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  • 301.
    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.

  • 302.
    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

  • 303.
    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.

  • 304.
    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.

  • 305.
    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, 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 electricarc attached on a non-homogeneous refractory cathode2018In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, p. 31-45Article in journal (Refereed)
  • 306.
    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.

  • 307.
    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.))
  • 308.
    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)
  • 309.
    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.

  • 310.
    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.

  • 311.
    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.

  • 312.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköpings universitet, Konstruktionsmaterial.
    Zhang, Pimin
    Linköpings universitet, Konstruktionsmaterial.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Department of Engineering Science, University West, Trollhättan.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång.
    Peng, Ru Lin
    Linköpings universitet, Konstruktionsmaterial.
    Hot gas corrosion and its influence on the thermal cycling performance of suspension plasma spray TBCs2019In: Proceedings of ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition, New York, NY: American Society of Mechanical Engineers , 2019, article id GT2019-90104,, V006T24A001Conference paper (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs) manufactured with suspension plasma spray (SPS) are promising candidates for use in gas turbines due to their high strain tolerance during thermal cyclic fatigue (TCF). However, corrosion often occurs alongside thermal fatigue and coating durability under these conditions is highly desirable. The current study focuses on understanding the corrosion behavior and its influence on the thermal cyclic fatigue life of SPS TBCs. Corrosion tests were conducted at 780 OC using a mixed-gas (1SO2-0.1CO-20CO2-N2(bal.) in vol. %) for 168h. They were later thermally cycled between 100-1100 ⁰C with a 1h hold time at 1100 ⁰C. Corrosion test results indicated that the damage predominantly started from the edges and a milder damage was observed at the center. Nickel sulfide was observed on top of the top coat and also in the columnar gaps of the top coat. Chromium oxides were observed inside the top coat columnar gaps but close to the bond coat/top coat interface. They were believed to reduce the strain tolerance of SPS TBCs to an extent and also amplify the thermal mismatch stresses during TCF tests. This, together with a fast growth of alumina during the TCF, resulted in a significant drop in the TCF life compared to the standard TCF tests.

  • 313.
    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.

  • 314.
    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).

  • 315.
    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)
  • 316.
    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)
  • 317.
    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.

  • 318.
    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)
  • 319.
    Joshi, Shrikant V.
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Nylén, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Advanced Coatings by Thermal Spray Processes2019In: Technologies, E-ISSN  2227-7080, Vol. 7, no 4, p. 1-14, article id 79Article in journal (Refereed)
    Abstract [en]

    Coatings are pivotal in combating problems of premature component degradation in aggressive industrial environments and constitute a strategic area for continued development. Thermal spray (TS) coatings offer distinct advantages by combining versatility, cost-effectiveness, and the ability to coat complex geometries without constraints of other in-chamber processes. Consequently, TS techniques like high-velocity oxy-fuel (HVOF) and atmospheric plasma spray (APS) are industrially well-accepted. However, they have reached limits of their capabilities while expectations from coatings progressively increase in pursuit of enhanced efficiency and productivity. Two emerging TS variants, namely high-velocity air-fuel (HVAF) and liquid feedstock thermal spraying, offer attractive pathways to realize high-performance surfaces superior to those hitherto achievable. Supersonic HVAF spraying provides highly adherent coatings with negligible porosity and its low processing temperature also ensures insignificant thermal ‘damage’ (oxidation, decarburization, etc.) to the starting material. On the other hand, liquid feedstock derived TS coatings, deposited using suspensions of fine particles (100 nm–5 µm) or solution precursors, permits the production of coatings with novel microstructures and diverse application-specific architectures. The possibility of hybrid processing, combining liquid and powder feedstock, provides further opportunities to fine tune the properties of functional surfaces. These new approaches are discussed along with some illustrative examples.

  • 320. 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)
  • 321. Joshi, Shrikant V.
    et al.
    Srivastava, P.
    Lifetime determining factors during thermal cycling of zirconia based thermal barrier coatings1995In: Surface Engineering, ISSN 0267-0844, E-ISSN 1743-2944, Vol. 11, no 3, p. 233-239Article in journal (Refereed)
    Abstract [en]

    Plasma sprayed yttria stabilised zirconia (YSZ) coatings were investigated to assess the factors influencing their durability during thermal cycling. For any given powder, the best performance was found to be achieved at an optimum plasma arc current, all other spray parameters being held constant. The YSZ overlayer thickness was found to be an important lifetime determining factor. Use of a NiCoCrAlY bond coat instead of Ni–Cr led to a substantial improvement in coating lifetime, with the enhancement provided by NiCoCr AlY becoming more pronounced with increasing porosity level of the ceramic overlayer. A post-coating heat treatment was also found to be beneficial to coating longevity. The relative ranking of magnesium zirconate and YSZ coatings was found to depend upon the thermal cycle adopted during testing, which has important implications in designing accelerated tests to evaluate coating performance.

  • 322.
    Jäger, Henrik
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Swerea-KIMAB AB, 164 40, Stockholm, Sweden.
    Tamil Alagan, Nageswaran
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Holmberg, Jonas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Swerea-IVF AB, 431 22, Mölndal, Sweden.
    Beno, Tomas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Vretland, Anders
    GKN Aerospace Engine Systems AB, 461 81, Trollhättan, Sweden.
    EDS Analysis of Flank Wear and Surface Integrity in Machining of Alloy 718 with Forced Coolant Application2016In: Procedia CIRP, ISSN 2212-8271, E-ISSN 2212-8271, Vol. 45, p. 271-274Article in journal (Refereed)
    Abstract [en]

    There has been extensive research on forced coolant application, usually known as high pressure coolant, in machining heat resistant super alloys. This technology has shown to improve the tool life, chip segmentation, surface integrity and reduce the temperature in the cutting zone. A number of studies have been done on hydraulic parameters of the coolant. This study has been focused on residues on the flank face of the insert and residual stress on the workpiece surface generated by regular and modified cutting inserts. To identify any residual elements, analysis were done by energy dispersive X-ray spectrometer, EDS, on regular as well as modified inserts in combination with forced coolant application on both rake and flank face. The investigations have shown that the temperature gradient in the insert has changed between the regular and modified cutting inserts and that the tool wear and surface roughness is significantly affected by the modified cutting tool.

