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  • 1.
    Cederberg, Emil
    et al.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för svetsteknologi (SV).
    Hosseini, Vahid
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för svetsteknologi (SV).
    Kumara, Chamara
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Karlsson, Leif
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för svetsteknologi (SV).
    Physical simulation of additively manufactured super duplex stainless steels: microstructure and properties2020Ingår i: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 34, artikel-id 101269Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The behavior of high performance super duplex stainless steel (SDSS) during additive manufacturing (AM) has been investigated using a novel arc heat treatment technique. Tungsten inert gas (TIG) arc pulses were applied on a disc shaped sample mounted on a water-cooled chamber to physically simulate AM thermal cycles. SDSS base metal and a duplicated additively manufactured structure (DAMS) were used as initial microstructures. Samples were melted one, five, or 15 times by arc heat treatment. Samples were also produced with a controlled slope down of the current to create slower cooling compared to pulsing. Microstructure characterization and modelling were performed to study the evolution of microstructure and properties with successive AM cycles. Microstructural changes were dependent on the number of reheating cycles, cooling rate, and peak temperature. In particular, the DAMS austenite morphology and fraction changed after reheating to peak temperatures above 700 °C. Nitrides and sigma were observed in the high and low temperature heat affected zones, respectively. Sensitization to corrosion was more pronounced in reheated DAMS than in the base metal. Hardness was increased more by multiple remelting/reheating than by slow cooling. It was found that AM thermal cycles significantly affect SDSS properties especially for an initial microstructure similar to that produced by AM. © 2020 Elsevier B.V.

  • 2.
    Goel, Sneha
    et al.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Sittiho, Anumat
    University of Idaho, Department of Chemical and Materials Engineering, Moscow, ID 83844, United States.
    Charit, Indrajit
    University of Idaho, Department of Chemical and Materials Engineering, Moscow, ID 83844, United States.
    Klement, Uta
    Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, Sweden.
    Joshi, Shrikant V.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Forskningsmiljön produktionsteknik(PTW).
    Effect of post-treatments under hot isostatic pressure on microstructural characteristics of EBM-built Alloy 7182019Ingår i: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 28, s. 727-737Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electron beam melting (EBM) has emerged as an important additive manufacturing technique. In this study, Alloy 718 produced by EBM was investigated in as-built and post-treated conditions for microstructural characteristics and hardness. The post-treatments investigated were hot isostatic pressing (HIP) and combined HIP + heat treatment (HIP + HT) carried out as a single cycle inside the HIP vessel. Both the post-treatments resulted in significant decrease in defects inevitably present in the as-built material. The columnar grain structure of the as-built material was found to be maintained after post-treatment, with some sporadic localized grain coarsening noted. Although HIP led to complete dissolution of δ and γ′′ phase, stable NbC and TiN (occasionally present) particles were observed in the post-treated specimens. Significant precipitation of γ′′ phase was observed after HIP + HT, which was attributed to the two-step aging heat treatment carried out during HIP + HT. The presence of γ′′ phase or otherwise was correlated to the hardness of the material. While the HIP treatment resulted in drop in hardness, HIP + HT led to 'recovery' of the hardness to values exceeding those exhibited by the as-built material. © 2019 Elsevier B.V.

  • 3.
    Karimi Neghlani, Paria
    et al.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Sadeghi, Esmaeil
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Ålgårdh, Joakim
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT). GE Additive | Arcam EBM, Mölnlycke (SWE).
    Keshavarzkermani, Ali
    Multi‑Scale Additive Manufacturing Lab, Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo (CAN).
    Esmaeilizadeh, Reza
    Multi‑Scale Additive Manufacturing Lab, Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo (CAN).
    Toyserkani, Ehsan
    Multi‑Scale Additive Manufacturing Lab, Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo (CAN).
    Andersson, Joel
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för svetsteknologi (SV).
    Columnar-to-equiaxed grain transition in powder bed fusion via mimicking casting solidification and promoting in situ recrystallization2021Ingår i: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 46, artikel-id 102086Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Columnar grain structure typically formed along the build direction in the electron beam-powder bed fusion (EBPBF) technique leads to anisotropic physical and mechanical properties. In this study, casting solidification condition was mimicked, and in situ recrystallization was promoted in EB-PBF to facilitate columnar-to-equiaxed grain structure transition in Alloy 718. This is achieved via a unique linear melting strategy coupled with a specific selection of process parameters in EB-PBF. It was found that site-specific melting using line order number (LON) function affected the cooling rate and temperature gradient, which controlled grain morphology and texture. A high LON resulted in a large equiaxed grain zone with a random texture, whereas a fixed LON with a high areal energy density led to a strong texture. The main driving force in the formation of cracks and shrinkage defects during the transition was investigated. A high LON at a fixed areal energy density reduced the average total shrinkage defects and crack length. The hardness was decreased through the transition, which was linked to the reduction in the size of the gamma ‘’ precipitates.

