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  • 301.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Innovatum AB, Trollhättan, Sweden.
    Aashuri, H.
    Sharif Univ Technol, Mat Sci & Engn Dept, Azadi Ave, Tehran, Iran.
    Kokabi, A. H.
    Sharif Univ Technol, Mat Sci & Engn Dept, Azadi Ave, Tehran, Iran.
    Effect of welding parameters on semisolid stir welding of Mg-9Al-1Zn magnesium alloy2016In: Transactions of Nonferrous Metals Society of China, ISSN 1003-6326, E-ISSN 2210-3384, Vol. 26, no 10, p. 2586-2594Article in journal (Refereed)
    Abstract [en]

    Semisolid stir welding of AZ91 was investigated with focus on the joining temperature and rotational speed. An Mg-25% Zn interlayer was located between two AZ91 pieces and the system was heated up to the semisolid state of base metal and interlayer. The weld seam was stirred using a drill-tip at different joining temperatures and rotational speeds. Optical and scanning electron microscopes were employed to study microstructure, cavity formation, and segregation. Hardness profile and shear punch test were also employed to rank the welds based on their quality and homogeneity. Results showed that the lowest cavity content (2.1%) with the maximum ultimate shear strength (about 188 MPa) was obtained in weld with the joining temperature of 530 degrees C and the rotational speed of 1600 r/min. Low quality welds and a reduction of ultimate shear strength were observed at very high or low rotational speeds and joining temperatures. The process, in conclusion, produced close mechanical properties to those of the base metal and homogenous quality throughout the joint, when the intermediate temperature and rotational speeds were employed.

  • 302.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Eyzop, Daniel
    Outokumpu Stainless AB, Avesta Research Centre, Avesta, Sweden.
    Östberg, Agneta
    Sandvik Materials Technology, Sandviken, Sweden.
    Janiak, Paul
    Swerea KIMAB AB, Kista, Sweden.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Ferrite content measurement in super duplex stainless steel welds2019In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 63, no 2, p. 551-563Article in journal (Refereed)
    Abstract [en]

    Approaches to determining ferrite fraction (%) and ferrite number (FN) were examined for super duplex stainless steel (SDSS) welds. A reference sample was produced by bead-on-plate gas–tungsten arc welding of a type-2507 SDSS plate. By comparing different etchants and measurement practices, it was realized that etching with modified Beraha followed by computerized image analysis (IA) was the most accurate and quickest technique to measure ferrite fraction, which determined the same ferrite fraction (68.0 ± 2.6%) as that measured by electron diffraction backscattered analysis (67.6 ± 2.3%). A Round Robin test was performed on a reference sample at University West, Swerea KIMAB, Outokumpu Stainless, and Sandvik Materials Technology to investigate the repeatability of the technique. The ferrite fraction measurements performed at different laboratories showed very small variations, which were in the range of those seen when changing microscope in the same laboratory. After verification of the technique, the relationship between ferrite fraction and ferrite number (measured with FERITSCOPE®) was determined using 14 single (root) pass welds, including butt, corner, and T-, V-, and double V-joint geometries. The best-fit equation found in this study was ferrite number (FN) = 1.1 × ferrite fraction (%). To conclude, the ferrite fraction technique suggested in the present paper was accurate and repeatable, which made it possible to determine a ferrite fraction–ferrite number formula for SDSS single-pass welds.

  • 303.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Hogskolan Vast.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Effect of multipass TIG welding on the corrosion resistance and microstructure of a super duplex stainless steel2017In: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176, Vol. 68, no 4, p. 405-415Article in journal (Refereed)
    Abstract [en]

    This is a study of the effect of repetitive TIG (tungsten inert gas) welding passes, melting and remelting the same material volume on microstructure and corrosion resistance of 2507 (EN 1.4410) super duplex stainless steel. One to four weld passes were autogenously (no filler added) applied on a plate using two different arc energies and with pure argon shielding gas. Sensitization testing showed that multipass remelting resulted in significant loss of corrosion resistance of the weld metal, in base material next to the fusion boundary, and in a zone 1 to 4 mm from the fusion boundary. Metallography revealed the main reasons for sensitization to be a ferrite-rich weld metal and precipitation of nitrides in the weld metal, and adjacent heat affected zone together with sigma phase formation at some distance from the fusion boundary. Corrosion properties cannot be significantly restored by a post weld heat treatment. Using filler metals with higher nickel contents and nitrogen containing shielding gases, are therefore, recommended. Welding with a higher heat input and fewer passes, in some cases, can also decrease the risk of formation of secondary phases and possible corrosion attack.

  • 304.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Multipass Autogenous TIG Welding of Super Duplex Stainless2015In: 16th national conference of welding and inspection, Yazd, Iran: Proceedings, Yazd, 2015Conference paper (Refereed)
    Abstract [en]

    Multipass welding of super duplex stainless steels (SDSS) needs further characterization due to their growing applications inpetrochemical and offshore industries. This study, as a result, is aimed at investigating the effects of the number of passesand the arc energy on the microstructure and properties of 2507-type SDSS (UNS S32750). From one to four TIG weldpasses were autogenously applied on a plate using two different arc energies and with pure argon gas as the shielding gas.Chemical analysis showed increasing nitrogen loss with an increasing number of passes and increasing arc energy.Microstructural analyses revealed formation of nitrides in the weld metal and heat affected zone, and sigma phase at somedistance from the fusion boundary. Thermal cycle analysis in combination with Thermo-Calc calculations indicated thatexcessive reheating cause degradation of corrosion properties of multipass weldments, by reducing the pitting resistanceequivalent number of austenite to less than 40. Multipass welding resulted in a more ferritic weld metal microstructure and anincreased hardness.Recommendations, based on the present study, are as follows: 1) Corrosion attack can occur not only in the weld zone andnext to the fusion boundary, but also in a location at some distance from the fusion zone due to reheating in the sigma phaseformation temperature range. This should be considered in inspection procedures 2) Nitrogen loss degrades the mechanicaland corrosion properties of weldments even when welding with a low heat input. Using filler metals with higher nickelcontents and nitrogen containing shielding gases are therefore recommended. 3) It is often recommended to use a heat inputin the lower end of the recommended 0.3-1.5 kJ/mm range in multipass welding of super duplex stainless steels. However,welding with a higher heat input and fewer passes, in some cases, can decrease the risk of formation of secondary phases.

  • 305.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Högström, Mats
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Valiente Bermejo, María Asunción
    University West, Department of Engineering Science, Division of Welding Technology.
    Stridh, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Wire-arc additive manufacturing of a duplex stainless steel: thermal cycle analysis and microstructure characterization2019In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 63, no 4, p. 975-987Article in journal (Refereed)
    Abstract [en]

    The evolution of microstructures with thermal cycles was studied for wire-arc additive manufacturing of duplex stainless steel blocks. To produce samples, arc energy of 0.5kJ/mm and interlayer temperature of 150 degrees C were used as low heat input-low interlayer temperature (LHLT) and arc energy of 0.8kJ/mm and interlayer temperature of 250 degrees C as high heat input-high interlayer temperature (HHHT). Thermal cycles were recorded with different thermocouples attached to the substrate as well as the built layers. The microstructure was analyzed using optical and scanning electron microscopy. The results showed that a similar geometry was produced with 14 layers4 beads in each layerfor LHLT and 15 layers3 beads in each layerfor HHHT. Although the number of reheating cycles was higher for LHLT, each layer was reheated for a shorter time at temperatures above 600 degrees C, compared with HHHT. A higher austenite fraction (+8%) was achieved for as-deposited LHLT beads, which experienced faster cooling between 1200 and 800 degrees C. The austenite fraction of the bulk of additively manufactured samples, reheated several times, was quite similar for LHLT and HHHT samples. A higher fraction of secondary phases was found in the HHHT sample due to longer reheating at a high temperature. In conclusion, an acceptable austenite fraction with a low fraction of secondary phases was obtained in the bulk of wire-arc additively manufactured duplex stainless steel samples (35-60%), where higher austenite fractions formed with a larger number of reheating cycles as well as longer reheating at high peak temperatures (800-1200 degrees C).

