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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.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, Olanrewaju A.
    University of Manitoba, Winnipeg, Canada.
    Brodin, Håkan
    Siemens Industrial Turbomachinery AB, Finspang, Sweden .
    Pederson, Robert
    GKN Aerospace, Redditch, United Kingdom.
    Laser beam powder bed fusion and post processing of alloy 247LC2019In: MS and T 2019 - Materials Science and Technology, Materials Science and Technology , 2019, p. 27-34Conference paper (Refereed)
    Abstract [en]

    Alloy 247LC is sensitive to cracking during laser beam powder bed fusion (PBF-LB) manufacturing. Post processing is thus required to close cracks and achieve desired properties. In this study, samples of Alloy 247LC were manufactured by PBF-LB and subsequently post processed by hot isostatic pressing (HIP), HIP + solution and ageing heat treatments. The microstructure was characterized. Results showed cracks in the as-built condition. Cracks were not detected after HIP. Bright microconstituents were observed in the region between the cells, mainly, because of the partitioning of Hf and Ta into the intercellular region, where they presumably form carbides. What is assumed to be oxides were prominent in the microstructure. Thermodynamic calculations showed rapid formation of ?’ precipitates in the alloy, due to the high total concentration of Al and Ta and this was linked to the high hardness values in the as-built condition. © 2019 MS&T19®

  • 5.
    Adegoke, Olutayo
    et al.
    Siemens Energy, 61283 Finspång (SWE).
    Kumara, Chamara
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. FEV Sverige AB, Nohabgatan 12A, 46153 Trollhättan (SWE).
    Thuvander, Matttias
    Department of Physics, Chalmers University of Technology, 41296 Gothenburg (SWE).
    Deirmina, Faraz
    Siemens Energy, 61283 Finspång (SWE).
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Brodin, Håkan
    Siemens Energy, 61283 Finspång (SWE).
    Harlin, Peter
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Sandvik Additive Manufacturing, 81181 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, Vol. 171, p. -12, 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. 

  • 6.
    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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  • 7.
    Agili, Uchechukwu Daniel
    University West, Department of Engineering Science, Division of Welding Technology.
    Numerical Simulation of Aluminium Butt-weld2020Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of this study was to investigate the effect of the welding heat input on the heat affected zone (HAZ)in AA6005-T6 aluminium alloy for a butt-welded joint using gas metal arc welding by evaluating the thermal cycles, metallography and the resulting mechanical properties in the zone. This study involved using a welding experiment, numerical simulation, physical simulation and mechanical tests. The welding was carried out using the pulsed gas metal arc welding (GMAW) transfer and type J thermocouples were used to get the thermal cycles in the HAZ. Simufact® Welding was utilised for the numerical simulation. Optical microscope was used to evaluate the microstructures and Vickers microhardness test was done along the weld cross-section. The thermal cycles of thealuminium alloy and a thermal model for the experimental setup was developed. The HAZ was located on the weld cross-section with a mean hardness of 63.7HV0.1, which is considerably lower when compared with the base metal which has a hardness of 100HV0.1. This indicates thermal softening occurred due to the heat input to the material. There is a match in the hardness values of the Gleeble samples and the locations on the weld cross section suggested by the model showing validity of the simulation. This thesis work isused to assess the implications of heat input in aluminium weld joints, identify the HAZ and its mechanical properties in the design of welding process parameters for automobile parts. The Welding parameters can be optimized to reduce the amount of heat input into the weld as this will directly affect the mechanical properties int he HAZ.

  • 8.
    Ahmadpour, Ali
    et al.
    Amirkabir University of Technology, Department of Mechanical Engineering, Tehran, Iran.
    Noori Rahim Abadi, Seyyed Mohammad Ali
    University West, Department of Engineering Science, Division of Welding Technology.
    Thermal-hydraulic performance evaluation of gas-liquid multiphase flows in a vertical sinusoidal wavy channel in the presence/absence of phase change2019In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 138, p. 677-689Article in journal (Refereed)
    Abstract [en]

    Turbulent gas-liquid multiphase flows with and without phase change in a vertical wavy channel are addressed. The multiphase flow field is resolved using the volume of fluid method (VOF), and the flow equations are discretized and numerically solved by the well-known finite volume method. As a multiphase system without mass transfer, air/water flow is considered. It is shown that numerical simulation is well capable of predicting the various multiphase flow regimes ranging from slug to bubbly flows inside wavy channels. Moreover, accurate predictions of overall pressure drop are provided by numerical solutions for various air and water flow rates and the phase shift angle between wavy channel walls. Additionally, condensing flows of refrigerant R134a are simulated inside wavy channels. It is found that for almost all the cases considered in the present study, the convective heat transfer coefficient is higher in wavy channels in respect to straight channels. However, a significant pressure drop penalty is observed especially for high mass fluxes across wavy channels. Therefore, the use of the wavy channels for the enhancement of condensing heat transfer is only advisable for low mass fluxes with the phase shift angle of 180°. © 2019 Elsevier Ltd

  • 9.
    Amouzgar, Kaveh
    et al.
    University of Skovde, Jonkoping University.
    Strömberg, Niclas
    University West, Department of Engineering Science, Division of Welding Technology. Jonkoping University, Orebro Univ, University University West - Sweden.
    An approach towards generating surrogate models by using RBFN with a priori bias2014In: PROCEEDINGS OF THE ASME INTERNATIONAL DESIGN ENGINEERING TECHNICAL CONFERENCES AND COMPUTERS AND INFORMATION IN ENGINEERING CONFERENCE, 2014, VOL 2B, AMER SOC MECHANICAL ENGINEERS , 2014, Vol. 2BConference paper (Refereed)
    Abstract [en]

    In this paper, an approach to generate surrogate models constructed by radial basis function networks (RBFN) with a priori bias is presented. RBFN as a weighted combination of radial basis functions only, might become singular and no interpolation is found. The standard approach to avoid this is to add a polynomial bias, where the bias is defined by imposing orthogonality conditions between the weights of the radial basis functions and the polynomial basis functions. Here, in the proposed a priori approach, the regression coefficients of the polynomial bias are simply calculated by using the normal equation without any need of the extra orthogonality prerequisite. In addition to the simplicity of this approach, the method has also proven to predict the actual functions more accurately compared to the RBFN with a posteriori bias. Several test functions, including Rosenbrock, Branin-Hoo, Goldstein-Price functions and two mathematical functions (one large scale), are used to evaluate the performance of the proposed method by conducting a comparison study and error analysis between the RBFN with a priori and a posteriori known biases. Furthermore, the aforementioned approaches are applied to an engineering design problem, that is modeling of the material properties of a three phase spherical graphite iron (SGI). The corresponding surrogate models are presented and compared.

  • 10.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Fabrication and Weldability Aspects of Ni- and Ni–Fe Based Superalloys: A Review2023In: Proceedings of the 10th International Symposium on Superalloy 718 and Derivatives / [ed] Eric A. Ott, Joel Andersson, Chantal Sudbrack, Zhongnan Bi, Kevin Bockenstedt, Ian Dempster, Michael Fahrmann, Paul Jablonski, Michael Kirka, Xingbo Liu, Daisuke Nagahama, Tim Smith, Martin Stockinger, Andrew Wessman, Springer Cham , 2023, p. 659-696Conference paper (Refereed)
    Abstract [en]

    Superalloys are commonly used in structural components of aero-engines. Superalloys in general, Ni- and Ni–Fe-based superalloys, belong to an important group of materials used in aerospace applications. Fabrication and associated weldability aspects of structural components for the hot section of aero-engine gas turbines continue to be of high importance to the manufacturing industry within this discipline. Cracking and specifically hot cracking as well as strain age cracking is a serious concern during the welding and additive manufacturing (AM) of these structural components. The cracking phenomena can occur during welding, AM or subsequent heat treatment of precipitation-hardening superalloys. The cracking behaviour can be influenced by several factors, i.e., chemical composition in terms of hardening elements and impurities, the microstructure of base material, and weld zone, together with corresponding welding, AM and post-treatment process parameters. This paper provides a review of Ni- and Ni–Fe-based superalloys concerning fabrication and weldability aspects within the context of structural components of aero-engines. Also, the paper offers insight and analyses to research publication data of welding and AM of superalloys in the context of annual publication developed over the years as well as specific contributions from countries, affiliations, and specific researchers.

  • 11.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Review of Weldability of Precipitation Hardening Ni- and Fe-Ni-Based Superalloys2018In: Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives: Energy, Aerospace, and Industrial Applications / [ed] Ott, E., Liu, X., Andersson, J., Bi, Z., Bockenstedt, K., Dempster, I., Groh, J., Heck, K., Jablonski, P., Kaplan, M., Nagahama, D. and Sudbrack, C., Springer, 2018, p. 899-916Conference paper (Refereed)
    Abstract [en]

    Fabrication and welding of structural components for the hot section of aero-engines continues to be of high importance to the manufacturing industry of aero-engines. This paper discusses and reviews the literature on hot cracking and strain age cracking, cracking phenomena that can occur during welding or subsequent heat treatment of precipitation hardened Ni- and Fe-Ni-based superalloys. The influence of chemical composition in terms of i.e. hardening elements and impurities, microstructure of base material and weld zone, together with welding processes and corresponding parameters and heat input are discussed and related to the cracking susceptibility of different nickel based superalloys.

