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Alvi, S., Neikter, M., Antti, M.-L. & Akhtar, F. (2021). Tribological performance of Ti6Al4V at elevated temperatures fabricated by electron beam powder bed fusion. Tribology International, 153, Article ID 106658.
Open this publication in new window or tab >>Tribological performance of Ti6Al4V at elevated temperatures fabricated by electron beam powder bed fusion
2021 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 153, article id 106658Article in journal (Refereed) Published
Abstract [en]

Electron beam powder bed fusion (EBPBF) is a beneficial processing route to fabricate Ti6Al4V alloy for aerospace applications due to its relatively low lead time and the possibility of topology optimization. The dry sliding wear behavior of EBPBF-Ti6Al4V against steel and alumina counterballs from room temperature (RT) to 500 °C was investigated to evaluate the influence of EBPBF processing and microstructure on the wear properties for broadening the application criteria of this lightweight alloy. The wear tests revealed that the wear rate decreased with increasing temperature due to formation of stable oxide glaze layer. This study reveals elevated temperature sliding wear behavior, wear mechanisms and microstructural changes below the wear track of EBPBF Ti6Al4V alloy against steel and alumina counterbodies.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Electron beam powder bed fusion, Wear properties, Ti6Al4V, High temperature tribology, Additive manufacturing, Aerospace
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-80882 (URN)10.1016/j.triboint.2020.106658 (DOI)000582755900089 ()2-s2.0-85091248818 (Scopus ID)
Note

Validerad;2020;Nivå 2;2020-09-28 (alebob)

Available from: 2020-09-22 Created: 2020-09-22 Last updated: 2023-09-05Bibliographically approved
Neikter, M., Colliander, M., de Andrade Schwerz, C., Hansson, T., Åkerfeldt, P., Pederson, R. & Antti, M.-L. (2020). Fatigue Crack Growth of Electron Beam Melted Ti-6Al-4V in High-Pressure Hydrogen. Materials, 13(6), Article ID 1287.
Open this publication in new window or tab >>Fatigue Crack Growth of Electron Beam Melted Ti-6Al-4V in High-Pressure Hydrogen
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2020 (English)In: Materials, E-ISSN 1996-1944, Vol. 13, no 6, article id 1287Article in journal (Refereed) Published
Abstract [en]

Titanium-based alloys are susceptible to hydrogen embrittlement (HE), a phenomenon that deteriorates fatigue properties. Ti-6Al-4V is the most widely used titanium alloy and the effect of hydrogen embrittlement on fatigue crack growth (FCG) was investigated by carrying out crack propagation tests in air and high-pressure H2 environment. The FCG test in hydrogen environment resulted in a drastic increase in crack growth rate at a certain Δ K, with crack propagation rates up to 13 times higher than those observed in air. Possible reasons for such behavior were discussed in this paper. The relationship between FCG results in high-pressure H2 environment and microstructure was investigated by comparison with already published results of cast and forged Ti-6Al-4V. Coarser microstructure was found to be more sensitive to HE. Moreover, the electron beam melting (EBM) materials experienced a crack growth acceleration in-between that of cast and wrought Ti-6Al-4V.

Place, publisher, year, edition, pages
MDPI, 2020
Keywords
fatigue crack growth (FCG), electron beam melting (EBM), Ti-6Al-4V, hydrogen embrittlement (HE)
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-78500 (URN)10.3390/ma13061287 (DOI)000529208000026 ()32178389 (PubMedID)2-s2.0-85082593205 (Scopus ID)
Note

Validerad;2020;Nivå 2;2020-04-15 (alebob)

Available from: 2020-04-15 Created: 2020-04-15 Last updated: 2025-04-17Bibliographically approved
Neikter, M., Woracek, R., Durniak, C., Persson, M., Antti, M.-L., Åkerfeldt, P., . . . Strobl, M. (2020). Texture of electron beam melted Ti-6Al-4V measured with neutron diffraction. In: P. Villechaise, B. Appolaire, P. Castany, M. Dehmas, C. Delaunay, J. Delfosse, A. Denquin, E. Gautier, L. Germain, N. Gey, T. Gloriant, J.-Y. Hascoët, S. Hémery, Y. Millet, D. Monceau, F. Pettinari-Sturmel, M. Piellard, F. Prima and B. Viguier (Ed.), : . Paper presented at 14th World Conference on Titanium (Ti 2019), 10-14 June, 2019, Nantes, France. EDP Sciences, Article ID 03021.
Open this publication in new window or tab >>Texture of electron beam melted Ti-6Al-4V measured with neutron diffraction
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2020 (English)In: / [ed] P. Villechaise, B. Appolaire, P. Castany, M. Dehmas, C. Delaunay, J. Delfosse, A. Denquin, E. Gautier, L. Germain, N. Gey, T. Gloriant, J.-Y. Hascoët, S. Hémery, Y. Millet, D. Monceau, F. Pettinari-Sturmel, M. Piellard, F. Prima and B. Viguier, EDP Sciences, 2020, article id 03021Conference paper, Published paper (Refereed)
Abstract [en]