  • 323.
    Kanhed, Satish
    et al.
    Laboratory for Biomaterials, Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur, 208016, Uttar Pradesh, India.
    Awasthi, Shikha
    Laboratory for Biomaterials, Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur, 208016, Uttar Pradesh, India.
    Goel, Sneha
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Pandey, Aditi
    Laboratory for Biomaterials, Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur, 208016, Uttar Pradesh, India.
    Sharma, Rajeev
    Laboratory for Biomaterials, Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur, 208016, Uttar Pradesh, India.
    Upadhyaya, Anish
    Powder Metallurgy Laboratory, Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur, 208016, Uttar Pradesh, India.
    Balani, Kantesh
    Laboratory for Biomaterials, Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur, 208016, Uttar Pradesh, India.
    Porosity distribution affecting mechanical and biological behaviour of hydroxyapatite bioceramic composites2017In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 43, no 13, p. 10442-10449Article in journal (Refereed)
    Abstract [en]

    The present work aims to the study of developing porosity in hydroxyapatite (HAp) scaffold by using graphite porogen (with 0-30 vol%) followed by engineering the changes achieved by conventional- (CS) and microwave sintering (MS) techniques. The generated porosity was controlled between similar to 6-27% as the porogen concentration increases in HAp scaffold. Voronoi tessellation was utilized in order to evaluate the distribution of pores. The enhanced mechanical properties including fracture toughness (0.83 MPa m(1/2)), fracture strength (7.5 MPa), and hardness (183.7 VHN) were observed for microwave sintered HAp scaffold with 8% porosity. The fitting between porosity and fracture strength elicited that microwave sintered HAp with 8% porosity provides maximum crack-propagation resistance while restricting grain size (similar to 0.23 mu m) and eliciting high extent of sintering (similar to 1.34) because of their rapid heating rates. The cell viability (MTT assay) and cell culture confirm the cytocompatibility of porous HAp for application as bone implant that need accelerated replacement of bone tissues.

  • 324.
    Kanhed, Satish
    et al.
    Biomaterials Processing and Characterization Laboratory Department of Materials Science and Engineering Indian Institute of Technology Kanpur Kanpur-208016, Uttar Pradesh, India.
    Awasthi, Shikha
    Biomaterials Processing and Characterization Laboratory Department of Materials Science and Engineering Indian Institute of Technology Kanpur Kanpur-208016, Uttar Pradesh, India.
    Midha, Swati
    Department of Textile Technology Indian Institute of Technology Delhi New Delhi, 110016, India.
    Nair, Jitin
    Biomaterials Processing and Characterization Laboratory Department of Materials Science and Engineering Indian Institute of Technology Kanpur Kanpur-208016, Uttar Pradesh, India.
    Nisar, Ambreen
    Biomaterials Processing and Characterization Laboratory Department of Materials Science and Engineering Indian Institute of Technology Kanpur Kanpur-208016, Uttar Pradesh, India.
    Patel, Anup Kumar
    Biomaterials Processing and Characterization Laboratory Department of Materials Science and Engineering Indian Institute of Technology Kanpur Kanpur-208016, Uttar Pradesh, India.
    Pandey, Aditi
    Biomaterials Processing and Characterization Laboratory Department of Materials Science and Engineering Indian Institute of Technology Kanpur Kanpur-208016, Uttar Pradesh, India.
    Sharma, Rajeev
    Biomaterials Processing and Characterization Laboratory Department of Materials Science and Engineering Indian Institute of Technology Kanpur Kanpur-208016, Uttar Pradesh, India.
    Goel, Sneha
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Biomaterials Processing and Characterization Laboratory Department of Materials Science and Engineering Indian Institute of Technology Kanpur Kanpur-208016, Uttar Pradesh, India.
    Upadhyaya, Anish
    Powder Metallurgy Laboratory Department of Materials Science and Engineering Indian Institute of Technology Kanpur Kanpur-208016, Uttar Pradesh, India.
    Ghosh, Sourabh
    Department of Textile Technology Indian Institute of Technology Delhi New Delhi, 110016, India.
    Balani, Kantesh
    Biomaterials Processing and Characterization Laboratory Department of Materials Science and Engineering Indian Institute of Technology Kanpur Kanpur-208016, Uttar Pradesh, India.
    Microporous Hydroxyapatite Ceramic Composites as Tissue Engineering Scaffolds: An Experimental and Computational Study2018In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. 20, no 7, article id 1701062Article in journal (Refereed)
    Abstract [en]

    Bone‐tissue engineering mandates the development of multi‐functional bioactive porous hydroxyapatite (HAp) scaffolds. Herein, microwave sintered HAp/ZnO and HAp/Ag composite scaffolds with ≈5–19% porosity are developed using 0–30 vol% graphite as a porogen. The mechanical properties of the porous scaffold are analyzed in detail, revealing that even being more porous, the reinforcement of ZnO (9% porosity, hardness of 2.8 GPa, and toughness of 3.5 MPa.m1/2) has shown to have better hardness and fracture toughness when compared to Ag (5% porosity, hardness of 1.6 GPa, and toughness of 2.6 MPa.m1/2). The flexural strength obtained experimentally are complemented with a finite‐element technique that adopts microstructural features in visualizing the effect of porosity on stress distribution. The antibacterial efficacy and cytocompatibility of these composites are validated by increased metabolic activity and conspicuous cell‐matrix interactions. The anticipation of the results reveal that HAp/ZnO (9% porosity) and HAp/Ag (5% porosity) composites can be used as a potential multi‐functional bone implant scaffolds.

