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  • 1.
    Goetz, Inga K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics. Materials Chemistry, RWTH Aachen University, Aachen, Germany.
    Pacheco, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Hassila, Carl J.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Schneider, Jochen M.
    Hans, Marcus
    Convective Flow Redistribution of Oxygen by Laser Melting of a Zr-Based Amorphous Alloy2023In: Materials, E-ISSN 1996-1944, Vol. 16, no 11, article id 4113Article in journal (Refereed)
    Abstract [en]

    Oxygen impurities play a crucial role in the glass-forming ability and crystallisation behaviour of metallic glasses. In the present work, single laser tracks were produced on Zr59.3-xCu28.8 Al10.4Nb1.5Ox substrates (x = 0.3, 1.3) to study the redistribution of oxygen in the melt pool under laser melting, which provides the basis for laser powder bed fusion additive manufacturing. Since such substrates are commercially not available, they were fabricated by arc melting and splat quenching. X-ray diffraction revealed that the substrate with 0.3 at.% oxygen was X-ray amorphous, while the substrate with 1.3 at.% oxygen was partially crystalline. Hence, it is evident that the oxygen content affects the crystallisation kinetics. Subsequently, single laser tracks were produced on the surface of these substrates, and the melt pools attained from the laser processing were characterised by atom probe tomography and transmission electron microscopy. Surface oxidation and subsequent convective flow redistribution of oxygen by laser melting were identified as causes of the presence of CuOx and crystalline ZrO nanoparticles in the melt pool. Bands of ZrO likely originate from surface oxides that were moved deeper into the melt pool by convective flow. The findings presented here highlight the influence of oxygen redistribution from the surface into the melt pool during laser processing.

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  • 2.
    Hassila, Carl Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science.
    Additive Manufacturing of Ni-Fe Superalloys: Exploring the Alloying Envelope and the Impact of Process on Mechanical Properties2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Additive manufacturing of metals has received a lot of attention in the last decade as this family of manufacturing processes allows the manufacturing of complicated geometries which would be difficult to produce using conventional manufacturing techniques. Additive manufacturing of the Ni-Fe based superalloys 625 and 718 using the Powder Bed Fusion – Laser Beam (PBF-LB) process is facilitated by the fact that these alloys were developed as weldable alternatives to other high-strength, high-temperature Ni-based superalloys. However, given that these alloys were developed with casting and forging as the main manufacturing route, the alloying composition of these alloys may possibly be tuned to better suit the PBF-LB process. In this thesis, small changes to the alloy 625 and 718 alloy compositions were made, with the goal of either improving material properties or reducing the environmental footprint of the produced materials. For alloy 718, the influence of carbon content on the resulting microstructure and mechanical properties was investigated both in the as-built and heat-treated conditions using tensile and impact testing. A similar study, but also including corrosion experiments, was performed on an alloy 625 composition which had been tuned to allow it to be atomized using nitrogen instead of argon, a transition that results in environmental benefits as argon gas carries with it a larger environmental footprint compared to nitrogen gas. In addition to the above, as the process conditions in the PBF-LB process have a strong influence on the developing microstructure, their influence on rolling contact fatigue and residual stresses in printed alloys 625 and 718 were investigated. Rolling contact fatigue experiments were performed on alloy 625 and were complemented by a fractographic study which showed that the different grain structures achieved depending on the used process condition affected the pitting damage development. Meanwhile, the residual stress experiments were performed on PBF-LB processed alloy 625 and 718. The residual stresses in the materials were first calculated using experimental data attained from high energy synchrotron diffraction experiments. These results were then compared to the predicted stresses from a thermo-mechanical model. The thermomechanical model included a built-in mechanism-based material model which was shown to successfully simulate relaxation effects stemming from the cyclic heating of the material during the PBF-LB process. Lastly, a modelling approach using the thermo-mechanical model was developed which allowed the model to successfully predict the stresses also when using different scanning strategies.

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  • 3.
    Hassila, Carl Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Harlin, P.
    Sandvik Mat Technol AB, Sandviken, Sweden.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Rolling contact fatigue crack propagation relative to anisotropies in additive manufactured Inconel 6252019In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 426-427, no Part B, p. 1837-1845Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing is steadily gaining acceptance in certain industry segments as a process for the manufacturing of dense metallic components. The Ni-based superalloys belonging to the Inconel family have for many years been in focus for AM research and AM produced components are now becoming commercially available. However, it is still unclear how the microstructural anisotropy, inherent to most AM materials, affects the material performance in a given application. The anisotropy may e.g. influence the mechanical properties and the performance in certain tribological situations, such as when subjected to rolling contact fatigue. Like most AM methods, the powder bed fusion - laser beam process gives the produced components a relatively rough surface. To perform well in demanding tribological situations, the components are commonly machined to a smooth finish. In this work, Inconel 625 produced using PBF-LB is evaluated in a rolling contact fatigue test. Test cylinders (empty set 10 mm) have been produced using different build directions and scan strategies, resulting in varying microstructures and textures. In the rolling contact fatigue test, a cylindrical sample is mounted between two empty set 140 mm metal rollers, pulled together via a spring. After testing, the contact tracks are studied using SEM and EBSD to reveal cracks. Cracks were analysed with respect to the microstructure and anisotropies. It was found that the anisotropy influences both the nucleation and growth of cracks. The AM produced specimens were also found to be more prone to transgranular cracking than conventional Inconel 625, which predominantly displayed intergranular cracks.

