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  • 1.
    Draxler, Joar
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Åkerström, P.
    Lulea University of Technology, 97187 Luleå, Sweden.
    Edberg, J.
    Lulea University of Technology, 97187 Luleå, Sweden.
    Lindgren, L. -E
    Lulea University of Technology, 97187 Luleå, Sweden.
    Singh, S.
    Chalmers University of Technology, 41296 Goteborg, Sweden .
    Raza, Tahira
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    A numerical model for simulating the effect of strain rate on eutectic band thickness2020In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 64, p. 1635-1658Article in journal (Refereed)
    Abstract [en]

    Large tensile strains acting on the solidifying weld metal can cause the formation of eutectic bands along grain boundaries. These eutectic bands can lead to severe liquation in the partially melted zone of a subsequent overlapping weld. This can increase the risk of heat-affected zone liquation cracking. In this paper, we present a solidification model for modeling eutectic bands. The model is based on solute convection in grain boundary liquid films induced by tensile strains. The proposed model was used to study the influence of strain rate on the thickness of eutectic bands in Alloy 718. It was found that when the magnitude of the strain rate is 10 times larger than that of the solidification rate, the calculated eutectic band thickness is about 200 to 500% larger (depending on the solidification rate) as compared to when the strain rate is zero. In the paper, we also discuss how eutectic bands may form from hot cracks. © 2020, The Author(s).

  • 2.
    Karimi Neghlani, Paria
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Raza, Tahira
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence of laser exposure time and point distance on 75-μm-thick layer of selective laser melted Alloy 7182018In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 94, no 5-8, p. 2199-2207Article in journal (Refereed)
    Abstract [en]

    A systematic matrix with 25 samples, using five different point distances and five laser exposure times, depositing 75-μm-thick layers of Alloy 718 has been studied. The work has concentrated on defects formed, hardness of the deposits, and the microstructure. Relatively large amount of defects, both lack of fusion and porosity, was found in several of the specimens in the deposits. The defects were never possible to fully eliminate, but a significant decrease, mainly in the lack of fusion, was seen with increasing laser exposure time. The gas porosity on the other hand was not affected to any larger degree, except for the lowest laser energy input, where a slight increase in porosity was seen. A small increase in hardness was noted with increasing laser energy input. The width of the deposited beads increased with increasing laser energy, while the depth of deposits was more or less constant. However, for the lowest combination of point distance and laser exposure time, quite deep and narrow beads were formed. A comparison was made with deposition of 50-μm-thick layers, with quite similar laser energy input, but with some variation in detailed deposition parameters. It was found that the 75-μm-thick layers contained less lack of fusion, particularly for small point distances. The amount of porosity was also less, but that did not vary with deposition parameters.© 2017 The Author(s)

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  • 3.
    Raza, Tahira
    University West, Department of Engineering Science, Division of Welding Technology.
    A review of selective laser melting: Process parameters and its influence on microstructure, defects and strength in superalloy Alloy 718.2016Conference paper (Other academic)
  • 4.
    Raza, Tahira
    University West, Department of Engineering Science, Division of Welding Technology.
    Process Understanding and Weldability of Laser-Powder Bed Fusion Manufactured Alloy 7182020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Laser-powder bed fusion (L-PBF) is an additive manufacturing (AM) process that involves building components by fusing fine metal powders using laser. There is no universal set of process parameters that can yield optimum results for all the different materials, geometries, and L-PBF machines. The research performed at hand regarding the process parameters showed that laser power, scanning speed, laser exposure time, and laser point distance are the most influential process parameters to decrease the amount of lack of fusion. In contrast, gas porosities are unavoidable in the L-PBF material because they can occur either because of powder particles containing inherent gas pores from the powder atomisation process or entrapped shielding gas during the L-PBF process. 