  • 325.
    Karimi Neghlani, Paria
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Electron beam melting of Alloy 718: Influence of process parameters on the microstructure2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Additive manufacturing (AM) is the name given to the technology of building 3D parts by adding layer-by-layer of materials, including metals, plastics, concrete, etc. Of the different types of AM techniques, electron beam melting (EBM), as a powder bed fusion technology, has been used in this study. EBM is used to build parts by melting metallic powders by using a highly intense electron beam as the energy source. Compared to a conventional process, EBM offers enhanced efficiency for the production of customized and specific parts in aerospace, space, and medical fields. In addition, the EBM process is used to produce complex parts for which other technologies would be either expensive or difficult to apply. This thesis has been divided into three sections, starting from a wider window and proceeding to a smaller one. The first section reveals how the position-related parameters (distance between samples, height from build plate, and sample location on build plate) can affect the microstructural characteristics. It has been found that the gap between the samples and the height from the build plate can have significant effects on the defect content and niobium-rich phase fraction. In the second section, through a deeper investigation, the behavior of Alloy 718 during the EBM process as a function of different geometry-related parameters is examined by building single tracks adjacent to each other (track-by-track) andsingle-wall samples (single tracks on top of each other). In this section, the main focus is to understand the effect of successive thermal cycling on microstructural evolution. In the final section, the correlations between the main machine-related parameters (scanning speed, beam current, and focus offset) and the geometrical (melt pool width, track height, re-melted depth, and contact angle) and microstructural (grain structure, niobium-rich phase fraction, and primary dendrite arm spacing) characteristics of a single track of Alloy 718 have been investigated. It has been found that the most influential machine-related parameters are scanning speed and beam current, which have significant effects on the geometry and the microstructure of the single-melted tracks.

  • 326.
    Karimi Neghlani, Paria
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Deng, Dunyong
    Linköping University, Division of Engineering Materials, Linköping, Sweden.
    Sadeghimeresht, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Olsson, Jonas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Ålgårdh, Joakim
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Swerea KIMAB AB, Kista, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Microstructure Development in Track-by-Track Melting of EBM-Manufactured Alloy 7182018In: 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. 643-654Conference paper (Refereed)
    Abstract [en]

    Electron beam melting (EBM) is a powder-bed fusion process within the group of additive manufacturing (AM) technology that is used to fabricate high performance metallic parts. Nickel-Iron base superalloys, such as Alloy 718, are subjected to successive heating and cooling at temperatures in excess of 800 °C during the EBM process. Characterization of the dendritic structure, carbides, Laves and δ-phase were of particular interest in this study. These successive thermal cycles influence the microstructure of the material resulting in a heterogeneous structure, especially in the building direction. Hence, the aim of this study was to gain increased fundamental understanding of the relationship between the processing history and the microstructure formed within a single layer. Different numbers of tracks with equal heights were for this purpose produced, varying from one to ten tracks. All tracks used the same process parameters regardless of number and/or position. Microstructure characteristics (sub-grain structure, grain structure and phases) were analyzed by optical microscopy, scanning electron microscopy equipped with energy disperse spectroscopy and electron backscatter diffraction. The direction of dendrites changed in the overlap zones within the tracks due to re-melting of material in the overlap zone. The primary dendrite arm spacings slightly increased along multi-tracks owing to a slight decrease in cooling rate by addition of the next tracks. Epitaxial growth of grains were observed in all samples due to partial re-melting of grains in previous layers and surface nucleation was also found to occur in all tracks.

  • 327.
    Karimi Neghlani, Paria
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Raza, Tahira
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence of laser exposure time and point distance on 75-μm-thick layer of selective laser melted Alloy 7182018In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 94, no 5-8, p. 2199-2207Article in journal (Refereed)
    Abstract [en]

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

  • 328.
    Karimi Neghlani, Paria
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Sadeghi, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Ålgårdh, Joakim
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Powder Materials & Additive Manufacturing, Swerea KIMAB AB, Kista, 164 40, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    EBM-manufactured single tracks of Alloy 718: Influence of energy input and focus offset on geometrical and microstructural characteristics2019In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 148, p. 88-99Article in journal (Refereed)
    Abstract [en]

    Electron beam melting-powder bed fusion (EBM-PBF) is an additive manufacturing process, which is able to produce parts in layer-by-layer fashion from a 3D model data. Currently application of this technology in parts manufacturing with high geometrical complexity has acquired growing interest in industry. To recommend the EBM process into industry for manufacturing parts, improved mechanical properties of final part must be obtained. Such properties highly depend on individual single melted track and single layer. In EBM, interactions between the electron beam, powder, and solid underlying layer affect the geometrical (e.g., re-melt depth, track width, contact angle, and track height) and microstructural (e.g., grain structure, and primary dendrite arm spacing) characteristics of the melted tracks. The core of the present research was to explore the influence of linear energy input parameters in terms of beam scanning speed, beam current as well as focus offset and their interactions on the geometry and microstructure of EBM-manufactured single tracks of Alloy 718. Increased scanning speed led to lower linear energy input values (<0.9 J/mm) in an specific range of the focus offset (0–10 mA) which resulted in instability, and discontinuity of the single tracks as well as balling effect. Decreasing the scanning speed and increasing the beam current resulted in higher melt pool depth and width. By statistical evaluations, the most influencing parameters on the geometrical features were primarily the scanning speed, and secondly the beam current. Primary dendrite arm spacing (PDAS) slightly decreased by increasing the scanning speed using lower beam current values as the linear energy input decreased. By increasing the linear energy input, the chance of more equiaxed grain formation was high, however, at lower linear energy input, mainly columnar grains were observed. The lower focus offset values resulted in more uniform grains along the 〈001〉 crystallographic direction. © 2018 Elsevier Inc. 

