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  • 51.
    Faisal, Nadimul Haque
    et al.
    School of Engineering, Robert Gordon University, Garthdee Road, Aberdeen (GBR).
    Prathuru, Anil
    School of Engineering, Robert Gordon University, Garthdee Road, Aberdeen (GBR).
    Ahmed, Rehan
    School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh (GBR).
    Rajendran, Vinooth
    School of Engineering, Robert Gordon University, Garthdee Road, Aberdeen (GBR).
    Hossain, Mamdud
    School of Engineering, Robert Gordon University, Garthdee Road, Aberdeen, (GBR).
    Venkatachalapathy, Viswanathan
    School of Engineering, London South Bank University, 103 Borough Road, London (GBR).
    Katiyar, Nirmal Kumar
    School of Engineering, London South Bank University, 103 Borough Road, London, (GBR).
    Li, Jing
    Department of Chemical & Process Engineering, University of Surrey, Guildford (GBR).
    Liu, Yuheng
    Department of Chemical & Process Engineering, University of Surrey, Guildford (GBR).
    Cai, Qiong
    Department of Chemical & Process Engineering, University of Surrey, Guildford (GBR).
    Horri, Bahman Amini
    Department of Chemical & Process Engineering, University of Surrey, Guildford (GBR).
    Thanganadar, Dhinesh
    School of Water, Energy and Environment, Cranfield University, Cranfield (GBR).
    Sodhi, Gurpreet Singh
    School of Water, Energy and Environment, Cranfield University, Cranfield (GBR).
    Patchigolla, Kumar
    School of Water, Energy and Environment, Cranfield University, Cranfield (GBR).
    Fernandez, Carlos
    School of Pharmacy and Life Sciences, Robert Gordon University, Garthdee Road, Aberdeen (GBR).
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Govindarajan, Sivakumar
    Centre for Engineered Coatings, International Advanced Research Centre for Powder Metallurgy and New Materials, Balapur, Hyderabad, 500 005 Telangana (IND).
    Kurushina, Victoria
    School of Engineering, Robert Gordon University, Garthdee Road, Aberdeen (GBR).
    Katikaneni, Sai
    Research and Development Centre, Saudi Aramco, Dhahran (SAU).
    Goel, Saurav
    School of Engineering, London South Bank University, 103 Borough Road, London (GBR).
    Application of Thermal Spray Coatings in Electrolysers for Hydrogen Production: Advances, Challenges, and Opportunities2022In: ChemNanoMat, E-ISSN 2199-692X, Vol. 8, no 12, article id e202200384Article in journal (Refereed)
    Abstract [en]

    Thermal spray coatings have the advantage of providing thick and functional coatings from a range of engineering materials. The associated coating processes provide good control of coating thickness, morphology, microstructure, pore size and porosity, and residual strain in the coatings through selection of suitable process parameters for any coating material of interest. This review consolidates scarce literature on thermally sprayed components which are critical and vital constituents (e. g., catalysts (anode/cathode), solid electrolyte, and transport layer, including corrosion-prone parts such as bipolar plates) of the water splitting electrolysis process for hydrogen production. The research shows that there is a gap in thermally sprayed feedstock material selection strategy as well as in addressing modelling needs that can be crucial to advancing applications exploiting their catalytic and corrosion-resistant properties to split water for hydrogen production. Due to readily scalable production enabled by thermal spray techniques, this manufacturing route bears potential to dominate the sustainable electrolyser technologies in the future. While the well-established thermal spray coating variants may have certain limitations in the manner they are currently practiced, deployment of both conventional and novel thermal spray approaches (suspension, solution, hybrid) is clearly promising for targeted development of electrolysers.

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  • 52.
    Fefekos, Alexandros G.
    et al.
    University West, Department of Engineering Science.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Mahade, Satyapal
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. GKN Aerospace Sweden AB, Trollhättan (SWE).
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Effect of spray angle and substrate material on formation mechanisms and properties of HVAF sprayed coatings2023In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 452, article id 129115Article in journal (Refereed)
    Abstract [en]

    Thermally sprayed coatings are often used to enhance the surface properties (wear resistance, corrosion resistance, etc.) of engineering components in order to extend their performance and service lifetime. Typically, the industrial components to be coated possess complex geometries and are fabricated using different materials, which can influence the deposited coating’s microstructure and performance. High-velocity air fuel (HVAF) process is a relatively new thermal spray processing technique that has shown tremendous potential to deposit high performance coatings for durable industrial components. However, no detailed studies have been reported on HVAF sprayed coating formation mechanisms so far in relation to the spray angle and substrate properties, and the influence of coating material on the above. The objective of this work was to study the influence of spray angles and substrate materials on splat characteristics, coating microstructure evolution, properties and performance for two distinct coating materials. In this study, one cermet (WC-CoCr) and one metallic (Inconel 625) feedstock were deposited onto three different substrates (aluminium alloy, carbon steel and Hastelloy-X) utilising different spray angles (40°, 60° and 90°). The coating evolution was analysed utilising SEM/EDS, image analysis, and micro-indentation. To determine the tribological performance, coatings were subjected to dry sliding wear test utilising alumina ball as counter surface and specific wear rates were obtained. The results showed that initial splat characteristics were substantially altered on changing the substrate and the spray angle. However, the final coating properties were not affected significantly even though the deposition rate was reduced significantly at lower spray angle, suggesting the versatility of the HVAF process. 

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  • 53.
    Frost, R. J. W.
    et al.
    Department of Physics and Astronomy, Uppsala University, Uppsala (SWE); Department of Physics, Lund University, Lund (SWE).
    Thomas, C. A.
    Accelerator Division, European Spalation Source (ESS), Lund (SWE).
    Elfman, M.
    Department of Physics, Lund University, Lund (SWE).
    Johansson, R.
    Accelerator Division, European Spalation Source (ESS), Lund (SWE).
    Hartl, M.
    Accelerator Division, European Spalation Source (ESS), Lund (SWE).
    Kocevar, H.
    Accelerator Division, European Spalation Source (ESS), Lund (SWE).
    Michel, K.
    Accelerator Division, European Spalation Source (ESS), Lund (SWE).
    Joshi, Shrikant V.
    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.
    Preliminary results from a study of luminescent materials: For application in the beam imaging system at the ESS2023In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 540, p. 227-233Article in journal (Refereed)
    Abstract [en]

    As part of the development of the beam imaging system at the European Spallation Source, luminescent screens have been fabricated by the flame spraying of scintillating materials onto stainless steel backings. A total of seven screens were produced, three of chromia alumina (Al2O3:Cr), two of YAG (Y3Al5O12:Ce) and two of a 50/50 mix of these. The properties of these screens under proton irradiation were evaluated using a2.55 MeV proton beam at currents of up to 10 μA. Irradiation times were up to 25 h per sample, during which luminescence-, spectrographic-, thermal- and current-data was sampled at a rate of 1 Hz. Preliminary results of these measurements are reported here; with a quantitative analysis presented for one of the chromia alumina screens and a qualitative comparison of all three material types. The luminescent yield for chromia alumina was determined to be around 2000 photons/MeV for a virgin screen, and was found to drop to 1.5% after 167 mC of proton irradiation. A recovery of the luminescence of chromia alumina to >60% was observed after beam current was reduced for an 8 h period. Observations indicate that the YAG and mixed composition screens retain higher luminescence than the chromia alumina even at temperatures of over 200 ◦C. It is indicated that the luminescence from YAG feeds the R-lines of chromia alumina in the mixed composition screens. 

