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Fredriksson, Gunnel
Publications (10 of 27) Show all publications
Vilardell, A. M., Fredriksson, G., Yadroitsev, I. & Krakhmalev, P. (2019). Fracture mechanisms in the as-built and stress-relieved laser powder bed fusion Ti6Al4V ELI alloy. Optics and Laser Technology, 109, 608-615
Open this publication in new window or tab >>Fracture mechanisms in the as-built and stress-relieved laser powder bed fusion Ti6Al4V ELI alloy
2019 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 109, p. 608-615Article in journal (Refereed) Published
Abstract [en]

The influence of a stress-relief treatment on impact and fatigue properties of Ti6Al4V ELI samples manufactured by laser powder bed fusion was analyzed. The heat treatment resulted in removal of residual stresses, coarsening of needles and formation of precipitations between needles. In both, impact and fatigue tests, crack development was correlated to microstructural features. Fracture analysis was carried out by means of optical and electron microscopy to reveal the influence of microstructure on crack development. Ductile fracture was the dominating fracture mode at impact testing. Pore formation and coalescence were the main crack formation mechanisms. The microstructural changes led to a decrease in impact toughness after heat treatment. Presumably, this was a result of the precipitations between needles. Fatigue results showed multiple crack nucleation at the surface in both, as-built and stress-relieved material. The crack propagation rate was slightly higher and the crack was less deflected in the stress-relieved material due to the stress relief and coarsening of the microstructure.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Fracture analysis, Impact and fatigue properties, Laser powder bed fusion, Stress-relief treatment, Ti6A4V ELI, Aluminum alloys, Coarsening, Cracks, Ductile fracture, Fatigue testing, Fracture testing, Heat treatment, Impact testing, Microstructural evolution, Needles, Residual stresses, Stress relief, Titanium alloys, Crack propagation rate, Laser powders, Microstructural changes, Microstructural features, Optical and electron microscopies, Fatigue of materials
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-69444 (URN)10.1016/j.optlastec.2018.08.042 (DOI)000446949600074 ()2-s2.0-85053287726 (Scopus ID)
Available from: 2018-10-02 Created: 2018-10-02 Last updated: 2019-01-31Bibliographically approved
Åsberg, M., Fredriksson, G., Hatami, S., Fredriksson, W. & Krakhmalev, P. (2019). Influence of post treatment on microstructure, porosity and mechanical properties of additive manufactured H13 tool steel. Materials Science & Engineering: A, 742, 584-589
Open this publication in new window or tab >>Influence of post treatment on microstructure, porosity and mechanical properties of additive manufactured H13 tool steel
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2019 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 742, p. 584-589Article in journal (Refereed) Published
Abstract [en]

Additive manufacturing (AM) is an attractive manufacturing technology in tooling applications. It provides unique opportunities to manufacture tools with complex shapes, containing inner channels for conformal cooling. In this investigation, H13, a widely used tool steel, was manufactured using a laser powder bed fusion method. Microstructure, tensile mechanical properties, hardness, and porosity of the AM H13 after stress relieve (SR), standard hardening and tempering (SR + HT), and hot isostatic pressing (SR + HIP + HT) were investigated. It was found that the microstructure of directly solidified colonies of prior austenite, which is typical for AM, disappeared after austenitizing at the hardening heat treatment. In specimens SR + HT and SR + HIP + HT, a microstructure similar to the conventional but finer was observed. Electron microscopy showed that SR and SR + HT specimens contained lack of fusion, and spherical gas porosity, which resulted in remarkable scatter in the observed elongation to break values. Application of HIP resulted in the highest strength values, higher than those observed for conventional H13 heat treated in the same way. The conclusion is that HIP promotes reduction of porosity and lack of fusion defects and can be efficiently used to improve the mechanical properties of AM H13 tool steel.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Additive manufacturing, Hot work tool steel H13, Laser powder bed fusion, Mechanical properties, Post treatment, 3D printers, Hardening, Hot isostatic pressing, Hot working, Microstructure, Porosity, Tool steel, Tools, Elongation to break, H-13 tool steels, Hot-work tool steel, Laser powders, Manufacturing technologies, Strength values, Tensile mechanical properties
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science
Identifiers
urn:nbn:se:kau:diva-70411 (URN)10.1016/j.msea.2018.08.046 (DOI)000457814400060 ()2-s2.0-85056673446 (Scopus ID)
Available from: 2018-12-05 Created: 2018-12-05 Last updated: 2019-02-21Bibliographically approved
Vilardell, A. M., Krakhmalev, P., Fredriksson, G., Cabanettes, F., Sova, A., Valentin, D. & Bertrand, P. (2018). Influence of surface topography on fatigue behavior of Ti6Al4V alloy by laser powder bed fusion. In: Procedia CIRP: . Paper presented at 10th CIRP Conference on Photonic Technologies, LANE 2018, 3 September 2018 through 6 September 2018 (pp. 49-52). Elsevier
Open this publication in new window or tab >>Influence of surface topography on fatigue behavior of Ti6Al4V alloy by laser powder bed fusion
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2018 (English)In: Procedia CIRP, Elsevier, 2018, p. 49-52Conference paper (Refereed)
Abstract [en]