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  • 4.
    Hassila, Carl Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science.
    Harlin, Peter
    Sandvik AB.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science. Uppsala University.
    Influence of Nitrogen Content on Microstructure and Mechanical Properties of Laser Powder Bed Fusion Processed Alloy 6252020In: World PM 2020, 27/6-1/7 2020, Montreal, Kanada, 2020Conference paper (Refereed)
    Abstract [en]

    Alloy 625 is a nickel-based alloy used for high temperature applications and corrosive environments. The compositional specification of alloy 625 is quite wide, which makes it possible to tune the alloy composition to allow for a higher nitrogen content. In this study we investigate two such tuned 625 powders having different nitrogen contents and how their respective nitrogen contents effect the properties of the fused material after processing in laser powder bed fusion. The microstructural characteristics and the mechanical performance of the fused materials were evaluated both in the as-built material condition and after hot isostatic pressing (HIP). The mechanical evaluation includes tensile and impact testing as well as Vickers indentation. Results from microstructural characterisation displays small variations in the as-built condition whilst the alloys have a significantly different response on the performed HIP cycle. The variations in microstructure after HIP has also a direct impact on resulting mechanical properties.

  • 5.
    Holmberg, Jonas
    et al.
    RISE Res Inst Sweden AB, Dept Mfg Proc, Argongatan 30, Mölndal, Sweden..
    Berglund, Johan
    RISE Res Inst Sweden AB, Dept Mfg Proc, Argongatan 30, Mölndal, Sweden..
    Brohede, Ulrika
    Swerim AB, Dept Prod Technol, Isafjordsgatan 28A, Kista, Sweden..
    Åkerfeldt, Pia
    Luleå Univ Technol, Div Mat Sci, SE-97187 Luleå, Sweden..
    Sandell, Viktor
    Luleå Univ Technol, Div Mat Sci, SE-97187 Luleå, Sweden..
    Rashid, Amir
    KTH Royal Inst Technol, Dept Prod Engn, Brinellvagen 68, SE-10044 Stockholm, Sweden..
    Zhao, Xiaoyu
    KTH Royal Inst Technol, Dept Prod Engn, Brinellvagen 68, SE-10044 Stockholm, Sweden..
    Dadbakhsh, Sasan
    KTH Royal Inst Technol, Dept Prod Engn, Brinellvagen 68, SE-10044 Stockholm, Sweden..
    Fischer, Marie
    Chalmers Univ Technol, Dept Ind & Mat Sci, Horsalsvagen 7B, Gothenburg, Sweden..
    Hryha, Eduard
    Chalmers Univ Technol, Dept Ind & Mat Sci, Horsalsvagen 7B, Gothenburg, Sweden..
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science.
    Karlsson Hassila, Carl Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science.
    Hosseini, Seyed
    RISE Res Inst Sweden AB, Dept Mfg Proc, Argongatan 30, Mölndal, Sweden..
    Machining of additively manufactured alloy 718 in as-built and heat-treated condition: surface integrity and cutting tool wear2024In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 130, p. 1823-1842Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing (AM) using powder bed fusion is becoming a mature technology that offers great possibilities and design freedom for manufacturing of near net shape components. However, for many gas turbine and aerospace applications, machining is still required, which motivates further research on the machinability and work piece integrity of additive-manufactured superalloys. In this work, turning tests have been performed on components made with both Powder Bed Fusion for Laser Beam (PBF-LB) and Electron Beam (PBF-EB) in as-built and heat-treated conditions. The two AM processes and the respective heat-treatments have generated different microstructural features that have a great impact on both the tool wear and the work piece surface integrity. The results show that the PBF-EB components have relatively lower geometrical accuracy, a rough surface topography, a coarse microstructure with hard precipitates and low residual stresses after printing. Turning of the PBF-EB material results in high cutting tool wear, which induces moderate tensile surface stresses that are balanced by deep compressive stresses and a superficial deformed surface that is greater for the heat-treated material. In comparison, the PBF-LB components have a higher geometrical accuracy, a relatively smooth topography and a fine microstructure, but with high tensile stresses after printing. Machining of PBF-LB material resulted in higher tool wear for the heat-treated material, increase of 49%, and significantly higher tensile surface stresses followed by shallower compressive stresses below the surface compared to the PBF-EB materials, but with no superficially deformed surface. It is further observed an 87% higher tool wear for PBF-EB in as-built condition and 43% in the heat-treated condition compared to the PBF-LB material. These results show that the selection of cutting tools and cutting settings are critical, which requires the development of suitable machining parameters that are designed for the microstructure of the material.