  • 306.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Physical and kinetic simulation of nitrogen loss in high temperature heat affected zone of duplex stainless steels2019In: Materialia, ISSN 2589-1529, Vol. 6, article id 100325Article in journal (Refereed)
    Abstract [en]

    High temperature heat affected zone (HTHAZ) of duplex stainless steels is prone to local corrosion attack due to a high ferrite fraction and nitride formation. Literature commonly attributes formation of this undesirable microstructure to rapid cooling from high peak temperatures. However, this study investigated the possible role of nitrogen loss in HTHAZ using a combination of physical and kinetics simulation. Applying a stationary gas-tungsten arc (GTA) on a water-cooled plate, a technique known as arc heat treatment, showed that considerable nitrogen loss occurred already after 0.5 min up to 150 µm from the fusion boundary. This zone was extended to 1300 µm after 600 min arc heat treatment. The results of bead-on-plate GTA welding and Gleeble testing replicating the thermal cycle in HTHAZ showed that the ferrite fraction of the real HTHAZ was 7% higher than that for Gleeble samples. This agrees with results from arc heat treatment, where ferrite fraction was found to increase due to nitrogen loss. Numerical and Dictra approaches were developed to simulate the kinetics of nitrogen loss in HTHAZ considering ferrite as the nitrogen rapid diffusion path towards the weld pool. Simulation showed good agreement with both welding and physical simulation. A combination of thermodynamic and kinetics simulations properly predicted the ferrite fraction at 1100 °C for different arc heat treatment times. In conclusion, the experiments (physical simulations and GTA welding) and kinetics simulation showed that nitrogen was lost from HTHAZ to the weld pool. © 2019 Acta Materialia Inc.

  • 307.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Innovatum AB., Trollhättan, Trollhättan, Sweden.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Engelberg, D.
    University of Manchester, School of Materials, M13 9PL, Manchester, United Kingdom.
    Wessman, Sten
    University West, Department of Engineering Science, Division of Welding Technology.
    Correction to: Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals (Welding in the World, (2018), 62, 3, (517-533), 10.1007/s40194-018-0548-z)2018In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 62, no 4, p. 893-Article in journal (Refereed)
    Abstract [en]

    Unfortunately due to typesetting mistakes, Tables 4-€“6 have been displayed erroneously in the article. © 2018, International Institute of Welding.

  • 308.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Innovatum AB.,Trollhättan, Trollhättan, Sweden.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Engelberg, Dirk
    The University of Manchester, School of Materials,Manchester,UK.
    Wessman, Sten
    University West, Department of Engineering Science, Division of Welding Technology.
    Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals2018In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 62, no 3, p. 517-533Article in journal (Refereed)
    Abstract [en]

    Super duplex stainless steel (SDSS) weld metal microstructures, covering the complete temperature range from ambient to liquidus, were produced by arc heat treatment for 1 and 10 min. Temperature modeling and thermodynamic calculations complemented microstructural studies, hardness mapping and sensitization testing. After 1 min, intermetallics such as sigma and chi phase had precipitated, resulting in moderate sensitization at 720–840 °C. After 10 min, larger amounts of intermetallics resulted in hardness up to 400 HV0.5 and more severe sensitization at 580–920 °C. Coarse and fine secondary austenite precipitated at high and low temperatures, respectively: The finer secondary austenite was more detrimental to corrosion resistance due to its lower content of Cr, Mo, and N as predicted by thermodynamic calculations. Increased hardness and etching response suggest that 475 °C embrittlement had occurred after 10 min. Results are summarized as time-temperature-precipitation and property diagrams for hardness and sensitization.

  • 309.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Engelberg, Dirk
    The University of Manchester, School of Materials, Manchester M13 9PL, UK.
    Roy, Matthew J.
    The University of Manchester, School of Mechanical, Aerospace and Civil Engineering,Manchester M13 9PL, UK.
    Kumara, Chamara
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    A novel arc heat treatment technique for producing graded microstructures through controlled temperature gradients2017In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 121, no May, p. 11-23Article in journal (Refereed)
    Abstract [en]

    This paper introduces a novel arc heat treatment technique to produce samples with graded microstructures through the application of controlled temperature gradients. Steady state temperature distributions within the sample can be achieved and maintained, for times ranging from a few seconds to several hours. The technique reduces the number of samples needed to characterize the response of a material to thermal treatments, and can consequently be used as a physical simulator for materials processing. The technique is suitable for conventional heat treatment analogues, welding simulations, multi-step heat treatments, and heat treatments with controlled heating and cooling rates. To demonstrate this technique, a super duplex stainless steel was treated with a stationary TIG arc, to confirm the relationship between generated steady-state temperature fields, microstructure development, hardness, and sensitization to corrosion. Metallographic imaging and hardness mapping provided information about graded microstructures, confirming the formation of secondary phases and microstructure sensitization in the temperature range 850–950 °C. Modelling of temperature distributions and thermodynamic calculations of phase stabilities were used to simulate microstructure development and associated welding cycles.

  • 310.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Wessman, Sten
    University West, Department of Engineering Science, Division of Welding Technology. Swerea KIMAB AB, P.O. Box 7047, Kista, Sweden.
    Fuertes, Nuria
    Swerea KIMAB AB, P.O. Box 7047, Kista, Sweden.
    Effect of sigma phase morphology on the degradation of properties in a super duplex stainless steel2018In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 11, no 6, article id 933Article in journal (Refereed)
    Abstract [en]

    Sigma phase is commonly considered to be the most deleterious secondary phase precipitating in duplex stainless steels, as it results in an extreme reduction of corrosion resistance and toughness. Previous studies have mainly focused on the kinetics of sigma phase precipitation and influences on properties and only a few works have studied the morphology of sigma phase and its influences on material properties. Therefore, the influence of sigma phase morphology on the degradation of corrosion resistance and mechanical properties of 2507 super duplex stainless steel (SDSS) was studied after 10 h of arc heat treatment using optical and scanning electron microscopy, electron backscattered diffraction analysis, corrosion testing, and thermodynamic calculations. A stationary arc was applied on the 2507 SDSS disc mounted on a water-cooled chamber, producing a steady-state temperature gradient covering the entire temperature range from room temperature to the melting point. Sigma phase was the major intermetallic precipitating between 630 °C and 1010 °C and its morphology changed from blocky to fine coral-shaped with decreasing aging temperature. At the same time, the average thickness of the precipitates decreased from 2.9 Όm to 0.5 Όm. The chemical composition of sigma was similar to that predicted by thermodynamic calculations when formed at 800-900 °C, but deviated at higher and lower temperatures. The formation of blocky sigma phase introduced local strain in the bulk of the primary austenite grains. However, the local strain was most pronounced in the secondary austenite grains next to the coral-shaped sigma phase precipitating at lower temperatures. Microstructures with blocky and coral-shaped sigma phase particles were prone to develop microscale cracks and local corrosion, respectively. Local corrosion occurred primarily in ferrite and in secondary austenite, which was predicted by thermodynamic calculations to have a low pitting resistance equivalent. To conclude, the influence of sigma phase morphology on the degradation of properties was summarized in two diagrams as functions of the level of static load and the severity of the corrosive environment. © 2018 by the authors.

