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  • 1.
    Balachandramurthi, Arun Ramanathan
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Moverare, Johan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Linköping University, Department of Management and Engineering, Linköping, 58183, Sweden.
    Hansson, Thomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. GKN Aerospace Sweden AB, Trollhättan, 46181, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Anisotropic fatigue properties of Alloy 718 manufactured by Electron Beam Powder Bed Fusion2020In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 141, article id 105898Article in journal (Refereed)
    Abstract [en]

    In this study, Alloy 718 specimens manufactured by Electron Beam Powder Bed Fusion process are subjected to two different post-treatments to have different microstructural features. Low cycle fatigue testing has been performed both parallel and transverse to the build direction. EB-PBF Alloy 718 exhibits anisotropic fatigue behaviour; the fatigue life is better along the parallel direction compared to the transverse direction. The anisotropy in fatigue life is related to the anisotropy in the Young’s modulus. The pseudo-elastic stress vs. fatigue life approach is presented as a potential solution to handle anisotropy in fatigue life assessment of additively manufactured engineering components. © 2020 The Authors

  • 2. Kjellsson, Henrik
    et al.
    Balachandramurthi, Arun Ramanathan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Moverare, Johan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Department of Management and Engineering, Linköping University, 58183, Linköping (SWE).
    Hansson, Thomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    High Temperature Fatigue Performance of Electron Beam Powder Bed Fusion Manufactured Alloy 7182022In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 53, p. 2496-2514Article in journal (Refereed)
    Abstract [en]

    The microstructure and mechanical properties of additively manufactured (AM) parts have been shown to be different from that of cast and wrought counterparts. In this study, electron beam powder bed fusion (EB-PBF) fabricated Alloy 718 was exposed to three different heat treatment routes followed by strain-controlled fatigue testing at 550 degrees C. The fatigue tests were performed with specimens built with their center axis parallel and transverse relative to the build direction. The microstructure showed saturated precipitation of delta-Ni3Nb after repeated solution treatment at 954 degrees C. In contrast, no delta-Ni3Nb precipitates could be observed after a single-step solution treatment at 1025 degrees C. However, the disparity of secondary phases showed no noticeable influence on the fatigue life. A significant difference in fatigue behavior was noted between the parallel and transverse directions. The specimens loaded parallel to the elongated grains showed on average similar to 5x greater life in comparison to the perpendicularly loaded specimens. Compared to corresponding heat-treated material conditions tested at ambient temperature, the specimens showed lower life at high strain amplitude and superior life at low strain amplitude. Moreover, competitive internal and surface failure modes were observed at the lower strain amplitudes while for the higher strain ranges, surface failure modes dominated. (C) The Author(s) 2022

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  • 3.
    Neikter, Magnus
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Luleå University of Technology, Division of Materials Science, Luleå, 97181, Sweden;Chalmers University of Technology, .
    Colliander, Magnus
    Chalmers University of Technology,Department of Applied Physics, Göteborg, 41296, Sweden.
    de Andrade Schwerz, C.
    GKN Aerospace Engine Systems, Trollhättan, 46138, Sweden.
    Hansson, Thomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. GKN Aerospace Engine Systems, Trollhättan, 46138, Sweden.
    Åkerfeldt, Pia
    Luleå University of Technology, Division of Materials Science, Luleå, 97181, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Antti, Marta-Lena
    Luleå University of Technology, Division of Materials Science, Luleå, 97181, Sweden.
    Fatigue crack growth of electron beam melted TI-6AL-4V in high-pressure hydrogen2020In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 13, no 6, article id 1287Article in journal (Refereed)
    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 DK, 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. © 2020 by the authors.

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  • 4.
    Neikter, Magnus
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Edin, Emil
    Division of Materials Science, Luleå University of Technology, 97187 Luleå (SWE).
    Proper, Sebastian
    esearch Institutes of Sweden, 41314 Gothenburg (SWE).
    Bhaskar, Phavan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Nekkalapudi, Gopi Krishna
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Linde, Oscar
    GKN Aerospace Sweden AB, 46181 Trollhättan (SWE).
    Hansson, Thomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Tensile Properties of 21-6-9 Austenitic Stainless Steel Built Using Laser Powder-Bed Fusion2021In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 14, no 15, article id 4280Article in journal (Refereed)
    Abstract [en]

    Alloy 21-6-9 is an austenitic stainless steel with high strength, thermal stability at high temperatures, and retained toughness at cryogenic temperatures. This type of steel has been used for aerospace applications for decades, using traditional manufacturing processes. However, limited research has been conducted on this alloy manufactured using laser powder-bed fusion (LPBF). Therefore, in this work, a design of experiment (DOE) was performed to obtain optimized process parameters with regard to low porosity. Once the optimized parameters were established, horizontal and vertical blanks were built to investigate the mechanical properties and potential anisotropic behavior. As this alloy is exposed to elevated temperatures in industrial applications, the effect of elevated temperatures (room temperature and 750 degrees C) on the tensile properties was investigated. In this work, it was shown that alloy 21-6-9 could be built successfully using LPBF, with good properties and a density of 99.7%, having an ultimate tensile strength of 825 MPa, with an elongation of 41%, and without any significant anisotropic behavior.