  • 329.
    Karimi Neghlani, Paria
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Sadeghi, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Ålgårdh, Joakim
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. GE Additive | Arcam EBM, Designvägen 2, Mölnlycke, 435 33, Sweden.
    Harlin, P.
    Sandvik Additive Manufacturing, Sandviken, 811 81, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Effect of build location on microstructural characteristics and corrosion behavior of EB-PBF built Alloy 7182020In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 106, no 7-8, p. 3597-3607Article in journal (Refereed)
    Abstract [en]

    Electron beam-powder bed fusion (EB-PBF), a high-temperature additive manufacturing (AM) technique, shows great promise in the production of high-quality metallic parts in different applications such as the aerospace industry. To achieve a higher build efficiency, it is ideal to build multiple parts together with as low spacing as possible between the respective parts. In the EB-PBF technique, there are many unknown variations in microstructural characteristics and functional performance that could be induced as a result of the location of the parts on the build plate, gaps between the parts and part geometry, etc. In the present study, the variations in the microstructure and corrosion performance as a function of the parts location on the build plate in the EB-PBF process were investigated. The microstructural features were correlated with the thermal history of the samples built in different locations on the build plate, including exterior (the outermost), middle (between the outermost and innermost), and interior (the innermost) regions. The cubic coupons located in the exterior regions showed increased level (~ 20 %) of defects (mainly in the form of shrinkage pores) and lower level (~ 30-35 %) of Nb-rich phase fraction due to their higher cooling rates compared to the interior and middle samples. Electrochemical investigations showed that the location indirectly had a substantial influence on the corrosion behavior, verified by a significant increase in polarization resistance (Rp) from the exterior (2.1 ± 0.3 kΩ.cm2) to interior regions (39.2 ± 4.1 kΩ.cm2). © 2020, The Author(s).

  • 330.
    Karimi Neghlani, Paria
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Sadeghimeresht, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Deng, D.
    Linköping University, Division of Engineering Materials, Department of Management and Engineering, Linköping, 581 83, Sweden.
    Gruber, H.
    University of Chalmers, Division of Materials and Manufacture, Industrial and Materials Science, Gothenburg, 412 96, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Nylen, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Influence of build layout and orientation on microstructural characteristics of electron beam melted Alloy 7182018In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 99, no S1, p. 2903-2913Article in journal (Refereed)
    Abstract [en]

    Effects of build layout and orientation consisting of (a) height from the build plate (Z-axis), (b) distance between samples, and (c) location in the build plate (X-Y plane) on porosity, NbC fraction, and hardness in electron beam melted (EBM) Alloy 718 were studied. The as-built samples predominantly showed columnar structure with strong ˂001˃ crystallographic orientation parallel to the build direction, as well as NbC and ÎŽ-phase in inter-dendrites and grain boundaries. These microstructural characteristics were correlated with the thermal history, specifically cooling rate, resulted from the build layout and orientation parameters. The hardness and NbC fraction of the samples increased around 6% and 116%, respectively, as the height increased from 2 to 45 mm. Moreover, by increasing the height, formation of ÎŽ-phase was also enhanced associated with lower cooling rate in the samples built with a greater distance from the build plate. However, the porosity fraction was unaffected. Increasing the sample gap from 2 to 10 mm did not change the NbC fraction and hardness; however, the porosity fraction increased by 94%. The sample location in the build chamber influenced the porosity fraction, particularly in interior and exterior areas of the build plate. The hardness and NbC fraction were not dependent on the sample location in the build chamber. © 2018, The Author(s).

  • 331.
    Karimi Neghlani, Paria
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Sadeghimeresht, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Åkerfeldt, Pia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Luleå, 971 87, Sweden.
    Ålgårdh, Joakim
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Powder Materials & Additive Manufacturing, Swerea KIMAB AB, Kista, 164 40, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Influence of successive thermal cycling on microstructure evolution of EBM-manufactured alloy 718 in track-by-track and layer-by-layer design2018In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 160, p. 427-441Article in journal (Refereed)
    Abstract [en]

    Successive thermal cycling (STC) during multi-track and multi-layer manufacturing of Alloy 718 using electron beam melting (EBM) process leads to a microstructure with a high degree of complexity. In the present study, a detailed microstructural study of EBM-manufactured Alloy 718 was conducted by producing samples in shapes from one single track and single wall to 3D samples with maximum 10 longitudinal tracks and 50 vertical layers. The relationship between STC, solidification microstructure, interdendritic segregation, phase precipitation (MC, δ-phase), and hardness was investigated. Cooling rates (liquid-to-solid and solid-to-solid state) was estimated by measuring primary dendrite arm spacing (PDAS) and showed an increased cooling rate at the bottom compared to the top of the multi-layer samples. Thus, microstructure gradient was identified along the build direction. Moreover, extensive formation of solidification micro-constituents including MC-type carbides, induced by micro-segregation, was observed in all the samples. The electron backscatter diffraction (EBSD) technique showed a high textured structure in 〈001〉 direction with a few grains misoriented at the surface of all samples. Finer microstructure and possibility of more γ″ phase precipitation at the bottom of the samples resulted in slightly higher (~11%) hardness values compared to top of the samples. © 2018 Elsevier Ltd

  • 332.
    Karimi Neghlani, Paria
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Schnur, Christopher
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Sadeghi, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Contour design to improve topographical and microstructural characteristics of Alloy 718 manufactured by electron beam-powder bed fusion technique2020In: Additive Manufacturing, ISSN 2214-8604, Vol. 32, article id 101014Article in journal (Refereed)
    Abstract [en]

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

  • 333.
    Karlsson, Leif
    et al.
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Hurtig, Kjell
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Influence of dilution on properties of high strength steel weld metals2014In: Biuletyn Instytutu Spawalnictwa W Gliwicach: Rocznik 58, 2014, p. 65-71Conference paper (Refereed)
  • 334.
    Karlsson, Leif
    et al.
    University West, Department of Engineering Science, Divison of Natural Sciences, Surveying and Mechanical Engineering.
    Svensson, Lars-Erik
    University West, Department of Engineering Science, Division of Production Engineering.
    Hurtig, Kjell
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Efficient welding of high strength steel2014In: Proceedings of the 6th International Swedish Production Symposium 2014 / [ed] Stahre, Johan, Johansson, Björn & Björkman, Mats, 2014, p. 1-8Conference paper (Refereed)
    Abstract [en]

     Producing welds with properties matching those of the steel is a challenge at high strength levels. The present study investigated how cooling rates and dilution affects strength and toughness when welding steels with yield strengths of 777 MPa and 1193 MPa. Overmatching weld metal strength was achieved for the less strong steel and weld strengths >1000 MPa were recorded for the stronger steel. Fracture in transverse tensile testing was always located in base material or HAZ. Low dilution, rapid cooling and single pass welding contributed to higher strength. Impact toughness was higher for lower strength and low dilution.