  • 311.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Innovatum AB., Trollhättan, Trollhättan, Sweden.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Örnek, Cem
    KTH Royal Institute of Technology, Department of Chemical Science and Engineering, Division of Surface and Corrosion Science, Stockholm, Sweden, Department of Corrosion in Energy and Processing Industry, Swerea KIMAB AB, P.O. Box 7047, Kista, Sweden.
    Reccagni, Pierfranco
    The University of Manchester, School of Materials, Manchester, United Kingdom.
    Wessman, Sten
    University West, Department of Engineering Science, Division of Welding Technology.
    Engelberg, Dirk
    The University of Manchester, School of Materials, Manchester, United Kingdom.
    Microstructure and functionality of a uniquely graded super duplex stainless steel designed by a novel arc heat treatment method2018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 139, p. 390-400Article in journal (Refereed)
    Abstract [en]

    A novel arc heat treatment technique was applied to design a uniquely graded super duplex stainless steel (SDSS), by subjecting a single sample to a steady state temperature gradient for 10 h. A new experimental approach was used to map precipitation in microstructure, covering aging temperatures of up to 1430 °C. The microstructure was characterized and functionality was evaluated via hardness mapping. Nitrogen depletion adjacent to the fusion boundary depressed the upper temperature limit for austenite formation and influenced the phase balance above 980 °C. Austenite/ferrite boundaries deviating from Kurdjumov–Sachs orientation relationship (OR) were preferred locations for precipitation of σ at 630–1000 °C, χ at 560–1000 °C, Cr2N at 600–900 °C and R between 550 °C and 700 °C. Precipitate morphology changed with decreasing temperature; from blocky to coral-shaped for σ, from discrete blocky to elongated particles for χ, and from polygonal to disc-shaped for R. Thermodynamic calculations of phase equilibria largely agreed with observations above 750 °C when considering nitrogen loss. Formation of intermetallic phases and 475 °C-embrittlement resulted in increased hardness. A schematic diagram, correlating information about phase contents, morphologies and hardness, as a function of exposure temperature, is introduced for evaluation of functionality of microstructures. © 2018 The Authors

  • 312.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Shabestari, S.G.
    Iran University of Science and Technology (IUST), Center of Excellence for High Strength Alloys Technology (CEHSAT), School of Metallurgy and Materials Engineering, Narmak, Tehran, Iran.
    Study on the eutectic and post-eutectic reactions in LM13 aluminum alloy using cooling curve thermal analysis technique2016In: Journal of thermal analysis and calorimetry (Print), ISSN 1388-6150, E-ISSN 1588-2926, Vol. 124, no 2, p. 611-617Article in journal (Refereed)
    Abstract [en]

    Effect of non-equilibrium solidification conditions on the eutectic and post-eutectic reactions temperature and percentage of the phases were investigated using computer-aided cooling curve thermal analysis. In addition, hardness, secondary dendrite arm spacing, and maximum pore size were studied at different cooling conditions. Cooling curves were determined by setting thermocouples in the center of the molds. Solid fractions were calculated by Newtonian baseline technique. Results showed that increasing the cooling rate shifted the temperature of post-eutectic reaction upward, except final reaction. Higher cooling rate increased eutectic percentage about 4 %, but reduced total percentage of post-eutectic phases. Additionally, increasing the cooling rate shortened the maximum porosity diameter and secondary dendrite arm spacing and increased the hardness of the alloy. © 2015 Akadémiai Kiadó, Budapest, Hungary

  • 313.
    Hosseini, Vahid
    et al.
    University West, Department of Engineering Science, Division of Welding Technology. Innovatum AB Trollhättan,Trollhättan,Sweden.
    Thuvander, Mattias
    Chalmers University of Technology, Department of Physics, Gothenburg,Sweden.
    Wessman, Sten
    University West, Department of Engineering Science, Division of Welding Technology.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Welding Technology.
    Spinodal Decomposition in Functionally Graded Super Duplex Stainless Steel and Weld Metal2018In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 49A, no 7, p. 2803-2816Article in journal (Refereed)
    Abstract [en]

    Low-temperature phase separations (T < 500 °C), resulting in changes in mechanical and corrosion properties, of super duplex stainless steel (SDSS) base and weld metals were investigated for short heat treatment times (0.5 to 600 minutes). A novel heat treatment technique, where a stationary arc produces a steady state temperature gradient for selected times, was employed to fabricate functionally graded materials. Three different initial material conditions including 2507 SDSS, remelted 2507 SDSS, and 2509 SDSS weld metal were investigated. Selective etching of ferrite significantly decreased in regions heat treated at 435 °C to 480 °C already after 3 minutes due to rapid phase separations. Atom probe tomography results revealed spinodal decomposition of ferrite and precipitation of Cu particles. Microhardness mapping showed that as-welded microstructure and/or higher Ni content accelerated decomposition. The arc heat treatment technique combined with microhardness mapping and electrolytical etching was found to be a successful approach to evaluate kinetics of low-temperature phase separations in SDSS, particularly at its earlier stages. A time-temperature transformation diagram was proposed showing the kinetics of 475 °C-embrittlement in 2507 SDSS.

  • 314.
    Hurtig, Kjell
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    A critical analysis of weld heat input measurement through a water-cooled stationary anode calorimeter2015In: Proceedings of JOM 18 International conference on joining materials, Helsingör, Danmark, april 26-29, 2015, JOM-institute , 2015, p. 1-19Conference paper (Refereed)
    Abstract [en]

    A comprehensive model on heat transfer in welded plates is able to calculate the amount of heat losses from the surfaces. A model demands as input parameter the amount of heat delivered to the plate, independently of any loss (called here gross heat input for clarity). However, the great discrepancies among the results of calorimetric measurements have left many researchers skeptical about using this parameter in modeling as absolute term. The objective of this work was to assess the use of a water-cooled stationary anode calorimeter to obtain not only arc efficiency, but also gross heat input. A series of tests was carried out to determine the effect of current, material type and water flow rate on the calorimeter performance, as well as to evaluate some measures for reducing the calorimeter intrinsic errors. Finally, a sensitivity test was conducted to estimate the effect of measurement inaccuracies on the absorbed heat and arc efficiency values. The results showed that this calorimetric approach is a simple way for measuring gross heat inputs in arc welding. Nevertheless some improvement to reduce heat losses from the top surface and boost heat sinking from the opposite surface of the test coupon must be applied. This calorimeter is, on the other hand, highly sensitive to the parameter measurements, leading to errors up to ± 0.09 in arc efficiency determination if the instrument is not properly calibrated and installed.

  • 315.
    Hurtig, Kjell
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Choquet, Isabelle
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    A critical analysis of weld heat input measurement through a water-cooled stationary anode calorimeter2016In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 21, no 5, p. 339-350Article in journal (Refereed)
    Abstract [en]

    Comprehensive models of heat transfer require specification of the total amount of heat received by the workpiece. The objective of this work was to critically examine the use of a water-cooled stationary anode calorimeter to obtain both arc efficiency and total heat input into the workpiece. For simplicity and clarity, this last quantity is called the gross heat input. The effects of current, material type and water flow rate on the calorimeter performance were determined experimentally. Some measures for reducing errors in calorimetry were evaluated. Improvements were made to reduce heat losses from the top surface of the test coupon and boost heat removal from the opposite surface. A sensitivity test was conducted to estimate the effect of measurement inaccuracies. The results demonstrate the effectiveness of calorimetry for measuring gross heat input in arc welding.

  • 316. Islavath, N.
    et al.
    Ramasamy, E.
    Das, D.
    Joshi, Shrikant. V.
    Spray coated seed layer for scalable synthesis of aligned ZnO nanowire arrays on FTO substrate and their photovoltaic properties2015In: Ceramics International, Vol. 41, no 3, p. 4118-4122Article in journal (Refereed)
    Abstract [en]

    Spray coating has been employed as a non-vacuum route for deposition of a ZnO seed layer on large-area fluorine-doped tin oxide (FTO) glass substrates. Optimization of spray parameters, particularly precursor flow rate and volume, was found to yield preferably oriented and uniform ZnO seed layer. Vertically aligned single crystalline ZnO nanowire arrays with controlled features were grown on aforementioned substrate at 95 °C by a hydrothermal method. The current-voltage characteristics of dye-sensitized solar cells fabricated with the aligned ZnO nanowire arrays as photoanode have demonstrated a maximum photocurrent density of 1.86 mA cm-2 under 1 sun illumination (100 mW cm-2, AM 1.5G). © 2014 Elsevier Ltd and Techna Group S.r.l.