    To fully utilise the L-PBF technique as a commercial production process, joining of small parts to build large-sized or complex shaped components, such as structural components for jet engines, can be a solution. The as-built microstructure of L-PBF-manufactured superalloy Alloy 718, which is the material in focus in the present research, has grains mostly oriented in the building direction of the part with a very fine cellular-dendritic structure within them. The microstructure of the alloy also contains NbC, TiN and low melting Laves phase in the interdendritic regions and along the grain boundaries. The specimens in this study were subjected to different heat treatments, such as hot isostatic pressing (HIP), solution heat treatment, and solution and ageing heat treatment, prior to welding, to study the effect of these heat treatments on the microstructure of the L-PBF-718 with regard to the susceptibility towards heat-affected zone (HAZ) liquation cracking during welding. Results showed that L-PBF-718 was susceptible to HAZ cracking during welding in all material conditions. L-PBF-718 subjected to HIP was more prone to HAZ cracking while welding and revealed a lower ductility behaviour in comparison to L-PBF-718 in the as-builtixcondition and wrought Alloy 718. The welding direction with respect to the graingrowth direction in L-PBF-718 was also found to have a significant influence onhot cracking susceptibility. The extent of HAZ cracking was observed to besmaller in samples welded parallel to the elongated grain orientation than insamples where the welding was performed perpendicular to it.

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  • 5.
    Raza, Tahira
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Adegoke, Olutayo
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Siemens Energy, Finspång (SWE).
    Squillaci, Linda
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. GKN Aerospace Engine Systems, Trollhättan (SWE).
    Neikter, Magnus
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Processing of high-performancematerials by laser beam-powderbed fusion2023In: Additive Manufacturing of High-Performance Metallic Materials / [ed] Pederson, Robert, Andersson, Joel & Joshi, Shrikant V., Elsevier, 2023, 1., p. 182-229Chapter in book (Refereed)
    Abstract [en]

    Processing of high-performance materials by laser beam powder bed fusion (LB-PBF) provides an alternative manufacturing route to, i.e., investment casting and is suitable for production of high-performance materials having complex geometry such as turbine blades. The main benefit of powder bed fusion in general is associated with the fact that increased geometrical complexity does not add any cost. However, the processability of the alloys of interest is closely linked to process parameters where highperformance materials belong to a special class of materials that need substantial attention to avoid problems, not at least with regard to different types of cracking. In this chapter, the relationship between process parameter-microstructure-defect relationship will be discussed and analyzed.

  • 6.
    Raza, Tahira
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, L. E.
    University West, Department of Engineering Science, Division of Welding Technology.
    A review of the effect of selective laser melting process parameters and its influence on microstructure, defects and strength in the iron-nickel based superalloy Alloy 7182016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, p. 1-8Conference paper (Refereed)
    Abstract [en]

    This review presents a basic insight into the powder-bed fusion process selective laser melting (SLM), with focus on the microstructure and mechanical properties of the iron-nickel based superalloy Alloy 718. The microstructures and mechanical properties of SLM components are highly affected by the process parameters. Laser power, scanning speed, powder layer thickness and hatch distance, are the primary process parameters which can be adjusted in order to influence the microstructure and minimize potential defects. SLM-manufactured Alloy 718 generally produce a columnar microstructure which is a result of epitaxial formation and dendritic grain growth in the build direction (perpendicular to the substrate). Gas porosity, lack of fusion and residual stresses are process induced problems observed in SLM-manufactured Alloy 718. The microstructure of the as-manufactured Alloy 718 is susceptible to microsegregation of Nb and Mo as well as to subsequent non-equilibrium phase transformation. A post-process heat treatment of as-manufactured Alloy 718 is required in order to improve general mechanical properties and to relieve the residual stresses. The tensile strength, yield strength and hardness of heat treated SLM-manufactured Alloy 718 are comparable to that of wrought material.