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  • 54.
    Ganvir, Ashish
    et al.
    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.
    Yao, Yiming
    Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, 41296, Sweden.
    Vadali, Srikanth V.S.S.
    University of Hyderabad, School of Engineering Sciences and Technology, Hyderabad, 500046, India.
    Klement, Uta
    Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, 41296, Sweden.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    A facile approach to deposit graphenaceous composite coatings by suspension plasma spraying2019In: Coatings, ISSN 2079-6412, Vol. 9, no 3, article id 171Article in journal (Refereed)
    Abstract [en]

    This paper demonstrates, for the first time ever, the deposition of graphenaceous composite coatings using an easy, yet robust, suspension plasma spraying (SPS) process. As a case study, a composite coating comprising 8 wt.% of yttria-stabilized-zirconia (8YSZ) and reinforced with graphene oxide (GO) was deposited on a steel substrate. The coatings were sprayed using an 8YSZ-GO mixed suspension with varied plasma spray parameters. Establishing the possibility of retaining the graphene in a ceramic matrix using SPS was of specific interest. Electron microscopy and Raman spectroscopy confirmed the presence of graphenaceous material distributed throughout the coating in the 8YSZ matrix. The experimental results discussed in this work confirm that SPS is an immensely attractive pathway to incorporate a graphenaceous material into virtually any matrix material and can potentially have major implications in enabling the deposition of large-area graphene-containing coatings for diverse functional applications. © 2019 by the authors.

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  • 55.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Calinas, Rosa Filomena
    Innovnano Materials, Coimbra, Portugal.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Curry, Nicholas
    Treibacher Industries AG, Althofen, Austria.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Experimental visualization of microstructure evolution during suspension plasma spraying of thermal barrier coatings2019In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 39, no 2-3, p. 470-481Article in journal (Refereed)
    Abstract [en]

    This paper investigates the evolution of microstructure of thermal barrier coatings (TBCs) produced by suspension plasma spraying (SPS) through a careful experimental study. Understanding the influence of different suspension characteristics such as type of solvent, solid load content and median particle size on the ensuing TBC microstructure, as well as visualizing the early stages of coating build-up leading to formation of a columnar microstructure or otherwise, was of specific interest. Several SPS TBCs with different suspensions were deposited under identical conditions (same substrate, bond coat and plasma spray parameters). The experimental study clearly revealed the important role of suspension characteristics, namely surface tension, density and viscosity, on the final microstructure, with study of its progressive evolution providing invaluable insights. Variations in suspension properties manifest in the form of differences in droplet momentum and trajectory, which are found to be key determinants governing the resulting microstructure (e.g., lamellar/vertically cracked or columnar).

  • 56.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Curry, Nicholas
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Joshi, Shrikant
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Vilemova, Monika
    IPP.
    Pala, Zdenek
    IPP.
    Influence of Microstructure on Thermal Properties of Axial Suspension Plasma-Sprayed YSZ Thermal Barrier Coatings2016In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 25, no 1-2, p. 202-212Article in journal (Refereed)
    Abstract [en]

    Suspension plasma spraying is a relatively new thermal spaying technique to produce advanced thermal barrier coatings (TBCs) and enables production of coatings with a variety of structures—highly dense, highly porous, segmented, or columnar. This work investigates suspension plasma-sprayed TBCs produced using axial injection with different process parameters. The influence of coating microstructure on thermal properties was of specific interest. Tests carried out included microstructural analysis, phase analysis, determination of porosity, and pore size distribution, as well as thermal diffusivity/conductivity measurements. Results showed that axial suspension plasma spraying process makes it possible to produce various columnar-type coatings under different processing conditions. Significant influence of microstructural features on thermal properties of the coatings was noted. In particular, the process parameter-dependent microstructural attributes, such as porosity, column density, and crystallite size, were shown to govern the thermal diffusivity and thermal conductivity of the coating.

  • 57.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Goel, Sneha
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Govindarajan, Sivakumar
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), 500005 Hyderabad (IND).
    Jahagirdar, Adwait Rajeev
    University West, Department of Engineering Science.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Klement, Uta
    Chalmers University of Technology, Gothenburg, (SWE).
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Tribological performance assessment of Al2O3-YSZ composite coatings deposited by hybrid powder-suspension plasma spraying2021In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 409, p. 1-13, article id 126907Article in journal (Refereed)
    Abstract [en]

    The advent of high-throughput plasma spray systems that allow axial feeding encourages the study of using liquid feedstock for various next-generation functional applications. The current study explores the benefit of such a plasma spray system to deposit hybrid powder-suspension Al2O3-YSZ ceramic matrix composite (CMC) coatings for tribological applications. The tribological performance of the hybrid processed CMC coatings was assessed using scratch, ball-on-plate wear and erosion tests and compared with that of monolithic powder-derived Al2O3 coatings. As-deposited and tribo-tested coatings were characterized using Scanning Electron Microscopy, X-ray Diffraction and Energy Dispersive Spectroscopy to analyse their microstructure and phase constitution. The results showed that the tribological performance of the hybrid powder-suspension Al2O3-YSZ CMC coating was significantly improved by enhancing the wear resistance under scratch, dry sliding ball-on-plate and erosion tests as compared to the conventional APS deposited monolithic Al2O3 coating. About 36% decrease in the dry sliding ball-on-plate specific wear rate and up to 50% decrease in the erosion wear rate was noted in the hybrid powder-suspension Al2O3-YSZ CMC coating as compared to the conventional APS deposited monolithic Al2O3 coating. The study concludes that the hybrid powder-suspension route can create CMC coatings with unique multi-length scale microstructures which can be attractive for combining different tribological attributes in the same coating system.

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  • 58.
    Ganvir, Ashish
    et al.
    University of Turku, Turku (FIN).
    Jahagirdar, Adwait Rajeev
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Mulone, Antonio
    Chalmers University of Technology, Gothenburg.
    Örnfeldt, Louise
    Chalmers University of Technology, Gothenburg.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Klement, Uta
    Chalmers University of Technology, Gothenburg.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Novel utilization of liquid feedstock in high velocity air fuel (HVAF) spraying to deposit solid lubricant reinforced wear resistant coatings2021In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 295, article id 117203Article in journal (Refereed)
    Abstract [en]

    The ability to axially inject liquid feedstock has encouraged the thermal spray research community to explore this concept to deposit coatings for various next generation functional applications. The current study explores the utilization of liquid feedstock in high velocity air fuel (HVAF) spraying to deposit solid lubricant reinforced wear resistant coatings for the first time. The study successfully demonstrates the use of a powder-suspension hybrid processing approach to incorporate a solid lubricant Boron Nitride (as suspension) in a wear resistant Cr3C2–NiCr (as powder) cermet matrix. Coatings were characterized using Scanning Electron Microscopy and Raman Spectroscopy to analyze their microstructure and phase constitution. The results show that the tribological performance of the hexagonal boron nitride (hBN)-incorporated composite coating was significantly better than the traditional powder-derived Cr3C2–NiCr coating. Such hBN-incorporated composite coatings are needed to improve the mechanical properties and enhance the overall tribological performance of metallic components used in various applications, especially at high temperature such as cylinder bore, pistons, deformation tools, etc. The limitations of liquid based lubricants at high temperature motivates the use of hBN reinforced composite coatings as it can form a protective solid lubrication tribo-film. The study concludes that the emerging HVAF technology can accommodate liquid feedstock and be successfully utilized to deposit hybrid powder-suspension composite coatings to create multi length scale microstructures which can be attractive for combining different tribological attributes in the same coatings system.

