics were observed, suggesting the occurrence ofincomplete reduction reaction in isolated regions. The reduced iron droplets were prone toacquire a sphere-like shape and concentrated mainly near the surface of the Al2O3 melt or at theinterface with the iron oxide. Both SEM, EDS and WDS analyses were employed to analyzechemical composition, microstructure and morphological appearances of the reaction products.High-speed imaging was used to study the process phenomena and observe differences in themovement behavior of the particles. Furthermore, the measurements acquired from X-raycomputed microtomography revealed that approximately 2.4 % of iron was reduced during thelaser processing of Fe2O3-Al powder bed, most likely due to insufficient reaction time orinappropriate equivalence ratio of the two components.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2023
Keywords
iron ore, aluminum, reduction, sustainability, laser powder bed fusion, additive manufacturing
National Category
Metallurgy and Metallic Materials Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-95787 (URN)10.2351/7.0000856 (DOI)000952257600002 ()2-s2.0-85150388187 (Scopus ID)
Funder
Swedish Energy Agency, 51021-1, P2022-00202
Note

Validerad;2023;Nivå 2;2023-04-12 (hanlid);

Available from: 2023-03-02 Created: 2023-03-02 Last updated: 2024-03-07Bibliographically approved
6. In-situ observation of melt pool phenomena in directed energy deposition of iron ore andaluminum materials
Open this publication in new window or tab >>In-situ observation of melt pool phenomena in directed energy deposition of iron ore andaluminum materials
Show others...
(English)In: Article in journal (Refereed) Submitted
Abstract [en]

This study reports on the high-speed imaging investigation possibilities of laser beammaterialsurface interaction when processing Fe2O3-Al powders and an Fe2O3 powder-AlSI5wire combination in directed energy deposition. In-situ observation of various melt poolphenomena and exothermic reaction behavior of the material systems using high-speed imagingwas at the focus of this research work. Depending on the feed material arrangement (powderpowderor powder-wire) and process parameters, significant differences in the melt poolformation were observed, including melt pool separation into two distinct phases and theoccurrence of thermite reaction at different stages of the process. In addition to that, theinfluence of feed materials and laser power on the thermite reaction time was discussed in detail,showing their dissimilar behavior. During laser processing of the powder-powder arrangement,the reaction duration increased with the increase of laser power, whereas the powder-wireconfiguration demonstrated the opposite trend, most likely due to the smaller surface contactarea, developed between the iron ore particles and the AlSi5 wire. Chemical composition,morphological appearances and phase accumulation were analyzed using scanning electronmicroscopy and energy-dispersive X-ray spectroscopy. The obtained data were used toestablish a connection between the melt pool and the reaction products. High-speed imagingwas utilized throughout the experiments to observe and capture the process phenomena.

National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:ltu:diva-95788 (URN)
Available from: 2023-03-02 Created: 2023-03-02 Last updated: 2023-03-02

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