  • 7.
    Raza, Tahira
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Microstructure of Selective Laser Melted Alloy 718 in As-Manufactured and Post Heat Treated Condition2018In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 25, p. 450-458Article in journal (Refereed)
    Abstract [en]

    Manufacturing of Alloy 718 with selective laser melting (SLM) process faces several challenges. One of the challenges is the process-induced porosities in as-manufactured SLM parts. Another challenge is the microstructure of Alloy 718 that contains a high amount of segregating elements, such as MC-type carbides and γ/Laves phase eutectics in interdendritic regions. The microstructural heterogeneity in the as-manufactured SLM part unavoidably leads to mechanical heterogeneity and hence, post-processing heat treatments become necessary to achieve a homogeneous microstructure. Therefore, by investigating various post heat treatment options the knowledge on how to decrease/eliminate these segregations will be developed. © 2018 Elsevier B.V. All rights reserved.

  • 8.
    Raza, Tahira
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Varestraint testing of selective laser additive manufactured alloy 718: influence of grain orientation2019In: Metals, E-ISSN 2075-4701, Vol. 9, no 10, article id 1113Article in journal (Refereed)
    Abstract [en]

    The effect of grain orientation on hot cracking susceptibility of selective laser additive manufactured Alloy 718 was investigated by Varestraint testing. Electron backscattered diffraction showed that cracks in heat affected zone (HAZ) of the welded samples occurred in high angle grain boundaries. The extent of HAZ cracking was smaller in samples tested parallel to the elongated grain orientation and larger in samples transverse to the elongated grain orientation. However, for solidification cracking in the weld metal, no significant difference with respect to grain orientation in the base metal was found. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.

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  • 9.
    Raza, Tahira
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Varestraint weldability testing of additive manufactured alloy 7182018In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 23, no 7, p. 606-611Article in journal (Refereed)
    Abstract [en]

    The weldability in terms of susceptibility towards hot cracking of selective laser melted (SLM) Alloy 718 was investigated and wrought Alloy 718 was used as reference material. Varestraint testing was carried out by means of investigating the weldability in three conditions; (1) SLM as-built, (2) hot isostatic pressing at 1160°C at 105MPa for 3h and (3) wrought Alloy 718 in the mill-annealed condition. The material exhibited intergranular cracking in all three conditions; however,theSLMHIPedconditionhadanincreasedmagnitudeofcracksusceptibilityatallstrain levels.TheincreasedsensitivityoftheHIPedmaterialwasduetothesignificantlylargergrainsize incomparison.TheSLMas-builtconditionshowedthesamedegreeofcrackingasthewrought material.

  • 10.
    Raza, Tahira
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Asala, Gbenga
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, MB R3T 5V6, Canada.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, Olanrewaju Akanbi
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, MB R3T 5V6, Canada.
    Influence of Heat Treatments on Heat Affected Zone Cracking of Gas Tungsten Arc Welded Additive Manufactured Alloy 7182019In: Metals, E-ISSN 2075-4701, Vol. 9, no 8, article id 881Article in journal (Refereed)
    Abstract [en]

    The weldability of additive manufactured Alloy 718 was investigated in various heat-treated conditions. The microstructure of the base metal was examined in detail in order to understand the effect of different pre-weld heat treatments; i.e., solution, solution and aging, and hot isostatic pressing. After welding, the variation in total crack lengths, maximum crack length and the total number of cracks in the heat affected zone (HAZ) were used as criteria for the cracking susceptibility of each material condition where wrought Alloy 718 was used as the reference material. Selective laser melting (SLM) manufactured Alloy 718 was susceptible to HAZ cracking in all material conditions. Total crack lengths in HAZ were highest in the SLM as-built condition and lowest in the SLM hot isostatic pressed condition. The cracks that were found in the HAZ of the welded materials consisted of liquation cracks, with eutectic product surrounding the cracks, as well as cracks from which liquation products were absent.