Texture in materials is important as it contributes to anisotropy in the bulk mechanical properties. Ti-6Al-4V built with the additive manufacturing process (AM) electron beam melting (EBM) has been found to have anisotropic mechanical properties. Therefore, this work has been performed to investigate the texture variations of EBM built Ti-6Al-4V with neutron time of flight (TOF). For the work, samples were produced with different build geometries off-set by 90 degrees. A cast sample was additionally analyzed to investigate the bulk texture of conventionally manufactured material. Microstructural characterization was performed and the cast material was found to have a coarse colony α microstructure, whereas the EBM built material had a finer basket weave microstructure. Overall, the texture of the EBM built material was found to be weak having an multiple of random distribution (MRD) index of ~1 for the α phase, whilst the cast material possessed more than twice the amount of preferred orientation i.e. MRD 2.51 for the α phase.

Place, publisher, year, edition, pages
EDP Sciences, 2020
Series
MATEC Web of Conferences, E-ISSN 2261-236X
Keywords
Neutron time-of-flight diffraction, texture, Ti-6Al-4V, electron beam melting, cast
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-82374 (URN)10.1051/matecconf/202032103021 (DOI)
Conference
14th World Conference on Titanium (Ti 2019), 10-14 June, 2019, Nantes, France
Funder
Swedish National Space BoardEU, European Research CouncilLuleå University of TechnologyWallenberg Foundations
Note

Finansiär: OP RDE.MEYS (CZ.02.1.01/0.0/0.0/16013/0001794)

Available from: 2021-01-14 Created: 2021-01-14 Last updated: 2023-09-05Bibliographically approved
Neikter, M., Huang, A. & Wu, X. (2019). Microstructural characterization of binary microstructure pattern in selective laser-melted Ti-6Al-4V. The International Journal of Advanced Manufacturing Technology, 104(1-4), 1381-1391
Open this publication in new window or tab >>Microstructural characterization of binary microstructure pattern in selective laser-melted Ti-6Al-4V
2019 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 104, no 1-4, p. 1381-1391Article in journal (Refereed) Published
Abstract [en]

Selective laser melting (SLM) is an additive manufacturing process that offers efficient manufacturing of complex parts with good mechanical properties. For SLM, process parameters and post-processing are of importance as they affect the microstructure and consequently the mechanical properties. A feature in the microstructure, which is formed in SLM due to the fast cooling rate, is a binary microstructure pattern (BMP). The BMP is found in the horizontal plane and is formed with various laser scan angles between adjacent layers. The easiest distinguishable strategy is 90°, which renders a shape similar to a chessboard. In this work, the BMP phenomenon was investigated in detail and a microstructural characterization was performed on the fine microstructure zone (FMZ) that separates the coarse microstructure zones (CMZ), by using light optical and scanning electron microscopes (SEM) that were equipped with electron backscattered (EBSD) and energy dispersive x-ray spectroscopy (EDS) detectors. Moreover, the effect of the process parameter hatch distance on the BMP was investigated and the overlapping between neighboring scan tracks in SLM was found to influence the size of the BMP, while the thickness of the FMZ remained constant. Different post-SLM heat treatments were performed and it was shown that the BMP retained unless the heat treatment temperature reached above the β transus temperature. EBSD and β grain reconstruction were performed as well to reveal the columnar β grain orientations. The result showed that each CMZ and FMZ originates from a respective parent β grains.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Selective laser melting (SLM), Microstructure, Chessboard, Ti-6Al-4V, Prior beta
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-75750 (URN)10.1007/s00170-019-04002-8 (DOI)000483808200099 ()2-s2.0-85068749877 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-09-11 (johcin)

Available from: 2019-08-29 Created: 2019-08-29 Last updated: 2025-04-24Bibliographically approved
Neikter, M. (2019). Microstructure and hydrogen embrittlement of additively manufactured Ti-6Al-4V. (Doctoral dissertation). Luleå: Luleå University of Technology
Open this publication in new window or tab >>Microstructure and hydrogen embrittlement of additively manufactured Ti-6Al-4V
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Mikrostruktur och väteförsprödning av additivt tillverkad Ti-6Al-4V
Abstract [en]

