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  • 1.
    Adegoke, Olutayo
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Brodin, Håkan
    Materials Technology Additive Manufacturing Product Development-Industrial Gas Turbines, Siemens Industrial Turbomachinery, Finspång, SE-612 83, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Influence of laser powder bed fusion process parameters on voids, cracks, and microhardness of nickel-based superalloy alloy 247LC2020In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 13, no 17, article id 3770Article in journal (Refereed)
    Abstract [en]

    The manufacturing of parts from nickel-based superalloy Alloy 247LC by laser powder bed fusion (L-PBF) is challenging, primarily owing to the alloy’s susceptibility to cracks. Apart from the cracks, voids created during the L-PBF process should also be minimized to produce dense parts. In this study, samples of Alloy 247LC were manufactured by L-PBF, several of which could be produced with voids and crack density close to zero. A statistical design of experiments was used to evaluate the influence of the process parameters, namely laser power, scanning speed, and hatch distance (inherent to the volumetric energy density) on void formation, crack density, and microhardness of the samples. The window of process parameters, in which minimum voids and/or cracks were present, was predicted. It was shown that the void content increased steeply at a volumetric energy density threshold below 81 J/mm3. The crack density, on the other hand, increased steeply at a volumetric energy density threshold above 163 J/mm3. The microhardness displayed a relatively low value in three samples which displayed the lowest volumetric energy density and highest void content. It was also observed that two samples, which displayed the highest volumetric energy density and crack density, demonstrated a relatively high microhardness; which could be a vital evidence in future investigations to determine the fundamental mechanism of cracking. The laser power was concluded to be the strongest and statistically most significant process parameter that influenced void formation and microhardness. The interaction of laser power and hatch distance was the strongest and most significant factor that influenced the crack density. © 2020 by the authors.

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  • 2.
    Adegoke, Olutayo
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Brodin, Håkan
    Siemens Industrial Turbomachinery, Finspång, 612 83, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Review of laser powder bed fusion of gamma-prime-strengthened nickel-based superalloys2020In: Metals, ISSN 2075-4701, Vol. 10, no 8, article id 996Article in journal (Refereed)
    Abstract [en]

    This paper reviews state of the art laser powder bed fusion (L-PBF) manufacturing of γ′ nickel-based superalloys. L-PBF resembles welding; therefore, weld-cracking mechanisms, such as solidification, liquation, strain age, and ductility-dip cracking, may occur during L-PBF manufacturing. Spherical pores and lack-of-fusion voids are other defects that may occur in γ′-strengthened nickel-based superalloys manufactured with L-PBF. There is a correlation between defect formation and the process parameters used in the L-PBF process. Prerequisites for solidification cracking include nonequilibrium solidification due to segregating elements, the presence of liquid film between cells, a wide critical temperature range, and the presence of thermal or residual stress. These prerequisites are present in L-PBF processes. The phases found in L-PBF-manufactured γ′-strengthened superalloys closely resemble those of the equivalent cast materials, where γ, γ′, and γ/γ′ eutectic and carbides are typically present in the microstructure. Additionally, the sizes of the γ′ particles are small in as-built L-PBF materials because of the high cooling rate. Furthermore, the creep performance of L-PBF-manufactured materials is inferior to that of cast material because of the presence of defects and the small grain size in the L-PBF materials; however, some vertically built L-PBF materials have demonstrated creep properties that are close to those of cast materials.© 2020 by the authors. Licensee MDPI, Basel, Switzerland.

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  • 3.
    Adegoke, Olutayo
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Brodin, Håkan
    Siemens Industrial Turbomachinery, 612 83, Finspång (SWE).
    Pederson, Robert
    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. Sandvik Additive Manufacturing, Sandviken (SWE).
    Influence of laser powder bed fusion process parameters on the microstructure and cracking susceptibility of nickel-based superalloy Alloy 247LC2022In: Results in Materials, ISSN 2590-048X, Vol. 13, article id 100256Article in journal (Refereed)
    Abstract [en]

    Microstructures of material conditions of nickel-based superalloy Alloy 247LC fabricated using laser powder bed fusion (L-PBF) were investigated. Experiments designed in a prior study revealed the L-PBF process parameters for which the material conditions displayed a reduced susceptibility to cracking. Certain process parameters produced material conditions with an increased susceptibility to cracking. In this study, the material conditions were investigated in detail to reveal their microstructure and to determine the cause of cracking. The reason for the transition between a reduced to an increased susceptibility to cracking was examined. The results revealed solidification cracking occurred at high-angle grain boundaries. Solidification cracking may have been promoted at high-angle grain boundaries because of the undercooling contribution of the grain boundary energy. Furthermore, Si segregation was observed in the cracks. Thus, the presence of Si most likely promoted solidification cracking. It was observed that a high crack density, which occurred in the high energy density material condition, was associated with a large average grain size. The fact that certain combination of process parameters produced microstructures with a low susceptibility to cracking, indicates that reliable Alloy 247LC material may be printed using L-PBF by employing improved process parameters. © 2022

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  • 4.
    Adegoke, Olutayo
    et al.
    Siemens Energy, Finspång (SWE).
    Kumara, Chamara
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. FEV Sverige AB, Trollhättan (SWE).
    Thuvander, Matttias
    Department of Physics, Chalmers University of Technology, Gothenburg (SWE).
    Deirmina, Faraz
    Siemens Energy, Finspång (SWE).
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Brodin, Håkan
    Siemens Energy, Finspång (SWE).
    Harlin, Peter
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Sandvik Additive Manufacturing, Sandviken (SWE).
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Scanning electron microscopy and atom probe tomography characterization of laser powder bed fusion precipitation strengthening nickel-based superalloy2023In: Micron, ISSN 0968-4328, E-ISSN 1878-4291, Vol. 171, article id 103472Article in journal (Refereed)
    Abstract [en]

    Atom probe tomography (APT) was utilized to supplement scanning electron microscopy (SEM) characterizationof a precipitation strengthening nickel-based superalloy, Alloy 247LC, processed by laser powder bed fusion (LPBF). It was observed that the material in the as-built condition had a relatively high strength. Using both SEMand APT, it was concluded that the high strength was not attributed to the typical precipitation strengtheningeffect of γ’. In the absence of γ’ it could be reasonably inferred that the numerous black dots observed in thecells/grains with SEM were dislocations and as such should be contributing significantly to the strengthening.Thus, the current investigation demonstrated that relatively high strengthening can be attained in L-PBF even inthe absence of precipitated γ’. Even though γ’ was not precipitated, the APT analysis displayed a nanometer scalepartitioning of Cr that could be contributing to the strengthening. After heat-treatment, γ’ was precipitated and itdemonstrated the expected high strengthening behavior. Al, Ta and Ti partitioned to γ’. The strong partitioningof Ta in γ’ is indicative that the element, together with Al and Ti, was contributing to the strain-age crackingoccurring during heat-treatment. Cr, Mo and Co partitioned to the matrix γ phase. Hf, Ta, Ti and W were found inthe carbides corroborating previous reports that they are MC. 