  • 317.
    Islavath, Nanaji
    et al.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India; School of Engineering Sciences and Technology, University of Hyderabad, Hyderabad 500046, India.
    Das, Dibakar
    School of Engineering Sciences and Technology, University of Hyderabad, Hyderabad 500046, India.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Ramasamy, Easwaramoorthi
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Seed layer-assisted low temperature solution growth of 3D ZnO nanowall architecture for hybrid solar cells2017In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 116, p. 219-226Article in journal (Refereed)
    Abstract [en]

    Aligned metal oxide nanostructures carry electrons efficiently, and are therefore ideal building blocks for next-generation optoelectronic devices. Herein, we report the seed-layer-assisted low-temperature solution growth of aligned 3D ZnO nanowall architecture on arbitrary substrates. By introducing a controlled amount of Al into a seed-layer, the morphology of ZnO nanostructure is gradually changed from nanowire to 3D nanowalls. Time-dependent growth experiments suggest that hydroxyl-ions present in growth solution react with Al to form Al(OH)4 which in turn binds to the positively charged Zn2 +surface and partially blocking ZnO growth along the (0001) direction and promoting lateral growth. Such aligned 3D ZnO nanowall architecture, with the unique combination of high surface-area and cage-like pores, grown on seed-layer coated transparent conductive substrate is found to be beneficial for electron transporting material (ETM) in perovskite solar cells and a maximum photocurrent density (JSC) of 7.5 mA.cm− 2 and a power conversion efficiency (η) of 2.4% are demonstrated. Our facile approach readily allows further growth of ZnO nanowires on 3D ZnO nanowall surface; thereby improving the perovskite-ZnO interface and increasing the JSC and η to 9.7 and 3.3%, respectively. This 3D ZnO nanowall-nanowire architecture opens up a novel configuration for designing high-performance optoelectronic devices.

  • 318.
    Islavath, Nanaji
    et al.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Saroja, S.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Reddy, K Srinivas
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Harikesh, P.C.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Veerappan, G.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Ramasamy, Easwaramoorthi
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Effect of hole-transporting materials on the photovoltaic performance and stability of all-ambient-processed perovskite solar cells2017In: Journal of Energy Chemistry, ISSN 2095-4956, Vol. 26, no 3, p. 584-591Article in journal (Refereed)
    Abstract [en]

    High-efficiency perovskite solar cells (PSCs) reported hitherto have been mostly prepared in a moisture and oxygen-free glove-box atmosphere, which hampers upscaling and real-time performance assessment of this exciting photovoltaic technology. In this work, we have systematically studied the feasibility of all-ambient-processing of PSCs and evaluated their photovoltaic performance. It has been shown that phase-pure crystalline tetragonal MAPbI3 perovskite films are instantly formed in ambient air at room temperature by a two-step spin coating process, undermining the need for dry atmosphere and post-annealing. All-ambient-processed PSCs with a configuration of FTO/TiO2/MAPbI3/Spiro-OMeTAD/Au achieve open-circuit voltage (990 mV) and short-circuit current density (20.31 mA/cm2) comparable to those of best reported glove-box processed devices. Nevertheless, device power conversion efficiency is still constrained at 5% by the unusually low fill-factor of 0.25. Dark current–voltage characteristics reveal poor conductivity of hole-transporting layer caused by lack of oxidized spiro-OMeTAD species, resulting in high series-resistance and decreased fill-factor. The study also establishes that the above limitations can be readily overcome by employing an inorganic p-type semiconductor, copper thiocyanate, as ambient-processable hole-transporting layer to yield a fill-factor of 0.54 and a power conversion efficiency of 7.19%. The present findings can have important implications in industrially viable fabrication of large-area PSCs.

    The poor conductivity of ambient-processed spiro-OMeTAD HTM layer caused by lack of oxidation is identified as a major performance limiting factor and successfully overcome by replacing with stable inorganic CuSCN.

  • 319.
    Jacobsson, J
    et al.
    Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg, Sweden; Research and Technology Department, GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Brederholm, Anssi
    Aalto University School of Engineering, Helsinki, Finland.
    Hänninen, Hannu
    Aalto University School of Engineering, Helsinki, Finland.
    Weldability of Ni-Based Superalloys Waspaloy® and Haynes® 282®: A Study Performed with Varestraint Testing2016In: Research & Reviews: Journal of Material Sciences, ISSN 2347-2278, Vol. 4, no 4, p. 3-11Article in journal (Refereed)
    Abstract [en]

    There is a need for materials with high strength, oxidation resistance, thermal stability and adequate weldability in order to facilitate the production of large structural jet engine components. Therefore, the weldability of Waspaloy® and Haynes® 282® have been evaluated using the Varestraint weldability test. The experiments reveal that Waspaloy® has a higher susceptibility to hot cracking compared to Haynes® 282®. This conclusion is supported by increased total crack length (10 mm or more) and larger brittle temperature range (approx. 65°C) for Waspaloy® when compared to Haynes® 282® in Varestraint and Gleeble hot ductility tests, respectively. The cracking in Haynes® 282® seems to be connected with a secondary phase which presumably can be associated with Ti-Mo based MC-type carbide observed in the fusion zone. Also, a surrounding segregated area is present near this secondary phase as well as along the grain boundaries. Furthermore, micro-Vickers hardness results revealed more or less the same weld metal hardness (260- 280 HV) but a difference in the base metal hardness. The weld metal hardness of Waspaloy® was lower than that of the base metal hardness, while Haynes® 282® had a higher hardness in comparison.

  • 320.
    Jacobsson, Jonny
    et al.
    Chalmers University of Technology in the Department of Industrial and Material Science, Gothenburg, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Brederholm, Anssi
    Aalto University in Helsinki, Department of Engineering Design and Production, Finland.
    Hänninen, Hannu
    Aalto University, Department of Engineering Design and Production, Aalto University, Finland.
    Weldability of superalloys alloy 718 and ATI® 718Plus™: A study performed by Varestraint testing2017In: Materialprüfung (München), ISSN 0025-5300, E-ISSN 2195-8572, Vol. 59, no 9, p. 769-773Article in journal (Refereed)
    Abstract [en]

    In this study, the old and well-known alloy 718 is compared with the newly developed ATI® 718Plus™ from the weldability point of view. This is done in order to gain new information that have not been documented and established yet among the high-temperature materials with high strength, oxidation resistance, thermal stability and sufficient weldability, yet. ATI® 718Plus™ shows a lower sensitivity to hot cracking than alloy 718 with approximately 10 mm total crack length (TCL) difference in Varestraint testing. In the solution-annealed condition at 982°C for 4.5 h followed by air cooling, the crack sensitivity is decreased as compared to the mill-annealed condition. Along the crack path and also ahead of the crack tip, γ-Laves eutectic is present in both alloys. The microhardness measurements showed similar hardness level of 250 HV in the weld metal of both alloys and even in the parent material of alloy 718. ATI® 718Plus™ parent metal had hardness of 380 HV and a small increase of less than 50 HV was observed for both studied alloys in the heat affected zone (HAZ). For the same grain size of ATI® 718Plus™ (8.3 μm) and alloy 718 (15.6 μm), the susceptibility to liquation cracking may increase with increasing grain size. With a small grain size, there is a possibility to accommodate more trace elements (B, S, P) due to the larger grain boundary area. The impurity elements were found in relatively small precipitates, typically borides (0.2 μm), phosphides (0.1 to 0.5 μm) and carbo-sulphides. The solidification sequence of alloy 718 and ATI® 718Plus™ is relatively similar, where the liquid starts to solidify as γ-phase followed by γ/MC reaction at about 1260 °C and then final γ/Laves eutectic reaction at around 1150 °C. Detailed knowledge about weldability of alloy 718 and ATI® 718Plus™ can be used for material selection.

  • 321.
    Jacobsson, Jonny
    et al.
    Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg, Sweden / Research and Technology Department, GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Brederholm, Anssi
    Aalto University School of Engineering, Helsinki, Finland.
    Hänninen, Hannu
    Aalto University School of Engineering, Helsinki, Finland.
    Weldability Study of Superalloys Waspaloy® and Haynes® 282®2016In: 10th International Conference on Trends in Welding Research & 9th International Welding Symposium of Japan Welding Society (9WS), October 11-14, 2016, Tokyo, Japan: Proceedings, 2016, p. 325-328Conference paper (Other academic)
    Abstract [en]

    The weldability of Waspaloy® and Haynes® 282® have been evaluated using the Varestraint weldability test. The experiments reveal that Waspaloy® has a higher susceptibility to hot cracking compared to Haynes® 282®. This conclusion is supported by increased total crack length (10 mm or more) for Waspaloy® when compared to Haynes® 282® in Varestraint test. The cracking in Haynes® 282® seems to be connected with a secondary phase which presumably can be associated with Ti-Mo based MC-type carbide observed in the fusion zone. Also, a surrounding segregated area is present near this secondary phase as well as along the grain boundaries. Furthermore, micro-Vickers hardness results revealed more or less the same weld metal hardness (260-280 HV) but a difference in the base metal hardness. The weld metal hardness of Waspaloy® was lower than that of the base metal hardness, while Haynes® 282® had a higher hardness in comparison.