This article deals with the understanding of the influence of surface topography on fatigue behavior of Ti6Al4V alloy specimens produced by laser powder bed fusion (LPBF). The same laser parameters and scan strategy were used for all specimens, giving a sample density higher than 99.5 %. Two different surface topographies were obtained by using the top and side surfaces of the specimens. The surface topography and morphology were investigated by optical surface profilometry and focus variation microscopy. Four-point bending fatigue test was performed on specimens with top and side surfaces as the highest stressed surface respectively. Machined specimens were used as reference. The features of the fracture surface, such as crack initiation and propagation, were analyzed by focus variation and scanning electron microscopy (SEM). Both, fatigue results and fracture surface investigations, were correlated and discussed in relation to surface topography and microstructure, as well as manufacturing parameters. 

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Fatigue test, Fracture mechanisms, Laser powder bed fusion, Surface topography, Ti6Al4V alloy, Aluminum alloys, Fatigue of materials, Fatigue testing, Fracture, Scanning electron microscopy, Ternary alloys, Titanium alloys, Topography, Crack initiation and propagation, Fatigue behavior, Four point bending, Fracture surfaces, Laser powders, Manufacturing parameters, Ti-6Al-4V alloy
National Category
Physical Sciences
Research subject
Materials Science
Identifiers
urn:nbn:se:kau:diva-70594 (URN)10.1016/j.procir.2018.08.028 (DOI)2-s2.0-85057393814 (Scopus ID)
Conference
10th CIRP Conference on Photonic Technologies, LANE 2018, 3 September 2018 through 6 September 2018
Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2019-04-25Bibliographically approved
Krakhmalev, P., Fredriksson, G., Svensson, K., Yadroitsev, I., Yadroitsava, I., Thuvander, M. & Peng, R. (2018). Microstructure, solidification texture, and thermal stability of 316 L stainless steel manufactured by laser powder bed fusion. Metals, 8(8), 1-18, Article ID 643.
Open this publication in new window or tab >>Microstructure, solidification texture, and thermal stability of 316 L stainless steel manufactured by laser powder bed fusion
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2018 (English)In: Metals, ISSN 2075-4701, Vol. 8, no 8, p. 1-18, article id 643Article in journal (Refereed) Published
Abstract [en]

This article overviews the scientific results of the microstructural features observed in 316 L stainless steel manufactured by the laser powder bed fusion (LPBF) method obtained by the authors, and discusses the results with respect to the recently published literature. Microscopic features of the LPBF microstructure, i.e., epitaxial nucleation, cellular structure, microsegregation, porosity, competitive colony growth, and solidification texture, were experimentally studied by scanning and transmission electron microscopy, diffraction methods, and atom probe tomography. The influence of laser power and laser scanning speed on the microstructure was discussed in the perspective of governing the microstructure by controlling the process parameters. It was shown that the three-dimensional (3D) zig-zag solidification texture observed in the LPBF 316 L was related to the laser scanning strategy. The thermal stability of the microstructure was investigated under isothermal annealing conditions. It was shown that the cells formed at solidification started to disappear at about 800 °C, and that this process leads to a substantial decrease in hardness. Colony boundaries, nevertheless, were quite stable, and no significant grain growth was observed after heat treatment at 1050 °C. The observed experimental results are discussed with respect to the fundamental knowledge of the solidification processes, and compared with the existing literature data.

Place, publisher, year, edition, pages
MDPI AG, 2018
Keywords
316 L stainless steel, Cellular solidification, Electron microscopy, Laser powder bed fusion, Solidification texture, Thermal stability of microstructure
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-69224 (URN)10.3390/met8080643 (DOI)000443616400079 ()2-s2.0-85052594962 (Scopus ID)
Available from: 2018-09-14 Created: 2018-09-14 Last updated: 2019-04-26Bibliographically approved
Åsberg, M., Fredriksson, G., Hatami, S. & Fredriksson, W. (2017). Influence of HIP on microstructure, pore elimination and tensile properties of SLM manufactured H13 tool steel. In: : . Paper presented at Euromat 2017 (European Congress and Exibition om Advanced Materials and Proccesses), Thessaloniki, Greece, 17 – 22 September, 2017..
Open this publication in new window or tab >>Influence of HIP on microstructure, pore elimination and tensile properties of SLM manufactured H13 tool steel
2017 (English)Conference paper, Oral presentation only (Other academic)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-63810 (URN)
Conference
Euromat 2017 (European Congress and Exibition om Advanced Materials and Proccesses), Thessaloniki, Greece, 17 – 22 September, 2017.
Available from: 2017-09-19 Created: 2017-09-19 Last updated: 2019-10-14Bibliographically approved
Krakhmalev, P., Yadroitsava, I., Fredriksson, G. & Yadroitsev, I. (2017). Microstructural and thermal stability of selective laser melted 316L stainless steel single tracks. South African Journal of Industrial Engineering, 28(1), 12-19
Open this publication in new window or tab >>Microstructural and thermal stability of selective laser melted 316L stainless steel single tracks
2017 (English)In: South African Journal of Industrial Engineering, ISSN 1012-277X, E-ISSN 2224-7890, Vol. 28, no 1, p. 12-19Article in journal (Refereed) Published
Abstract [en]