The work of this doctoral thesis has been performed between the 24th of August 2015 to the 6th of September 2019. The general purpose of this work has been to increase the knowledge of additively manufactured Ti-6Al-4V when it comes to microstructure, texture and hydrogen embrittlement. Several additive manufacturing (AM) processes have been addressed, the main focus, however, has been on the two processes electron beam melting (EBM) and selective laser melting (SLM). The work has been performed at Luleå University of Technology and at Monash Centre of Additive Manufacturing (MCAM), which is a part of Monash University, Melbourne Australia. GKN Aerospace Engine Systems has been involved in the work as a collaborative industrial partner. Where the main interaction and support has been between GKN in Trollhättan, Sweden. GKNs facility in Filton, United Kingdom, however, has also been involved in sample production. The texture measurements using neutron time of flight (TOF) diffraction were performed in Dubna, Russia at Frank Laboratory of Neutron Physics at the Joint Institute for Nuclear Research, using the spektrometer kolitshestvennovo analiza tekstury (SKAT) instrument and in Los Alamos at Los Alamos Neutron Science Center, using the texture instrument high pressure preferred orientation (HIPPO). The interest of specifically additively manufactured Ti-6Al-4V originates from GKN Aerospace Engine Systems as they have been contracted to manufacture parts for the Ariane rockets. In aerospace, weight is of utter importance as reduced weight of the components reduce the fuel costs and makes it possible to transport increased loads. Therefore, titanium has been suggested to replace heavier metal alloys (such as nickel-based superalloys) due to titanium’s high specific strength and overall good properties. The work has been managed under the supervision of Professor Marta-Lena Antti, Professor Robert Pederson and Dr. Pia Åkerfeldt at Luleå University of Technology and by Professor Xinhua Wu and Professor Aijun Huang at MCAM. The project has been financed by three parties Space for Innovation and Growth (RIT), Nationellt Rymdtekniskt Forskningsprogram (NRFP) and the Graduate School of Space Technology. The thesis is composed of a literature review along with the appended papers that have been written throughout the duration of the project. The purpose of the literature review is to give the reader a broader knowledge and context about the theory behind the work conducted during the Ph.D. project. The thesis commences with a theoretical background about titanium, its crystal structures, microstructure, and AM. The chapter about AM is divided into three sub-chapters, explaining the two different AM sub-groups directed energy deposition (DED) and powder bed fusion (PBF). Then the chapter finalizes with explaining the benefits and drawbacks with AM. Once these subjects been explained there is a chapter explaining AM built Ti-6Al-4V. The theme of this chapter is the differences in the microstructure of AM built and conventional built Ti-6Al-4V, where phenomena like chessboard pattern and layers bands are discussed, followed by a comparative section of the mechanical properties. The chapter about AM built Ti-6Al-4V is followed by a chapter about texture where the two texture techniques electron backscattered diffraction (EBSD) and neutron (TOF) diffraction are explained. The literature review then continues with the chapters neutron tomography, hydrogen embrittlement, and fatigue crack growth. Then there is a chapter about the materials and experimental methods that have been used to perform all the experiments, then a summary of all the papers and conclusions. After the conclusions, the thesis finalizes with a chapter about possible future work and an outlook into the future of AM. In the end, the papers I to IV are appended.  

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
Ti-6Al-4V, Additive Manufacturing, Texture, Microstructure, Hydrogen Embrittlement
National Category
Materials Chemistry Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-73905 (URN)978-91-7790-396-3 (ISBN)978-91-7790-397-0 (ISBN)
Public defence
2019-09-23, E246, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2019-05-13 Created: 2019-05-11 Last updated: 2023-09-05Bibliographically approved
Maimaitiyili, T., Woracek, R., Neikter, M., Boin, M., Wimpory, R. C., Pederson, R., . . . Bjerkén, C. (2019). Residual Lattice Strain and Phase Distribution in Ti-6Al-4V Produced by Electron Beam Melting. Materials, 12(4), Article ID 667.
Open this publication in new window or tab >>Residual Lattice Strain and Phase Distribution in Ti-6Al-4V Produced by Electron Beam Melting
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2019 (English)In: Materials, E-ISSN 1996-1944, Vol. 12, no 4, article id 667Article in journal (Refereed) Published
Abstract [en]