  • 5.
    Adegoke, Olutayo
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Polisetti, Satyanarayana Rao
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Xu, Jinghao
    Linköpings universitet, Linköping.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Brodin, Håkan
    Siemens Industrial Turbomachinery, Finspång.
    Pederson, Robert
    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. Sandvik Additive Manufacturing, Sandviken.
    Influence of laser powder bed fusion process parameters on the microstructure of solution heat-treated nickel-based superalloy Alloy 247LC2022In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 183, article id 111612Article in journal (Refereed)
    Abstract [en]

    In this study, Alloy 247LC samples were built with different laser powder bed fusion (L-PBF) process parameters. The samples were then subjected to solution heat treatment at 1260 °C for 2 h. The grain size of all the samples increased significantly after the heat treatment. The relationship between the process parameters and grain size of the samples was investigated by performing a design of experiment analysis. The results indicated that the laser power was the most significant process parameter that influenced the grain height and aspect ratio. The laser power also significantly influenced the grain width. The as-built and as-built + heat-treated samples with high, medium, and low energy densities were characterized using a field emission gun scanning electron microscope equipped with an electron backscatter diffraction detector. The micrographs revealed that the cells present in the as-built samples disappeared after the heat treatment. Isolated cases of twinning were observed in the grains of the as-built + heat-treated samples. The disappearance of cells, increase in the grain size, and appearance of twins suggested that recrystallization occurred in the alloy after the heat treatment. The occurrence of recrystallization was confirmed by analyzing the grain orientation spread of the alloy, which was lower and more predominantly <1° in the as-built + heat-treated conditions than in the as-built conditions. The microhardness of the as-built + heat-treated samples were high which was plausible because γ’ precipitates were observed in the samples. However, the L-PBF process parameters had a very low correlation with the microhardness of the as-built + heat-treated samples.

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  • 6.
    Andersson, Joel
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Hosseini, Vahid
    University West, Department of Engineering Science, Division of Welding Technology.
    Neikter, Magnus
    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.
    Welding of special alloys2023In: Welding of Metallic Materials: Methods, Metallurgy, and Performance / [ed] Fuad Khoshnaw, Elsevier , 2023, p. 279-316Chapter in book (Other academic)
    Abstract [en]

    Specialty alloys are a broad group of materials providing superior properties to common materials and are therefore used for more demanding applications. Specialty alloys require sophisticated manufacturing routes, e.g., vacuum metallurgy, to account for all the alloying elements needed to finalize the specific alloy for its intended purpose. The alloys of Duplex stainless steels, superalloys, and Titanium alloys are examples of so-called specialty alloys where aerospace, chemical, and petrochemical industries are just a few areas mentioned where these specialty alloys are frequently used. Duplex stainless steel, had superior mechanical properties and corrosion resistance, making them a sustainable choice for a wide variety of applications i.e., petrochemical industries. The superalloys, and especially the precipitation hardening ones belong to a unique plethora of alloys commonly used in aerospace as well as land-based gas turbines which possess superb mechanical performance at elevated temperatures. However, the superalloys are unfortunately very challenging to process, not at least regarding weld cracking. With their high specific strength and corrosion resistance, titanium alloys are favorable for numerous applications. However, they react readily with oxygen at elevated temperatures and therefore inert atmosphere must be used during welding. 

  • 7.
    Anti, Marta-Lena
    et al.
    Luleå University of Technology, Division of Materials Science, Sweden.
    Collado Ciprés, V
    Sandvik Coromant, Stockholm, Sweden.
    Mouzon, J
    Linnaeus University, Department of Cultural Sciences, Kalmar, Sweden.
    Åkerfeldt, P.
    Luleå University of Technology, Division of Materials Science, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Effect of silicon on creep properties of titanium 6Al-2Sn-4Zr-2Mo alloy2020In: MATEC Web of Conferences, E-ISSN 2261-236X, Vol. 321, article id 04021Article in journal (Refereed)
    Abstract [en]

    The alloy Ti-6Al-2Sn-4Zr-2Mo is a titanium alloy for elevated temperatures often used in aerospace applications. Minor additions of silicon have proven to improve the creep resistance of this alloy. In this work, three different amounts of silicon (0.015, 0.07 and 0.162 wt% Si) were added to cast Ti-6242 and creep tests were performed at different temperatures and loads. Creep resistance increased significantly with silicon addition by means of silicide precipitation hindering dislocations movement. Silicon rich nanoparticles in the microstructure were detected and their effect on creep resistance was investigated. The instruments used in this study were light optical microscope (LOM) and scanning electron microscopy (SEM).

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  • 8.
    Balachandramurthi, Arun Ramanathan
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Jaladurgam, Nitesj Raj
    Chalmers University of Technology, Department of Physics, Gothenburg, SE-412 96, Sweden.
    Kumara, Chamara
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Hansson, Tomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. GKN Aerospace Sweden AB, Trollhättan, SE-461 38, Sweden.
    Moverare, Johan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Linköping University, Department of Management and Engineering, Linköping, SE 581 83, Sweden.
    Gårdstam, Johannes
    Qunitus Technologies AB, Västerås, SE-721 66, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    On the microstructure of laser beam powder bed fusion alloy 718 and its influence on the low cycle fatigue behaviour2020In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 13, no 22, article id 5198Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing of Alloy 718 has become a popular subject of research in recent years. Understanding the process-microstructure-property relationship of additively manufactured Alloy 718 is crucial for maturing the technology to manufacture critical components. Fatigue behaviour is a key mechanical property that is required in applications such as gas turbines. Therefore, in the present work, low cycle fatigue behaviour of Alloy 718 manufactured by laser beam powder bed fusion process has been investigated. The material was tested in as-built condition as well as after two different thermal post-treatments. Three orientations with respect to the building direction were tested to evaluate the anisotropy. Testing was performed at room temperature under controlled amplitudes of strain. It was found that defects, inclusions, strengthening precipitates, and Young’s modulus influence the fatigue behaviour under strain-controlled conditions. The strengthening precipitates affected the deformation mechanism as well as the cycle-dependent hardening/softening behaviour. The defects and the inclusions had a detrimental effect on fatigue life. The presence of Laves phase in LB-PBF Alloy 718 did not have a detrimental effect on fatigue life. Young’s modulus was anisotropic and it contributed to the anisotropy in strain-life relationship. Pseudo-elastic stress vs. fatigue life approach could be used to handle the modulus-induced anisotropy in the strain-life relationship. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.