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  • 6.
    Lindwall, J.
    et al.
    Luleå Univ Technol, Dept Engn Sci & Math, S-97187 Luleå, Sweden..
    Hassila, Carl Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science.
    Marattukalam, Jithin J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Lundbäck, A.
    Luleå Univ Technol, Dept Engn Sci & Math, S-97187 Luleå, Sweden..
    Boundary conditions for simulation of powder bed fusion for metallic glass formation: measurements and calibrations2019In: Second International Conference on Simulation for Additive Manufacturing (Sim-AM 2019) / [ed] Auricchio, F Rank, E Steinmann, P Kollmannsberger, S Morganti, S, International Centre for Numerical Methods in Engineering , 2019, p. 51-59Conference paper (Refereed)
    Abstract [en]

    A finite element model for prediction of the temperature field in the powder bed fusion process is presented and compared to measurements. Accurate temperature predictions at the base plate are essential to accurately predict the formation of crystals in a metallic glass forming material. The temperature measurements were performed by equipping the base plate with thermocouples during manufacturing of a cylinder with the glass forming alloy AMZ4. Boundary conditions for heat losses through the base plate/machine contact interfaces was calibrated to fit the measurements. Additional heat losses was used to account for radiation at the top surface and conduction through the powder bed. An interface boundary condition based on conservation of heat flux was examined to match the heat flow to the machine structure and the temperature predictions was satisfying. Still, temperature predictions with a constant heat transfer coefficient matched the measurements within 1.5 degrees C during the entire building process of about 9 hours.

  • 7.
    Lindwall, Johan
    et al.
    Luleå Univ Technol, Dept Engn Sci & Math, SE-97187 Luleå, Sweden..
    Ericsson, Anders
    Lund Univ, Div Solid Mech, Box 118, SE-22100 Lund, Sweden..
    Marattukalam, Jithin James
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Hassila, Carl Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science.
    Karlsson, Dennis
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström. Sandvik Mat Technol, SE-81181 Sandviken, Sweden..
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Fisk, Martin
    Lund Univ, Div Solid Mech, Box 118, SE-22100 Lund, Sweden.;Malmö Univ, Mat Sci & Appl Math, SE-20506 Malmö, Sweden..
    Lundback, Andreas
    Luleå Univ Technol, Dept Engn Sci & Math, SE-97187 Luleå, Sweden..
    Simulation of phase evolution in a Zr-based glass forming alloy during multiple laser remelting2022In: JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, ISSN 2238-7854, Vol. 16, p. 1165-1178Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing by laser-based powder bed fusion is a promising technique for bulk metallic glass production. But, reheating by deposition of subsequent layers may cause local crystallisation of the alloy. To investigate the crystalline phase evolution during laser scanning of a Zr-based metallic glass-forming alloy, a simulation strategy based on the finite element method and the classical nucleation theory has been developed and compared with experimental results from multiple laser remelting of a single-track. Multiple laser remelting of a single-track demonstrates the crystallisation behaviour by the influence of thermal history in the reheated material. Scanning electron microscopy and transmission electron microscopy reveals the crystalline phase evolution in the heat affected zone after each laser scan. A trend can be observed where repeated remelting results in an increased crystalline volume fraction with larger crystals in the heat affected zone, both in simulation and experiment. A gradient of cluster number density and mean radius can also be predicted by the model, with good correlation to the experiments. Prediction of crystallisation, as presented in this work, can be a useful tool to aid the development of process parameters during additive manufacturing for bulk metallic glass formation.(c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

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  • 8.
    Malmelöv, Andreas
    et al.
    Luleå Univ Technol, Mech Solid Mat, SE-97187 Luleå, Sweden..
    Hassila, Carl Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science.
    Fisk, Martin
    Malmö Univ, Mat Sci & Appl Math, SE-20506 Malmö, Sweden.;Lund Univ, Div Solid Mech, POB 118, SE-22100 Lund, Sweden..
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Applied Material Science.
    Lundbäck, Andreas
    Luleå Univ Technol, Mech Solid Mat, SE-97187 Luleå, Sweden..
    Numerical modeling and synchrotron diffraction measurements of residual stresses in laser powder bed fusion manufactured alloy 6252022In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 216, article id 110548Article in journal (Refereed)
    Abstract [en]

    Residual stresses in metal additive manufactured components are a well-known problem. It causes dis-tortion of the samples when removing them from the build plate, as well as acting detrimental with regard to fatigue. The understanding of how residual stresses in a printed sample are affected by process parameters is crucial to allow manufacturers to tune their process parameters, or the design of their com-ponent, to limit the negative influence of residual stresses. In this paper, residual stresses in additive manufactured samples are simulated using a thermo-mechanical finite element model. The elasto-plastic behavior of the material is described by a mechanism-based material model that accounts for microstructural and relaxation effects. The heat source in the finite element model is calibrated by fitting the model to experimental data. The residual stress field from the finite element model is compared with experimental results attained from synchrotron X-ray diffraction measurements. The results from the model and measurement give the same trend in the residual stress field. In addition, it is shown that there is no significant difference in trend and magnitude of the resulting residual stresses for an alterna-tion in laser power and scanning speed.

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