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  • 59.
    Ganvir, Ashish
    et al.
    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.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Vassen, Robert
    Forschungszentrum Jülich GmbH, IEK-1, Jülich, Germany.
    Tailoring columnar microstructure of axial suspension plasma sprayed TBCs for superior thermal shock performance2018In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 144, p. 192-208Article in journal (Refereed)
    Abstract [en]

    This paper investigates the thermal shock behavior of thermal barrier coatings (TBCs) produced by axial suspension plasma spraying (ASPS). TBCs with different columnar microstructures were subjected to cyclic thermal shock testing in a burner rig. Failure analysis of these TBCs revealed a clear relationship between lifetime and porosity. However, tailoring the microstructure of these TBCs for enhanced durability is challenging due to their inherently wide pore size distribution (ranging from few nanometers up to few tens of micrometers). This study reveals that pores with different length scales play varying roles in influencing TBC durability. Fracture toughness shows a strong correlation with the lifetime of various ASPS TBCs and is found to be the prominent life determining factor. Based on the results, an understanding-based design philosophy for tailoring of the columnar microstructure of ASPS TBCs for enhanced durability under cyclic thermal shock loading is proposed. © 2018 The Authors

  • 60.
    Ganvir, Ashish
    et al.
    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.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Influence of Isothermal Heat Treatment on Porosity and Crystallite Size in Axial Suspension Plasma Sprayed Thermal Barrier Coatings for Gas Turbine Applications2017In: Coatings, ISSN 2079-6412, Vol. 7, no 1, p. 1-14, article id 4Article in journal (Refereed)
    Abstract [en]

    xial suspension plasma spraying (ASPS) is an advanced thermal spraying technique, which enables the creation of specific microstructures in thermal barrier coatings (TBCs) used for gas turbine applications. However, the widely varying dimensional scale of pores, ranging from a few nanometers to a few tenths of micrometers, makes it difficult to experimentally measure and analyze porosity in SPS coatings and correlate it with thermal conductivity or other functional characteristics of the TBCs. In this work, an image analysis technique carried out at two distinct magnifications, i.e., low (500×) and high (10,000×), was adopted to analyze the wide range of porosity. Isothermal heat treatment of five different coatings was performed at 1150 °C for 200 h under a controlled atmosphere. Significant microstructural changes, such as inter-columnar spacing widening or coalescence of pores (pore coarsening), closure or densification of pores (sintering) and crystallite size growth, were noticed in all the coatings. The noted changes in thermal conductivity of the coatings following isothermal heat treatment are attributable to sintering, crystallite size growth and pore coarsening

  • 61. Geetha, M.
    et al.
    Sathish, S.
    Chava, K.
    Joshi, S. V.
    Detonation gun sprayed Al2O3-13TiO(2) coatings for biomedical applications2014In: Surface Engineering, ISSN 0267-0844, E-ISSN 1743-2944, Vol. 30, no 4, p. 229-236Article in journal (Refereed)
    Abstract [en]

    The present work deals with the investigation of the corrosion and sliding wear behaviour of detonation gun sprayed (DG) conventional and nanostructured Al2O3-13TiO(2) coatings deposited on a biomedical grade Ti-13Nb-13Zr alloy. The microstructure and phase composition of the coatings were characterised by scanning electron microscopy (SEM) and X-ray diffraction ( XRD). Hardness measurements were carried out using a Vickers hardness testing machine. The experimental results suggested that the nano structured Al2O3- 13TiO(2) coating exhibited 43 and 33% increase respectively in corrosion and wear resistances compared to the conventional Al2O3-13TiO(2) coating. This improvement in the above properties of nanostructured Al2O3-13TiO(2) coating is due to the presence of larger volume fraction of nanosized particles and lower porosity attained by spraying using DG.

  • 62. George, J.
    et al.
    Bhargava, P.
    Rao, D. S.
    Joshi, S. V.
    Integrity of detonation sprayed CrxCy-NiCr coating under exposure to thermal cycling2006In: Advances in Applied Ceramics: Structural, Functional and Bioceramics, ISSN 1743-6753, E-ISSN 1743-6761, Vol. 105, no 3, p. 148-152Article in journal (Refereed)
    Abstract [en]

    CrxCy-NiCr coatings with thickness in the range 200-250 mu m were deposited by detonation spray coating on a nickel base superalloy (IN718) substrate and subjected to thermal cycling. Each thermal cycle involved heating to 650 degrees C, the creep temperature of the IN718 substrate, followed by a dwell and then natural cooling to ambient temperature. With thermal cycling, the bulk of the coatings experienced preferential oxidation along the splat boundaries, contributing to an increase in porosity and cracking. Despite the development of porosity and cracks, no spallation of coatings was observed even after nearly 600 thermal cycles. The microhardness of coatings did not undergo significant change, owing to oxide formation and retention of the total carbide content of Cr3C2, Cr7C3 and Cr23C6. The wear behaviour of the as sprayed and thermally cycled coated samples was evaluated in abrasive and erosive wear modes. Wear measurements on as sprayed and thermally cycled coatings showed virtually no deterioration in properties even after exposure to nearly 600 thermal cycles.

  • 63.
    Goel, Sneha
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Ahlfors, Magnus
    Quintus Technologies AB, Västerås, Sweden.
    Bahbou, Fouzi
    ARCAM AB, Mölndal, Sweden.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Effect of Different Post-treatments on the Microstructure of EBM-Built Alloy 7182019In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 28, no 2, p. 673-680Article in journal (Refereed)
    Abstract [en]

    Electron beam melting (EBM) of Alloy 718 is of rapidly growing interest as it allows cost-effective production of complex components. However, the inherent flaws in the component in as-built state are of concern in view of the severe working conditions in which Alloy 718 components typically operate. The present work entails an investigation of changes in microstructure that accompany some post-treatments that are being widely considered to address defects in EBM processed Alloy 718. The effect of two different post-treatments, namely hot isostatic pressing (HIP) and a combined HIP + heat treatment (HT) carried out inside the HIP vessel, have been studied and results from as-built and post-treated specimens were compared in terms of porosity/lack-of-fusion, microstructure, phase constitution (NbC content, ÎŽ-phase) and micro-hardness. Post-treatment resulted in reduction in defect content by more than an order of magnitude. HIPing led to complete dissolution of ÎŽ phase. In comparison to as-built material, HIPed specimens exhibited significant drop in hardness. However, a sharp ‘recovery’ of hardness to yield values higher than in as-built condition was observed after HIP + HT and can be attributed to precipitation of γ′′ phase. © 2018, The Author(s).