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  • 11.
    Sjölie, Daniel
    et al.
    University West, School of Business, Economics and IT, Divison of Informatics.
    Mortensen, Zakarias
    University West, School of Business, Economics and IT, Divison of Informatics.
    Larsson, Clara
    University West, School of Business, Economics and IT, Divison of Informatics.
    Raza, Tahira
    University West, Department of Engineering Science, Division of Welding Technology.
    Li, Peigang
    University West, Department of Engineering Science, Division of Welding Technology.
    Valiente Bermejo, María Asunción
    University West, Department of Engineering Science, Division of Welding Technology.
    Integration of Research on Immersive Learning Environments and Education in Welding2024In: Sustainable Production through Advanced Manufacturing, Intelligent Automation and Work Integrated Learning: Proceedings of the 11th Swedish Production Symposium (SPS2024) / [ed] Joel Andersson, Shrikant Joshi, Lennart Malmsköld, Fabian Hanning, IOS Press, 2024, Vol. 52, p. 660-671Chapter in book (Refereed)
    Abstract [en]

    The integration of virtual reality (VR) laboratories into welding education presents an array of potential advantages. It can be used at campus or in distance, and it offers an alternative when access to traditional laboratories is challenging. The economic benefits, including savings on material preparation and energy costs, along with the environmental, health and safety advantages of mitigating exposure to welding fumes, arc radiation, and electrical hazards, add further value and contribute to sustainability in welding education. The work presented here is an example of the integration of education in the areas of welding and informatics and research on immersive learning. A multidisciplinary team worked on the development of an immersive learning environment, including virtual laboratory areas for welding processes as well as for microstructural inspection of welds.

    During the project, this learning environment, and the contained virtual laboratories, have been implemented by the researchers with the support from IT students, and tested, and improved with the feedback provided by students in welding technology, materials science, and manufacturing courses. Overall, more than twenty students from Informatics have been involved throughout the project, resulting in five bachelor theses, three master theses, three course projects in Immersive computing, and two course projects focusing on web development. The involvement of IT students has not only supported the development of the virtual learning environment, but it has also created new avenues for future research and developments in immersive computing.

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  • 12.
    Swaminathan, Kameshwaran
    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.
    Raza, Tahira
    University West, Department of Engineering Science, Division of Welding Technology.
    Harlin, Peter
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Characterization of Laser Powder Bed Fusion of Nickel-Based Superalloy Haynes 2822023In: Proceedings of the 10th International Symposium on Superalloy 718 and Derivatives / [ed] Eric A. Ott, Joel Andersson, Chantal Sudbrack, Zhongan Bi, Kevin Bockenstedt, Ian Dempster, Michael Fahrmann, Paul Jablonski, Michael Kirka, Xingbo Liu, Daisuke Nagahama, Tim Smith, Martin Stockinger, Andrew Wessman, Springer, 2023, p. 553-570Conference paper (Refereed)
    Abstract [en]

    Nickel-based superalloy Haynes 282 specimens were manufactured using the Laser Powder Bed Fusion process with a powder layer thickness of 60 and 90 microns to study the effect of laser power, laser scan speed, and hatch distance on the melt pool dimensions and porosity. The melt pool dimensions and porosity were measured at the center of the cubes parallel to the build direction. Variation of melt pool depth and overlap exist within the same sample signifying the scatter present in the process. Laser scan speed was found to be the most significant parameter for porosity and hatch distance was found to be the most significant parameter affecting the average melt pool overlap depth in the cubes built with 60 microns layer thickness. Interaction of speed and hatch distance was found to be the most significant parameter for porosity and Laser scan speed was the most significant parameter for average melt pool overlap depth in cubes built with 90 microns layer thickness. Comparison of measured responses with individual parameters provides partial trends of melt pool dimensions and porosity. As the heat input is captured better in line energy and area energy density, a better trend of the melt pool dimensions data and marginal trend of porosity in comparison with energy densities is discussed. The ratio of maximum length to minimum length of defects such as porosity and lack of fusion is measured to determine the shape of the defects and averaged to provide insight into the dominant shape of defect for a given set of parameters.

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