  • 9.
    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, Sweden.
    Dixit, Nikhil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Deng, Dunyong
    Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Microstructural influence on fatigue crack propagation during high cycle fatigue testing of additively manufactured Alloy 7182019In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 149, p. 82-94Article in journal (Refereed)
    Abstract [en]

    A study of the microstructure of additively manufactured Alloy 718 was performed in order to better understand the parameters that have an influence on the fatigue properties of the material. The specimens were manufactured using two powder bed fusion techniques – Electron Beam Melting (EBM) and Selective Laser Melting (SLM). Four point bending fatigue tests were performed at room temperature with a stress ratio of R = 0.1 and 20 Hz frequency, on material that was either in hot isostatically pressed (HIP) and solution treated and aged (STA) condition or in STA condition without a prior HIP treatment. The grains in the SLM material in the HIP + STA condition have grown considerably both in the hatch and the contour regions; EBM material, in contrast, shows grain growth only in the contour region. Fractographic analysis of the specimens in HIP + STA condition showed a faceted appearance while the specimens in STA condition showed a more planar crack appearance. The crack propagation occurred in a transgranular mode and it was found that precipitatessuch as NbC, TiN or δ-phase, when present, did not affect the crack path. The areas with larger grains corresponded to the faceted appearance of the fracture surface. This could be attributed to the plastic zone ahead of the crack tip being confined within one grain, in case of the larger grains, which promotes single shear crack growth mode

  • 10.
    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, Sweden.
    Dixit, Nikhil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence of defects and as-built surface roughness on fatigue properties of additively manufactured Alloy 7182018In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 735, p. 463-474Article in journal (Refereed)
    Abstract [en]

    Electron beam melting (EBM) and Selective Laser Melting (SLM) are powder bed based additive manufacturing (AM) processes. These, relatively new, processes offer advantages such as near net shaping, manufacturing complex geometries with a design space that was previously not accessible with conventional manufacturing processes, part consolidation to reduce number of assemblies, shorter time to market etc. The aerospace and gas turbine industries have shown interest in the EBM and the SLM processes to enable topology-optimized designs, parts with lattice structures and part consolidation. However, to realize such advantages, factors affecting the mechanical properties must be well understood – especially the fatigue properties. In the context of fatigue performance, apart from the effect of different phases in the material, the effect of defects in terms of both the amount and distribution and the effect of “rough” as-built surface must be studied in detail. Fatigue properties of Alloy 718, a Ni-Fe based superalloy widely used in the aerospace engines is investigated in this study. Four point bending fatigue tests have been performed at 20 Hz in room temperature at different stress ranges to compare the performance of the EBM and the SLM material to the wrought material. The experiment aims to assess the differences in fatigue properties between the two powder bed AM processes as well as assess the effect of two post-treatment methods namely – machining and hot isostatic pressing (HIP). Fractography and metallography have been performed to explain the observed properties. Both HIPing and machining improve the fatigue performance; however, a large scatter is observed for machined specimens. Fatigue properties of SLM material approach that of wrought material while in EBM material defects severely affect the fatigue life. © 2018 Elsevier B.V.

  • 11.
    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

  • 12.
    Balachandramurthi, Arun Ramanathan
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Olsson, Jonas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Ålgårdh, Joakim
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Powder Materials & Additive Manufacturing, Swerim AB, SE-164 40, Kista, Sweden.
    Snis, Anders
    Arcam EBM, SE-431 37, Mölndal, Sweden.
    Moverare, Johan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Linköping University, Department of Management and Engineering,SE-581 83, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Microstructure tailoring in Electron Beam Powder Bed Fusion Additive Manufacturing and its potential consequences2019In: Results in Materials, ISSN 2590-048X, Vol. 1Article in journal (Refereed)
    Abstract [en]

    Electron Beam Powder Bed Fusion process for Alloy 718 was investigated, in the sense of microstructural evolution with varying process conditions. The existence of a geometric relationship between the melt front and the processing parameters was observed. By understanding and capitalizing on this relationship, it was possible to obtain columnar, equiaxed or bimodal microstructure.

  • 13.
    Balachandramurthi Ramanathan, Arun
    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, SE 581 83 Linköping, Sweden.
    Mahade, Satyapal
    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.
    Additive Manufacturing of Alloy 718 via Electron Beam Melting: Effect of Post-Treatment on the Microstructure and the Mechanical Properties.2018In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 1, article id E68Article in journal (Refereed)
    Abstract [en]

    Alloy 718 finds application in gas turbine engine components, such as turbine disks, compressor blades and so forth, due to its excellent mechanical and corrosion properties at elevated temperatures. Electron beam melting (EBM) is a recent addition to the list of additive manufacturing processes and has shown the capability to produce components with unique microstructural features. In this work, Alloy 718 specimens were manufactured using the EBM process with a single batch of virgin plasma atomized powder. One set of as-built specimens was subjected to solution treatment and ageing (STA); another set of as-built specimens was subjected to hot isostatic pressing (HIP), followed by STA (and referred to as HIP+STA). Microstructural analysis of as-built specimens, STA specimens and HIP+STA specimens was carried out using optical microscopy and scanning electron microscopy. Typical columnar microstructure, which is a characteristic of the EBM manufactured alloy, was observed. Hardness evaluation of the as-built, STA and HIP+STA specimens showed that the post-treatments led to an increase in hardness in the range of ~50 HV1. Tensile properties of the three material conditions (as-built, STA and HIP+STA) were evaluated. Post-treatments lead to an increase in the yield strength (YS) and the ultimate tensile strength (UTS). HIP+STA led to improved elongation compared to STA due to the closure of defects but YS and UTS were comparable for the two post-treatment conditions. Fractographic analysis of the tensile tested specimens showed that the closure of shrinkage porosity and the partial healing of lack of fusion (LoF) defects were responsible for improved properties. Fatigue properties were evaluated in both STA and HIP+STA conditions. In addition, three surface conditions were also investigated, namely the 'raw' as-built surface, the machined surface with the contour region and the machined surface without the contour region. Machining off the contour region completely together with HIP+STA led to significant improvement in fatigue performance.

  • 14.
    Cedergren, Stefan
    et al.
    a Research and Technology, GKN Aerospace Sweden AB, Trollhättan, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Machinability of cast titanium alloy Ti-6Al-4V with addition of boron2020In: MATEC Web of Conferences, E-ISSN 2261-236X, Vol. 321, article id 11077Article in journal (Refereed)
    Abstract [en]

    Cast titanium products generally have coarser microstructures compared to wrought, which explains their limited mechanical properties. However, instead of additional thermo-mechanical processing steps, as in the case of wrought components, the microstructure of castings can be refined by additions of boron. This enhances yield strength, tensile strength and ductility. In order to investigate the influence on machining of this microstructural refinement, cutting tests were performed in three different Ti-6Al-4V castings, having 0, 0.06 and 0.11 wt.% boron. Five machinability criteria were studied; cutting force, chip breakability, burr formation, surface roughness and tool wear. The results show anisotropic deformation behavior in chips when alpha colony size is on the same order of magnitude as the primary deformation zone, or larger. There was little or no influence on cutting forces and burr formation, however chip breakability and tool life was reduced when boron was added. Surface roughness showed a more complex behavior where 0.06 wt.% boron resulted in rougher surfaces compared to the other compositions at low feed rate.