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  • 64.
    Goel, Sneha
    et al.
    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, Althofen, 9330, Austria (AUT).
    Govindarajan, Sivakumar
    International Advanced Research Center for Powder Metallurgy and New Materials, Hyderabad, 500 005, India (IND).
    Wiklund, Urban
    Uppsala University, Applied Materials Science, Uppsala, 75121, Sweden.
    Gaudiuso, Caterina
    University of Bari, Physics Department, via Amendola 173, Bari, 70126, Italy (ITA).
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Axial plasma spraying of mixed suspensions: A case study on processing, characteristics, and tribological behavior of Al2O3-YSZ coatings2020In: Applied Sciences, E-ISSN 2076-3417, Vol. 10, no 15, article id 5140Article in journal (Refereed)
    Abstract [en]

    Thermal spraying deploying liquid feedstock offers an exciting opportunity to obtain coatings with characteristics vastly different from those produced using conventional spray-grade powders. The most extensively investigated variant of this technique is Suspension Plasma Spraying (SPS), which utilizes a suspension of fine powders in an appropriate medium. The relatively recent advent of axial feed capable plasma spray systems can enable higher throughputs during SPS, provides the possibility for spraying with longer stand-off distances, and also permit the use of suspensions with higher solid loading. The present work investigates axial plasma sprayed coatings produced using a mixed suspension of fine (submicron or nano-sized) powders of Al2O3 and YSZ as a case study. Deposition of the mixed suspension using axial injection plasma spraying, comprehensive evaluation of characteristics of the resulting coatings, and assessment of their tribological behavior were of particular interest. Evaluation of surface morphology, microstructure, and hardness of the coatings reveals that axial SPS of mixed suspensions provides an exciting pathway to realize finely structured multi-constituent coatings using suspensions with as high as 40 wt. % solid loading. The study of scratch, dry sliding wear, and erosion behavior also specifically shows that the addition of YSZ in the Al2O3 matrix can improve the tribological properties of the coating. © 2020 by the authors.

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  • 65.
    Goel, Sneha
    et al.
    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 Ind AG, Althofen, Austria.
    Wiklund, U.
    Uppsala Univ, Dept Technol, Mat Sci Div, S-75121 Uppsala, Swede.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Axial suspension plasma spraying of Al2O3 coatings for superior tribological properties2017In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 315, p. 80-87Article in journal (Refereed)
    Abstract [en]

    Suspension plasma spray is a relatively new thermal spray technique which enables feeding of fine powder to produce advanced coatings for varied applications. This work investigates the difference in structure and performance of Al2O3 coatings manufactured using conventional micron-sized powder feedstock and a suspension of sub-micron to few micron sized powder. Axial injection was implemented for deposition in both cases. The effect of feedstock size and processing on the tribological performance of the two coatings was of specific interest. The coatings were characterized by Optical and Scanning Electron Microscopy, micro-hardness and scratch resistance testing, and their dry sliding wear performance evaluated. The suspension sprayed coatings yielded significantly higher scratch resistance, lower friction coefficient and reduced wear rate compared to conventional coatings. The improved tribological behaviour of the former is attributable to finer porosity, smaller splat sizes, and improved interlamellar bonding. (C) 2017 Elsevier B.V. All rights reserved.

  • 66.
    Goel, Sneha
    et al.
    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.
    Joshi, Shrikant
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Deposition of Novel Composite Coatings by Suspension-Powder Hybrid Plasma Spraying2016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, p. 1-8Conference paper (Refereed)
    Abstract [en]

    Suspension Plasma Spray (SPS) is an emerging technique which overcomes the difficulties typically associated with feeding of fine (submicron or nano-sized) powders in conventional atmospheric plasma spraying (APS) to obtain superior coating properties for various engineering applications. The advent of plasma spray systems that allow axial injection of feedstock, which considerably improves thermal exchange between the plasma plume and the injected feedstock, has enabled substantial enhancement in deposition rates/efficiencies to make SPS techno-commercially exciting. The present study utilizes both the above advances in plasma spraying to demonstrate the ability to deposit novel coating architectures by sequential/simultaneous axial injection of both powder and a suspension feedstock. The results reveal that composite coatings uniquely combining the micron-size features arising from the spray-grade powder and the submicron or nano-sized features attributable to the suspension, can be conveniently realized using the above approach. Three different kinds of coating architectures were generated, namely layered, composite, and functionally graded. The sprayed coatings were extensively characterized for attributes such as surface morphology, microstructure, and composition particularly in the case of composite coatings.

  • 67.
    Goel, Sneha
    et al.
    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.
    Wiklund, U.
    Uppsala University, Materials Science Division, Uppsala, Sweden.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Hybrid powder-suspension Al2O3-ZrO2 coatings by axial plasma spraying: Processing, characteristics & tribological behaviour2017In: Proceedings of the International Thermal Spray Conference & Exposition, New York: Curran Associates, Inc , 2017, Vol. 1, p. 374-379Conference paper (Refereed)
    Abstract [en]

    The ability of suspension plasma spraying (SPS) to overcome difficulties associated with feeding of fine (submicron or nano-sized) powders and achieve more refined microstructures than possible in atmospheric plasma spraying (APS) is well established. In recent times, the use of axial injection plasma spray systems has yielded substantial enhancement in deposition rates/efficiencies due to improved thermal exchange between the plasma plume and injected feedstock. The present paper describes utilization of both the above advances in plasma spraying to create various function-dependent coating architectures through simultaneous and/or sequential spraying of hybrid powder-suspension feedstock. A specific variant of such hybrid axial plasma spraying that enables deposition of composite coatings by simultaneous injection of a powder and a suspension is discussed in particular detail. Results obtained using an Al2O3-ZrO2 material system as a case study reveal that composite coatings combining the micron-size features arising from the spray-grade Al2O3 powder and submicron or nano-sized features attributable to the ZrO2 suspension can be conveniently realized. The surface morphology, microstructure, and composition of these coatings, as well as their tribological behaviour determined using scratch and ball-on-disc tests, are presented herein. The utility of this method to develop a wide array of composite coatings is also discussed. 

  • 68.
    Goel, Sneha
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Bourreau, Kévin
    University of Limoges, Specialty Materials, Limoges 87000, France (FRA).
    Olsson, Jonas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Klement, Uta
    Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg 41296, Sweden.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Can Appropriate Thermal Post-Treatment Make Defect Content in as-Built Electron Beam Additively Manufactured Alloy 718 Irrelevant?2020In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 13, no 3, article id 536Article in journal (Refereed)
    Abstract [en]

    Electron beam melting (EBM) is gaining rapid popularity for production of complex customized parts. For strategic applications involving materials like superalloys (e.g., Alloy 718), post-treatments including hot isostatic pressing (HIPing) to eliminate defects, and solutionizing and aging to achieve the desired phase constitution are often practiced. The present study specifically explores the ability of the combination of the above post-treatments to render the as-built defect content in EBM Alloy 718 irrelevant. Results show that HIPing can reduce defect content from as high as 17% in as-built samples (intentionally generated employing increased processing speeds in this illustrative proof-of-concept study) to <0.3%, with the small amount of remnant defects being mainly associated with oxide inclusions. The subsequent solution and aging treatments are also found to yield virtually identical phase distribution and hardness values in samples with vastly varying as-built defect contents. This can have considerable implications in contributing to minimizing elaborate process optimization efforts as well as slightly enhancing production speeds to promote industrialization of EBM for applications that demand the above post-treatments.