    Ladda ner fulltext (pdf)
    Additive Manufacturing
  • 4.
    Karimi Neghlani, Paria
    et al.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Schnur, Christopher
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Sadeghi, Esmaeil
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Andersson, Joel
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för svetsteknologi (SV).
    Contour design to improve topographical and microstructural characteristics of Alloy 718 manufactured by electron beam-powder bed fusion technique2020Ingår i: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 32, artikel-id 101014Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Additive manufacturing (AM) processes are being frequently used in industry as they allow the manufacture ofcomplex parts with reduced lead times. Electron beam-powder bed fusion (EB-PBF) as an AM technology isknown for its near-net-shape production capacity with low residual stress. However, the surface quality andgeometrical accuracy of the manufactured parts are major obstacles for the wider industrial adoption of thistechnology, especially when enhanced mechanical performance is taken into consideration. Identifying theorigins of surface features such as satellite particles and sharp valleys on the parts manufactured by EB-PBF isimportant for a better understanding of the process and its capability. Moreover, understanding the influence ofthe contour melting strategy, by altering process parameters, on the surface roughness of the parts and thenumber of near-surface defects is highly critical. In this study, processing parameters of the EB-PBF techniquesuch as scanning speed, beam current, focus offset, and number of contours (one or two) with the linear meltingstrategy were investigated. A sample manufactured using Arcam-recommended process parameters (threecontours with the spot melting strategy) was used as a reference. For the samples with one contour, the scanningspeed had the greatest effect on the arithmetical mean height (Sa), and for the samples with two contours, thebeam current and focus offset had the greatest effect. For the samples with two contours, a lower focus offset andlower scan speed (at a higher beam current) resulted in a lower Sa; however, increasing the scan speed for thesamples with one contour decreased Sa. In general, the samples with two contours provided a lower Sa (∼22 %)but with slightly higher porosity (∼8 %) compared to the samples with one contour. Fewer defects were detected with a lower scanning speed and higher beam current. The number of defects and the Sa value for thesamples with two contours manufactured using the linear melting strategy were ∼85 % and 16 %, respectively,lower than those of the reference samples manufactured using the spot melting strategy.

  • 5.
    Kumara, Chamara
    et al.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Segerstark, Andreas
    GKN Aerospace Engine Systems AB, Trollhättan, SE-461 81, Sweden.
    Hanning, Fabian
    Chalmers University of Technology, Department of Industrial and Materials Science, 412 96 Gothenburg, Sweden.
    Dixit, Nikhil
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Joshi, Shrikant V.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Moverare, Johan
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT). Division of Engineering Materials, Department of Management and Engineering, Linköping University, SE-58183 Linköping, Sweden.
    Nylén, Per
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Microstructure modelling of laser metal powder directed energy deposition of alloy 7182019Ingår i: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 25, s. 357-364Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A multi-component and multi-phase-field modelling approach, combined with transformation kinetics modelling, was used to model microstructure evolution during laser metal powder directed energy deposition of Alloy 718 and subsequent heat treatments. Experimental temperature measurements were utilised to predict microstructural evolution during successive addition of layers. Segregation of alloying elements as well as formation of Laves and δ phase was specifically modelled. The predicted elemental concentrations were then used in transformation kinetics to estimate changes in Continuous Cooling Transformation (CCT) and Time Temperature Transformation (TTT) diagrams for Alloy 718. Modelling results showed good agreement with experimentally observed phase evolution within the microstructure. The results indicate that the approach can be a valuable tool, both for improving process understanding and for process development including subsequent heat treatment.

  • 6.
    Lindgren, Lars-Erik
    et al.
    Luleå University of Technology, Luleå, Sweden.
    Lundbäck, Andreas
    Luleå University of Technology, Luleå, Sweden.
    Fisk, Martin
    Malmö University, Malmö, Sweden,.
    Pederson, Robert
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Andersson, Joel
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för svetsteknologi (SV).
    Simulation of additive manufacturing using coupled constitutive and microstructure models2016Ingår i: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 12, nr Part B, s. 144-158Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper describes the application of modeling approaches used in Computational Welding Mechanics (CWM) applicable for simulating Additive Manufacturing (AM). It focuses on the approximation of the behavior in the process zone and the behavior of the solid material, particularly in the context of changing microstructure. Two examples are shown, one for the precipitation hardening Alloy 718 and one for Ti-6Al-4V. The latter alloy is subject to phase changes due to the thermal cycling

  • 7.
    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
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Bjerkén, C.
    Malmö University, Malmö, Sweden.
    Alpha texture variations in additive manufactured Ti-6Al-4V investigated with neutron diffraction2018Ingår i: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 23, s. 225-234Artikel i tidskrift (Refereegranskat)
    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.

  • 8.
    Sadeghi, Esmaeil
    et al.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Karimi Neghlani, Paria
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Israelsson, Niklas
    GE Additive – Arcam EBM, Mölnlycke, Sweden.
    Shipley, James
    Quintus Technologies AB, Västerås, Sweden.
    Månsson, Tomas
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Hansson, Thomas
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT). GKN Aerospace Engine Systems, Sweden.
    Inclusion-induced fatigue crack initiation in powder bed fusion of Alloy 7182020Ingår i: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 36, artikel-id 101670Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

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