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  • 15. Davies, P.
    et al.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Welding Technology. University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Institute of Structural Materials, College of Engineering, Swansea University, Bay Campus, Fabian Way, Swansea SA1 8EN, United Kingdom.
    Coleman, M.
    Institute of Structural Materials, College of Engineering, Swansea University, Bay Campus, Fabian Way, Swansea SA1 8EN, United Kingdom.
    Birosca, S.
    Institute of Structural Materials, College of Engineering, Swansea University, Bay Campus, Fabian Way, Swansea SA1 8EN, United Kingdom.
    The hierarchy of microstructure parameters affecting the tensile ductility in centrifugally cast and forged Ti-834 alloy during high temperature exposure in air2016In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 117, p. 51-67Article in journal (Refereed)
    Abstract [en]

    Ductility regression is the main concern in using Ti-834 titanium alloy at temperatures above 500 °C for aerospace applications. The reduction of ductility in titanium alloys at high temperatures is strongly correlated to the exposure time. In the current study the effect of prolonged exposure at 500 °C on the tensile ductility of two differently processed Ti-834 alloys was investigated. In order to simulate actual Ti-834 processing routes, forged and centrifugally cast materials were used. The tensile tests were conducted on various specimens exposed at 500 °C for 100, 200 and 500 h to observe microstructure feature changes. Moreover, the effect of microstructure, microtexture, α-case, α2 and silicide precipitate coarsening during high temperature exposure was studied thoroughly. The cast alloy was found to have a minimum ductility and failed at 1.8% strain after exposure at 500 °C/500 h when the α-case layer was retained during testing, whilst, the ductility of the forged alloy was unaffected. The effects of individual microstructural parameters on the ductility regression in Ti-834 alloy were quantified. The results showed that 7.1% strain differences between the cast and forged alloy are related to microstructural variations including; morphology, lath widths, grain size and shape, grain orientations and microtexture. A total of 9.6% strain loss was observed in centrifugally cast Ti-834 after aging at 500°C/500 h and quantified as follow; 3.6% due to α-case formation during high temperature exposure, 0.2% due to α2-precipitates coarsening, 4.4% due to further silicide formation and coarsening, 1.4% due to additional microstructure changes during high temperature exposure. Furthermore, silicide coarsening on α/β phase boundaries caused large void formation around the precipitates. A theoretical model supported by experimental observations for silicide precipitation in fully colony and duplex microstructures was established. The element partitioning during exposure caused Al and Ti depletion in the vicinity of the β phase in the lamellae, i.e., αs area. This resulted in lowering the strength of the alloy and facilitated the formation of Ti3(SiZr)2 precipitates. The Al depletion and nano-scale partitioning observed at the αs/β boundaries resulted in easy crack initiation and promoted propagation in the centrifugally cast colony microstructure and reduced the basal slip τcrss. Furthermore, silicides were not formed in αp (high Al, Ti and low Zr areas) in the forged duplex microstructure that promoted superior mechanical performance and ductility over the cast alloy.

    Graphical abstract

  • 16.
    Fargas, G.
    et al.
    Universitat Politècnica de Catalunya, CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Barcelona, 08019, Spain. Centre for Research in Multiscale Engineering of Barcelona, Universitat Politècnica de Catalunya, Campus Diagonal Besòs-EEBE, Barcelona, 08019, Spain.
    Roa, J. J.
    Universitat Politècnica de Catalunya, CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Barcelona, 08019, Spain. Centre for Research in Multiscale Engineering of Barcelona, Universitat Politècnica de Catalunya, Campus Diagonal Besòs-EEBE, Barcelona, 08019, Spain.
    Sefer, B.
    Universitat Politècnica de Catalunya, CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Barcelona, 08019, Spain. Centre for Research in Multiscale Engineering of Barcelona, Universitat Politècnica de Catalunya, Campus Diagonal Besòs-EEBE, Barcelona, 08019, Spain. University of Erlangen-Nuremberg, Institute for Surface Science and Corrosion, Department of Materials Science and Engineering, Erlangen, D-91058, Germany.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Welding Technology.
    Antti, M. -L
    Division of Materials Science, Luleå University of Technology, Luleå, S-97187, Sweden.
    Mateo, A.
    Universitat Politècnica de Catalunya, CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Barcelona, 08019, Spain. Centre for Research in Multiscale Engineering of Barcelona, Universitat Politècnica de Catalunya, Campus Diagonal Besòs-EEBE, Barcelona, 08019, Spain.
    Influence of cyclic thermal treatments on the oxidation behavior of Ti-6Al-2Sn-4Zr-2Mo alloy2018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 145, p. 218-224Article in journal (Refereed)
    Abstract [en]

    Ti-6Al-2Sn-4Zr-2Mo is one of the most common titanium alloys for aerospace industry. This alloy experiences oxidation phenomenon at elevated temperatures. In the present study, cyclic thermal treatments were performed in air at 500, 593 and 700 °C, up to 500 cycles, in order to determine the oxidation kinetics and to analyze the oxide scale and alpha-case formation. Moreover, results were compared to those achieved under isothermal conditions to elucidate differences between both thermal conditions. In this sense, metallographic techniques and X-ray diffraction, together with a detailed advanced characterization of the microstructure by Field Emission Scanning Electron Microscopy and Focus Ions Beam, were used to analyze surface oxidation evolution. Results pointed out that cyclic treatments induced a strong increase of the weight gain compared to isothermal treatments. The analysis of the oxide scale revealed the formation of not only rutile, as isothermal treatments, but also anatase. Thickness of the oxide scale was higher for cyclic conditions, while alpha case did not exceed values reached by isothermal treatments and even became lower at 500 °C.

  • 17.
    Fargas, Gemma
    et al.
    Universitat Politècnica de Catalunya, CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Universitat Politècnica de Catalunya, Barcelona, Spain.
    Roa, Joan Josep
    Universitat Politècnica de Catalunya, CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metallúrgica, Barcelona, Spain.
    Sefer, Birhan
    Universitat Politècnica de Catalunya, CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metallúrgica, Barcelona, Spain, Luleå University of Technology, Division of Materials Science, S-97187 Luleå, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Welding Technology.
    Antti, Marta Lena
    Luleå University of Technology, Division of Materials Science, S-97187 Luleå, Sweden.
    Mateo, Antonio M.
    Universitat Politècnica de Catalunya, CIEFMA/EEBE, Departament de Ciència dels Materials i Enginyeria Metallúrgica, Barcelona, Spain.
    Oxidation behavior of TI-6Al-4V alloy exposed to isothermal and cyclic thermal treatments2017In: Proceedings of the conference METAL 2017, TANGER Ltd. , 2017, p. 1573-1579Conference paper (Other academic)
    Abstract [en]

    One of the most common titanium alloys for aerospace industry is Ti-6Al-4V (usually designed as Ti-64) which is used for manufacturing aero-engine components, such as fan discs, compressor discs, blades andstators. The maximum service temperature for this alloy is limited partly because of degradation of mechanical properties at elevated temperatures (above 480 ºC). During the first stage of oxidation the oxidescale is protective, whereas after prolonged oxidation time it loses its protective nature and favours higher diffusion of oxygen through the oxide. In the present study, cyclic thermal treatments were performed in air at 500 and 700 ºC, up to 500 hours, and compared with similar studies carried out on isothermal oxidation conditions. The evolution of the surface oxidation was analyzed by metallographic techniques and X-ray diffraction, together with a detailed advanced characterization of the microstructure by Scanning Electron Microscopy and Focus Ions Beam. The results point out that the cyclic thermal treatments induced a strong increase of the weight gain compared to isothermal treatments. The analysis of the oxide scale revealed not only the presence of rutile, at 700 ºC, but also anatase and TiOx at 500 ºC for both isothermal and cyclic thermal treatments. At 700 ºC, thermal stress caused by cyclic thermal treatments promoted the fracture of the oxide after the first 20 hours.