  • 12.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Welding metallurgy and weldability of superalloys2020In: Metals, ISSN 2075-4701, Vol. 10, no 1, article id 143Article in journal (Refereed)
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  • 13.
    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. © 2023 Elsevier Inc. All rights reserved.

  • 14.
    Ariaseta, Achmad
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Khan, Abdul Khaliq
    Manitoba Institute for Materials, University of Manitoba, Winnipeg, MB R3T2N2 (CAN).
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, Olanrewaju
    Department of Mechanical Engineering, University of Manitoba, Winnipeg, MB R3T 5V6 (CAN).
    Microstructural study of keyhole TIG welded nickel-based superalloy G272023In: Materials Characterization, Vol. 204, article id 113178Article in journal (Refereed)
    Abstract [en]

    The weld fusion zone (FZ) microstructure obtained after keyhole tungsten inert gas welding and post-weld solution heat treatments (PWSHTs) of a new nickel (Ni)-based superalloy called G27 is studied, and the grain growth behavior in the base material (BM) during PWSHTs is characterized. Microsegregation-induced interdendritic microconstituents in the FZ of as-welded G27 are identified by analytical (scanning) transmission electron microscopy ((S)TEM) as niobium (Nb)-rich MC carbides, Nb-rich Laves eutectic constituents, γ’ and η phases. The Laves eutectics are generally considered brittle and can adversely affect the mechanical properties of the weldment; thus, an hour PWSHTs were performed at 954 °C–1060 °C to eliminate the γ/Laves eutectics. PWSHT up to 1010 °C results in only partial removal of Laves eutectics with an excessive formation of η phase surrounding the Laves phase. Complete dissolution of Laves eutectics with no η phase formation is achieved after a PWSHT is performed at 1060 °C. Relative to INCONEL® alloy 718, the complete elimination of the γ/Laves eutectic constituents in the FZ of G27 through a PWSHT was proven to be achieved without causing excessive grain growth in the BM, which could be due to the pinning effect of the fine molybdenum (Mo)-rich precipitates, that are formed during solution heat treatment and identified as hexagonal close-packed phase particles through extensive (S)TEM analyses.

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  • 15.
    Ariaseta, Achmad
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Pick, Dario
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, Olanrewaju
    Department of Mechanical Engineering, University of Manitoba, Winnipeg, MB, R3T 5V6 (CAN).
    Keyhole TIG Welding of New Co-Lean Nickel-Based Superalloy G272023In: Proceedings of the 10th International Symposium on Superalloy 718 and Derivatives / [ed] Eric A. Ott, Joel Andersson, Chantal Sudbrack, Zhongnan Bi, Kevin Bockenstedt, Ian Dempster, Michael Fahrmann, Paul Jablonski, Michael Kirka, Xingbo Liu, Daisuke Nagahama, Tim Smith, Martin Stockinger, Andrew Wessman, Springer Cham , 2023, p. 807-824Conference paper (Refereed)
    Abstract [en]

    The influence of keyhole TIG (K-TIG) welding parameters on the weld geometry and defects of a new Co-lean nickel-based superalloy G27 was studied, and the microstructures of the heat-affected zone (HAZ) and fusion zone (FZ) of the K-TIG-welded Alloy G27 were characterized. No cracks are found in the FZ and HAZ. Minimum weld width and face underfill statistically were significantly influenced by travel speed and interaction current*travel speed. Root excess weld metal was only significantly influenced by travel speed. Face excess weld metal was significantly influenced by all the factors, including their interaction. On the other hand, all the factors, including their interaction, did not significantly influence the average pore diameter. In the FZ microstructure, interdendritic microconstituents are identified as (Nb, Ti)C particles and γ/Laves eutectic constituents. In addition, a plate-like phase is observed surrounding the Laves phase, and γʹ precipitates are found to be inhomogeneously precipitated in the FZ. In the partially melted zone (PMZ), (Nb, Ti)C, Laves phase, γʹ precipitates, and plate-like particles are found in the liquated and resolidified regions, suggesting the solidification behavior in PMZ is likely to follow a similar pattern to the one observed in FZ.

  • 16.
    Ariaseta, Achmad
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Department of Metallurgical Engineering, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung 40132, (IDN)).
    Sadeghinia, Nima
    University West, Department of Engineering Science.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence Of Keyhole Tig Welding Parameters On Weld Geometry Of Newly-Developed Superalloy Vdm Alloy 7802022In: ICAS PROCEEDINGS33th Congress of the International Council of the Aeronautical SciencesStockholm, Sweden, 2022, Vol. 5, p. 3516-3530Conference paper (Refereed)
    Abstract [en]

    The welding process and the associated control, to a certain degree, have enhanced remarkably in the last decades. One of the recent processes is keyhole TIG (K-TIG) welding, which allows better control and the capability to use lower heat input and higher power density during the welding compared to the conventional one, being essential when joining sophisticated materials utilized in the hot sections of aircraft engines such as nickel-based superalloys. The recent trend in the fabrication of hot sections of aero-engines has been preferably carried out by joining small pieces of superalloys by the welding process instead of casting a single large component due to several benefits, such as lowering the total weight of the components and improving the design flexibility. VDM Alloy 780, a new polycrystalline nickel-based superalloy with service temperature capabilities up to 750 °C, is a promising material to be employed in the fabrication of hot structural parts of an aero-engine. For aerospace manufacturers, producing a superalloy weld bead geometry that meets stringent quality requirements for aerospace applications is crucial. To do so, understanding the influence of welding parameters on weld geometry becomes indispensable, especially when welding a new superalloy using a relatively new welding technique. Hence, in this article, the influence of K-TIG welding parameters on the weld geometry of VDM Alloy 780 has been investigated.

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  • 17.
    Ariaseta, Achmad
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Department of Metallurgical Engineering, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung (IDN).
    Sadeghinia, Nima
    University West, Department of Engineering Science.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, Olanrewaju
    Department of Mechanical Engineering, University of Manitoba, Winnipeg, MB, R3T 5V6, (CAN).
    Keyhole TIG welding of newly developed nickel-based superalloy VDM Alloy 7802023In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 67, no 1, p. 209-222Article in journal (Refereed)
    Abstract [en]

    The influence of keyhole TIG (K-TIG) welding parameters on the weld geometry and defects of a new nickel-based superalloy VDM Alloy 780 alloy were investigated using a statistical design of experiment, and the microstructures of the heat-affected zone (HAZ) and fusion zone (FZ) of the K-TIG-welded VDM Alloy 780 were characterized. No cracks are found in the FZ and HAZ. Travel speed significantly influences the minimum weld width (Wm), face and root excess weld metal, face underfill, and average pore diameter. Welding current and the interaction current*travel speed significantly influence the face and root excess weld metals, respectively. Interdendritic microconstituents in the FZ are identified as (Nb,Ti)C particles and γ/Laves eutectic constituents based on SEM–EDS analysis. In addition, plate-like precipitates likely to be δ/η phase are observed surrounding the interdendritic Laves eutectics, and γ′ precipitates are found to be inhomogeneously precipitated in the FZ. In the partially melted zone (PMZ), (Nb,Ti)C, Laves phase, and plate-like particles are found in the liquated and resolidified regions. Constitutional liquation of (Nb,Ti)C in HAZ is observed where the liquated (Nb,Ti)C appears to be associated with the γ/Laves eutectic as a resolidified product. © 2022, The Author(s).

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  • 18.
    Aryal, Pradip
    University West, Department of Engineering Science, Division of Welding Technology.
    Gas Metal Arc Melt Pool Modelling: Effect of welding position and electromagnetic force mode2021Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Gas metal arc is a high-efficiency and widely used heat source for metal processing applied predominantly in welding and additive manufacturing. In this study, it was applied to welding. It offers high productivity, low production and investment cost, as well as suffers from some drawbacks such as humping or undercut when welding large parts that are curved and impose changing the orientation of the welding torch along the joint path. Deeper process understanding was therefore sought to mitigate these drawbacks. The difficulty is then the non-lineardependence of the process to the welding parameters and material properties. Besides, visual observation of this process is also difficult. For instance, the elevated temperature and the intense radiative emission from the electric arc, smoke, spatter, as well as the non-transparency of the processed alloy can hinder in-process observation or limit it. Process simulation provides a complementary means to reach process knowledge. It was thus the approach used in this study. For this, a thermo-fluid melt pool model that can predict melting and solidification, track free surface deformation, metal transfer, and coalescence with the melt pool was developed. Two main research questions were identified and addressed.The first one led to studying the effect of the substrate orientation during multilayer welding of a V-groove joint with INVAR and gas metal arc. It was foundthat the force balance in the melt pool changes significantly when the workpieceorientation is changed, resulting in distinct melt flow patterns, melt pool and bead geometries, and in some conditions defect initiation such as humping, undercut, and lack of fusion. As a result, multi-layer welding with flat substrate and downhill welding of a 20◦ inclined substrate are recommended with these process conditions. On the contrary, welding of a side inclined substrate and uphill welding of a 20◦ inclined substrate are not recommended. The second question gave rise to the comparative investigation of the three electromagnetic force models commonly used when modelling a melt pool produced by an electric arc. The underlying modelling assumptions were retrieved and investigated. It was found that each of these three models predicts a different melt flow pattern, different heat convection, melt pool shape, free surface oscillation, and interaction with the transferred metal drops, and thus result in different bead geometry. All these models can be adjusted to predict the penetration depth, however, only the most complete of them is recommended for developing a predictive melt pool model. For this, it is proposed as a future work to improve this model through predicting an electromagnetic force that takes also into account the local deformation of the free surface.