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  • 69.
    Goel, Sneha
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Mehtani, Hitesh
    Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, India (IND).
    Yao, Shu-Wei
    Xi’an Jiaotong University, School of Materials Science and Engineering, Xi’an, 710049, China (CHN).
    Samajdar, Indradev
    Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai, 400076, India (IND).
    Klement, Uta
    Chalmers University of Technology, Gothenburg, Sweden.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    As-Built and Post-treated Microstructures of an Electron Beam Melting (EBM) Produced Nickel-Based Superalloy2020In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 51, no 12, p. 6546-6559Article in journal (Refereed)
    Abstract [en]

    The microstructures of an electron beam melted (EBM) nickel-based superalloy (Alloy 718) were comprehensively investigated in as-built and post-treated conditions, with particular focus individually on the contour (outer periphery) and hatch (core) regions of the build. The hatch region exhibited columnar grains with strong texture in the build direction, while the contour region had a mix of columnar and equiaxed grains, with no preferred crystallographic texture. Both regions exhibited nearly identical hardness and carbide content. However, the contour region showed a higher number density of fine carbides compared to the hatch. The as-built material was subjected to two distinct post-treatments: (1) hot isostatic pressing (HIP) and (2) HIP plus heat treatment (HIP + HT), with the latter carried out as a single cycle inside the HIP vessel. Both post-treatments resulted in nearly an order of magnitude decrease in defect content in hatch and contour regions. HIP + HT led to grain coarsening in the contour, but did not alter the microstructure in the hatch region. Different factors that may be responsible for grain growth, such as grain size, grain orientation, grain boundary curvature and secondary phase particles, are discussed. The differences in carbide sizes in the hatch and contour regions appeared to decrease after post-treatment. After HIP + HT, similar higher hardness was observed in both the hatch and contour regions compared to the as-built material.

  • 70.
    Goel, Sneha
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Neikter, Magnus
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Capek, J.
    Paul Scherrer Institute, Laboratory for Neutron Scattering and Imaging, , Villigen PSI, CH-5232, Switzerland (CHE).
    Polatidis, Efthymios
    Paul Scherrer Institute, Laboratory for Neutron Scattering and Imaging, , Villigen PSI, CH-5232, Switzerland (CHE).
    Colliander, Magnus Hörnqvist
    Chalmers University of Technology, Gothenburg, 41296, Sweden .
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Residual stress determination by neutron diffraction in powder bed fusion-built Alloy 718: Influence of process parameters and post-treatment2020In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 195, article id 109045Article in journal (Refereed)
    Abstract [en]

    Alloy 718 is a nickel-based superalloy that is widely used as a structural material for high-temperature applications. One concern that arises when Alloy 718 is manufactured using powder bed fusion (PBF) is that residual stresses appear due to the high thermal gradients. These residual stresses can be detrimental as they can degrade mechanical properties and distort components. In this work, residual stresses in PBF built Alloy 718, using both electron and laser energy sources, were measured by neutron diffraction. The effects of process parameters and thermal post-treatments were studied. The results show that thermal post-treatments effectively reduce the residual stresses present in the material. Moreover, the material built with laser based PBF showed a higher residual stress compared to the material built with electron-beam based PBF. The scanning strategy with the lower amount of residual stresses in case of laser based PBF was the chessboard strategy compared to the bi-directional raster strategy. In addition, the influence of measured and calculated lattice spacing (d0) on the evaluated residual stresses was investigated. © 2020 The Authors

  • 71.
    Goel, Sneha
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Olsson, Jonas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Ahlfors, Magnus
    Quintus Technologies AB, Västerås, Sweden.
    Klement, Uta
    Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, Sweden.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    The Effect of Location and Post-treatment on the Microstructure of EBM-Built 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. 115-129Conference paper (Refereed)
    Abstract [en]

    Additive manufacturing (AM) of Ni-based superalloys such as Alloy 718 may obviate the need for difficult machining and welding operations associated with geometrically intricate parts, thus potentially expanding design possibilities and facilitating cost-effective manufacture of complex components. However, processing AM builds completely free from defects, which may impair mechanical properties such as fatigue and ductility, is challenging. Anisotropic properties, microstructural heterogeneities and local formation of undesired phases are additional concerns that have motivated post-treatment of AM builds. This work investigates the microstructural changes associated with post-treatment of Alloy 718 specimens produced by Electron Beam Melting (EBM) for as-built microstructures at 3 build heights: near base plate, in the middle of build and near the top of the build. Two different post-treatment conditions, hot isostatic pressing (HIP) alone and a combined HIP with solutionising and two-step aging were examined and compared to the results for the as-built condition. The influence of various post-treatments on minor phase distributions (δ, γ″, carbides), overall porosity, longitudinal grain widths and Vickers microhardness was considered. The HIP treatment led to significant reduction in overall porosity and dissolution of δ phase, which led to appreciable grain growth for both post-treatment conditions. The variation in hardness noted as a function of build height for the as-built specimens was eliminated after post-treatment. Overall, the hardness was found to decrease after HIP and increase after the full HIP, solutionising and aging treatment, which was attributed to dissolution of γ″ during HIP and its re-precipitation in subsequent heat treatment steps.

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  • 72.
    Goel, Sneha
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. VTT Technical Research Centre of Finland, Espoo (FIN).
    Shipley, James
    Quintus Technologies AB, Västerås (SWE).
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Thermal post-treatment of additively manufactured components2023In: Additive Manufacturing of High-Performance metallic Materials / [ed] Pederson, Robert, Andersson, Joel & Joshi, Shrikant V., Elsevier, 2023, 1., p. 358-427Chapter in book (Refereed)
    Abstract [en]

    Metal additive manufacturing (AM) processes have been receiving growing industrial attention in recent times for near net shape manufacture of complex parts with traditionally difficult-to-machine materials, such as high-performance super alloys and Titanium alloys. AM processing of these materials is especially promising for aerospace and other industrial sectors that value design flexibility, rapid production, and reduction in wastage of expensive feedstock. However, depending upon the specific AM technique employed, AM-built parts may be characterized by one or more of the following: defects, presence of undesirable phases, absence of desired hardening precipitates, anisotropy in properties, etc. Consequently, thermal post-treatment can be a crucial step in any robust production process aimed at ensuring that the AM-built components eventually meet critical service requirements. Depending upon the alloy in question, thermal post-treatments can comprise hot isostatic pressing and heat treatment. This chapter outlines the main drivers for thermal post-treatment in case of AM processed super alloys and Ti alloys, as well as the typical stages involved based on the alloy or application in question. The influence of each stage of post-treatment, as well as the associated time-temperature schedules, on microstructure, phase constitution, and mechanical properties is also discussed, using illustrative examples from AM-built Alloy 718 and Ti-6Al-4V.