  • 322.
    Jafari, R.
    et al.
    Tarbiat Modares University, Department of Material Science and Engineering, Tehran, 14 115, Iran.
    Sadeghi, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    High-temperature corrosion performance of HVAF-sprayed NiCr, NiAl, and NiCrAlY coatings with alkali sulfate/chloride exposed to ambient air2019In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, article id 108066Article in journal (Refereed)
    Abstract [en]

    The high-temperature corrosion of high velocity air-fuel (HVAF) thermal spray Ni21Cr, Ni5Al, and Ni21Cr7AlY coatings was investigated at 600 °C for 168 h in ambient air under KCl and 50-50 mol% KCl–K2SO4 salts. Chlorination-oxidation cycle and breakdown of the corrosion products layer were the dominant corrosion mechanism in the chromia-forming Ni21Cr and Ni21Cr7AlY coatings exposed to KCl. KCl–K2SO4 was less corrosive to the chromia-forming coatings as K2SO4 was less reactive to the protective Cr-rich oxide. The alumina-forming NiAl exhibited a better corrosion performance under KCl, though it partially suffered from selective sulfidation when exposed to the mixed salt. © 2019 Elsevier Ltd

  • 323.
    Jafari, R.
    et al.
    Tarbiat Modares University, Department of Material Science and Engineering, Tehran, 14115, Iran.
    Sadeghimeresht, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Shahrabi Farahani, T.
    Tarbiat Modares University, Department of Material Science and Engineering, Tehran, 14115, Iran.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    KCI-induced corrosion behavior of HVAF-sprayed Ni-based coatings in ambient air2017In: Proceedings of the International Thermal Spray Conference & Exposition (ITSC 2017), Curran Associates, Inc. , 2017, Vol. 2, p. 946-950Conference paper (Refereed)
    Abstract [en]

    It is well known that the presence of KCl deposited on superheater tubes in biomass- and waste-fired boilers leads to a severe corrosion and premature damage. In order to protect such critical components which are routinely exposed to aggressive environments, thermal spray coatings are frequently proposed as a potential solution. By virtue of the techno-commercial benefits that provides as a direct outcome of its ability to cost-effectively deposit coatings virtually free of porosity and in situ formed oxides, the high velocity air-fuel (HVAF) process offers a particularly attractive approach. In the present work, the influence of KCl on the oxidation behavior of four HVAF-sprayed Ni-based coatings (Ni21Cr, Ni5AI, Ni21Cr7AI1Y, and Ni21Cr9Mo) has been investigated. The coatings were deposited onto specimens of 16Mo3 steel, a widely used boiler tube material. High temperature corrosion tests were carried out in ambient air at 600°C, with 0.1 mg/cm2 KCl being sprayed onto the samples prior to the exposure. Uncoated substrates and an identical test environment without KCl were used as reference. SEM/EDS and XRD techniques were utilized to characterize the as-sprayed and exposed samples. The results showed that the small addition of KCl significantly accelerated damage to the coatings. It was further revealed that the alumina-forming NiAl coating was capable of forming a more protective oxide scale compared to other chromia and mixed-oxide scale forming coatings. In general, the oxidation resistance of the coatings based on the kinetic studies had the following ranking (from the best to the worst): NiAl >NiCr> NiCrAlY> NiCrMo. © Copyright 2017 by DVS Media GmbH. All rights reserved.

  • 324.
    Jafari, R.
    et al.
    Department of Material Science and Engineering, Tarbiat Modares University, Tehran, Iran.
    Sadeghimeresht, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Shahrabi Farahani, T.
    Department of Material Science and Engineering, Tarbiat Modares University, Tehran, Iran .
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    KCl-induced corrosion behavior of HVAF-sprayed Ni-based coatings in ambient air2017Conference paper (Other academic)
  • 325.
    Jafari, Reza
    et al.
    Tarbiat Modares University, Department of Material Science and Engineering, Tehran, Iran.
    Sadeghimeresht, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Shahrabi Farahani, Taghi
    Tarbiat Modares University, Department of Material Science and Engineering, Tehran, Iran.
    Huhtakangas, Matti
    M. H. Engineering AB, Karlskoga, Sweden .
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    KCl-Induced High Temperature Corrosion Behavior of HVAF-Sprayed Ni-Based Coatings in Ambient Air2018In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 27, no 3, p. 500-511Article in journal (Refereed)
    Abstract [en]

    KCl-induced high temperature corrosion behavior of four HVAF-sprayed Ni-based coatings (Ni21Cr, Ni5Al, Ni21Cr7Al1Y, and Ni21Cr9Mo) under KCl deposit has been investigated in ambient air at 600°C up to 168h. The coatings were deposited onto 16Mo3 steel - a widely used boiler tube material.Uncoated substrate, 304L and Sanicro25 were used as reference materials in the test environment.SEM/EDS and XRD techniques were utilized to characterize the as-sprayed and exposed samples.The results showed that the small addition of KCl significantly accelerated degradation to the coatings. All coatings provided better corrosion resistance compared to the reference materials. The alumina-forming Ni5Al coating under KCl deposit was capable of forming a more protective oxide scale compared to the chromia-forming coatings as penetration of Cl through diffusion paths was hindered. Both active corrosion and chromate formation mechanisms were found to be responsible for Page 1 of 23ASM the corrosion damages. The corrosion resistance of the coatings based on the microstructure analysis and kinetics had the following ranking (from the best to worst): Ni5Al >Ni21Cr> Ni21Cr7Al1Y>Ni21Cr9Mo.

  • 326.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Welding Technology.
    Modelling of cathode-plasma interaction in short high-intensity electric arc: Application to Gas Tungsten Arc Welding2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In arc welding the quality of the weld is strongly influenced by the thermal history of the workpiece which is itself governed by the electric arc heat source. The models for predicting weld properties thus need a good evaluation of the distribution of the heat input from thearc to the workpiece. To have a predictive model of arc heat source it is necessary to take into account the cathode and its coupling with the plasma. The coupling allows to calculate the temperature and current density distributions along the cathode surface rather than prescribing them. This thesis focuses on the arc-cathode coupling for a plasma assumed to be in local thermal equilibrium. A self-consistent coupling boundary model for high-intensity electric arc on a refractory cathode (thoriated tungsten) was developed accounting for the physics of the sub-layers of the cathode layer and the non-uniformity of the cathode surface physical state. The cathode layer model accounts for the non-equilibria in the cathode layer. It was tested in one-dimensional calculations and then extended to a cathode-plasma coupling boundary condition for gas tungsten arc implemented in OpenFOAM. Different modelling assumptions commonly used for developing the model were questioned and investigated. It was checked that the secondary electron emission is negligible compared to the effect of emitted electrons and ions. It was verified that it is justified to neglect the space charge of emitted electron when calculating the cathode surface electric field. It was verified that Richardson-Dushman electron emission law supplemented with Schottky correction is used within its domain of validity in GTA applications even for low work function emitters. It was shown that the radiative absorption of the cathode surface is not negligible compared to the radiative emission. The cathode layer model was also further developed to take into account the in homogeneity of the cathode material. It was shown that the cathode in homogeneityhas a significant effect on the size of the arc attachment and consequently on the cathode surface and the plasma temperature. Good agreement was obtained with the measured cathode surface and plasma temperatures without imposing any adjustable parameters. The results showed that the proposed model, which is only based on physical principles, is ableto predict the trends observed experimentally.