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  • 19.
    Aryal, Pradip
    University West, Department of Engineering Science, Division of Welding Technology.
    Metal fusion using pulsed GasMetal Arc: Melt pool modellingand CFD simulation2023Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Pulsed gas metal arc is a highly efficient technique used in manufacturing processes like welding and additive manufacturing. It offers high productivity and cost benefits but it is also prone to defect formation when process parameters are not properly controlled and optimized. A deeper process understanding can support achieving improved process control and mitigate these potential drawbacks. Nevertheless, there are still several challenges. For instance, the correlation between the input and output process parameters is non-linear and complex due to the multi-physics nature of the process. In addition, the elevated temperature and the intense radiative emission from the arc, along with the smoke, and the non-transparency of metal, make in-process observation challenging. Modelling and simulation offer a complementary approach to gain a deeper process understanding. In this study, a thermo- and fluid dynamics model was developed, focusing on the melt pool and metal deposition, while simplifying the arc to boundary conditions (decoupled approach). This model incorporates various forces and phenomena such as thermocapillary and electromagnetic forces, melting and solidification, and tracking of surface deformation and droplet coalescence.

    In the first part of the thesis, the developed model was applied to investigate the effect of workpiece orientations on the melt pool dynamics and reinforced bead geometry in multi-layer gas metal arc welding of a V-groove joint. The comparison of the predicted fusion zone with macrographs obtained from the experiments showed good qualitative agreement. It was found that the force balance in the melt pool changes significantly when changing the workpiece orientation by as little as 20◦ relative to the flat position. This results in distinct melt flow patterns, melt pool shapes, bead geometries, and in some cases, defect formation such as humping, undercut, and insufficient fusion. It was concluded that to avoid these defects a lower angle range is necessary for multilayer welding with the uphill orientation and side inclination.

    The second part of the thesis focused on analyzing different variants of the model for the electromagnetic force with a decoupled approach. Three commonly used models were compared: (1) the analytical models proposed by Kou and Sun inintegral form, (2) by Tsao and Wu in algebraic form, and (3) the partial differential equations governing the electric and magnetic fields. The comparative investigation was supported by experimental tests that also provided estimates of unknown model parameters and validation data. It was found that the distinct assumptions on which these models rely are not all justified. They resulted inpredicting different melt flow patterns and amplitude of the free surface oscillations, as well as different melt pool shapes and bead geometries. Model (3) is recommended to advance to a predictive melt pool model and was subsequentlyused in the remaining work of the thesis.

    Furthermore, the literature shows that modeling the effect of pulsed arc on the melt pool using a decoupled approach involves various simplifications. Arc pulsation affects energy and force balance in the melt pool through arc heat flux, arc pressure, and electromagnetic force. A systematic investigation of model variants considering pulsing was conducted using previously documented experimental test cases. The results showed that the influence of arc pressure was insignificant in those cases. However, model variants simplifying arc pulsing to a time-averaged effect underestimated the amplitude of the Marangoni flow and downward flow compared to a more comprehensive approach that considered the time dependence of arc pulsation. Thus, it is recommended to use a meltpool model that accounts for the time-dependent arc pulsation, which was also subsequently utilized in the remaining work of the thesis.

    The electromagnetic force models discussed earlier assume a stationary free surface when computing the electromagnetic force. However, this force is often at leading order in the vicinity of the arc. In the same region, the metal drop transfer leads to a periodic deformation of the melt pool free surface. In the final part of the thesis, the model was extended to account for free surface deformation when computing the electromagnetic force. This extension was applied to experimental test cases, and a comparison was made with simulation results obtained using the stationary electromagnetic force model. Significant differences in the results were observed, particularly in predicting the experimentally observed fingertip-shaped fusion zone geometry. The proposed improvement in the electromagnetic force model provided better predictions in this regard.

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  • 20.
    Aryal, Pradip
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Nilsson, Håkan
    Chalmers University of Technology Mechanics and Maritime Sciences, Fluid Dynamics, SE-412 96 Gothenburg, (SWE).
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Effect of Substrate Orientation on Melt Pool during Multi-Layer Deposition in V-Groove with Gas Metal Arc2021In: Proceedings of the 7th World Congress on Mechanical, Chemical, and Material Engineering (MCM'21) / [ed] Huihe Qiu, 2021, article id HTFF 130Conference paper (Refereed)
    Abstract [en]

    Thermo-fluid dynamic and experimental approaches are used to investigate the influence of 20° uphill, downhill and sideway substrate orientation during metal deposition over a previously deposited bead in a V-groove. The computational fluid dynamic model with free surface deformation and metal transfer gives insight into the melt pool flow and causes of defect formation observed on the solidified beads. The experimental metallographs, high-speed images and computational results show good agreement. It is found that the deposition of a second layer on a smooth first layer cooled down to room temperature leads to large changes in melt pool flow patternat 20° substrate inclination compared to flat condition. It results in undercut and humps with the uphill orientation and undercut with the side inclination. Therefore, lower angle range is necessary for multilayer gas metal arc deposition for these two last configurations.

  • 21.
    Aryal, Pradip
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Production Systems.
    Nilsson, H.
    Department of Mechanics and Maritime Sciences, Chalmers University of Technology, Gothenburg.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Comparative study of the main electromagnetic models applied to melt pool prediction with gas metal arc: Effect on flow, ripples from drop impact, and geometry2022In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 194, article id 123068Article in journal (Refereed)
    Abstract [en]

    The present work concerns the electromagnetic force models in computational fluid dynamics simulations of melt pools produced with electric arcs. These are commonly applied to gas metal arcs with metal transfer, in welding and additive manufacturing. Metal drop impact on the melt pool is thus included in this study. The electromagnetic force models applied in literature use either numerical solutions of Poisson equations or one of the two analytical models developed by Kou and Sun, or Tsao and Wu. These models rely on assumptions for which the effect on the melt pool predictions remains to be understood. The present work thoroughly investigates those assumptions and their effects. It has been supported by dedicated experimental tests that did provide estimates of unknown model parameters and validation data. The obtained results show that the assumptions that fundamentally distinguish these three models change the electromagnetic force, including the relation between its components. These changes, which can also be spatially non-uniform, are large. As a result, these models lead to significantly different recirculation flow pattern, thermal convection, melt pool morphology, bead dimensions, and free surface response to the metal transfer. We conclude by proposing conditions in which each of these models is suited or questionable.

  • 22.
    Asala, G.
    et al.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, Canada.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, Olanrewaju
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, Canada.
    Microstructure Dependence of Dynamic Impact Behaviour of ATI 718plus® Superalloy2018In: Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives: Energy, Aerospace, and Industrial Applications / [ed] Ott, E., Liu, X., Andersson, J., Bi, Z., Bockenstedt, K., Dempster, I., Groh, J., Heck, K., Jablonski, P., Kaplan, M., Nagahama, D. and Sudbrack, C., Springer, 2018, p. 369-378Conference paper (Refereed)
    Abstract [en]

    ATI 718Plus® is a γ′-strengthened nickel-based superalloy developed to substitute the widely used Alloy 718 in aero-engine applications. This newer superalloy is a candidate material for aero-engine turbine structures, with the requirement to withstand impact loading occurring at high strain rates during turbine blade out events. Furthermore, the understanding of the high strain rate response of ATI 718Plus® is important in optimising its machinability during cutting operations. To predict and model the behaviour of ATI 718Plus® during these events and in other dynamic impact applications, proper understanding of the high strain rate behaviour of the alloy is important, but not presently available. Therefore, in this work, the influence of microstructural condition and strain rates on dynamic impact behaviour of ATI 718Plus®, using a modified version of direct impact Hopkinson bar, is investigated. It is observed that the age-hardened alloy exhibits a significantly reduced strain hardening and strain rate hardening capabilities compared to the solution heat treated microstructure. Furthermore, microstructural examination of the deformed samples shows that the formation of adiabatic shear bands, which usually serve as damage nucleation site, is substantially suppressed in the solution heat treated microstructure, while the aged microstructure exhibits high propensity to form localised shear bands.