Residual stress/strain and microstructure used in additively manufactured material are strongly dependent on process parameter combination. With the aim to better understand and correlate process parameters used in electron beam melting (EBM) of Ti-6Al-4V with resulting phase distributions and residual stress/strains, extensive experimental work has been performed. A large number of polycrystalline Ti-6Al-4V specimens were produced with different optimized EBM process parameter combinations. These specimens were post-sequentially studied by using high-energy X-ray and neutron diffraction. In addition, visible light microscopy, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) studies were performed and linked to the other findings. Results show that the influence of scan speed and offset focus on resulting residual strain in a fully dense sample was not significant. In contrast to some previous literature, a uniform α- and β-Ti phase distribution was found in all investigated specimens. Furthermore, no strong strain variations along the build direction with respect to the deposition were found. The magnitude of strain in α and β phase show some variations both in the build plane and along the build direction, which seemed to correlate with the size of the primary β grains. However, no relation was found between measured residual strains in α and β phase. Large primary β grains and texture appear to have a strong effect on X-ray based stress results with relatively small beam size, therefore it is suggested to use a large beam for representative bulk measurements and also to consider the prior β grain size in experimental planning, as well as for mathematical modelling.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
residual stress/strain, electron beam melting, diffraction, Ti-6Al-4V, electron backscattered diffraction, X-ray diffraction
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-73158 (URN)10.3390/ma12040667 (DOI)000460793300117 ()30813435 (PubMedID)2-s2.0-85062212588 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-03-11 (johcin)

Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2025-04-25Bibliographically approved
Neikter, M., Woracek, R., Maimaitiyili, T., Scheffzük, C., Strobl, M., Antti, M.-L., . . . Bjerkén, C. (2018). Alpha texture variations in additive manufactured Ti-6Al-4V investigated with neutron diffraction. Additive Manufacturing, 23, 225-234
Open this publication in new window or tab >>Alpha texture variations in additive manufactured Ti-6Al-4V investigated with neutron diffraction
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2018 (English)In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 23, p. 225-234Article in journal (Refereed) Published
Abstract [en]

Variation of texture in Ti-6Al-4V samples produced by three different additive manufacturing (AM) processes has been studied by neutron time-of-flight (TOF) diffraction. The investigated AM processes were electron beam melting (EBM), selective laser melting (SLM) and laser metal wire deposition (LMwD). Additionally, for the LMwD material separate measurements were done on samples from the top and bottom pieces in order to detect potential texture variations between areas close to and distant from the supporting substrate in the manufacturing process. Electron backscattered diffraction (EBSD) was also performed on material parallel and perpendicular to the build direction to characterize the microstructure. Understanding the context of texture for AM processes is of significant relevance as texture can be linked to anisotropic mechanical behavior. It was found that LMwD had the strongest texture while the two powder bed fusion (PBF) processes EBM and SLM displayed comparatively weaker texture. The texture of EBM and SLM was of the same order of magnitude. These results correlate well with previous microstructural studies. Additionally, texture variations were found in the LMwD sample, where the part closest to the substrate featured stronger texture than the corresponding top part. The crystal direction of the α phase with the strongest texture component was [112¯3].

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-70649 (URN)10.1016/j.addma.2018.08.018 (DOI)000453495500022 ()2-s2.0-85051782355 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-08-29 (andbra)

Available from: 2018-08-29 Created: 2018-08-29 Last updated: 2025-02-05Bibliographically approved
Neikter, M., Forsberg, F., Pederson, R., Antti, M.-L., Åkerfeldt, P., Larsson, S., . . . Puyoo, G. (2018). Defect characterization of electron beam melted Ti-6Al-4V and Alloy 718 with X-ray microtomography. Aeronautics and Aerospace Open Access Journal, 2(3), 139-145
Open this publication in new window or tab >>Defect characterization of electron beam melted Ti-6Al-4V and Alloy 718 with X-ray microtomography
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2018 (English)In: Aeronautics and Aerospace Open Access Journal, ISSN 2576-4500, Vol. 2, no 3, p. 139-145Article in journal (Refereed) Published
Abstract [en]