  • 327.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Modelling of Electric Arc Welding: arc-electrode coupling2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Arc welding still requires deeper process understanding and more accurateprediction of the heat transferred to the base metal. This can be provided by CFD modelling.Most works done to model arc discharge using CFD consider the arc corealone. Arc core simulation requires applying extrapolated experimental data asboundary conditions on the electrodes. This limits the applicability. To become independent of experimental input the electrodes need to be included in the arcmodel. The most critical part is then the interface layer between the electrodesand the arc core. This interface is complex and non-uniform, with specific physicalphenomena.The present work reviews the concepts of plasma and arc discharges that areuseful for this problem. The main sub-regions of the model are described, andtheir dominant physical roles are discussed.The coupled arc-electrode model is developed in different steps. First couplingsolid and fluid regions for a simpler problem without complex couplinginterface. This is applied to a laser welding problem using the CFD softwareOpenFOAM. The second step is the modelling of the interface layer betweencathode and arc, or cathode layer. Different modelling approaches available inthe literature are studied to determine their advantages and drawbacks. One ofthem developed by Cayla is used and further improved so as to satisfy the basicprinciples of charge and energy conservation in the different regions of thecathode layer. A numerical procedure is presented. The model, implementedin MATLAB, is tested for different arc core and cathode conditions. The maincharacteristics calculated with the interface layer model are in good agreementwith the reference literature. The future step will be the implementation of theinterface layer model in OpenFOAM.

  • 328.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Choquet, Isabelle
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    A review of cathode-arc coupling modeling in GTAW2016In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 60, no 4, p. 821-835Article in journal (Refereed)
    Abstract [en]

    Material properties of welds are strongly influenced by the thermal history, including the thermo-fluid and electromagnetic phenomena in the weld pool and the arc heat source. A necessary condition for arc heat source models to be predictive is to include the plasma column, the cathode, and the cathode layer providing their thermal and electric coupling. Different cathode layer models based on significantly different physical assumptions are being used. This paper summarizes today’s state of the art of cathode layer modeling of refractory cathodes used in GTAW at atmospheric pressure. The fundamentals of the cathode layer and its physics are addressed. The main modeling approaches, namely (i) the diffusion approach, (ii) the partial LTE approach, and (iii) the hydrodynamic approach are discussed and compared. The most relevant publications are systematically categorized with regard to the respective physical phenomena addressed. Results and process understanding gained with these models are summarized. Finally, some open questions are underlined.

  • 329.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nilsson, Håkan
    Chalmers University of Technology.
    Effect of cathode model on arc attachment for short high-intensity arc on a refractory cathode2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 3 November 2016, p. 1-17, article id 485201Article in journal (Other academic)
    Abstract [en]

    Various models coupling the refractory cathode, the cathode sheath and the arc at atmospheric pressure exist. They assume a homogeneous cathode with a uniform physical state, and differ by the cathode layer and the plasma arc model. However even the most advanced of these models still fail in predicting the extent of the arc attachment when applied to short high-intensity arcs such as gas tungsten arcs. Cathodes operating in these conditions present a non-uniform physical state. A model taking into account the first level of this non-homogeneity is proposed based on physical criteria. Calculations are done for 5 mm argon arcs with a thoriated tungsten cathode. The results obtained show that radiative heating and cooling of the cathode surface are of the same order. They also show that cathode inhomogeneity has a significant effect on the arc attachment, the arc temperature and pressure. When changing the arc current (100 A, 200 A) the proposed model allows predicting trends observed experimentally that cannot be captured by the homogeneous cathode model unless restricting a priori the size of the arc attachment. The cathode physics is thus an important element to include to obtain a comprehensive and predictive arc model

  • 330.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nilsson, Håkan
    Chalmers University of Technology.
    Modelling of electrode-arc coupling in electric arc welding2014In: Proceedings of The 6th International Swedish Production Symposium 2014 16-18 September 2014 / [ed] Johan Stahre, Björn Johansson,Mats Björkman, 2014, p. 1-8Conference paper (Refereed)
    Abstract [en]

    Modelling of the arc in electric arc welding is significant to achieve a better pro-cess understanding, thus gain better weld quality and a more efficient production process.It requires knowing the conditions at the surfaces of the anode and cathode. These condi-tions are very difficult to set from measurements and should be calculated. This requiresmodelling the complex physics of the electrode layer coupling electrode and arc. Thispaper presents a self-consistent electrode layer model that 1) is suited to welding applica-tions, 2) accounts for the known physics taking place, and 3) satisfies the basic conservationrequirements. The model is tested for different conditions. Its potentiality for welding ap-plications is shown through calculations coupling plasma arc, electrode and cathode layermodels. The calculations are done for both tungsten and thoriated tungsten electrode.

  • 331.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Mechanical Engineering. University West, Department of Engineering Science, Division of Welding Technology.
    Nilsson, Håkan
    Chalmers University of technology, Applied Mechanics.
    Numerical modelling of shielding gas flow and heat transfer in laser welding process2012In: Proceedings of the 5th International Swedish Production Symposium, SPS12 / [ed] The Swedish Production Academy on October 2012, Linköping, 2012, , p. 7p. 1-7Conference paper (Refereed)
    Abstract [en]

    In the present work a three-dimensional model has been developed to study shieldinggas flow and heat transfer in a laser welding process using computational fluid dynamics.This investigation was motivated by problems met while using an optical system totrack the weld path. The aim of this study was to investigate if the shielding gas flowcould disturb the observation area of the optical system. The model combines heatconduction in the solid work piece and thermal flow in the fluid region occupied by theshielding gas. These two regions are coupled through their energy equations so asto allow heat transfer between solid and fluid region. Laser heating was modelled byimposing a volumetric heat source, moving along the welding path. The model wasimplemented in the open source software OpenFOAM and applied to argon shieldinggas and titanium alloy Ti6Al4V base metal. Test cases were done to investigate theshielding gas flow produced by two components: a pipe allowing shielding the melt,and a plate allowing shielding the weld while it cools down. The simulation results confirmedthat these two components do provide an efficient shielding. They also showedthat a significant amount of shielding gas flows towards the observation area of the opticalsystem intended to track the weld path. This is not desired since it could transportsmoke that would disturb the optical signal. The design of the shielding system thusneeds to be modified.

  • 332.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Nilsson, Håkan
    Chalmers University of Technology, Department of Mechanics and Maritime Sciences, 412 96 Gothenburg, Sweden.
    Jasak, Hrvoje
    University of Zagreb, Faculty of Mechanical Engineering and Naval Architecture, 10 000 Zagreb, Croatia.
    Coupling boundary condition for high-intensity electric arc attached on a non-homogeneous refractory cathode2018In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 222, p. 31-45Article in journal (Refereed)
    Abstract [en]

    The boundarycoupling high-intensity electricarc and refractory cathode is characterized bythree sub- layers: the cathode sheath,the Knudsen layerand the pre-sheath. A self-consistent coupling boundarycondition accounting for these three sub-layers is presented; its novel propertyis to take into account a non-uniform distribution of electronemitters on the surface of the refractory cathode. This non- uniformity is due to cathode non-homogeneity induced by arcing.The computational model is appliedto a one-dimensional test case to evaluate the validity of different modelingassumptions. It is also applied coupling a thoriated tungstencathode with an argon plasma(assumed to be in local thermal equilibrium) to compare the calculation results with uniform and non-uniform distribution of the electron emitters to experimental measurements. The resultsshow that the non-uniformity of the electronemitters’ distribution has a significant effect on the calculated properties. It leads to good agreementwith the cathode surfacetemperature, and with the plasmatemperature in the hottest region.Some differences are observedin colder plasmaregions, where deviation from local thermalequilibrium is known to occur.

  • 333.
    Javidi Shirvan, Alireza
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nilsson, Håkan
    Chalmers University of Technology.
    Jasak, Hrvoje
    Chalmers University of Technology.
    Coupling boundary condition for high-intensity electricarc attached on a non-homogeneous refractory cathode2016In: Article in journal (Other academic)
  • 334.
    Jellbo, Oskar
    et al.
    University West, Department of Engineering Science, Division of Process and Product Development.
    Sjöström, Rikard
    PLANs forsknings- och tillämpningskonferens 2006: effektivitet och samverkan i försörjningskedjor2006Conference proceedings (editor) (Other academic)
  • 335.
    Jiang, Janna
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Fasth, Angelica
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylen, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Choi, W.B.
    Center for Thermal Spray Research, Stony Brook, NY, USA.
    Microindentation and Inverse Analysis to Characterize Elastic-Plastic Properties for Thermal Sprayed Ti2AlC and NiCoCrAlY2009In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 18, no 2, p. 194-200Article in journal (Refereed)
    Abstract [en]

    Elastic-plastic material properties for HVOF sprayed Ti2AlC (sprayed with Maxthal 211 powder) and plasma sprayed NiCoCrAlY coatings were investigated using modeling and experimental Berkovich microindentation. Optical microstructure evaluations were also performed. The theories of Hertz, Oliver and Pharr were combined with finite element analysis for extracting the material properties. Empirically based material models for both thermal sprayed Ti2AlC and NiCoCrAlY coatings are proposed.