  • 23.
    Asala, G.
    et al.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, Canada.
    Khan, A. K.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, Canada.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Mechanical Engineering. University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, O. A.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, Canada.
    Microstructural Analyses of ATI 718Plus® Produced by Wire-ARC Additive Manufacturing Process2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, no 9, p. 4211-4228Article in journal (Refereed)
    Abstract [en]

    A detailed microstructural study of ATI 718Plus superalloy produced by the wire-arc additive manufacturing (WAAM) process was performed through the use of scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron probe micro-analysis (EPMA), and electron backscatter diffraction (EBSD). Extensive formation of eutectic solidification microconstituents including Laves and MC-type carbide phases, induced by micro-segregation, are observed in the build of the alloy in the as-deposited condition. Notwithstanding the significant segregation of niobium (Nb), which has been reported to promote the formation of the delta-phase in ATI 718Plus, only eta-phase particles are observed in the deposit. Excessive precipitation of eta-phase particles is found to be linked to Laves phase particles that are partially dissolved in the deposit after post-deposition heat treatment (PDHT). The EBSD analysis shows a high textured build in the aOE (c) 100 > directions with only a few misoriented grains at the substrate-deposit boundary and the top of the deposit. Investigation on the hardness of the build of the alloy, in the as-deposited condition, showed a softened zone about 2 mm wide at the deposited metal heat affected zone (DMHAZ), which has not been previously reported and potentially damaging to the mechanical properties. An extensive analysis with the use of both microstructural characterization tools and theoretical calculations shows that the DMHAZ has the lowest volume fraction of strengthening precipitates (gamma’ and gamma aEuro(3)) in terms of their number density, which therefore induces the observed softness. Delayed re-precipitation kinetics and the extent of the precipitation of gamma’ and gamma aEuro(3) in the DMHAZ which is related to the diffusion of segregated solute elements from the interdendritic regions are attributed to this phenomenon. The microstructural analyses discussed in this work are vital to adequate understanding of properties of ATI 718Plus produced by the additive manufacturing process technique.

  • 24.
    Asala, Gbenga
    et al.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, R3T 5V6, Canada.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, Olanrewaj A.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, R3T 5V6, Canada.
    Analysis and constitutive modelling of high strain rate deformation behaviour of wire-arc additive-manufactured ATI 718Plus superalloy2019In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 103, no 1-4, p. 1419-1431Article in journal (Refereed)
    Abstract [en]

    A fundamental prerequisite for obtaining realistic finite element simulation of machining processes, which has become a key machinability assessment for metals and alloys, is the establishment of a reliable material model. To obtain the constitutive model for wire-arc additive-manufactured ATI 718Plus, Hopkinson pressure bar is used to characterise the flow stress of the alloy over a wide range of temperatures and strain rates. Experiment results show that the deformation behaviours of as-deposited ATI 718Plus superalloy are influenced by the applied strain rate, test temperature and strain. Post-deformation microstructures show localised deformation within the deposit, which is attributable to the heterogeneous distribution of the strengthening precipitates in as-deposited ATI 718Plus. Furthermore, cracks are observed to be preferentially initiated at the brittle eutectic solidification constituents within the localised band. Constitutive models, based on the strain-compensated Arrhenius-type model and the modified Johnson-Cook model, are developed for the deposit based on experimental data. Standard statistical parameters, correlation coefficient (R), root-mean-square error (RMSE) and average absolute relative error (AARE) are used to assess the reliability of the models. The results show that the modified Johnson-Cook model has better reliability in predicting the dynamic flow stress of wire-arc-deposited ATI 718Plus superalloy. © 2019, Springer-Verlag London Ltd., part of Springer Nature.

  • 25.
    Asala, Gbenga
    et al.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, Canada.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, Olanrewaj A.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, Canada.
    Hot corrosion behaviour of wire-arc additive manufactured Ni-based superalloy ATI 718Plus®2019In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 158, article id 108086Article in journal (Refereed)
    Abstract [en]

    The hot corrosion behaviour of wire-arc additive manufactured and wrought ATI 718Plus® are studied. ATI 718Plus® produced by the additive manufacturing process, in the as-processed condition, exhibits a significantly lower hot corrosion resistance in comparison to the wrought alloy. Analytical electron microscopy and spectroscopy techniques, with corroboration by thermodynamic calculations, are used to identify the underlying cause of the poor hot corrosion resistance. Based on the understanding accrued from the analyses, post-processing heat treatments are used to improve the hot corrosion resistance, which is valuably pertinent to the application of ATI 718Plus® produced by additive manufacturing in hot corrosive environments. © 2019 Elsevier Ltd

  • 26.
    Asala, Gbenga
    et al.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, R3T 5V6, Canada.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, Olanrewaj A.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, R3T 5V6, Canada.
    Improved dynamic impact behaviour of wire-arc additive manufactured ATI 718Plus®2018In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 738, p. 111-124Article in journal (Refereed)
    Abstract [en]

    The dynamic response and impact resistance of wire-arc additive manufactured (AMed) and wrought ATI 718Plus in different heat treatment conditions are characterised by using a direct impact Hopkinson pressure bar system. In addition, microstructural analyses of the alloys, before and after impact, are characterised by using advanced microscopy techniques, including scanning electron and transmission electron microscopies. The experimental results show that the impact resistance of the AMed alloy in the as-processed condition is inferior to that of the wrought alloy. The lower impact resistance is attributed to the presence of eutectic solidification constituents in the interdendritic regions and to the inhomogeneous distribution of the strengthening precipitates in the deposit. After the application of the recommended heat treatment for ATI 718Plus, excessive formation of η-phase particles are observed in the microstructure in addition to Laves phase particles. Since the recommended heat treatment for ATI 718Plus is not sufficient to eliminate the deleterious phases and optimise the properties of the alloy, a novel heat treatment procedure is proposed. Dynamic impact study of the AMed alloy after the application of the proposed approach shows that the alloy exhibits a dynamic response and impact resistance comparable to those of the wrought alloy. Furthermore, under high impact momentum, both the wrought and the AMed alloys fail due to the adiabatic shear band. A transmission electron microscopy analysis of the deformed alloys suggests the dissolution of the γ’ precipitates in the shear band as well as in the adjacent regions to the shear band. Increase in the rate of dissolution of the precipitates due to strain-assisted diffusion coupled with an increase in the adiabatic temperature during deformation, are likely causes of the dissolution of the precipitates in the shear band regions. © 2018 Elsevier B.V.

  • 27.
    Asala, Gbenga
    et al.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, Canada (CAN).
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Ojo, Olanrewaju A.
    University of Manitoba, Department of Mechanical Engineering, Winnipeg, Canada (CAN).
    A study of the dynamic impact behaviour of IN 718 and ATI 718Plus® superalloys2019In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 99, no 4, p. 419-437Article in journal (Refereed)
    Abstract [en]

    The dynamic impact response of IN 718 and ATI 718Plus®, in both the solution heat treated and age-hardened conditions, were investigated at different deformation temperatures and strain rates using a direct impact Hopkinson pressure bar. Analyses of the results provide a vital but previously not reported information that the ATI 718Plus® offers a higher resistance to damage during high strain rate ballistic impact deformation compared to the most widely used Iron-nickel based superalloy, Inconel 718. ATI 718Plus® showed higher strain hardening and strain rate sensitivity, in both heat treatment conditions, than IN 718. The difference in the deformation behaviour of both alloys, in the annealed condition, is attributable to the compositional modification in ATI 718Plus® which has been reported to lower its stacking fault energy and increases the tendency for deformation twinning. However, in the age-hardened condition, the difference is believed to be related to the disparity in the operative strengthening mechanism, of the precipitates present in both alloys. Furthermore, a higher susceptibility to strain location and the formation of adiabatic shear band, in aged IN 718, is attributable to the stronger temperature-softening characteristics observed in the alloy and to the limited strain hardening tendency under dynamic impact loading. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.

  • 28.
    Aydin, Gökçe
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Valiente Bermejo, Maria Asunción
    University West, Department of Engineering Science, Division of Welding Technology.
    Högström, Mats
    University West, Department of Engineering Science, Division of Welding Technology.
    Şelte, Aydın
    Uddeholms AB, 683 85 Hagfors (SWE).
    Oikonomou, Christos
    Uddeholms AB, 683 85 Hagfors (SWE).
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence of laser metal deposition process parameters on a precipitation hardening stainless steel2023In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 67, no 4, p. 1067-1080Article in journal (Refereed)
    Abstract [en]

    The combination of corrosion resistance and mechanical properties of martensitic precipitation hardening stainless steels (MPHSS) makes them well suited for demanding applications in aerospace, high-pressure gas bottles, or in injection molding of corrosive plastics. Directed energy deposition methods and specifically the laser metal deposition process with powder as feedstock (LMDp) have the potential to be applied in the production of such components. It is well-known that the geometrical features of the deposited beads such as aspect ratio and dilution are crucial for process efficiency and deposition quality. Therefore, this work aims at understanding the influence of the process parameters and the resulting microstructure of a MPHSS modified PH 13-8Mo alloy when using LMDp. Design of experiment (DoE) was used to plan and analyze the influence and interaction of the different LMDp process variables in the geometry of the deposits. It was found that height, width, and depth were statistically significantly influenced by speed, while height was also considerably influenced by the powder feeding rate. In terms of laser power, it was the most significant factor for the width and the depth, but it did not significantly affect the height of the beads. The results showed that the as-deposited microstructure of the modified PH 13-8Mo under the LMDp conditions investigated in this work consists of a martensitic matrix with some amount of primary δ ferrite. The presence of a low amount of retained austenite and aluminum-enriched inclusions was confirmed. This work enhances the fundamental process and material understanding of LMDp of the modified PH 13-8Mo alloy as a first stage in the fabrication of additively manufactured components.