  • 335. Karthik, Dhadala
    et al.
    Pendse, Saloni
    Sakthivel, Shanmugasundaram
    Ramasamy, Easwaramoorthi
    Joshi, Shrikant Vishwanath
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    High performance broad band antireflective coatings using a facile synthesis of ink-bottle mesoporous MgF2 nanoparticles for solar applications2017In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 159, p. 204-211Article in journal (Refereed)
    Abstract [en]

    Ultra-low refractive index thin films suitable for practical antireflective (AR) applications must be highly transparent, economical, and durable against temperature and weather conditions. In this work, we present a high performance broad band antireflective coating using a facile synthesis of Ink-Bottle mesoporous MgF2 nanoparticles. The nanoparticles having high crystalline and dispersible properties were prepared by a deformation-reformation route from coarse commercial MgF2 hydrate powder by Lyothermal synthesis. These nanoparticles, after dispersion in a suitable solvent were used to develop a single layer AR coating by dip-coating technique. We precisely developed coatings tunable to achieve minimum reflection losses between 400 and 1500 nm. The AR coating exhibited nearly 100% transmittance within visible range (615–660 nm) and an average transmittance of 99% and 97% in the visible (400–800 nm) and active solar range (300–1500 nm) respectively. Further, use of the AR coating on PV glass led to a net improvement of 6% in efficiency for c-Si solar cells. This work opens a promising approach to improve the device performance of solar cells as well as solar collectors by developing broad band antireflective surfaces using mesoporous nanoparticles.

  • 336.
    Kiilakoski, Jarkko
    et al.
    Tampere University, Materials Science and Environmental Engineering, Tampere Finland.
    Trache, Richard
    Treibacher Industrie AG, Althofen, Austria.
    Björklund, Stefan
    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.
    Vuoristo, Petri
    Tampere University, Materials Science and Environmental Engineering, Tampere Finland.
    Process Parameter Impact on Suspension-HVOF-Sprayed Cr2O3 Coatings2019In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, no 8, p. 1933-1944Article in journal (Refereed)
    Abstract [en]

    Chromium oxide (Cr2O3) is commonly used as an atmospheric plasma-sprayed (APS) coating from powder feedstock in applications requiring resistance to sliding wear and corrosion, as well as amenability to texturing, e.g., in anilox rolls. Recently, high-velocity oxy-fuel spray methods involving suspension feedstock have been considered an extremely promising alternative to produce denser and more homogeneous chromium oxide coatings with lower as-sprayed surface roughness, higher hardness and potentially superior wear performance compared to conventional APS-sprayed coatings. In this study, the impact of process parameters namely auxiliary air cleaning nozzles and a transverse air curtain on suspension high-velocity oxy-fuel-sprayed Cr2O3 suspensions is presented. The produced coatings are characterized for their microstructure, mechanical properties and wear resistance by cavitation erosion. The results reveal the importance of optimized air nozzles and air curtain to achieve a vastly improved coating structure and performance.

  • 337.
    Kiilakoski, Jarmo
    et al.
    Tampere University, Materials Science and Environmental Engineering, Tampere Finland.
    Trache, Richard
    Treibacher Industrie AG, Althofen, Austria..
    Björklund, Stefan
    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.
    Vuoristo, Petri
    Tampere University, Materials Science and Environmental Engineering, Tampere Finland.
    Correction to: Process Parameter Impact on Suspension-HVOF-Sprayed Cr2O3 Coatings (Journal of Thermal Spray Technology, (2019), 28, 8, (1933-1944), 10.1007/s11666-019-00940-7)2019In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, no 8Article in journal (Refereed)
    Abstract [en]

    In the references section there is a correction to reference number 41. It should read as follows: V. Matikainen, S. Rubio Peregrina, N. Ojala, H. Koivuluoto, J. Schubert, S. HoudkovaÂŽ, and P. Vuoristo, Erosion Wear Performance of WC-10Co4Cr and Cr3C2– 25NiCr Coatings Sprayed with High-Velocity Thermal Spray Processes, Surf. Coat. Technol., 2019, 370, p 196- 212. © 2019, ASM International.

  • 338.
    Klement, Uta
    et al.
    Chalmers University of Technology, Sweden.
    Ekberg, Johanna
    Chalmers University of Technology, Sweden.
    Ganvir, Ashish
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    EBSD Analysis and Assessment of Porosity in Thermal Barrier Coatings Produced by Axial Suspension Plasma Spraying (ASPS)2017In: Materials Science Forum, THERMEC 2016: Chapter 2: Contributed Papers / [ed] C. Sommitsch, M. Ionescu, B. Mishra, E. Kozeschnik och T. Chandra, Trans Tech Publications, 2017, Vol. 879, p. 972-977Conference paper (Refereed)
    Abstract [en]

    Axial suspension plasma spraying (ASPS) is a relatively new, innovative spraying technique which has produced thermal barrier coatings (TBCs) with attractive properties such as high durability and low thermal conductivity. Using a suspension, it is possible to spray with finer powder particles resulting in coatings that have a columnar microstructure and contain a wide range of pore sizes, both nm-and μm-sized pores. To optimize the thermal properties and to maintain them during service of the components, it will be important to design TBCs with optimal porosity. Hence, an important part in the assessment of ASPS coatings is therefore the characterization of the microstructure and how it is build up, and the determination of porosity. Both aspects are addressed by performing measurement on splats and ASPS-coating using electron backscatter diffraction (EBSD) technique and by measuring porosity by Mercury Intrusion Porosimetry (MIP).