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  • 5.
    Sadeghi, Esmaeil
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Multi-Scale Additive Manufacturing Lab (MSAM), The University of Waterloo, Ontario (CAN).
    Asala, Gbenga
    Technology Access Centre for Aerospace & Manufacturing, Red River College, Manitoba (CAN).
    Karimi Neghlani, Paria
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Multi-Scale Additive Manufacturing Lab (MSAM), The University of Waterloo, Ontario (CAN).
    Deng, Dunyong
    Division of Engineering Materials, Linköping University, Linköping (SWE).
    Moverare, Johan
    Division of Engineering Materials, Linköping University, Linköping (SWE).
    Hansson, Thomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. GKN Aerospace Engine Systems, Trollhättan (SWE).
    Fatigue crack initiation and propagation in Alloy 718 with a bimodal grain morphology built via electron beam-powder bed fusion2021In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 827, article id 142051Article in journal (Refereed)
    Abstract [en]

    A unique melting strategy was implemented in electron beam-powder bed fusion (EB-PBF) of Alloy 718, resulting in the formation of a bimodal grain morphology consisting of fine equiaxed and columnar grains. The microstructure was preserved following various thermal post-treatments. The post-treated specimens were exposed to low cycle fatigue (LCF), and fatigue crack growth (FCG) tests in ambient air at 600 °C under pure and dwell-time (120 s) fatigue cycles. Clustered inclusions spanned a region of 100-600 µm in length acted as the crack initiation site, reducing the specimens' total fatigue life. When compared to pure fatigue cycles, dwell-time fatigue cycles reduced LCF life by approximately 35%, regardless of the thermal post-treatments. Due to a high fraction of grain boundary area in the as-built EB-PBF specimens, oxygen diffusion across the grain boundaries was enhanced. The intergranular fracture mode was favored in the plastic zone ahead of the crack tip, leading to rapid crack growth. No unbroken ligaments behind the crack front were found by high-resolution X-ray computed tomography, which was consistent with a large crack opening displacement linked to severe deformation around the crack tip. 

  • 6.
    Sadeghi, Esmaeil
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Karimi Neghlani, Paria
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Israelsson, Niklas
    GE Additive – Arcam EBM, Mölnlycke, Sweden.
    Shipley, James
    Quintus Technologies AB, Västerås, Sweden.
    Månsson, Tomas
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Hansson, Thomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. GKN Aerospace Engine Systems, Sweden.
    Inclusion-induced fatigue crack initiation in powder bed fusion of Alloy 7182020In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 36, article id 101670Article in journal (Refereed)
    Abstract [en]

    Fatigue crack initiation of Alloy 718 additively manufactured via electron beam-powder bed fusion (EB-PBF) process was investigated. The melt parameters were chosen to achieve sufficient energy input and minimize process-induced defects. A line offset of 200 µm with enough line energy was used, leading to the formation of wide and deep melt pools. This strategy facilitated the formation of equiaxed grains at the melt pools bottom, and short columnar grains within the melt pools aligned parallel to the build direction. The mixed grain morphology and texture were retained after various thermal post-treatments, including heat treatment (HT), hot isostatic pressing (HIP), and HIP-HT. Micron-sized non-metallic inclusions in the feedstock powder, such as Al-rich oxide and titanium nitride clustered during the EB-PBF process, and remained intact during the post-treatments. Low cycle fatigue cracks mainly originated from the non-metallic inclusions found near the surface of the test specimens. HIPing was able to remove a portion of the internal defects, including round-shaped and shrinkage pores; therefore, a small fatigue life enhancement was observed in HIP-HT compared to HT.

  • 7.
    Sandell, Viktor
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics,Luleå (SWE).
    Åkerfeldt, Pia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics,Luleå (SWE).
    Hansson, Thomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Luleå (SWE).
    Fatigue fracture characterization of chemically post-processed electron beam powder bed fusion Ti-6Al-4V2023In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 172, article id 107673Article in journal (Refereed)
    Abstract [en]

    The fatigue behavior of additively manufactured (AM) structural parts is sensitive to the surface and near-surface material conditions. Chemical post-processing surface treatments can be used to improve the surface condition of AM components, including complex geometries with surfaces difficult to access. In this work, surfaces of electron beam powder bed fusion (EB-PBF) produced Ti–6Al–4V were subject to two different chemical post-processing surface treatments, chemical milling and Hirtisation. As-built and machined surfaces, as well as hot isostatic pressing (HIP), treated conditions were also investigated. Fatigue testing was carried out in four-point bending. The investigation focused on the relationship between fracture mechanisms and fatigue life through fractographic study. It was found that a majority of fractures were initiated at internal surface-near defects or defects on the surface. Chemical post-processing was found to smoothen the surface but to leave a surface waviness. Material removal during post-processing could open up internal defects to the treated surface. In HIP-treated specimens, fractures initiated at defects open to the surface. Despite post-processing increasing the mean life of fatigue specimens, no significant improvements in the lowest tested life were observed for any specimen condition.