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  • 29.
    Babu, Bijish
    et al.
    Mechanics of Sold Materials, Luleå University of Technology, SE-971 87, Luleå, Sweden.
    Charles Murgau, Corinne
    University West, Department of Engineering Science, Avdelningen för svetsteknologi (SV).
    Lindgren, Lars-Erik
    Mechanics of Sold Materials, Luleå University of Technology, SE-971 87, Luleå, Sweden.
    Physically Based Constitutive Model of Ti-6Al-4V for Arbitrary Phase CompositionArticle in journal (Other academic)
    Abstract [en]

    The main challenge in producing aerospace components using Ti-6Al-4V alloy is to employ the optimum process window of deformation rate and temperature in order to achieve desired material properties. Understanding the microstructure property relationship qualitatively is not enough to achieve this goal. Developing advanced material models to be used in manufacturing process simulation is the key to iteratively computeand optimize the process. The focus in this work is on physically based flow stress models coupled with microstructure evolution models. Such a model can be used to simulate processes involving complex and cyclic thermo-mechanical loading

  • 30.
    Baghdadchi, Amir
    University West, Department of Engineering Science, Division of Welding Technology.
    Laser Welding and Additive Manufacturing of Duplex Stainless Steels: Properties and Microstructure Characterization2022Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Duplex stainless steels (DSS), with a ferritic-austenitic microstructure, are used ina wide range of applications thanks to their high corrosion resistance and excellent mechanical properties. However, efficient and successful production and joining of DSS require precise control of processes and an in-depth understanding o frelations between composition, processing thermal cycles, resulting microstructures and properties. In this study laser welding, laser reheating, and laser additive manufacturing using Laser Metal Deposition with Wire (LMDw) ofDSS and resulting weld and component microstructures and properties are explored.

    In the first part a lean FDX 27 duplex stainless steel, showing the transformation induced plasticity (TRIP) effect, was autogenously laser welded and laser reheated using pure argon or pure nitrogen as shielding gas. The weld metal austenite fraction was 22% for argon-shielding and 39% for nitrogen-shielding in as-welded conditions. Less nitrides were found with nitrogen-shielding compared to argonshielding. Laser reheating did not significantly affect nitride content or austenite fraction for argon-shielding. However, laser reheating of the nitrogen shieldedweld removed nitrides and increased the austenite fraction to 57% illustrating the effectiveness of this approach.

    Phase fraction analysis is important for DSS since the balance between ferrite and austenite affects properties. For TRIP steels the possibility of austenite tomartensite transformation during sample preparation also has to be considered. Phases in the laser welded and reheated FDX 27 DSS were identified and quantified using light optical microscopy (LOM) and electron backscatter diffraction (EBSD) analysis. An optimized Beraha color etching procedure was developed for identification of martensite by LOM. A novel step-by-step EBSD methodology was also introduced, which successfully identified and quantified martensite as well as ferrite and austenite. It was found that mechanical polishing produced up to 26% strain-induced martensite, while no martensite was observed after electrolytic polishing.In the second part a systematic four-stage methodology was applied to develop procedures for additive manufacturing of standard 22% Cr duplex stainless steel components using LMDw combined with the hot wire technology. In the four stages, single-bead passes, a single-bead wall, a block, and finally a cylinder with an inner diameter of 160 mm, thickness of 30 mm, and height of 140 mm were produced. The as-deposited microstructure was inhomogeneous and repetitive including highly ferritic regions with nitrides and regions with high fractions ofaustenite. Heat treatment for 1 hour at 1100 ̊C homogenized the microstructure, removed nitrides, and produced an austenite fraction of about 50%. Strength, ductility, and toughness were at a high level for the cylinder, comparable to those of wrought type 2205 steel, both as-deposited and after heat treatment. The highest strength was achieved for the as-deposited condition with a yield strength of 765 MPa and a tensile strength of 865 MPa, while the highest elongation of 35% was found after heat treatment. Epitaxial growth of ferrite during solidification, giving elongated grains along the build direction, resulted in anisotropy of toughness properties. The highest impact toughness energies were measured for specimens with the notch perpendicular to the build direction after heat treatment with close to 300 J at -10oC. It was concluded that implementing a systematic methodology with a stepwise increase in the deposited volume and geometrical complexity can successfully be used when developing additive manufacturing procedures for significantly sized metallic components.

    This study has illustrated that a laser beam can successfully be used as heat source in processing of duplex stainless steel both for welding and additive manufacturing. However, challenges like nitrogen loss, low austenite fractions and nitride formation have to be handled by precise process control and/or heat treatment.

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  • 31.
    Baghdadchi, Amir
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Cary, Claire
    Sridhar, Narasi
    Valiente Bermejo, Maria Asuncion
    Fink, Carolin
    Andersson, Joel
    Corrosion resistance and microstructure analysis of additively manufactured 22% chromium duplex stainless steel by laser metal deposition with wireIn: Journal of Materials Research and Technology, ISSN 2238-7854, Vol. 26, p. 6741-6756Article in journal (Refereed)
  • 32.
    Baghdadchi, Amir
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Hosseini, Vahid
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Promoting austenite formation in laser welding of duplex stainless steel-impact of shielding gas and laser reheating2021In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 65, p. 499-511Article in journal (Refereed)
    Abstract [en]

    Avoiding low austenite fractions and nitride formation are major challenges in laser welding of duplex stainless steels (DSS). The present research aims at investigating efficient means of promoting austenite formation during autogenous laser welding of DSS without sacrificing productivity. In this study, effects of shielding gas and laser reheating were investigated in welding of 1.5-mm-thick FDX 27 (UNS S82031) DSS. Four conditions were investigated: Ar-shielded welding, N2-shielded welding, Ar-shielded welding followed by Ar-shielded laser reheating, and N2-shielded welding followed by N2-shielded laser reheating. Optical microscopy, thermodynamic calculations, and Gleeble heat treatment were performed to study the evolution of microstructure and chemical composition. The austenite fraction was 22% for Ar-shielded and 39% for N2-shielded as-welded conditions. Interestingly, laser reheating did not significantly affect the austenite fraction for Ar shielding, while the austenite fraction increased to 57% for N2-shielding. The amount of nitrides was lower in N2-shielded samples compared to in Ar-shielded samples. The same trends were also observed in the heat-affected zone. The nitrogen content of weld metals, evaluated from calculated equilibrium phase diagrams and austenite fractions after Gleeble equilibrating heat treatments at 1100 °C, was 0.16% for N2-shielded and 0.11% for Ar-shielded welds, confirming the importance of nitrogen for promoting the austenite formation during welding and especially reheating. Finally, it is recommended that combining welding with pure nitrogen as shielding gas and a laser reheating pass can significantly improve austenite formation and reduce nitride formation in DSS laser welds. © 2020, The Author(s).

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  • 33.
    Baghdadchi, Amir
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Hosseini, Vahid
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Research Enviroment Production Technology West. University West, Department of Engineering Science, Division of Welding Technology.
    Identification and quantification of martensite in ferritic-austenitic stainless steels and welds2021In: Journal of Materials Research and Technology, ISSN 2238-7854, Vol. 15, p. 3610-3621Article in journal (Refereed)
    Abstract [en]

    This paper aims at the phase identification and quantification in transformation induced plasticity duplex stainless steel (TDSS) base and weld metal containing ferrite, austenite, and martensite. Light optical microscopy (LOM) and electron backscatter diffraction (EBSD) analysis were employed to analyze phases. Samples were either mechanically or electrolytically polished to study the effect of the preparation technique. Mechanical polishing produced up to 26% strain-induced martensite. Electrolytic polishing with 150 g citric acid, 300 g distilled water, 600 mL H3PO4, and 450 mL H2SO4 resulted in martensite free surfaces, providing high-quality samples for EBSD analysis. Martensite identification was challenging both with LOM, due to the similar etching response of ferrite and martensite, and with EBSD, due to the similar lattice structures of ferrite and martensite. An optimized Beraha color etching procedure was developed that etched martensite distinctively. A novel step-by-step EBSD methodology was also introduced considering grain size and orientation, which successfully identified and quantified martensite as well as ferrite and austenite in the studied TDSS. Although here applied to a TDSS, the presented EBSD methodology is general and can, in combination with knowledge of the metallurgy of the specific material and with suitable adaption, be applied to a multitude of multiphase materials. It is also general in the sense that it can be used for base material and weld metals as well as additive manufactured materials.