  • 339.
    Kovářík, Ondrej
    et al.
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic..
    Haušild, Petr
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic..
    Medricky, Jan
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic..
    Tomek, Libor
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic..
    Siegl, Jan
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic..
    Mušálek, Radek
    Institute of Plasma Physics CAS..
    Curry, Nicholas
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Fatigue crack growth in bodies with thermally sprayed coating2015In: Proceedings from the International Thermal Spray Conference (May 11–14, 2015, Long Beach, California, USA), ASM International, 2015, Vol. 1-2, p. 398-405Conference paper (Refereed)
    Abstract [en]

    Many applications of thermally sprayed coatings call for increased fatigue resistance of coated parts. Despite the intensive research in this area, the influence of coating on fatigue is still not completely understood. In this paper, the spatiotemporal localization of crack initiation and the dynamics of crack propagation are studied. The resonance bending fatigue test is employed to test flat specimens with both sides coated. Hastelloy-X substrates coated with classical TBC YSZ/NiCoCrAlY composites were tested. The strain distribution on the coating surface is evaluated by the digital image correlation method (DIC) through the whole duration of the fatigue test. Localization of crack initiation sites and the mode of crack propagation in the coated specimen are related to the observed resonance frequency. The individual phases of specimen degradation, i.e. the changes of material properties, crack initiation, and crack propagation are identified. The tested coatings strongly influenced the first two phases, the influence on the crack propagation was less significant. © Copyright (2015) by ASM International All rights reserved.

  • 340.
    Kovářík, Ondrej
    et al.
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Haušild, Petr
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Medřický, Jan
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic..
    Tomek, Libor
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Siegl, Jan
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Mušálek, Radek
    Institute of Plasma Physics CAS.
    Nicholas, Curry
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Fatigue Crack Growth in Bodies with Thermally Sprayed Coating2016In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 25, no 1-2, p. 311-320Article in journal (Refereed)
    Abstract [en]

    Many applications of thermally sprayed coatings call for increased fatigue resistance of coated parts. Despite the intensive research in this area, the influence of coating on fatigue is still not completely understood. In this paper, the localization of crack initiation sites and the dynamics of crack propagation are studied. The resonance bending fatigue test was employed to test flat specimens with both sides coated. Hastelloy-X substrates coated with classical thermal barrier coating consisting of yttria stabilized zirconia and NiCoCrAlY layers. The strain distribution on the coating surface was evaluated by the Digital Image Correlation method through the whole duration of the fatigue test. Localization of crack initiation sites and the mode of crack propagation in the coated specimen are related to the observed resonance frequency. The individual phases of specimen degradation, i.e., the changes of material properties, crack initiation, and crack propagation, were identified. The tested coatings strongly influenced the first two phases, and the influence on the crack propagation was less significant. In general, the presented crack detection method can be used as a sensitive nondestructive testing method well suited for coated parts. © 2015 ASM International

  • 341.
    Kovářík, Ondrej
    et al.
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Haušild, Petr
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Čapek, Jiří
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Medřický, Jan
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Siegl, Jan
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Mušálek, Radek
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Pala, Zdeněk
    Institute of Plasma Physics AS CR, v.v.i., Prague, Czech Republic.
    Curry, Nicholas
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Resonance bending fatigue testing with simultaneous damping measurement and its application on layered coatings2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 82, Part 2, p. 300-309Article in journal (Refereed)
    Abstract [en]

    Abstract The use of specimen loss factor as fatigue damage indicator of Hastelloy-X substrates with different surface treatments was investigated together with other fatigue damage indicators, namely resonance frequency and crack mouth length. The tested surface treatments included grit-blasting and plasma spraying of NiCoCrAlY bond coat and yttria stabilized zirconia (YSZ) top coat. The loss factors of fatigue test specimens were measured repeatedly during the resonance bending fatigue test using the conventional free decay method. The analysis of the damping spectra, i.e. the model describing the relation of loss factor to maximum macroscopic specimen strain εyy was drafted. The model is based on the combination of defect models developed by Göken and Riehemann (2004) and classical dislocation model of Granato and LÌcke (1956). It appears, that the damping spectra can be well approximated as a combination of two defect peaks (C1 and C2) and one dislocation peak (D1). The low strain defect peak (peak C1) is sensitive to the presence of fatigue cracks. The second defect peak (peak C2) can be attributed to the remaining substrate and coating defects such as embedded grit particles, coating porosity, surface roughness and sliding in the sample clamping area. The fatigue damage detection using the C1 peak magnitude was performed and its results were related to the crack length obtained by digital image correlation (DIC) method. In the crack initiation stage I., the C1 peak height shows different behavior than the resonance frequency and therefore provides new information. The underlying processes causing C1 peak changes need to be found yet, however. In the crack growth stage II., both resonance frequency and peak height C1 correlate with the measured fatigue crack size.