  • 73.
    Goel, Sneha
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Sittiho, Anumat
    University of Idaho, Department of Chemical and Materials Engineering, Moscow, ID 83844, United States.
    Charit, Indrajit
    University of Idaho, Department of Chemical and Materials Engineering, Moscow, ID 83844, United States.
    Klement, Uta
    Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, Sweden.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Effect of post-treatments under hot isostatic pressure on microstructural characteristics of EBM-built Alloy 7182019In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 28, p. 727-737Article in journal (Refereed)
    Abstract [en]

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

  • 74.
    Goel, Sneha
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Zaninelli, Enrico
    Department of Engineering Enzo Ferrari, University of Modena and Reggio Emilia, Modena (ITA).
    Gundgire, Tejas
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Ahlfors, Magnus
    Quintus Technologies AB, Västerås (SWE).
    Ojo, Olanrewaju
    Department of Mechanical Engineering, University of Manitoba, Winnipeg (CAN).
    Klement, Uta
    Chalmers University of Technology, Gothenburg, (SWE).
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Microstructure evolution and mechanical response-based shortening of thermal post-treatment for electron beam melting (EBM) produced Alloy 7182021In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 820, article id 141515Article in journal (Refereed)
    Abstract [en]

    Electron beam melting (EBM) produced Alloy 718 was subjected to thermal post-treatment involving hot isostatic pressing (HIPing) and heat treatment (HT). Subjecting the material to HIPing at 1120 degrees C led to significant densification. Study of microstructure evolution during HT (comprising of solution treatment and aging) showed possibility of significantly shortening the HT duration, particularly the time for two-step aging from the standard (8 h + 8 h) long cycle to possibly a shortened (4 h + 1 h) cycle. Another approach for shortening the post-treatment cycle by integrating the HIPing with HT inside the HIP vessel was also successfully implemented. The above observations were further substantiated by tensile response of the material subjected to the varied post-treatment cycles; out of all the post-treatments steps, tensile behaviour was observed to be mainly affected by the aging treatment. Further prospects for shortening the post-treatment protocol are also described, such as shortening of HIPing duration for the typical 4 h to 1 h cycle as well as possible elimination of solution treatment step from the entire post-treatment protocol specifically when prior HIPing is performed. Heat treatment with prior HIPing was found to be crucial for improving fatigue life, because subjecting EBM Alloy 718 to only HT, irrespective of the short or standard long protocol, rendered inferior fatigue response.

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  • 75.
    Goel, Sneha
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Zaninelli, Enrico
    Department of Engineering Enzo Ferrari, University of Modena and Reggio Emilia, 41100, Modena, Italy (ITA).
    Gårdstam, Johannes
    Quintus Technologies AB, 72166, Västerås, Sweden.
    Klement, Uta
    Chalmers University of Technology, Gothenburg, Sweden.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Microstructure evolution-based design of thermal post-treatments for EBM-built Alloy 7182020In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 56, no 2, p. 5250-5268Article in journal (Refereed)
    Abstract [en]

    Alloy 718 samples were fabricated by electron beam melting (EBM) additive manufacturing process. The work focused on systematic investigation of response of the material to various thermal post-treatments, involving hot isostatic pressing (HIPing), solution treatment (ST) and two-step aging, to tailor post-treatment procedure for EBM-built Alloy 718. Results showed that HIPing at lowered temperature can be used for attaining desired defect closure while preserving grain size. Subjecting the material to ST, with or without prior HIPing, mainly caused precipitation of δ phase at the grain boundaries with prior HIPing decreasing the extent of δ phase precipitation. Moreover, results suggest that the utility of ST, with prior HIPing, could be dictated by the need to achieve a certain δ phase content, as the typically targeted homogenization after ST had already been achieved through HIPing. Detailed investigation of microstructural evolution during subsequent aging with and without prior HIPing showed that a significantly shortened aging treatment (‘4 + 1’ h), compared to the ‘standard’ long treatment (‘8 + 8’ h) traditionally developed for conventionally produced Alloy 718, might be realizable. These results can have significant techno-economic implications in designing tailored post-treatments for EBM-built Alloy 718.

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  • 76.
    Gopal, Vasanth
    et al.
    Department of Physics, School of Advanced Sciences, VIT, Vellore 632014, India Centre for Biomaterials, Cellular and Molecular Theranostics, VIT, Vellore 632014, India.
    Goel, Sneha
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Manivasagam, Geetha
    Centre for Biomaterials, Cellular and Molecular Theranostics, VIT, Vellore 632014, India.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Performance of Hybrid Powder-Suspension Axial Plasma Sprayed Al2O3-YSZ Coatings in Bovine Serum Solution2019In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 12, article id E1922Article in journal (Refereed)
    Abstract [en]

    Ceramic coatings on metallic implants are a promising alternative to conventional implants due to their ability to offer superior wear resistance. The present work investigates the sliding wear behavior under bovine serum solution and indentation crack growth resistance of four coatings, namely (1) conventional powder-derived alumina coating (Ap), (2) suspension-derived alumina coating (As), (3) composite Al2O3-20wt % Yittria stabilized Zirconia (YSZ) coating (AsYs) deposited using a mixed suspension, and (4) powder Al2O3-suspension YSZ hybrid composite coating ApYs developed by axial feeding plasma spraying, respectively. The indentation crack growth resistance of the hybrid coating was superior due to the inclusion of distributed fine YSZ particles along with coarser alumina splats. Enhanced wear resistance was observed for the powder derived Ap and the hybrid ApYs coatings, whereas the suspension sprayed As and AsYs coatings significantly deteriorated due to extensive pitting.

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  • 77. Govindarajan, S.
    et al.
    Dusane, R. O.
    Joshi, S. V.
    In situ particle generation and splat formation during solution precursor plasma spraying of yttria-stabilized zirconia coatings2011In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 94, no 12, p. 4191-4199Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs) based on Yttria-stabilized Zirconia (YSZ) deposited by the solution precursor plasma spray (SPPS) technique have been claimed to exhibit superior durability compared to conventional plasma spraying and even electron-beam physical vapor deposition. This has been attributed to the interesting features, like vertical cracks, nanosized pores, and fine splats that are inherent to SPPS-deposited YSZ coatings. However, the mechanism of coating formation during SPPS processing is not yet well understood. This study is aimed at understanding the influence of some key SPPS process variables on in situ generated particles and subsequent splat formation to augment the current level of understanding. The plasma power employed was found to play a major role in governing the morphology and phase constitution of in situ generated particles. The shape and size of the YSZ splats were also significantly influenced by the plasma power, but the substrate pre-heat was also noted to be a major determining factor. It was further observed that the SPPS typically involved in situ generation of very fine particulates (50-500 nm) and splats (typically 200-2000 nm), which lead to its nano-porous and homogeneous microstructure. The YSZ coating characteristics were also found to correlate well with the above results. © 2011 The American Ceramic Society.

  • 78.
    Govindararajan, S.
    et al.
    International Advanced Research Center for Powder Metallurgy and New Materials, Balapur, Hyderabad, India.
    Dusane, R. O.
    Department of Metallurgical Engineering & Materials Science, Indian Institute of Technology, Powai, Mumbai, India.
    Joshi, Shrikant V.
    Understanding the Formation of Vertical Cracks in Solution Precursor Plasma Sprayed Yttria-Stabilized-Zirconia Coatings2014In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 97, p. 3396-3406Article in journal (Refereed)
    Abstract [en]

    Yttria-stabilized zirconia (YSZ) deposition by the solution precursor plasma spraying (SPPS) route has been of interest for potential thermal barrier coating (TBC) applications. It has been surmised that realization of unique microstructural features like vertical cracks, nanosized pores and fine splats in the TBCs can significantly enhance coating durability and performance. However, satisfactory control over the YSZ coating microstructure has been elusive in the absence of an adequate understanding of the mechanism responsible for coating deposition in SPPS. This study demonstrates the ability to tailor microstructure of deposited YSZ coatings over a wide range, from nano-porous coatings to a vertically cracked microstructure. Varying of precursor flow rate has been shown to dictate the pyrolysis events occurring in situ and, adopting this approach, YSZ coatings with widely varying microstructural features have been developed. The coatings have been characterized in detail and the observations correlated with in-flight particle generation and splat formation. These studies also provide useful insights into the possible origin of vertical cracks in the coating for which a mechanism is proposed.