  • 336.
    Jiang, Janna
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Numerical modelling of the compression behaviour of single-crystalline MAX-phase materials2010In: Advanced materials research, ISSN 1022-6680, Vol. 89-91, p. 262-267Article in journal (Refereed)
    Abstract [en]

    In this article a numerical model to describe the mechanical behaviour of nanophased singlecrystalline Ti3SiC2 is proposed. The approach is a two dimensional finite element periodic unit cell consisting of an elastic matrix interlayered with shear deformable slip planes which obey the Hill's yield criterion. The periodic unit cell is used to predict compression material behaviour of Ti3SiC2 crystals with arbitrary slip plane orientations. Stress strain relationships are derived for Ti 3SiC2, and the effect of slip plane volume fraction as well as orientation of the slip planes are investigated. The two main deformation mechanisms of the material namely; ordinary slip and so called kinking are considered in the study.

  • 337.
    Jiang, Janna
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Object-oriented finite element analysis to simulate microindentation of thermal sprayed MAX-phase coatings2009In: Proceedings - 2009 International Conference on Computer Modeling and Simulation, ICCMS 2009, 2009, p. 337-341Conference paper (Other (popular science, discussion, etc.))
  • 338.
    Jonnalagadda, K.P.
    et al.
    Linköping University.
    Mahade, Satyapal
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Curry, Nicholas
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Li, X-H.
    Siemens Industrial Turbomachinary, Finspång, Sweden.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Nylen, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Peng, R.L.
    Trebacher Indiustrie, Austria.
    Hot corrosion behavior of multi-layer suspension plasma sprayed Gd2Zr2O7 /YSZ thermal barrier coatings2016In: Thermal Spray 2016: Proceedings from the International Thermal Spray Conference in Shanghai, P.R China, May 10-12, 2016, DVS Media GmbH , 2016, Vol. 324, p. 261-266Conference paper (Refereed)
  • 339.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Linköping, 581 83, Sweden.
    Kramer, Stephanie
    Linköping University, Department of Management and Engineering, Linköping, 581 83, Sweden.
    Zhang, Pimin
    Linköping University, Department of Management and Engineering, Linköping, 581 83, Sweden.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Linköping, 581 83, Sweden.
    Mahade, Satyapal
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Curry, Nicholas
    Treibacher Industrie AG, Austria.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finsping, SE-61283, Sweden.
    Failure of multi-layer suspension plasma sprayed thermal barrier coatings in the presence of Na2SO4 and NaCI at 900 °C2018In: Proceedings of the International Thermal Spray Conference, Vol. 2018-May, p. 8-15Article in journal (Refereed)
    Abstract [en]

    The current investigation focuses on understanding the influence of a columnar microstructure and a sealing layer on the corrosion behavior of suspension plasma sprayed (SPS) thermal barrier coatings (TBCs). Two different TBC systems were studied in this work. First is a double layer made of a composite of gadolinium zirconate + yttria stabilized zirconia (YSZ) deposited on top of YSZ. Second is a triple layer made of dense gadolinium zirconate deposited on top of gadolinium zirconate + YSZ over YSZ. Cyclic corrosion tests were conducted between 25 °C and 900 °C with an exposure time of 8h at 900 °C. 75 wt. % Na2SO4 + 25 wt.% NaCI were used as the corrosive salts at a concentration of 6 mg/cm2. Scanning electron microscopy analysis of the samples' cross-sections showed that severe bond coat degradation had taken place for both TBC systems and the extent of bond coat degradation was relatively higher in the triple layer system. It is believed that the sealing layer in the triple layer system reduced the number of infiltration channels for the molten salts which resulted in overflowing of the salts to the coating edges and caused damage to develop relatively more from the edge. © 2018 ASM International® All rights reserved.

  • 340.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Mahade, Satyapal
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Curry, Nicholas
    Treibacher Ind AG, Althofen, Austria.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Nylen, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Hot Corrosion Mechanism in Multi-Layer Suspension Plasma Sprayed Gd2Zr2O7 /YSZ Thermal Barrier Coatings in the Presence of V2O5 + Na2SO42017In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 26, no 1-2, p. 140-149Article in journal (Refereed)
    Abstract [en]

    This study investigates the corrosion resistance of two-layer Gd2Zr2O7/YSZ, three-layer dense Gd2Zr2O7/ Gd2Zr2O7/YSZ, and a reference single-layer YSZ coating with a similar overall top coat thickness of 300-320 µm. All the coatings were manufactured by suspension plasma spraying resulting in a columnar structure except for the dense layer. Corrosion tests were conducted at 900 °C for 8 h using V2O5 and Na2SO4 as corrosive salts at a concentration of approximately 4 mg/cm2. SEM investigations after the corrosion tests show that Gd2Zr2O7-based coatings exhibited lower reactivity with the corrosive salts and the formation of gadolinium vanadate (GdVO4), accompanied by the phase transformation of zirconia was observed. It is believed that the GdVO4 formation between the columns reduced the strain tolerance of the coating and also due to the fact that Gd2Zr2O7 has a lower fracture toughness value made it more susceptible to corrosion-induced damage. Furthermore, the presence of a relatively dense layer of Gd2Zr2O7 on the top did not improve in reducing the corrosion-induced damage. For the reference YSZ coating, the observed corrosion-induced damage was lower probably due to combination of more limited salt penetration, the SPS microstructure and superior fracture toughness of YSZ.

  • 341.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Mahade, Satyapal
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Kramer, Stephanie
    Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Zhang, Pimin
    Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Curry, Nicholas
    Treibacher Industrie AG, Althofen, Austria.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB,Finspång,Sweden.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Failure of Multilayer Suspension Plasma Sprayed Thermal Barrier Coatings in the Presence of Na2SO4 and NaCl at 900 °C2019In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, no 1-2, p. 212-222Article in journal (Refereed)
    Abstract [en]

    The current investigation focuses on understanding the influence of a columnar microstructure and a sealing layer on the corrosion behavior of suspension plasma sprayed thermal barrier coatings (TBCs). Two different TBC systems were studied in this work. First is a double layer made of a composite of gadolinium zirconate + yttria stabilized zirconia (YSZ) deposited on top of YSZ. Second is a triple layer made of dense gadolinium zirconate deposited on top of gadolinium zirconate + YSZ over YSZ. Cyclic corrosion tests were conducted between 25 and 900 °C with an exposure time of 8 h at 900 °C. 75 wt.% Na2SO4 + 25 wt.% NaCl were used as the corrosive salts at a concentration of 6 mg/cm2. Scanning electron microscopy analysis of the samples’ cross sections showed that severe bond coat degradation had taken place for both the TBC systems, and the extent of bond coat degradation was relatively higher in the triple-layer system. It is believed that the sealing layer in the triple-layer system reduced the number of infiltration channels for the molten salts which resulted in overflowing of the salts to the sample edges and caused damage to develop relatively more from the edge.