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    JMR&T
  • 34.
    Baghdadchi, Amir
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Hosseini, Vahid
    University West, Department of Engineering Science, Division of Welding Technology.
    Valiente Bermejo, María Asunción
    University West, Department of Engineering Science, Division of Welding Technology.
    Axelsson, Björn
    Alfa Laval Tumba AB, Tumba (SWE).
    Harati, Ebrahim
    University West, Department of Engineering Science, Division of Welding Technology. ITW Welding AB,Partille (SWE).
    Högström, Mats
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Research Enviroment Production Technology West. University West, Department of Engineering Science, Division of Welding Technology.
    Wire laser metal deposition additive manufacturing of duplex stainless steel components -Development of a systematic methodology2021In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 14, no 23, article id 7170Article in journal (Refereed)
    Abstract [en]

    A systematic four-stage methodology was developed and applied to the Laser Metal Deposition with Wire (LMDw) of a duplex stainless steel (DSS) cylinder > 20 kg. In the four stages, single-bead passes, a single-bead wall, a block, and finally a cylinder were produced. This stepwise approach allowed the development of LMDw process parameters and control systems while the volume of deposited material and the geometrical complexity of components increased. The as-deposited microstructure was inhomogeneous and repetitive, consisting of highly ferritic regions with nitrides and regions with high fractions of austenite. However, there were no cracks or lack of fusion defects; there were only some small pores, and strength and toughness were comparable to those of the corresponding steel grade. A heat treatment for 1 h at 1100 degrees (C) was performed to homogenize the microstructure, remove nitrides, and balance the ferrite and austenite fractions compensating for nitrogen loss occurring during LMDw. The heat treatment increased toughness and ductility and decreased strength, but these still matched steel properties. It was concluded that implementing a systematic methodology with a stepwise increase in the deposited volume and geometrical complexity is a cost-effective way of developing additive manufacturing procedures for the production of significantly sized metallic components.

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    Materials
  • 35.
    Baghdadchi, Amir
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Hosseini, Vahid
    University West, Department of Engineering Science, Division of Welding Technology.
    Valiente Bermejo, María Asunción
    University West, Department of Engineering Science, Division of Welding Technology.
    Axelsson, Björn
    Alfa Laval Tumba AB, Tumba (SWE).
    Harati, Ebrahim
    University West, Department of Engineering Science, Division of Welding Technology. ITW Welding AB, Partille (SWE).
    Högström, Mats
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Wire laser metal deposition of 22% Cr duplex stainless steel: as-deposited and heat-treated microstructure and mechanical properties2022In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 57, no 21, p. 9556-9575Article in journal (Refereed)
    Abstract [en]

    Duplex stainless steel (DSS) blocks with dimensions of 150 × 70x30 mm3 were fabricated by Laser Metal Deposition with Wire (LMDw). Implementation of a programmable logic control system and the hot-wire technology provided a stable and consistent process producing high-quality and virtually defect-free deposits. Microstructure and mechanical properties were studied for as-deposited (AD) material and when heat-treated (HT) for 1 h at 1100 °C. The AD microstructure was inhomogeneous with highly ferritic areas with nitrides and austenitic regions with fine secondary austenite occurring in a periodic manner. Heat treatment produced a homogenized microstructure, free from nitrides and fine secondary austenite, with balanced ferrite and austenite fractions. Although some nitrogen was lost during LMDw, heat treatment or reheating by subsequent passes in AD allowed the formation of about 50% austenite. Mechanical properties fulfilled common requirements on strength and toughness in both as-deposited and heat-treated conditions achieving the highest strength in AD condition and best toughness and ductility in HT condition. Epitaxial ferrite growth, giving elongated grains along the build direction, resulted in somewhat higher toughness in both AD and HT conditions when cracks propagated perpendicular to the build direction. It was concluded that high-quality components can be produced by LMDw and that deposits can be used in either AD or HT conditions. The findings of this research provide valuable input for the fabrication of high-performance DSS AM components

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  • 36.
    Baghdadchi, Amir
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Movahedi, Mojtaba
    Department of Materials Science and Engineering, Sharif University of Technology, Tehran (IRN).
    Consumable pin-friction stir spot welding of Al-Mg-Si alloy via pre-created hole and refilling: Microstructure evolution, defects, and shear/tensile failure load2023In: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 237, no 17Article in journal (Refereed)
    Abstract [en]

    Since Al-Mg-Si alloys are widely used in the transportation industry, it is important to produce a sound and robust weld between the sheets of these alloys. The focus of this work is on the tensile-shear and cross-tension strengths of the consumable pin-friction stir spot welds (CP-FSSWs) without an exit-hole between the Al-6061 aluminum sheets. Before welding, a hole was created at the joint region in the base sheets and then, it was filled using a rotating consumable pin. The tensile-shear, cross-tension, and microhardness tests were employed to evaluate the mechanical properties of the spot welds. The results showed that the pre-created hole was entirely filled during the welding process. While a complete bond was formed between the consumable pin and the lateral surface of the hole, there were three distinct regions at the interface of the pin and the bottom of the hole: complete bond, kissing bond, and defects. Enhancement of the tool rotational speed decreased the area of the complete bond in the weld compared to the other regions. A linear relationship existed between the bonding area and weld failure load in the cross-tension test. The proposed relationship approved the impact of the swirly region at the interface of the base sheets on the weld strength. While in the cross-tension test, the weld failure load decreased from ∼2800 to ∼1950 N, it improved from ∼10,500 to ∼12,000 N in the tensile-shear test with enhancement of the tool rotational speed from 700 to 2000 rpm. The hardness measurements demonstrated that there was no common heat affected zone softening after CP-FSSW.  

  • 37.
    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.

  • 38.
    Bates, William P.
    et al.
    University West, Department of Engineering Science.
    Patel, Vivek
    University West, Department of Engineering Science, Division of Welding Technology.
    Rana, Harikrishna
    Department of Engineering, University of Palermo, Viale Delle SciePZe, 90128, Palermo (ITA).
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    De Backer, Jeroen
    University West, Department of Engineering Science, Division of Welding Technology. Friction Welding Process Section, TWI Ltd., Cambridge, CB21 6AL (GBR).
    Igestrand, Mattias
    University West, Department of Engineering Science, Division of Welding Technology.
    Fratini, Livan
    Department of Engineering, University of Palermo, Viale Delle SciePZe, 90128, Palermo (ITA).
    Correction to: Properties Augmentation of Cast Hypereutectic Al–Si Alloy Through Friction Stir Processing (Metals and Materials International, (2022), 10.1007/s12540-022-01207-7)2023In: Metals and Materials International, ISSN 1598-9623, E-ISSN 2005-4149, Vol. 29, article id 876Article in journal (Refereed)
    Abstract [en]

    The graphic abstract was missing from this article and it has been given in this correction. The original article has been corrected. © 2022, The Author(s) under exclusive licence to The Korean Institute of Metals and Materials.

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  • 39.
    Bates, William P.
    et al.
    Department of Engineering Science, University West, Trollhättan (SWE).
    Patel, Vivek
    University West, Department of Engineering Science, Division of Welding Technology.
    Rana, Harikrishna
    Department of Engineering, University of Palermo, Palermo (ITA).
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    De Backer, Jeroen
    University West, Department of Engineering Science, Division of Production Systems. Friction Welding Process Section, TWI Ltd., Cambridge (GBR).
    Igestrand, Mattias
    University West, Department of Engineering Science, Division of Welding Technology.
    Fratini, Livan
    Department of Engineering, University of Palermo, Palermo (ITA).
    Properties Augmentation of Cast Hypereutectic Al-Si Alloy Through Friction Stir Processing2022In: Metals and Materials International, ISSN 1598-9623, E-ISSN 2005-4149Article in journal (Refereed)
    Abstract [en]

    The present endeavour is to augment mechanical attributes via friction stir processing (FSP) in hypereutectic aluminium-silicon castings by the means of microstructural modifications and defects reduction. Wherein, the study proceeds with mainly two approaches namely, alteration in tool revolution (TR) and the number of FSP passes. The prepared specimens were evaluated investigating volume fraction of porosities, microstructural characterizations and microhardness. Therefrom, the specimen with highest number of passes delivered most uniform properties resulting from the reduction in casting porosities and refined silicon particle uniform distribution throughout friction stir processed zone. This endeavour may be considered as a footstep towards more industrial readied material transformation.

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    Springer
  • 40.
    Bayock, Francois Njock
    et al.
    Department of Mechanical Engineering, ENSET Douala, University of Douala, PO Box: 1872, Douala (CMR).
    Kah, Paul
    University West, Department of Engineering Science, Division of Welding Technology.
    Kibong, Marius
    Laboratory of Technologies and Applied Sciences, University Institute of Technology, University of Douala, PO Box 8698 Douala, (CMR).
    Timba, Sadrack
    Department of Mechanical Engineering, ENSET Douala, University of Douala, PO Box: 1872, Douala(CMR).
    Thermal induced residual stress and microstructural constituents of dissimilar S690QT high-strength steels and 316L austenitic stainless steel weld joints2021In: MATERIALS RESEARCH EXPRESS, E-ISSN 2053-1591, Vol. 8, no 7, p. 1-16Article in journal (Refereed)
    Abstract [en]

    The effect of thermal cycle on the residual stress, microstructural constituents, and alloying elements composition of dissimilar S690QT and 316L austenite stainless steel was studied. Finite element model (FEM) using ANSYS 19.1 software and an experimental investigation using gas metal arc welding (GMAW) process with fully austenite filler wire were applied to developed thermal cycle and evaluate residual stress in the heat-affected zone of both materials. The experimental data were recorded using a thermal-cycle sensor (TCS) and x-ray diffraction technique. A microstructural investigation was done using Scanning electron microscopy (SEM) and Energy-Dispersive x-ray Spectroscopy (EDS). The thermal cycle showed the maximum temperature (T (max)) in the HAZ of 316L side (850 degrees C) at a distance of 7 mm away from the centreline of the weld compare to S690QT side. The magnitude of tensile residual stresses in the 316L side decreased as welding heat input increased. The maximum residual stresses were observed on the S690QT side (700 MPa). Microstructural investigations revealed the formation of Bainite, and some retained of austenite at the temperature of 800 degrees C in the coarse grain heat-affected zone (CGHAZ) of S690QT. On 316L side, some grain boundary austenite (GBA), intragranular austenite (IGA), and carbides were observed in the CGHAZ. Compared to the initial microstructure of both materials, a slightly increase of Mn, Cr, and Si were observed at the respective values of 1.90%, 1.25%, and 0.40% on the S690QT side compared to the BM. For 316L side, it indicated an increase of Cr (26%), Mo (5.69%), and Ni (17%) in the alloying element composition compared to the BM. Applying 10 kJ cm(-1) of heat input produced an excellent mechanical property and reduced the formation of carbide, inter-granular corrosion in the microstructure of 316L side.