To remove residual stresses, an as-built SLM object is usually posttreated. This treatment can affect the microstructure, changing the final mechanical characteristics. This investigation is focused on the microstructural characterisation of 316L austenitic stainless steel in as-built and annealed conditions. The SLM microstructure was relatively stable up to 900°C, when cell boundaries start to disappear. At higher temperatures, an insignificant grain coarsening was detected. These microstructural changes caused a gradual drop in the hardness. The obtained result is background for the future development of post-treatment regimens to achieve a high level in the final mechanical properties of SLM objects.

Place, publisher, year, edition, pages
Stellenbosch University, 2017
Keywords
stainless steel, selective laser melting, microstructure, heat treatment
National Category
Manufacturing, Surface and Joining Technology
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-55209 (URN)10.7166/28-1-1466 (DOI)000403371900003 ()
Available from: 2017-06-20 Created: 2017-06-20 Last updated: 2018-08-20Bibliographically approved
Kazantseva, N., Krakhmalev, P., Fredriksson, G. & Yadroitsev, I. (2017). Twins in SLM Ti alloy [Letter to the editor]. Titan (2), 8-15
Open this publication in new window or tab >>Twins in SLM Ti alloy
2017 (English)In: Titan, ISSN 2075-2903, no 2, p. 8-15Article in journal, Letter (Refereed) Published
Place, publisher, year, edition, pages
Mezhgosudarstvennaya Assotsyatsiya Titan, 2017
Keywords
additive technologies, Ti-6Al-4V, twinning, TEM
National Category
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-63803 (URN)
Available from: 2017-09-19 Created: 2017-09-19 Last updated: 2019-07-12Bibliographically approved
Krakhmalev, P., Fredriksson, G., Yadroitsava, I., Kazantseva, N., Plessis, A. d. & Yadroitsev, I. (2016). Deformation Behavior and Microstructure of Ti6Al4V Manufactured by SLM. Physics Procedia, 83, 778-788
Open this publication in new window or tab >>Deformation Behavior and Microstructure of Ti6Al4V Manufactured by SLM
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2016 (English)In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 83, p. 778-788Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Ti6Al4V, tensile test, mechanical properties, porosity, microstructure, twinning
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-47569 (URN)10.1016/j.phpro.2016.08.080 (DOI)000387459400083 ()
Available from: 2017-01-04 Created: 2017-01-04 Last updated: 2019-06-10Bibliographically approved
Kazantseva, N., Krakhmalev, P., Fredriksson, G., Vinogradova, N. & Yadroitsev, I. (2016). Twins in SLM Ti-4Al-6V Alloys. In: : . Paper presented at "Actual problems of materials strength" (Aktualnie problemy prochnosti) - LXII International Conference, 24-27 May 2016, Sevastopol, Russia (pp. 219). Sevastopol: Sevastopol university
Open this publication in new window or tab >>Twins in SLM Ti-4Al-6V Alloys
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2016 (English)Conference paper, Oral presentation with published abstract (Refereed)
Place, publisher, year, edition, pages
Sevastopol: Sevastopol university, 2016
National Category
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-45818 (URN)978-5-9907602-7-1 (ISBN)
Conference
"Actual problems of materials strength" (Aktualnie problemy prochnosti) - LXII International Conference, 24-27 May 2016, Sevastopol, Russia
Available from: 2016-09-09 Created: 2016-09-09 Last updated: 2019-06-10Bibliographically approved
Krakhmalev, P., Fredriksson, G., Yadroitsava, I. & Yadroitsev, I. (2015). In situ heat treatment in selective laser melted martensitic AISI420 stainless steels. Materials & Design, 87, 380-385
Open this publication in new window or tab >>In situ heat treatment in selective laser melted martensitic AISI420 stainless steels
2015 (English)In: Materials & Design, ISSN 0264-1275, Vol. 87, p. 380-385Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Elsevier, 2015
Keywords
Microstructure, Martensitic stainless steel, In situ heat treatment, Selective laser melting
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-38882 (URN)10.1016/j.matdes.2015.08.045 (DOI)000363816000044 ()
Available from: 2015-12-11 Created: 2015-12-11 Last updated: 2017-12-06Bibliographically approved
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