  • 18.
    Goel, Sneha
    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.
    Capek, J.
    Paul Scherrer Institute, Laboratory for Neutron Scattering and Imaging, , Villigen PSI, CH-5232, Switzerland (CHE).
    Polatidis, Efthymios
    Paul Scherrer Institute, Laboratory for Neutron Scattering and Imaging, , Villigen PSI, CH-5232, Switzerland (CHE).
    Colliander, Magnus Hörnqvist
    Chalmers University of Technology, Gothenburg, 41296, Sweden .
    Joshi, Shrikant V.
    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.
    Residual stress determination by neutron diffraction in powder bed fusion-built Alloy 718: Influence of process parameters and post-treatment2020In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 195, article id 109045Article in journal (Refereed)
    Abstract [en]

    Alloy 718 is a nickel-based superalloy that is widely used as a structural material for high-temperature applications. One concern that arises when Alloy 718 is manufactured using powder bed fusion (PBF) is that residual stresses appear due to the high thermal gradients. These residual stresses can be detrimental as they can degrade mechanical properties and distort components. In this work, residual stresses in PBF built Alloy 718, using both electron and laser energy sources, were measured by neutron diffraction. The effects of process parameters and thermal post-treatments were studied. The results show that thermal post-treatments effectively reduce the residual stresses present in the material. Moreover, the material built with laser based PBF showed a higher residual stress compared to the material built with electron-beam based PBF. The scanning strategy with the lower amount of residual stresses in case of laser based PBF was the chessboard strategy compared to the bi-directional raster strategy. In addition, the influence of measured and calculated lattice spacing (d0) on the evaluated residual stresses was investigated. © 2020 The Authors

  • 19.
    Isoaho, Jerry
    et al.
    GKN Aerospace Engine Systems, Trollhättan (SWE).
    Dordlofva, Christo
    GKN Aerospace Engine Systems, Trollhättan (SWE); University of Technology, Luleå (SWE).
    Segerstark, Andreas
    GKN Aerospace Engine Systems, Trollhättan (SWE).
    Harlin, Peter
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Sandvik Additive Manufacturing, Sandviken (SWE).
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Applications of additive manufacturing: Selected case studies and future prospects2023In: Additive Manufacturing of High-Performance metallic Materials / [ed] Pederson, Robert, Andersson, Joel & Joshi, Shrikant V., Elsevier, 2023, 1, p. 676-716Chapter in book (Refereed)
    Abstract [en]

    From an industrial standpoint, cost is of one of the most important drivers for utilizing new technologies such as additive manufacturing (AM). Other important drivers for why AM can be an advantageous technology for component manufacturing is decreased manufacturing lead time, rapid demonstration capability, freedom of design/geometry, advancing technology development, and not least sustainability in terms of both material utilization and improved part/system performance. In this chapter, six selected “case studies” are compiled, in which AM techniques have been used to manufacture components for actual applications. In some case studies, a comparison between the additive manufacturing route and the corresponding conventional manufacturing route is also included.

  • 20.
    Mahade, Satyapal
    et al.
    GKN Aerospace, Trollhättan (SWE).
    Bhattacharya, Prajina
    GKN Aerospace, Trollhättan (SWE).
    Tolvanen, Sakari
    GKN Aerospace, Trollhättan (SWE).
    Pederson, Robert
    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.
    Processing of high-performance materials by laser directed energy deposition with wire2023In: Additive Manufacturing of High-Performance metallic Materials / [ed] Pederson, Robert, Andersson, Joel & Joshi, Shrikant V., Elsevier, 2023, 1., p. 260-305Chapter in book (Refereed)
    Abstract [en]

    Processing of metallic materials by Laser Directed Energy Deposition (LDED), with Wire (w) as the feedstock, enables the manufacturing of high precision, near-net shape components that require minimal postmachining, without compromising the performance. L-DEDw has also shown the capability to add intricate features on large structures, which makes it an attractive fabrication technique for aerospace application. The key merits of wire as the feedstock when compared to powder include; higher deposition rates, low porosity in the deposited material, excellent surface finish, and, ∼ 100% utilization of the feedstock. However, despite the attractive merits, the difference in solidification rates during L-DEDw processing when compared to other fabrication routes could induce high residual stresses, which can be detrimental to the integrity of cracksensitive alloys. Additionally, there exists an inherent challenge during L-DEDw fabrication, where controlling the process variables to ensure stable deposition conditions becomes essential to achieve repeatable, and desired results. The recent advancements in the area of monitoring and control systems, and their integration with L-DEDw processing, have enabled to overcome the processing instability related challenges. Furthermore, different L-DEDw processing strategies for alleviating residual stresses (tensile) accumulation in the deposits are discussed, which could enable defectfree, high-performance component fabrication. Although the utilization of L-DEDw for processing diverse alloy systems has been explored in the literature, the current chapter's scope is restricted to L-DEDw processing of Nickel-based and Titanium-based alloys, which are often utilized in the aeroengine. This work aims to provide a holistic perspective and shed light on the state-of-the-art, recent developments, sustainability aspects and future directions for L-DEDw processed, highperformance Ni-based and Ti-based alloys.

  • 21.
    Maimaitiyili, Tuerdi
    et al.
    Photons for Engineering and Manufacturing Group, Paul Scherrer Institute, 5232 Villigen, Switzerland ; Malmö universitet, Department of Materials Science and Applied Mathematics, 20506 Malmö, Sweden.
    Woracek, Robin
    European Spallation Source ERIC, 22100 Lund, Sweden ; Nuclear Physics Institute of the CAS, 250 68 Husinec—Rež, Czech Republic.
    Neikter, Magnus
    Luleå University of Technology, Division of Materials Science, 971 81 Luleå, Swed.
    Boin, Mirko
    Department of Microstructure and Residual Stress Analysis, Helmholtz-Zentrum Berlin für Materialien und Energie, 14109 Berlin, Germany.
    Wimpory, Robert C.
    Department of Microstructure and Residual Stress Analysis, Helmholtz-Zentrum Berlin für Materialien und Energie, 14109 Berlin, Germany.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Strobl, Markus
    European Spallation Source ERIC, 22100 Lund, Sweden ; Nuclear Physics Institute of the CAS, 250 68 Husinec—Rež, Czech Republic ;Neutron Imaging and Applied Materials Group, Paul Scherrer Institute, 5232 Villigen, Switzerland .
    Drakopoulos, Michael
    maging and Microscopy Group, Diamond Light Source Ltd., Oxfordshire OX11 0DE, UK.
    Schäfer, Norbert
    Department of Nanoscale Structures and Microscopic Analysis, Helmholtz-Zentrum Berlin für Materialien und Energie, 14109 Berlin, Germany.
    Bjerkén, Christina
    Malmö universitet, Department of Materials Science and Applied Mathematics, 20506 Malmö, Sweden.
    Residual Lattice Strain and Phase Distribution in Ti-6Al-4V Produced by Electron Beam Melting2019In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 4, article id 667Article in journal (Refereed)
    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.