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  • 41.
    Bayock, Francois Njock
    et al.
    Lappeenranta Lahti Univ Technol, Lab Welding Technol, POB 20, Lappeenranta 53851, Finland (FIN).
    Kah, Paul
    University West, Department of Engineering Science, Division of Welding Technology.
    Salminen, Antti
    Univ Turku, Dept Mech Engn, FI-20014 Turku, Finland (FIN).
    Belinga, Mvola
    Lappeenranta Lahti Univ Technol, Lab Welding Technol, POB 20, Lappeenranta 53851, Finland (FIN).
    Yang, Xiaochen
    Lappeenranta Lahti Univ Technol, Lab Welding Technol, POB 20, Lappeenranta 53851, Finland (FIN).
    Feasibility study of welding dissimilar Advanced and Ultra High Strength Steels2020In: Reviews on Advanced Materials Science, ISSN 1606-5131, E-ISSN 1605-8127, Vol. 59, no 1, p. 54-66Article in journal (Refereed)
    Abstract [en]

    This study concerns the weldability of dissimilar Ultra high-strength steel (UHSS) and advanced high-strength steel (AHSS), which is used in the modern machine industry. The materials offered superior strength as well as relatively low weight, which reduces microstructure contamination during a live cycle. The choice of the welding process base of the base material (BM) and welding parameters is essential to improve the weld joint quality. S700MC/S960QC was welded using a gas metal arc welding (GMAW) process and overmatched filler wire, which was performed using three heat input (7, 10, and 15 kJ/cm). The weld samples were characterized by a Vickers-hardness test, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The test reveals a decrease of softening areas in the HAZ and the formation of the stable formation of Bainite-Ferrite for S700MC and Bainite-martensite for S960QC when the heat input of 10 kJ/cm is used. It is recommended to use the GMAW process and Laser welding (Laser beam-MIG), with an optimal welding parameter, which will be achieved a high quality of manufacturing products.

  • 42.
    Bayock, Francois Njock
    et al.
    Department of Mechanical Engineering, ENSET Douala, University of Douala, P.O. Box: 1872, Douala (CMR).
    Mejouyo, Paul William Huisken
    Department of Mechanical Engineering, ENSET Douala, University of Douala, P.O. Box: 1872, Douala (CMR).
    Bisong, Mbelle Samuel
    Department of Mechanical Engineering, ENSET Douala, University of Douala, P.O. Box: 1872, Douala (CMR).
    Kah, Paul
    University West, Department of Engineering Science, Division of Welding Technology.
    Investigation of Microstructure, and Mechanical Properties of Dissimilar High and Ultra-High Steel Welded Joints: Application for Extreme Climate Conditions2022In: Metallurgical and Materials Engineering, ISSN 2217-8961, Vol. 28, no 4, p. 625-639Article in journal (Refereed)
    Abstract [en]

    The paper focuses on the technical challenges of producing high-quality welds in modern extreme climate conditions structures, as welds are typically the weakest part of welded structures. Welding is particularly difficult with high-strength and ultra-high-strength steels (HSS-UHSS), which are used in structures to reduce weight. The microstructural compositions and mechanical properties of dissimilar high-strength and ultra-high-strength steels were investigated in this study, which was performed with three different heat inputs (0.8, 1.2, and 1.8 kJ/mm). There was a 2.3Cr, 0.4Si, and 2.8Mn increase on the FGHAZ microstructure of the S960QC side, confirming the temperature increase in that zone. Microhardness results show softening (160 HV5) in the E500 side’s fine grain heat-affected zone (FGHAZ). Bending test results show that when the maximum force applied was 4000N, the fracture angle was close to 149°, and that the fracture zone was oriented exclusively in the FGHAZ, which had the higher softening zone. Tensile results show the fracture zone, which was oriented in the E500 side’s FGHAZ. It was suggested that a heat input of 1.2 kJ/mm be applied to the weld dissimilar joint of TMCP E500-S960QC, which will be beneficial for extreme climate conditions.  

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  • 43.
    Bolmsjö, Gunnar
    et al.
    Linnaeus University, Växjö, Sweden.
    Ferreira Magalhães, Ana Catarina
    University West, Department of Engineering Science, Division of Production Systems. University West, Department of Engineering Science, Division of Welding Technology.
    Cederqvist, L.
    SKB AB, Oskarshamn, Sweden.
    De Backer, Jeroen
    University West, Department of Engineering Science, Division of Production Systems.
    Robotic Friction Stir Welding of complex geometry and mixed materials2018In: 50th International Symposium on Robotics, ISR 2018, VDE Verlag GmbH , 2018, p. 35-41Conference paper (Refereed)
    Abstract [en]

    Friction stir welding (FSW) is a solid state process for joining materials which has demonstrated advantages compares with other methods which include joining of mixed materials, hard to weld alloys and consistent and high quality. This paper presents a study of robotic FSW initiated by Volvo Skövde plant to join an insert workpiece of extruded aluminium with a cylinder block of aluminium casting. A three-stage procedure was decided to determine the feasibility to apply robotic FSW. The stages included study of welding the mixed materials, weld along the complex joint line with holes and channels close to the joint, and finally welding the cylinder block. The results based on preliminary analysis indicate that the final tests were successful and the process is feasible for the challenging case study. However, further studies are recommended in order to identify the operating parameters window, tool design, and control of the process in order to optimize productivity and quality. © VDE VERLAG GMBH

  • 44.
    Cederberg, Emil
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence of welding and additive manufacturing thermal cycles on microstructure and properties of super duplex stainless steel base and weld metal studied by a physical simulation technique2018Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Super duplex stainless steel (SDSS) is known for its excellent combination of high corrosion resistance and strength. However, the main limitations in SDSS applications are the risk of getting an imbalanced ferrite and austenite fraction and the sensitivity to form intermetallic phases at temperatures between approximately 600-1000 °C. During welding of SDSS, the welding parameters must be selected carefully in order to avoid formation of intermetallic phases such as sigma phase due to slow cooling or multiple reheating. In addition, special care is needed to have a balanced ferrite and austenite fraction. In this work, the influence of multiple thermal cycles and cooling rate on the microstructure of SDSS base and weld metal was investigated. A novel heat treatment method, using a stationary TIG arc, was performed to produce the samples. The test discs were composed of base and weld metal. Five samples were produced including 1, 5, and 15 passes of rapid cooling, one sample with medium cooling and one with slow cooling. The cooling time between 1000-700 °C was aimed at being similar for the pair of 5 passes and medium cooling and the other pair of 15 passes and slow cooling. The material was characterized by light optical microscopy and scanning electron microscopy while hardness mapping and sensitization testing were employed to evaluate the properties. It was revealed that sigma phase was more prone to precipitate in the weld compared to the base metal when exposed to high ageing temperature and repeated thermal cycles. Slow cooling was found to promote sigma phase precipitation more than multiple reheating in the weld metal. In the base metal, a minor difference was found between the slowly cooled and multiple reheated samples. Rapid cooling in multiple reheating generated nitrides in the fusion boundary zone. As more reheating passes were applied, the amount of nitrides decreased. Multipass reheating cycles also resulted in increased hardness and nitrogen depletion adjacent to the fusion boundary zone causing the ferrite content to increase. Based on this study, less sigma phase precipitation in the weld metal was achieved when using multiple reheating passes with low heat input instead of a few passes with high heat input, providing equal accumulative heating time between 1000-700 °C. However, the influence of multiple reheating on the hardness was larger compared to slow cooling.

  • 45.
    Cederberg, Emil
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Hosseini, Vahid
    University West, Department of Engineering Science, Division of Welding Technology.
    Kumara, Chamara
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Physical simulation of additively manufactured super duplex stainless steels: microstructure and properties2020In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 34, article id 101269Article in journal (Refereed)
    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.