  • 79.
    Guerin, Elie
    et al.
    National School of Engineers, University of Limoges, Limoges, France.
    Sadeghimeresht, Esmaeil
    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.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Role of Chemistry on Corrosion Behavior of Various Ni-based HVAF-Sprayed Coatings in Simulated Boiler Environments2017Conference paper (Other academic)
  • 80.
    Gundgire, Tejas
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Goel, Sneha
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Klement, Uta
    Chalmers University of Technology, Department of Industrial and Material Science, Gothenburg, 41296, Sweden.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Response of different electron beam melting produced Alloy 718 microstructures to thermal post-treatments2020In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 167, article id 110498Article in journal (Refereed)
    Abstract [en]

    Electron beam melting (EBM) was used to produce Alloy 718 specimens with different microstructures (columnar, equiaxed and a combination thereof) by varying the process parameters. The present study aimed at assessing the response of such varying as-built microstructures to identical thermal post-treatments, which included hot isostatic pressing (HIPing) followed by heat treatment involving solution treatment and aging. The effect of these treatments on defect content, grain structure, hardness and phase constitution in the specimens was specifically analysed. Despite differences in defect content of as-built specimens with distinct microstructures, HIPing was effective in closing defects leading to samples exhibiting similar density. After HIPing, grains with equiaxed morphology or columnar grains with lower aspect ratio showed higher tendency for grain growth in comparison to the columnar grains with higher aspect ratio. The various factors affecting the stability of grains during HIPing of builds with distinct microstructures were investigated. These factors include texture, grain size, and secondary phase particles. The carbide sizes in the different as-built samples varied but were found to be largely unaffected by the post-treatments. Solution treatment following HIPing led to greater precipitation of grain boundary ÎŽ phase in regions with coarser grains than the smaller ones. After HIPing and heat treatment, all specimens exhibited similar precipitation of γ″ phase regardless of their grain morphology in the as-built condition. © 2020 The Author(s)

  • 81. Islavath, N.
    et al.
    Ramasamy, E.
    Das, D.
    Joshi, Shrikant. V.
    Spray coated seed layer for scalable synthesis of aligned ZnO nanowire arrays on FTO substrate and their photovoltaic properties2015In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 41, no 3, p. 4118-4122Article in journal (Refereed)
    Abstract [en]

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

  • 82.
    Islavath, Nanaji
    et al.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India; School of Engineering Sciences and Technology, University of Hyderabad, Hyderabad 500046, India.
    Das, Dibakar
    School of Engineering Sciences and Technology, University of Hyderabad, Hyderabad 500046, India.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Ramasamy, Easwaramoorthi
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Seed layer-assisted low temperature solution growth of 3D ZnO nanowall architecture for hybrid solar cells2017In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 116, p. 219-226Article in journal (Refereed)
    Abstract [en]

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

  • 83.
    Islavath, Nanaji
    et al.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Saroja, S.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Reddy, K Srinivas
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Harikesh, P.C.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Veerappan, G.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Ramasamy, Easwaramoorthi
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Effect of hole-transporting materials on the photovoltaic performance and stability of all-ambient-processed perovskite solar cells2017In: Journal of Energy Chemistry, ISSN 2095-4956, E-ISSN 2096-885X, Vol. 26, no 3, p. 584-591Article in journal (Refereed)
    Abstract [en]

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

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

  • 84.
    Jafari, R.
    et al.
    Tarbiat Modares University, Department of Material Science and Engineering, Tehran, 14115, Iran.
    Sadeghimeresht, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Shahrabi Farahani, T.
    Tarbiat Modares University, Department of Material Science and Engineering, Tehran, 14115, Iran.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    KCI-induced corrosion behavior of HVAF-sprayed Ni-based coatings in ambient air2017In: Proceedings of the International Thermal Spray Conference & Exposition (ITSC 2017), Curran Associates, Inc. , 2017, Vol. 2, p. 946-950Conference paper (Refereed)
    Abstract [en]

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

  • 85.
    Jafari, R.
    et al.
    Department of Material Science and Engineering, Tarbiat Modares University, Tehran, Iran.
    Sadeghimeresht, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Shahrabi Farahani, T.
    Department of Material Science and Engineering, Tarbiat Modares University, Tehran, Iran .
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    KCl-induced corrosion behavior of HVAF-sprayed Ni-based coatings in ambient air2017Conference paper (Other academic)
  • 86.
    Jafari, Reza
    et al.
    Tarbiat Modares University, Department of Material Science and Engineering, Tehran, Iran.
    Sadeghimeresht, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Shahrabi Farahani, Taghi
    Tarbiat Modares University, Department of Material Science and Engineering, Tehran, Iran.
    Huhtakangas, Matti
    M. H. Engineering AB, Karlskoga, Sweden .
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    KCl-Induced High Temperature Corrosion Behavior of HVAF-Sprayed Ni-Based Coatings in Ambient Air2018In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 27, no 3, p. 500-511Article in journal (Refereed)
    Abstract [en]

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

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  • 87. Joshi, S. V.
    A prediction model to assist plasma and HVOF spraying1992In: Materials Letters, Vol. 14, no 1, p. 31-36Article in journal (Refereed)
    Abstract [en]

    A theoretical prediction model is developed to estimate the in-flight velocity, temperature and size of a particle during plasma and HVOF spraying. The salient features of this model are outlined and the model predictions are examined through some example calculations performed under typical spraying conditions. Comparison with experimental data reveals that the present method enables accurate predictions. The principal advantages and shortcomings of the plasma and HVOF systems are also discussed based on the model estimates. © 1992.

  • 88. Joshi, S. V.
    Comparison of particle heat-up and acceleration during plasma and high velocity oxy-fuel spraying1992In: Powder Metallurgy International, Vol. 24, no 6, p. 373-378Article in journal (Refereed)
    Abstract [en]

    Development of protective coatings by means of the thermal spray techniques known as atmospheric plasma spraying and high velocity oxy-fuel (HVOF) spraying is gaining widespread industrial acceptability. The temperature and velocity profiles in a plasma flame and an oxy-fuel combustion flame are distinctly different and this is primarily responsible for the significantly varied behaviour of injected particles in the two cases. This study deals primarily with the comparison of particle heat-up and acceleration during powder spraying by the two above methods and is based on a recently developed prediction model to assist plasma and HVOF spraying. Illustrative results for a few powder materials are presented. The results reveal that the high-temperature plasma flame is capable of completely melting even high melting point ceramic powders which are extremely difficult to melt in an oxy-fuel combustion flame. However, the hypersonic oxy-fuel flame is found to accelerate the powder particles to considerably higher velocities than a plasma flame and is, therefore, better suited to obtaining dense and well-bonded coatings using metal and low-melting alloy powders. The influence of the powder injection parameters on particle behaviour in plasma and HVOF spraying is also investigated.