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  • 22.
    Neikter, Magnus
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Bhaskar, P.
    University West, Department of Engineering Science.
    Singh, S.
    Joining and Welding Research Institute, Osaka University, Osaka (JPN).
    Kadoi, K.
    Joining and Welding Research Institute, Osaka University, Osaka (JPN).
    Lyphout, Christophe
    Research Institutes of Sweden, Gothenburg (SWE).
    Svahn, F.
    GKN Aerospace Sweden AB, Trollhättan (SWE).
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Tensile properties of laser powder bed fusion built JBK-75 austenitic stainless steel2023In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 874, article id 144911Article in journal (Refereed)
    Abstract [en]

    Laser powder bed fusion (PBF-LB) is an additive manufacturing (AM) process that has several advantages to conventional manufacturing, such as near net-shaping capabilities and reduced material wastage. To be able to manufacture a novel material, however, one needs to first optimize the process parameters, to decrease porosity content as low as possible. Therefore, in this work the process parameters of PBF-LB built JBK-75 austenitic stainless steel, and its influence on porosity, microstructure, and hardness have been investigated. The least amount of porosity was found by using 132 W laser power, 750 mm/s scan speed, layer thickness 30 μm, and 0.12 mm hatch distance. These process parameters were then used to manufacture material for tensile testing, to investigate the tensile properties of PBF-LB built JBK-75 and potential anisotropic behavior. Hot isostatic pressing (HIP) was also performed in two sets of samples, to investigate the effect of pore closure on the tensile properties. The ultimate tensile strength (UTS) for the un-HIPed specimens was 1180 (horizontally built) and 1110 (vertically built) MPa. For the HIPed specimens, it was 1160 (horizontally built) and 1100 (vertically built) MPa. The anisotropic presence was explained by the presence of texture, with a multiple of random distribution (MRD) up to 4.34 for the {001} planes, and defects.

  • 23.
    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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  • 24.
    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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  • 25.
    Neikter, Magnus
    et al.
    Luleå University of Technology, Div. Material Science, Luleå, Sweden.
    Forsberg, Fredrik
    Luleå University of Technology, Div. Fluid and Experimental Mechanics, Luleå, Sweden.
    Lycksam, Henrik
    Luleå University of Technology, Div. Fluid and Experimental Mechanics, Luleå, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Welding Technology.
    Antti, Marta-Lena
    Luleå University of Technology, Div. Material Science, Luleå, Sweden.
    Microstructure and Defects in Additive Manufactured Titanium: a Comparison Between Microtomography and Optical Microscopy2017Conference paper (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 show that both techniques have their pros and cons:microtomography is the preferred choice for defect detection by analysing the full 3D sample volume, while light optical microscopy is better for analysing finer details in 2D.

  • 26.
    Neikter, Magnus
    et al.
    Luleå University of Technology, Luleå, Sweden.
    Woracek, R.
    European Spallation Source ERIC, Lund, Sweden. Nuclear Physics Institute of the CAZ, Czech Republic.
    Maimaitiyili, T.
    Paul Scherrer Institute, Villigen, Switzerland; Malmö University, Malmö, Sweden.
    Scheffzük, C.
    Karlsruhe Institute of Technology, Karlsruhe, Germany; Frank Laboratory of Neutron Physics, Dubna, Russian Federation.
    Strobl, M.
    Paul Scherrer Institute, Villigen, Switzerland; Niels Bohr Institute, Copenhagen, Denmark; Nuclear Physics Institute of the CAZ, Czech Republic.
    Antti, Marta-Lena
    Luleå University of Technology, Luleå, Sweden.
    Åkerfeldt, P.
    Luleå University of Technology, Luleå, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Bjerkén, C.
    Malmö University, Malmö, Sweden.
    Alpha texture variations in additive manufactured Ti-6Al-4V investigated with neutron diffraction2018In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 23, p. 225-234Article in journal (Refereed)
    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]. © 2018 Elsevier B.V.

  • 27.
    Neikter, Magnus
    et al.
    Luleå University of Technology, Division of Materials Science, Luleå 971 81, Sweden.
    Åkerfeldt, P.
    Luleå University of Technology, Division of Materials Science, Luleå 971 81, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Welding Technology.
    Antti, M. -L
    Luleå University of Technology, Division of Materials Science, Luleå 971 81, Sweden.
    Microstructural characterization and comparison of Ti-6Al-4V manufactured with different additive manufacturing processes2018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 143, p. 68-75Article in journal (Refereed)
    Abstract [en]

    In this work, the microstructures of Ti-6Al-4V manufactured by different additive manufacturing (AM) processes have been characterized and compared. The microstructural features that were characterized are the α lath thickness, grain boundary α (GB-α) thickness, prior β grain size and α colony size. In addition, the microhardnesses were also measured and compared. The microstructure of shaped metal deposited (SMD) Ti-6Al-4V material showed the smallest variations in α lath size, whereas the material manufactured with laser metal wire deposition-0 (LMwD-0) showed the largest variation. The prior β grain size was found to be smaller in material manufactured with powder bed fusion (PBF) as compared with corresponding material manufactured with the directed energy deposition (DED) processes. Parallel bands were only observed in materials manufactured with DED processes while being non-present in material manufactured with PBF processes.

  • 28.
    Neikter, Magnus
    et al.
    Luleå University of Technology, Division of Materials Science, Luleå.
    Åkerfeldt, P.
    Luleå University of Technology, Division of Materials Science, Luleå.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Welding Technology.
    Antti, M-L
    Luleå University of Technology, Division of Materials Science, Luleå.
    Microstructure characterisation of Ti-6Al-4V from different additive manufacturing processes2017In: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 258, p. 1-8, article id 012007Article in journal (Refereed)
    Abstract [en]

    The focus of this work has been microstructure characterisation of Ti-6Al-4V manufactured by five different additive manufacturing (AM) processes. The microstructure features being characterised are the prior β size, grain boundary α and α lath thickness. It was found that material manufactured with powder bed fusion processes has smaller prior β grains than the material from directed energy deposition processes. The AM processes with fast cooling rate render in thinner α laths and also thinner, and in some cases discontinuous, grain boundary α. Furthermore, it has been observed that material manufactured with the directed energy deposition processes has parallel bands, except for one condition when the parameters were changed, while the powder bed fusion processes do not have any parallel bands.