  • 46.
    Charles Murgau, Corinne
    University West, Department of Engineering Science, Division of Welding Technology.
    Microstructure model for Ti-6Al-4V used in simulation of additive manufacturing2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is devoted to microstructure modelling of Ti-6Al-4V. The microstructure and the mechanical properties of titanium alloys are highly dependent on the temperature history experienced by the material. The developed microstructure model accounts for thermaldriving forces and is applicable for general temperature histories. It has been applied to study wire feed additive manufacturing processes that induce repetitive heating and cooling cycles.The microstructure model adopts internal state variables to represent the microstructure through microstructure constituents' fractions in finite element simulation. This makes it possible to apply the model efficiently for large computational models of general thermomechanical processes. The model is calibrated and validated versus literature data. It is applied to Gas Tungsten Arc Welding -also known as Tungsten Inert Gas welding-wire feed additive manufacturing process.Four quantities are calculated in the model: the volume fraction of phase, consisting of Widmanstätten, grain boundary, and martensite. The phase transformations during cooling are modelled based on diffusional theory described by a Johnson-Mehl-Avrami-Kolmogorov formulation, except for diffusionless martensite formation where the Koistinen-Marburger equation is used. A parabolic growth rate equation is used for the to transformation upon heating. An added variable, structure size indicator of Widmanstätten, has also been implemented and calibrated. It is written in a simple Arrhenius format.The microstructure model is applied to in finite element simulation of wire feed additive manufacturing. Finally, coupling with a physically based constitutive model enables a comprehensive and predictive model of the properties that evolve during processing.

  • 47.
    Charles Murgau, Corinne
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Lundbäck, Andreas
    Division of Mechanics of Solid Materials, Luleå University of Technology, 971 81 Luleå, Sweden .
    Åkerfeldt, Pia
    Division of Materials Science, Luleå University of Technology, 971 81 Luleå, Sweden .
    Pederson, Robert
    GKN Aerospace Engine Systems, 461 81 Trollhättan, Sweden .
    Temperature and microstructure evolution in Gas Tungsten Arc Welding wire feed additive manufacturing of Ti-6Al-4V2019In: Materials, E-ISSN 1996-1944, Vol. 12, no 21, article id E3534Article in journal (Refereed)
    Abstract [en]

    The Finite Element Method (FEM) is used to solve temperature field and microstructure evolution during GTAW wire feed additive manufacturing process.The microstructure of titanium alloy Ti-6Al-4V is computed based on the temperature evolution in a point-wise logic. The methodology concerning the microstructural modeling is presented. A model to predict the thickness of the Į lath morphology is also implemented. The results from simulations are presented togethe rwith qualitative and quantitative microstructure analysis.

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  • 48.
    Chaudhari, Rakesh
    et al.
    Department of Mechanical Engineering, School of Technology, Pandit Deendayal Energy University, Gandhinagar 382007, Gujarat (IND).
    Parikh, Nipun
    Department of Mechanical Engineering, School of Technology, Pandit Deendayal Energy University, Gandhinagar 382007, Gujarat (IND).
    Khanna, Sakshum
    School of Technology, Pandit Deendayal Energy University, Gandhinagar 382007, Gujarat (IND).
    Vora, Jay
    Department of Mechanical Engineering, School of Technology, Pandit Deendayal Energy University, Gandhinagar 382007, Gujarat, (IND).
    Patel, Vivek
    University West, Department of Engineering Science, Division of Welding Technology.
    Effect of multi-walled structure on microstructure and mechanical properties of 1.25Cr-1.0Mo steel fabricated by GMAW-based WAAM using metal-cored wire2022In: Journal of Materials Research and Technology, ISSN 2238-7854, Vol. 21, p. 3386-3396Article in journal (Refereed)
    Abstract [en]

    Wire-arc additive manufacturing (WAAM) offers multiple benefits, such as high metal deposition, low capital cost, suitable mechanical properties, and reasonable costs. In the present work, Gas metal arc welding (GMAW) based WAAM was employed to manufacture a multi-walled component of 1.25Cr-0.5Mo at optimized parameters using metal-cored wire. The fabricated multi-walled structure was observed with seamless fusion and free from disbonding. The fabricated multi-walled component was studied through microstructure investigations, mechanical properties such as microhardness (MH), tensile test, and impact test at various positions (top side, middle side, and bottom side) of the built structure. Microstructure results have shown a tempered martensite structure in the bottom zone with coarse grains and finer microstructures in the middle and top zones. MH values throughout the component were uniform and thus indicated a similar nature to the multi-walled component. A comparison of tensile properties was carried out among the results of metal-cored wires and multi-walled structures to check the internal eminence of the obtained component. For all sides of the multi-walled structure, all the tensile properties were found to be in the range values of 1.25Cr-0.5Mo metal-cored wire. The results of all three conditions for impact toughness showed far better strength than the requirement. Fracture surface morphologies of tensile and impact test parts showed the presence of large dimples with the homogenous distribution. Thus, all the obtained results have suggested the suitability of the GMAWAM process for the fabrication of a multi-walled structure of 1.25Cr-0.5Mo metal-cored wire for various industrial applications.  

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  • 49.
    Chaudhari, Rakesh
    et al.
    Pandit Deendayal Petroleum University, Department of Mechanical Engineering, School of Technology, Raisan, Gandhinagar 382007, India (IND).
    Vora, Jay J
    Pandit Deendayal Petroleum University, Department of Mechanical Engineering, School of Technology, Raisan, Gandhinagar 382007, India (IND).
    Patel, Vivek
    University West, Department of Engineering Science, Division of Welding Technology. School of Material Science and Engineering, Northwestern Polytechnical University, Shaanxi 710072, China (CHN).
    López de Lacalle, L N
    University of the Basque Country, Department of Mechanical Engineering, Escuela Superior de Ingenieros Alameda de Urquijo s/n., 48013 Bilbao, Spain (ESP).
    Parikh, D M
    Pandit Deendayal Petroleum University, Department of Mechanical Engineering, School of Technology, Raisan, Gandhinagar 382007, India (IND).
    Effect of WEDM Process Parameters on Surface Morphology of Nitinol Shape Memory Alloy.2020In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 13, no 21, article id E4943Article in journal (Refereed)
    Abstract [en]

    Nickel-titanium shape memory alloys (SMAs) have started becoming popular owing to their unique ability to memorize or regain their original shape from the plastically deformed condition by means of heating or magnetic or mechanical loading. Nickel-titanium alloys, commonly known as nitinol, have been widely used in actuators, microelectromechanical system (MEMS) devices, and many other applications, including in the biomedical, aerospace, and automotive fields. However, nitinol is a difficult-to-cut material because of its versatile specific properties such as the shape memory effect, superelasticity, high specific strength, high wear and corrosion resistance, and severe strain hardening. There are several challenges faced when machining nitinol SMA with conventional machining techniques. Noncontact operation of the wire electrical discharge machining (WEDM) process between the tool (wire) and workpiece significantly eliminates the problems of conventional machining processes. The WEDM process consists of multiple input parameters that should be controlled to obtain great surface quality. In this study, the effect of WEDM process parameters on the surface morphology of nitinol SMA was studied using 3D surface analysis, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis. 3D surface analysis results indicated a higher value of surface roughness (SR) on the top of the work surface and a lower SR on the bottom portion of the work surface. The surface morphology of the machined sample obtained at optimized parameters showed a reduction in microcracks, micropores, and globules in comparison with the machined surface obtained at a high discharge energy level. EDX analysis indicated a machined surface free of molybdenum (tool electrode).

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  • 50.
    Chaudhary, Bhavesh
    et al.
    Department of Mechanical Engineering, IIT Indore, Simrol, MP, 453552 (IND).
    Jain, Neelesh Kumar
    Department of Mechanical Engineering, IIT Indore, Simrol, MP, 453552 (IND).
    Murugesan, Jayaprakash
    Department of Metallurgy Engineering and Materials Science, IIT Indore, Simrol, MP, 453552 (IND).
    Patel, Vivek
    University West, Department of Engineering Science, Division of Welding Technology.
    Exploring temperature-controlled friction stir powder additive manufacturing process for multi-layer deposition of aluminum alloys2022In: Journal of Materials Research and Technology - JMR&T, ISSN 2238-7854, Vol. 20, p. 260-268Article in journal (Refereed)
    Abstract [en]

    This paper presents preliminary study on multi-layer deposition of aerospace grade Al 6061 alloy by novel friction stir powder additive manufacturing process. Minimum temperature of deposition was in-situ maintained using close loop temperature-controlled system for minimizing thermal gradient in the build direction. Maximum temperature during the deposition was monitored in-situ using pyrometer and thermal imaging camera. Use of a tool with circumferential and radial grooves and continuous external heating facilitated smooth three-layer deposition of Al 6061 alloy with 60% deposition efficiency and 417 degrees C as maximum deposition temperature. Larger value of temperature at deposition zone improved material flowability and deposition quality. Microstructure of multi-layer deposition found to consist of fine sub-grains. Element analysis showed uniform distribution of major alloying elements in it. Phase analysis revealed Al along with Mg2Si hardening precipitates. Tensile strength and microhardness were close to the commercially available wrought AA6061-T4 alloy. It showed ductility with 16% elongation. The presented process is a viable alternative to fusion-based additive manufacturing processes for multi-layer depositions of aerospace grade and other lightweight alloys which are difficult-to-additively-manufacture. 

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