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  • 8.
    Squillaci, Linda
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Neikter, Magnus
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Hansson, Thomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Harlin, Peter
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Niklasson, Fredrik
    GKN Aerospace, Trollhättan (SWE).
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Extending powder particle size distribution of laser powder bed fusion Ti-6Al-4V: investigation of single tracks and multilayer experiments2023Conference paper (Other academic)
    Abstract [en]

    This paper explores the effects of varying process parameters (i.e., laser power, laser scanning speed, hatch distance) on the characteristics of single tracks, triple tracks and cubes, in order to provide answers to Research Question 1. A full factorial DoE approach was adopted to produce the experiments. Data was extracted from different sources to find correlations between tracks and multilayer geometries. A digital microscope was used to obtain height profiles, whilst polished/etched cross sections cut parallel to the build direction were imaged using a LOM to obtain measurements of track height, width, melt pool depth, subsurface porosity and residual defect content in cubes. Track height was found to exceed the recoated value of 70μm for both single and triple tracks. The width of single tracks showed a clear upward trend when displayed against VED, showing a lateral expansion as energy input increased. It was also revealed that single tracks expand laterally as they grow above the substrate, indicating swelling. The melt pool depth showed a steady upward trend when plotted against LED, though less systematic than track width. A martensitic microstructure was detected, with hierarchical α’ needles growing at prescribed crystallographic directions within vertical prior-β grains. A large portion of spatter particles and unmelted powder granules were detected on the substrate and tracks, with many accumulating on the side of the tracks forming a denudation zone.

  • 9.
    Thalavai Pandian, Karthikeyan
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Neikter, Magnus
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Bahbou, F.
    GE Additive, SE-435 33 Mölnlycke (SWE).
    Ganvir, A.
    GKN Aerospace Engine Systems, Trollhättan (SWE).
    Hansson, Thomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. GKN Aerospace Engine Systems, Trollhättan (SWE).
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Fatigue behavior of low-temperature hot isostatic pressed electron beam powder bed fusion manufactured Ti-6Al-4 V2023In: Journal of Alloys and Compounds, ISSN 0925-8388, Vol. 962, article id 171086Article in journal (Refereed)
    Abstract [en]

    Ti-6Al-4 V finds application in the fan and compressor modules of gas turbine engines due to its high specific strength. Ti-6Al-4 V components manufactured using one of the additive manufacturing (AM) techniques, the electron beam powder bed fusion (PBF-EB) process, has been an active area of research in the past decade. The fatigue life of such PBF-EB built Ti-6Al-4 V components is improved by hot isostatic pressing (HIP) treatment typically performed at about 920 ˚C. The HIP treatment at 920 ˚C results in coarsening of α laths and reduced static strength and therefore a low-temperature HIP treatment is performed at about 800 ˚C to limit the impact on static mechanical properties. In the present work, the low cycle fatigue and fatigue crack growth behavior of such a modified HIP (low-temperature HIP) treated material is assessed and compared with the respective data for the standard HIP-treated material. The modified HIP-treated material has fatigue performance comparable to the standard HIP-treated material. This work suggests that the modified HIP treatment improves the static mechanical properties without significantly impacting the fatigue performance. Also, fatigue life predictions were made from the measured defect size at the crack initiation site using a linear elastic fracture mechanics tool. The life predictions show good agreement with the experimental values for defects greater than the intrinsic crack length, where life is well predicted by large-crack growth methodology. 

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  • 10.
    Thalavai Pandian, Karthikeyan
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Neikter, Magnus
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Bahbou, Fouzi
    GE Additive, 435 33 Molnlycke (SWE).
    Hansson, Thomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. GKN Aerospace Engine Systems, 461 38 Trollhattan, (SWE).
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Elevated-Temperature Tensile Properties of Low-Temperature HIP-Treated EBM-Built Ti-6Al-4V.2022In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 15, no 10, article id 3624Article in journal (Refereed)
    Abstract [en]

    Evaluation of the high-temperature tensile properties of Ti-6Al-4V manufactured by electron beam melting (EBM) and subjected to a low-temperature hot isostatic pressing (HIP) treatment (800 °C) was performed in this study. The high-temperature tensile properties of as-built and standard HIP-treated (920 °C) materials were studied for comparison. Metallurgical characterization of the as-built, HIP-treated materials was carried out to understand the effect of temperature on the microstructure. As the HIP treatments were performed below the β-transus temperature (995 °C for Ti-6Al-4V), no significant difference was observed in β grain width between the as-built and HIP-treated samples. The standard HIP-treated material measured about 1.4×-1.7× wider α laths than those in the modified HIP (low-temperature HIP)-treated and as-built samples. The standard HIP-treated material showed about a 10-14% lower yield strength than other tested materials. At 350 °C, the yield strength decreased to about 65% compared to the room-temperature strength for all tested specimens. An increase in ductility was observed at 150 °C compared to that at room temperature, but the values decreased between 150 and 350 °C because of the activation of different slip systems.

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