  • 29.
    Odenberger, Eva-Lis
    et al.
    Luleå University of Technology, Division of Mechanics of Solid Materials, Luleå, SE-971 87, Sweden; Division Materials and Production, RISE IVF AB, RISE Research Institutes of Sweden, Vällaregatan 30, Olofström, SE-293 38, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Oldenburg, Mats
    Luleå University of Technology, Division of Mechanics of Solid Materials, Luleå, SE-971 87, Sweden.
    Finite element modeling and validation of springback and stress relaxation in the thermo-mechanical forming of thin Ti-6Al-4V sheets2019In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 104, no 9-12, p. 3429-3455Article in journal (Refereed)
    Abstract [en]

    In this work, a hot forming procedure is developed using computer-aided engineering (CAE) to produce thin Ti-6Al-4V sheet components in an effective way. Traditional forming methods involve time- and cost-consuming furnace heating and subsequent hot sizing steps. A material model for finite element (FE) analyses of sheet metal forming and springback at elevated temperatures in Ti-6Al-4V is calibrated and evaluated. The anisotropic yield criterion proposed by Barlat et al. 2003 is applied, and the time- and temperature-dependent stress relaxation behavior for elastic and inelastic straining are modeled using a Zener–Wert–Avrami formulation. Thermo-mechanical uniaxial tensile tests, a biaxial test, and uniaxial stress relaxation tests are performed and used as experimental reference to identify material model parameters at temperatures up to 700 °C. The hot forming tool setup is manufactured and used to produce double-curved aero engine components at 700 °C with different cycle times for validation purposes. Correlations between the predicted and measured responses such as springback and shape deviation show promising agreement, also when the forming and subsequent holding time was as low as 150 s. The short cycle time resulted in elimination of a detectable alpha case layer. Also, the tool surface coating extends the tool life in combination with a suitable lubricant. © 2019, The Author(s).

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  • 30.
    Pederson, Robert
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Additive Manufacturing of High-Performance Metallic Materials2023 (ed. 1.)Book (Refereed)
  • 31.
    Pederson, Robert
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Joshi, Shrikant V.
    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.
    Isoaho, Jerry
    GKN Aerospace Engine Systems,Trollhättan (SWE).
    Metal additive manufacturing: Motivation, process portfolio, and application potential2023In: Additive Manufacturing of High-Performance metallic Materials / [ed] Pederson, Robert, Andersson, Joel & Joshi, Shrikant V., Elsevier, 2023, 1, p. 20-40Chapter in book (Refereed)
    Abstract [en]

    The idea of adding material only where needed to manufacturesolid metallic high-performing components is intriguing andone of the main reasons for the great interest in additivemanufacturing (AM) around the world. Especially whensustainability comes into play, as in recent times more thanever, AM technology is most appropriate since it enables almostfull material utilization with minimal waste. From an economicstandpoint, this becomes particularly advantageous for moreexpensive materials such as superalloys and titanium alloys.However, the route of going from a CAD drawing of a part to anadditively manufactured final component that is qualified and inserial production involves numerous challenges. The intentionof this book is to shed light on and explain some of theassociated challenges beginning with the importance of thestarting material and how it is manufactured, i.e., wire orpowder, continuing into description of the conventional andPederson, R., Andersson, J., & Joshi, S. (2023). Additive manufacturing of high-performance metallic materials. Elsevier.Created from vast-ebooks on 2024-01-08 16:09:20. Copyright © 2023. Elsevier. All rights reserved.most commonly used AM processes, followed by postbuildtreatments and nondestructive evaluations, to eventuallyproduce the final part with mechanical performance consistentwith the application requirements. In the end, selected realindustry examples of AM parts for actual applications will bepresented

  • 32.
    Pixner, Florian
    et al.
    Graz University of Technology, Institute of Materials Science, Joining and Forming, Kopernikusgasse 24, 8010 Graz, Austria (AUT).
    Warchomicka, Fernando
    Graz University of Technology, Institute of Materials Science, Joining and Forming, Kopernikusgasse 24, 8010 Graz, Austria (AUT).
    Peter, Patrick
    Graz University of Technology, Institute of Materials Science, Joining and Forming, Kopernikusgasse 24, 8010 Graz, Austria (AUT).
    Steuwer, Axel
    Nelson Mandela University, Port Elizabeth 6031, South Africa (ZAF);University of Malta, Research Support Services, 2080 Msida, Malta (MLT).
    Colliander, Magnus Hörnqvist
    Chalmers University of Technology, Department of Applied Physics, 41296 Göteborg, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Enzinger, Norbert
    Graz University of Technology, Institute of Materials Science, Joining and Forming, Kopernikusgasse 24, 8010 Graz, Austria (AUT).
    Wire-Based Additive Manufacturing of Ti-6Al-4V Using Electron Beam Technique2020In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 13, no 15, article id E3310Article in journal (Refereed)
    Abstract [en]

    Electron beam freeform fabrication is a wire feed direct energy deposition additive manufacturing process, where the vacuum condition ensures excellent shielding against the atmosphere and enables processing of highly reactive materials. In this work, this technique is applied for the α + β-titanium alloy Ti-6Al-4V to determine suitable process parameter for robust building. The correlation between dimensions and the dilution of single beads based on selected process parameters, leads to an overlapping distance in the range of 70%-75% of the bead width, resulting in a multi-bead layer with a uniform height and with a linear build-up rate. Moreover, the stacking of layers with different numbers of tracks using an alternating symmetric welding sequence allows the manufacturing of simple structures like walls and blocks. Microscopy investigations reveal that the primary structure consists of epitaxial grown columnar prior β-grains, with some randomly scattered macro and micropores. The developed microstructure consists of a mixture of martensitic and finer α-lamellar structure with a moderate and uniform hardness of 334 HV, an ultimate tensile strength of 953 MPa and rather low fracture elongation of 4.5%. A subsequent stress relief heat treatment leads to a uniform hardness distribution and an extended fracture elongation of 9.5%, with a decrease of the ultimate strength to 881 MPa due to the fine α-lamellar structure produced during the heat treatment. Residual stresses measured by energy dispersive X-ray diffraction shows after deposition 200-450 MPa in tension in the longitudinal direction, while the stresses reach almost zero when the stress relief treatment is carried out.

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  • 33.
    Sefer, Birhan
    et al.
    Division of Materials Science, Luleå University of Technology, Luleå, Sweden / Department of Materials Science and Metallurgical Engineering, Universitat Politècnica de Catalunya, Barcelona, Spain.
    Dobryden, Illia
    Division of Materials Science, Luleå University of Technology, Luleå, Sweden / Division of Surface and Corrosion Science, KTH Royal Institute of Technology, Stockholm, Sweden.
    Almqvist, Nils
    Division of Materials Science, Luleå University of Technology, Luleå, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Welding Technology. Division of Materials Science, Luleå University of Technology, Luleå, Sweden / Research and Technology Centre, GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Antti, Marta-Lena
    Division of Materials Science, Luleå University of Technology, Luleå, Sweden.
    Chemical Milling of Cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo Alloys in Hydrofluoric-Nitric Acid Solutions2017In: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 73, no 4, p. 394-407Article in journal (Refereed)
    Abstract [en]

    The behavior of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo during chemical milling in hydrofluoric-nitric (HF-HNO3) acid solutions with 1:3 and 1:11 molar ratios was investigated using electrochemical and atomic force microscopy (AFM) techniques. Faster corrosion rate in 1:3 solutions was measured for Ti-6Al-4V than for Ti-6Al-2Sn-4Zr-2Mo, whereas in 1:11 solution Ti-6Al-2Sn-4Zr-2Mo exhibited higher corrosion rate. Scanning Kelvin probe force microscopy measurements revealed difference in the Volta potential between the α-laths and the β-layers in the Widmansttäten microstructure indicating operation of microgalvanic cells between the microconstituents when in contact with HF-HNO3 solution. The AFM topography measurements demonstrated faster corrosion of the α-laths compared to the β-layers, in both alloys. In 1:3 solutions, higher α/β height difference was measured in Ti-6Al-4V, whereas in 1:11 solution, the difference was higher in Ti-6Al-2Sn-4Zr-2Mo. The results revealed that the chemical milling behavior of the two investigated alloys is controlled by the microscopic corrosion behavior of the individual microconstituents.