  • 342.
    Jonnalagadda, Krishna Praveen
    et al.
    Linkoping University, Department of Manangement and Engineering,Linkoping, Sweden.
    Peng, Ru Lin
    Linkoping University, Department of Manangement and Engineering,Linkoping, Sweden.
    Mahade, Satyapal
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Nylén, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Curry, Nicholas
    Treibacher Industrie AG, Austria.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspang, Sweden.
    Hot corrosion behavior of multi-layer suspension plasma sprayed Gd2Zr2O7/YSZ thermal barrier coatings2017In: InterCeram: International Ceramic Review, ISSN 0020-5214, Vol. 66, no 5, p. 180-184Article in journal (Refereed)
    Abstract [en]

    This study investigates the corrosion resistance of double layer Gd2Zr2O7/YSZ, triple layer dense Gd2Zr2O7 / Gd2Zr2O7/YSZ and a reference single layer YSZ coating with a similar overall top coat thickness of 300-320 Όm. All the coatings were manufactured by suspension plasma spraying (SPS), resulting in a columnar structure. Corrosion tests were conducted at 900°C for 8 hours using vanadium pentoxide and sodium sulphate as corrosive salts at a concentration of 4 mg/cm2. SEM investigations after the corrosion tests show that Gd2Zr2O7 coatings exhibited lower corrosion resistance than the reference material, YSZ. Reaction between the corrosive salts and Gd2Zr2O7 results in the formation of gadolinium vanadate ( GdVO4) along the top surface and between the columns. While the stresses due to phase transformation of zirconia can be relieved to some extent by realigning of the columns in the top coat, it is believed that GdVO4 formation between the columns, along with low fracture toughness of Gd2Zr2O7 had resulted in lower corrosion resistance. Furthermore, the presence of a relatively dense layer of Gd2Zr2O7 on the top, as a preventive layer for salt infiltration, did not improve the corrosion resistance.

  • 343.
    Jorge, Vinicius Lemes
    et al.
    Universidade Federal de Uberlândia – UFU, Centro para Pesquisa e Desenvolvimento de Processos de Soldagem – Laprosolda, Uberlândia, MG, Brasil.
    Alves Santos, Cesar Henrique
    Universidade Federal de Uberlândia – UFU, Centro para Pesquisa e Desenvolvimento de Processos de Soldagem – Laprosolda, Uberlândia, MG, Brasil.
    Scotti, Fernando Matos
    Universidade Federal de Uberlândia – UFU, Centro para Pesquisa e Desenvolvimento de Processos de Soldagem – Laprosolda, Uberlândia, MG, Brasil.
    Larquer, Thiago Resende
    Universidade Federal de Uberlândia – UFU, Centro para Pesquisa e Desenvolvimento de Processos de Soldagem – Laprosolda, Uberlândia, MG, Brasil.
    Mota, Carolina Pimenta
    Instituto Federal de Educação, Ciência e Tecnologia do Triângulo Mineiro – IFTM, Patos de Minas, MG, Brasil.
    Reis, Ruham Pablo
    Universidade Federal de Uberlândia – UFU, Centro para Pesquisa e Desenvolvimento de Processos de Soldagem – Laprosolda, Uberlândia, MG, Brasil.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Welding Technology. Universidade Federal de Uberlândia – UFU, Centro para Pesquisa e Desenvolvimento de Processos de Soldagem – Laprosolda, Uberlândia, MG, Brasil.
    Development and Evaluation of Wire Feeding Pulsing Techniques for Arc Welding: Desenvolvimento e Avaliação de Técnicas para Pulsação da Alimentação de Arame em Soldagem a Arco2018In: Soldagem & Inspeção, ISSN 0104-9224, E-ISSN 1980-6973, Vol. 23, no 3, p. 326-339Article in journal (Refereed)
    Abstract [en]

    Applying pulsed wire feeding techniques is one of the new approaches for welding, such as for GTAW and GMAW. However, these techniques invariably require specific feeders and/or welding torches, limiting its implementation due to the high costs of the equipment. Thus, the current work aims to introduce and exploratorily evaluate techniques to pulse the wire feeding that works independently from the feeder and/or torch. The first technique is electromechanically driven, and the second one based on electromagnetics. The effects of amplitude and frequency of the pulsed feeding were evaluated in terms of weld bead formation over plates and of the corresponding electric signals. For GTAW, the pulsed wire feeding is capable of modifying the weld bead and make the metal transfer from the wire to the pool more regular. For GMAW, it was found that the pulsing of the wire feeding can interfere with the process, being capable of turning an irregular globular metal transfer into a regular one, while decreasing the mean current and affecting the bead formation. Overall, it is concluded that pulsed wire feeding can affect the processes, even when made independently from the feeder and torch, opening a field for development of derivative welding technologies.

  • 344.
    Jorge, Vinicius Lemes
    et al.
    University of Uberlandia, Center for Research and Development of Welding Processes of the Federal, Uberlandia, Brazil.
    Gohrs, Raul
    IMC Soldagem, Palhoça, Brazil.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Welding Technology.
    Active power measurement in arc welding and its role in heat transfer to the plate2017In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 61, no 4, p. 847-856Article in journal (Refereed)
    Abstract [en]

    A contemporary paper claimed that a method using the resistance of impedance (active power) for arc power calculation is more accurate than the conventional approach, with consequences on the actual heat transfer to the plate. However, despite the comprehensive reasoning, no heat-related results are shown in this intriguing paper to support the claim. Thus, the aim of this work was to apply the proposed method for determining the weight of active power in the total arc power. A series of weldments was carried out, by using GTAW in constant and pulsed current modes and short-circuiting GMAW with different inductance settings. The effect of the active power on the heat transfers to the plate was assessed by both bead cross-section geometries and calorimetry. The results showed that even a significant fraction of active power of the total power was reached, no changes in bead geometry or heat input were found. A review of the assumptions used in the primal paper showed that an arc is better represented by an ER circuit than by an RLC circuit. As a conclusion, the arc as a reactance-free load presents no component such as non-active power and the conventional approaches are accurate methods to measure arc power, representing the actual active power. © 2017, The Author(s).

  • 345.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Coating formation by solution precursor plasma spraying and prospects for powder-solution hybrid processing2016Conference paper (Other academic)
  • 346.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Experiences of spraying fine powders dissolved in alcohol or water2016Conference paper (Other academic)
  • 347.
    Joshi, Shrikant V.
    et al.
    Defence Metallurgical Research Lab., Hyderabad, India.
    Ganguli, D.
    Central Glass and Ceramic Research Inst., Calcutta, India.
    Plasma spraying of ceramic powders produced by the sol-gel technique1992In: Metals Materials and Processes, ISSN 0970-423X, Vol. 4, no 1, p. 33-42Article in journal (Refereed)
    Abstract [en]

    The development of plasma-sprayed protective layers to enhance the surface properties of critical engineering components represents one of the most promising achievements of materials technology in recent times. The important aspects associated with plasma spraying of ceramic powders are discussed and the influence of the powder characteristics on the quality of sprayed coatings is highlighted. The advantages of the sol-gel technique for preparing spray grade powders are briefly outlined. The sol-gel synthesis of a Yttria-stabilized-zirconia powder is discussed as a case study. Results of powder characterization studies and evaluation of its plasma sprayed coating are also presented.

  • 348.
    Joshi, Shrikant V.
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Goel, Sneha
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Björklund, S.
    Wiklund, U.
    Hybrid powder-suspension Al2O3-ZrO2 coatings by axial plasma spraying: Processing, characteristics & tribological behavior2017Conference paper (Other academic)
  • 349. Joshi, Shrikant V.
    et al.
    Sivakumar, G.
    Hybrid Processing with Powders and Solutions: A Novel Approach to Deposit Composite Coatings2015In: Journal of Thermal Spray Technology, Vol. 24, no 7, p. 1166-1186Article in journal (Refereed)
    Abstract [en]

    Thermal spraying employing either solution precursor or suspension feedstock offers an exciting opportunity to obtain coatings with microstructures and characteristics that differ vastly compared to those conventionally produced using spray-grade powders. Both solution precursor plasma spray and suspension plasma spray techniques have been explored extensively in recent years for depositing wide ranging ceramic coatings for various functional applications. Encouraged by the properties achieved using the above solution-based feedstocks, a hybrid approach involving dual injection of solutions and powders, either simultaneously or sequentially, has been proposed and demonstrated to yield novel coating architectures. Although prior work on such hybrid processing is very limited, this overview seeks to present the concept, outline associated challenges, and demonstrate its efficacy to realize coatings with exciting and unusual properties using some illustrative examples. © 2015 ASM International

  • 350. Joshi, Shrikant V.
    et al.
    Sivakumar, R.
    An Analytical Approach to Plasma Spraying1993In: Plasma spraying: Theory and applications / [ed] Suryanarayanan, R., New Jersey: World Scientific, 1993, p. 121-137Chapter in book (Refereed)
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