  • 342.
    Kovářík, Ondřej
    et al.
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Haušild, Petr
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Čapek, Jiří
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Medřický, Jan
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Siegl, Jan
    Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
    Mušálek, Radek
    Institute of Plasma Physics AS CR, v.v.i., Prague, Czech Republic.
    Pala, Zdeněk
    Institute of Plasma Physics AS CR, v.v.i., Prague, Czech Republic.
    Curry, Nicholas
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Damping measurement during resonance fatigue test and its application for crack detection in TBC samples2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 82, no Part 2, p. 300-309Article in journal (Refereed)
    Abstract [en]

    Abstract The use of specimen loss factor as fatigue damage indicator of Hastelloy-X substrates with different surface treatments was investigated together with other fatigue damage indicators, namely resonance frequency and crack mouth length. The tested surface treatments included grit-blasting and plasma spraying of NiCoCrAlY bond coat and yttria stabilized zirconia (YSZ) top coat. The loss factors of fatigue test specimens were measured repeatedly during the resonance bending fatigue test using the conventional free decay method. The analysis of the damping spectra, i.e. the model describing the relation of loss factor to maximum macroscopic specimen strain εyy was drafted. The model is based on the combination of defect models developed by Göken and Riehemann [1] and classical dislocation model of Granato and LÌcke [2]. It appears, that the damping spectra can be well approximated as a combination of two defect peaks (C1 and C2) and one dislocation peak (D1). The low strain defect peak (peak C1) is sensitive to the presence of fatigue cracks. The second defect peak (peak C2) can be attributed to the remaining substrate and coating defects such as embedded grit particles, coating porosity, surface roughness and sliding in the sample clamping area. The fatigue damage detection using the C1 peak magnitude was performed and its results were related to the crack length obtained by digital image correlation (DIC) method. In the crack initiation stage I., the C1 peak height shows different behavior than the resonance frequency and therefore provides new information. The underlying processes causing C1 peak changes need to be found yet, however. In the crack growth stage II., both resonance frequency and peak height C1 correlate with the measured fatigue crack size.

  • 343.
    Kuhn, Joel
    et al.
    University of Toronto, Department of Mechanical and Industrial Engineering, Toronto, ON, Canada.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Kesler, Oivera
    University of Toronto, Department of Mechanical and Industrial Engineering, Toronto, ON, Canada.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    The effect of fuel electrode roughness on the properties of plasma sprayed solid oxide cells2017In: ECS Transactions, ISSN 1938-5862, E-ISSN 1938-6737, Vol. 78, no 1, p. 1477-1487Article in journal (Refereed)
    Abstract [en]

    Solid oxide cell electrolytes fabricated by atmospheric plasma spraying are frequently found to have nonzero gas leak rates. Electrode surface roughness is known to have an influence on electrolyte leak rates. A jet of high velocity air, produced with an air knife, was aimed at the plasma plume during fuel electrode deposition to reduce the surface roughness prior to electrolyte deposition. The resulting fuel electrode masses, electrode compositions, and electrode surface roughnesses were measured for varying air knife inlet pressures. Surface asperity populations and maximum heights were significantly reduced using air knife pressures of > 6 bar at the expense of deposition efficiency. The distribution of surface gradients was also improved with the use of the air knife, but some regions with steep gradients still remained in surfaces prepared with an air knife pressure of 8 bar. © The Electrochemical Society.

  • 344.
    Kuhn, Joel
    et al.
    University of Toronto, Department of Mechanical and Industrial Engineering, Toronto, Ontario M5S 3G8, Canada.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Kesler, Olivera
    University of Toronto, Department of Mechanical and Industrial Engineering, Toronto, Ontario M5S 3G8, Canada.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    The Effect of Fuel Electrode Roughness on the Properties of Plasma Sprayed Solid Oxide Cells2018In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 165, no 9, p. F693-F701Article in journal (Refereed)
    Abstract [en]

    Solid oxide cell electrolytes fabricated by atmospheric plasma spraying are frequently found to have considerable gas leak rates.Electrode surface roughness is known to have an influence on electrolyte leak rates. A jet of high velocity air, produced with an airknife, was aimed at the plasma plume during fuel electrode deposition to reduce the surface roughness prior to electrolyte deposition.The resulting fuel electrode masses, electrode compositions, and electrode surface roughnesses were measured for varying air knifeinlet pressures. Surface asperity populations and maximum heights were significantly reduced using air knife pressures of >6 barat the expense of deposition efficiency. The nickel volume fraction in the fuel electrode increased slightly with increasing air knifepressure. Open circuit voltages were larger on the smoother fuel electrodes that were produced at higher air knife pressures, but nosignificant effect of air knife pressure on cell power density could be discerned.© 2018 The Electrochemical Society

  • 345.
    Kumar, M.
    et al.
    CGC College of Engineering, Landran, India.
    Singh, H.
    Singh, N.
    Chavan, N.
    Kumar, S.
    Joshi, Shrikant
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Development of high-performance cols-sprayed nano-structured NI-20Cr coatings for hash environment of power plant boilers2017Conference paper (Other academic)
  • 346. Kumar, M.
    et al.
    Singh, H.
    Singh, N.
    Joshi, Shrikant. V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Chavan, N.
    Kumar, S.
    Evaluation of high temperature oxidation behavior of a cold spray Ni-20Cr nano-structured coating2016Conference paper (Other academic)
  • 347.
    Kumar, Rajiv
    et al.
    IITB-Monash Research Academy, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
    Joardar, Joydip
    International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad, India.
    Raman, R.K. Singh
    Department of Mechanical and Aerospace Engineering, Monash University, VIC 3800 Australia.
    Raja, V.S.
    Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
    Joshi, Shrikant
    University West, Department of Engineering Science, Research Enviroment Production Technology West. International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad, India.
    Parida, S.
    Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
    Effect of chromium and aluminum addition on anisotropic and microstructural characteristics of ball milled nanocrystalline iron2016In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 671, p. 164-169Article in journal (Refereed)
    Abstract [en]

    Prior studies on synthesis of nanocrystalline elements have discussed the effect of ball milling on lattice parameter, crystallite size, and micro-strain. For elemental milled powders, the anisotropic peak broadening does not change with increasing milling time. However, the effect of alloying addition on the anisotropic behavior of ball milled nanocrystalline powders remains an unexplored area. Here we report the effect of chromium and aluminum addition on the anisotropic behavior of iron in nanocrystalline Fe–20Cr–5Al (wt%) alloy powders synthesized by ball milling. The experimental results show that the anisotropic behavior of iron changes towards isotropic with milling. This change was also correlated to the theoretically calculated anisotropic factor from the change in elastic constant of iron due to milling. Addition of alloying elements exhibited a monotonic rise in the lattice parameter with crystallite size, which was attributed to the excess grain boundary interfacial energy and excess free volume at grain boundaries. Transmission electron microscopy image confirmed the crystallite size and nature of dislocation obtained using modified Williamson-Hall method.