  • 34.
    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.

  • 35.
    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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  • 36.
    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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  • 37.
    Tolvanen, Sakari
    et al.
    Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Welding Technology. Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, Sweden.
    Klement, Uta
    Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, Sweden.
    Microstructure and Porosity of Laser Welds in Cast Ti-6Al-4V with Addition of Boron2018In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 49A, no 5, p. 1683-1691Article in journal (Refereed)
    Abstract [en]

    Addition of small amounts of boron to cast Ti-6Al-4V alloy has shown to render a finer microstructure and improved mechanical properties. For such an improved alloy to be widely applicable for large aerospace structural components, successful welding of such castings is essential. In the present work, the microstructure and porosity of laser welds in a standard grade cast Ti-6Al-4V alloy as well as two modified alloy versions with different boron concentrations have been investigated. Prior-β grain reconstruction revealed the prior-β grain structure in the weld zones. In fusion zones of the welds, boron was found to refine the grain size significantly and rendered narrow elongated grains. TiB particles in the prior-β grain boundaries in the cast base material restricted grain growth in the heat-affected zone. The TiB particles that existed in the as cast alloys decreased in size in the fusion zones of welds. The hardness in the weld zones was higher than in the base material and boron did not have a significant effect on hardness of the weld zones. The fusion zones were smaller in the boron-modified alloys as compared with Ti-6Al-4V without boron. Computed tomography X-ray investigations of the laser welds showed that pores in the FZ of the boron modified alloys were confined to the lower part of the welds, suggesting that boron addition influences melt pool flow. © 2018 The Author(s)

  • 38.
    Åkerfeldt, Pia
    et al.
    Luleå University of Technology,Division of Materials Science, Luleå, Sweden.
    Hörnqvist Colliander, Magnus
    Chalmers University of Technology, Department of Physics, Göteborg, Sweden.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Welding Technology. Luleå University of Technology,Division of Materials Science, Luleå, Sweden.
    Antti, Marta-Lena
    Luleå University of Technology,Division of Materials Science, Luleå, Sweden.
    Electron backscatter diffraction characterization of fatigue crack growth in laser metal wire deposited Ti-6Al-4V2018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 135, p. 245-256Article in journal (Refereed)
    Abstract [en]

    By additive manufacturing (AM) there is a feasibility of producing near net shape components in basically one step from 3D CAD model to final product. The interest for AM is high and during the past decade a lot of research has been carried out in order to understand the influence from process parameters on the microstructure and furthermore on the mechanical properties. In the present study laser metal wire deposition of Ti-6Al-4V has been studied in detail with regard to its fatigue crack propagation characteristics. Two specimen orientations, parallel and perpendicular to the deposition direction, have been evaluated at room temperature and at 250 °C. No difference in the fatigue crack growth rate could be confirmed for the two specimen orientations. However, in the fractographic study it was observed that the tortuosity varied between certain regions on the fracture surface. The local crack path characteristic could be related to the alpha colony size and/or the crystallographic orientation. Moreover, large areas exhibiting similar crystallographic orientation were observed along the prior beta grain boundaries, which were attributed to the wide alpha colonies frequently observed along the prior beta grain boundaries. © 2017 Elsevier Inc.

  • 39.
    Čapek, Jan
    et al.
    Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen (CHE).
    Polatidis, E.
    Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen (CHE).
    Casati, N.
    Materials Science Group, Photon Science Division, Paul Scherrer Institute, 5232 Villigen (CHE).
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Lyphout, C.
    epartment of Manufacturing, RISE IVF AB, Mölndal (SWE).
    Strobl, M.
    Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen (CHE).
    Influence of laser powder bed fusion scanning pattern on residual stress and microstructure of alloy 7182022In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 221, article id 110983Article in journal (Refereed)
    Abstract [en]

    A comprehensive investigation is undertaken on the effect of laser scanning pattern on the microstructure of cylindrical samples made of Alloy 718 processed by Laser Powder Bed Fusion. It is observed that the common alternate direction scanning of the laser results in a more homogeneous microstructure than the less common concentric line scans where significant microstructural heterogeneities are seen between the edges and the center of the sample. The investigation focuses on the precipitation, crystallographic texture, grain size, grain morphology and residual stresses utilizing synchrotron X-ray diffraction, neutron diffraction and electron microscopy. The heterogeneous microstructure of the sample processed with the concentric laser pattern influences the chemical composition of the matrix, which alters the reference “strain free” interplanar spacing used for evaluating the residual strain. The investigation underlines the significance of the processing parameters on the homogeneity of the microstructure and the effect of the chemical variations on the determination of residual stresses in materials such as Alloy 718, where strong local chemical variations occur because of different types and extent of precipitation. © 2022

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  • 40.
    Čapek, Jan
    et al.
    Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, Villigen-PSI, 5232, Switzerland (CHE).
    Polatidis, Efthymois
    Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, Villigen-PSI, 5232, Switzerland (CHE).
    Knapek, Michal
    Charles University, Faculty of Mathematics and Physics, Prague, 121 16, Czech Republic (CZE); Nuclear Physics Institute of the Czech Academy of Sciences, Řež, 250 68, Czech Republic (CZE).
    Lyphout, Christophe
    Research Institutes of Sweden, Lindholmspiren 7 A, Göteborg, 417 56, Sweden.
    Casati, Nicola
    Materials Science Group, Photon Science Division, Paul Scherrer Institute, Villigen-PSI, 5232, Switzerland (CHE).
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Strobl, Markus
    Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, Villigen-PSI, 5232, Switzerland (CHE); Nuclear Physics Institute of the Czech Academy of Sciences, Řež, 250 68, Czech Republic (CZE).
    The Effect of γ″ and δ Phase Precipitation on the Mechanical Properties of Inconel 718 Manufactured by Selective Laser Melting: An In Situ Neutron Diffraction and Acoustic Emission Study2020In: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 73, no 1, p. 223-232Article in journal (Refereed)
    Abstract [en]

    The deformation behavior of additively manufactured Alloy 718 in as-built condition and after annealing was studied in situ under tensile loading along the build direction. Pre-characterization by synchrotron X-ray diffraction and electron microscopy revealed a significant amount of γ″ precipitates in the as-built samples, whereas the γ″ phase was entirely consumed and needle-like δ precipitates appeared in the annealed sample. In situ neutron diffraction (ND) and acoustic emission (AE) enabled indirect observation of the role of the precipitates on the mechanical behavior. ND provided information on the load accommodation in the matrix, while AE detected a strong signal from the interaction of dislocations with the δ-phase precipitates during deformation of the annealed samples. The results imply that in the annealed samples the matrix sheds the load to the precipitates, while in the as-built material the matrix bares a significant load. © 2020, The Author(s).

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