Electron beam melting (EBM) is emerging as a promising manufacturing process where metallic components are manufactured from three-dimensional (3D) computer aided design models by melting layers onto layers. There are several advantages with this manufacturing process such as near net shaping, reduced lead times and the possibility to decrease weight by topology optimization, aspects that are of interest for the aerospace industry. In this work two alloys, Ti-6Al-4V and Alloy 718, widely used within the aerospace industry were investigated with X-ray microtomography (XMT), to characterize defects such as lack of fusion (LOF) and inclusions. It was furthermore possible to view the macrostructure with XMT, which was compared to macrostructure images obtained by light optical microscopy (LOM). XMT proved to be a useful tool for defect characterization and both LOF and un-melted powder could be found in the two investigated samples. In the EBM built Ti-6Al-4V sample high density inclusions, believed to be composed of tungsten, were found. One of the high-density inclusions was found to be hollow, which indicate that the inclusion stems from the powder manufacturing process and not related with the EBM process. By performing defect analyses with the XMT software it was also possible to quantify the amount of LOF and un-melted powder in vol%. From the XMT-data meshes were produced so that finite element method (FEM) simulations could be performed. From these FEM simulations the significant impact of defects on the material properties was evident, as the defects led to high stress concentrations. It could moreover, with FEM, be shown that the as-built surface roughness of EBM material is of importance as high surface roughness led to increased stress concentrations.

Place, publisher, year, edition, pages
MedCrave Group, 2018
Keywords
X-ray tomography, Ti-6Al-4V, Alloy 718, defects and electron beam melting
National Category
Metallurgy and Metallic Materials Other Materials Engineering Fluid Mechanics Applied Mechanics
Research subject
Engineering Materials; Solid Mechanics; Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-68924 (URN)10.15406/aaoaj.2018.02.00044 (DOI)
Available from: 2018-05-28 Created: 2018-05-28 Last updated: 2025-02-09Bibliographically approved
Saeidi, K., Neikter, M., Olsen, J., Shen, Z. J. & Akhtar, F. (2017). 316L stainless steel designed to withstand intermediate temperature. Materials & design, 135, 1-8
Open this publication in new window or tab >>316L stainless steel designed to withstand intermediate temperature
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2017 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 135, p. 1-8Article in journal (Refereed) Published
Abstract [en]

Austenitic stainless steel 316L was fabricated for withstanding elevated temperature by selective laser melting (SLM). Tensile tests at 800 °C were carried out on laser melted 316L with two different strain rates of 0.05 S− 1 and 0.25 S− 1. The laser melted 316L showed tensile strength of approximately 400 MPa at 800 °C, which was superior to conventional 316L. Analysis of fracture surface showed that the 316L fractured in mixed mode, ductile and brittle fracture, with an elongation of 18% at 800 °C. In order to understand the mechanical response, laser melted 316L was thermally treated at 800 °C for microstructure and phase stability. X-ray diffraction (XRD) and Electron back scattered diffraction (EBSD) of 316L treated at 800 °C disclosed a textured material with single austenitic phase. SEM and EBSD showed that the characteristic and inherent microstructure of laser melted 316L, consisting of elongated grains with high angle grain boundaries containing subgrains with a smaller misorientation, remained similar to as-built SLM 316L during hot tensile test at 800 °C. The stable austenite phase and its stable hierarchical microstructure at 800 °C led to the superior mechanical response of laser melted 316L.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-65565 (URN)10.1016/j.matdes.2017.08.072 (DOI)000413236300001 ()2-s2.0-85028815416 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-09-11 (andbra)

Available from: 2017-09-11 Created: 2017-09-11 Last updated: 2018-03-05Bibliographically approved
Neikter, M., Forsberg, F., Lycksam, H., Pederson, R. & Antti, M.-L. (2017). Microstructure and Defects in Additive Manufactured Titanium: a Comparison Between Microtomography and Optical Microscopy. In: : . Paper presented at 3rd International Conference on Tomography of Materials and Structures, Lund, Sweden, 26-30 June 2017.
Open this publication in new window or tab >>Microstructure and Defects in Additive Manufactured Titanium: a Comparison Between Microtomography and Optical Microscopy
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2017 (English)Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

The aim of this work has been to compare two different analysing methods;x-ray microtomography and light optical microscopy, when it comes to defects and microstructure of additively manufactured Ti-6Al-4V. The results showthat both techniqueshave theirpros and cons:microtomography is the preferred choicefor defect detectionby analysing the full 3D sample volume, while light optical microscopy is better for analysing finer details in 2D.

National Category
Metallurgy and Metallic Materials Other Materials Engineering Fluid Mechanics
Research subject
Engineering Materials; Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-65063 (URN)
Conference
3rd International Conference on Tomography of Materials and Structures, Lund, Sweden, 26-30 June 2017
Available from: 2017-08-14 Created: 2017-08-14 Last updated: 2025-02-09Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-3772-4371

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