  • 348.
    Kumar, Raju
    et al.
    Centre for Nanomaterials, International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad 500005, India.
    Govinadarajan, Sivakumar
    Centre for Engineered Coatings, International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad 500005, India.
    Janardhana, Reddy Kunda Siri Kiran
    Centre for Nanomaterials, International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad 500005, India.
    Rao, Tata Narasinga
    Centre for Nanomaterials, International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad 500005, India.
    Joshi, Shrikant
    University West, Department of Engineering Science, Research Enviroment Production Technology West. Centre for Engineered Coatings, International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad 500005, India.
    Anandan, Srinivasan
    Centre for Nanomaterials, International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad 500005, India.
    Facile One-Step Route for the Development of in Situ Cocatalyst-Modified Ti3+ Self-Doped TiO2 for Improved Visible-Light Photocatalytic Activity2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 41, p. 27642-27653Article in journal (Refereed)
    Abstract [en]

    Development of visible-light-driven photocatalysts by employing a relatively simple, efficient, and cost-effective one-step process is essential for commercial applications. Herein, we report for the first time the synthesis of in situ Cu-ion modified Ti3+ self-doped rutile TiO2 by such a facile one-step solution precursor plasma spray (SPPS) process using a water-soluble titanium precursor. In the SPPS process, Ti3+ self-doping on Ti4+ of rutile TiO2 is found to take place because of electron transfer from the created oxygen vacancies to Ti4+-ions. In situ Cu modification of the above Ti3+ self-doped rutile TiO2 by additionally introducing a Cu solution into plasma plume is also demonstrated. While the Ti3+ self-doping induces broad absorption in the visible-light region, the addition of Cu ion leads to even broader absorption in the visible region owing to resulting synergistic properties. The above materials were evaluated for various self-cleaning photocatalytic applications under visible-light illumination. Cu-ion modified Ti3+ self-doped rutile TiO2 is noted to exhibit a remarkably enhanced visible-light activity in comparison with Ti3+ self-doped rutile TiO2, with the latter itself outperforming commercial TiO2photocatalysts, thereby suggesting the suitability of the material for indoor applications. The broad visible-light absorption by Ti3+ self-doping, the holes with strong oxidation power generated in the valence band, and electrons in Ti3+ isolated states that are effectively separated into the high reductive sites of Cu ions upon visible-light irradiation, accounts for improved photocatalytic activity. Moreover, the synthesis process (SPPS) provides a valuable alternative to orthodox multistep processes for the preparation of such visible-light-driven photocatalysts.

  • 349.
    Kumar, S.
    et al.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur.Po, Hyderabad 500 005, India.
    Jyothirmayi, A.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur.Po, Hyderabad 500 005, India.
    Wasekar, Nitin
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur.Po, Hyderabad 500 005, India.
    Joshi, Shrikant
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Influence of annealing on mechanical and electrochemical properties of cold sprayed niobium coatings2016In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 296, p. 124-135Article in journal (Refereed)
    Abstract [en]

    Abstract In the present study, thick and dense niobium coatings were obtained using cold spray technique by using air as a process gas. Inter-splat boundaries are completely removed in the coatings heat treated at 1500 °C by the formation of equiaxed grains. Heat treatment reduces the porosity level to 0.1%. Inter-splat boundary bonding state of the heat treated coatings was investigated using micro-tensile testing, scratch testing and nanoindentation and compared with the bulk niobium. The elastic modulus of the cold spray coatings heat treated at 1500 °C exhibits as high as 103 GPa whereas the same for bulk is 105 GPa. The increase in mechanical strength of inter-splat boundary from as-sprayed condition to 1500 °C was estimated to be 750%. Similarly corrosion performance of heat treated coatings was also evaluated in 1 M KOH solution through potentiodynamic polarization as well as impedance spectroscopy studies. The corrosion rate for the coatings heat treated at 1500 °C was estimated to be 0.443 MPY which is comparable for the bulk (0.498 MPY). Coatings annealed at 1250 °C and above, which is very close to the recrystallization temperature of niobium, were found to perform almost as bulk niobium indicating exciting implications for various applications. Assessment of structure–property correlations was done based on the microstructure, porosity and inter-splat bonding state, together with the mechanical and corrosion properties of the heat treated tantalum cold sprayed coatings.

  • 350.
    Kumar, S.
    et al.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, India.
    Ramakrishna, M.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur Po, Hyderabad, 500 005, India.
    Chavan, N.M.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur Po, Hyderabad, 500 005, India.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur Po, Hyderabad, 500 005, India.
    Correlation of splat state with deposition characteristics of cold sprayed niobium coatings2017In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 130, p. 177-195Article in journal (Refereed)
    Abstract [en]

    The cold spray technique has a great potential to deposit refractory metals for a variety of potential applications. Cold spraying of different metals have been addressed comprehensively to understand the deposition characteristics of the coatings. Since there is no available data on the deposition characteristics of cold sprayed Niobium, impact behavior of splats at different deposition conditions were simulated and numerically analyzed using Finite Element Modeling (FEM) and correlated with the experimental observations that highlight the role of the velocity and temperature of the particle upon impact on the bonding features. The increase in temperature of the splat drastically reduces the flow stress at the interface leading to best inter-splat bonding state. The synergistic effect of the temperature and the velocity leads to the formation of very dense, defect free niobium coating associated with deformation localization including interface melting. Formation of nanocrystalline grains at the inter-splat boundary was confirmed through TEM and compared with the FEM findings. Finally, understanding the deformation and deposition behavior of refractory metal such as niobium will be helpful to engineer the coatings for potential applications.

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