  • 89. Joshi, S. V.
    Plasma spraying of Wc-Co part I: Theoretical investigation of particle heating and acceleration during spraying1993In: Journal of Thermal Spray Technology, Vol. 2, no 2, p. 127-130Article in journal (Refereed)
    Abstract [en]

    Plasma-sprayed WC-Co coatings are used extensively in a variety of wear-resistant applications. The quality of these sprayed coatings depends greatly on the temperature and velocity of the powder particles impacting the substrate. Because it is both expensive and difficult to experimentally determine these particle parameters, the present study deals with a theoretical investigation of particle heatup and acceleration during plasma spraying of WC-Co based on a recently developed model. The effect of WC-Co particle size on the evolution of particle temperature and velocity is examined through calculations performed under typical spraying conditions. The implications of the powder particles, assuming an off-axis trajectory during their traverse through the plasma flame, are also discussed. © 1993 ASM International.

  • 90. Joshi, S. V.
    et al.
    Liang, Q.
    Park, J. Y.
    Batdorf, J. A.
    Effect of quenching conditions on particle formation and growth in thermal plasma synthesis of fine powders1990In: Plasma Chemistry and Plasma Processing, Vol. 10, no 2, p. 339-358Article in journal (Refereed)
    Abstract [en]

    The vapor-phase synthesis of ultrafine powders in reactive thermal plasma systems is studied. A mathematical model is developed to determine the effect of quenching conditions on the size characteristics of powders produced. The particle nucleation is considered to be due to both condensation of product vapor and surface reaction between adsorbed reactant species. The particle growth is considered to be exclusively due to further condensation of product vapor. Numerical predictions on powder formation are explored through a case study for the synthesis of zinc oxide powders from zinc vapor and oxygen carried in argon gas. The results of the present srudy indicate that the size characteristics of plasma-produced powders can be significantly enhanced by gradual, regulated quenching, as opposed to the rapid quenching conventionally used in the past. The results further indicate that distribution of the quench gas along the reactor provides an effective means to accomplish the much desired control over the powder properties. © 1990 Plenum Publishing Corporation.

  • 91. Joshi, S. V.
    et al.
    Park, J. Y.
    Taylor, P. R.
    Richardson, L. S.
    Knudsen effect on plasma-particle mass transfer. I. Formulation and application to self-diffusion1986In: Plasma Chemistry and Plasma Processing, Vol. 6, no 3, p. 281-298Article in journal (Refereed)
    Abstract [en]

    The Knudsen effect on mass transfer between a plasma gas and a small particle is investigated. A predictive model is developed by incorporating the Z-potential approach into the jump theory. The predictions of the model are explored through a case study. The results indicate that the Knudsen effect is significant and depends strongly on the particle size and the surface conditions. The plasma and the particle surface temperatures are also found to be determining factors. Under certain conditions, it is observed that the Knudsen effect can enhance the plasma-particle mass transfer, contrary to the predictions of the previous near-isothermal models. © 1986 Plenum Publishing Corporation.

  • 92. Joshi, S. V.
    et al.
    Park, J. Y.
    Taylor, P. R.
    Richardson, L. S.
    Particle-gas mass transfer under plasma conditions1986In: International Journal of Heat and Mass Transfer, Vol. 29, no 10, p. 1565-1573Article in journal (Refereed)
    Abstract [en]

    A simple analytical method is proposed for particle-gas mass transfer calculations under plasma conditions. This method, called the Z-potential method, fully accounts for the temperature variation of the gas transport properties while permitting use of the convenient isothermal expression Sh = 2.0. The Z-potential approach is also found to be extremely useful in ascertaining the Knudsen discontinuum effect on mass transfer between the plasma gas and a small particle. A predictive model for the Knudsen effect, developed by combining the Z-potential approach with the jump theory, is illustrated in detail by means of a case study on a nitrogen plasma system. © 1986.

  • 93. Joshi, S. V.
    et al.
    Park, J. Y.
    Taylor, P. R.
    Richardson, L. S.
    The integral mean diffusivity for particle-gas mass transfer calculations under thermal plasma conditions1985In: Plasma Chemistry and Plasma Processing, Vol. 5, no 2, p. 143-161Article in journal (Refereed)
    Abstract [en]

    A new integral mean diffusivity is proposed for the calculation of the mass transfer rate around a small particle immersed in a thermal plasma gas. Analogous to the integral mean thermal conductivity widely used for the corresponding heat transfer calculations, the integral mean diffusivity greatly facilitates the use of the convenient isothermal correlation, Sh=2.0, for the gas-particle mass transfer calculations. The calculation method accounts for both ordinary molecular diffusion and thermal diffusion. The latter has been found to play a significant role under thermal plasma conditions. The use of the integral mean diffusivity is illustrated with an example calculation on an Ar-He plasma system. © 1985 Plenum Publishing Corporation.

  • 94. Joshi, S. V.
    et al.
    Sivakumar, G.
    Raghuveer, T.
    Dusane, R. O.
    Hybrid Plasma-Sprayed Thermal Barrier Coatings Using Powder and Solution Precursor Feedstock2014In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 23, no 4, p. 616-624Article in journal (Refereed)
    Abstract [en]

    A novel approach of hybridizing the conventional atmospheric plasma spraying (APS) technique with the solution precursor plasma spray (SPPS) route to achieve thermal barrier coatings (TBCs) with tailored configurations is presented. Such a hybrid process can be conveniently adopted for forming composite, multi-layered and graded coatings employing simultaneous and/or sequential feeding of solution precursor as well as powder feedstock, yielding distinct TBC microstructures that bear promise to further extend coating durability. TBC specimens generated using conventional APS technique, the SPPS method and through APS-SPPS hybrid processing have been comprehensively characterized for microstructure, phase constitution, hardness and thermal cycling life, and the results were compared to demonstrate the advantages that can ensue from hybrid processing.

  • 95. Joshi, S. V.
    et al.
    Sivakumar, R.
    Particle behaviour during high velocity oxy-fuel spraying1991In: Surface and Coatings Technology, Vol. 50, no 1, p. 67-74Article in journal (Refereed)
    Abstract [en]

    A comprehensive one-dimensional model recently developed by the authors is used to investigate particle behaviour associated with the high velocity oxy-fuel (HVOF) spraying process. Using the spraying of WC-12%Co powder as a case study, it is shown that the Knudsen non-continuum effects can have an immense influence on the gas-solid heat and momentum transfer processes. Consistent with actual practical experience during HVOF spraying, the results of this study reveal that the low temperatures provided by the oxy-fuel combustion flame preclude complete melting of many ceramic powders possessing high melting points. However, it is shown that powders of metals and the low melting point alloys can be completely molten in the oxy-fuel flame. With WC-12%Co powder, it is found that only particles smaller than 45 μm in size can be fully molten and this is in excellent agreement with the empirically established HVOF coating practice. The results also indicate that the hypersonic flame accelerates the powder particles to very high velocities, around 700 m s-1 in some instances, and such high particle velocities are primarily responsible for the HVOF technique yielding dense and well-bonded coatings which are superior to plasma-sprayed coatings. © 1991.

  • 96. Joshi, S. V.
    et al.
    Sivakumar, R.
    Prediction of in-flight particle parameters during plasma spraying of ceramic powders1992In: Materials Science and Technology, Vol. 8, no 6, p. 481-488Article in journal (Refereed)
    Abstract [en]

    A theoretical prediction model is presented to estimate the in-flight velocity, temperature, and size of a ceramic particle traversing through a plasma flame. The model accounts for the various phenomena that can influence the transport rate calculations in plasma spraying operations, which typically involve very fine particles (<50 μm) subjected to an extremely non-isothermal environment. The mathematical formulation simultaneously considers internal heat conduction in particles, accounts for the steep temperature gradients that prevail in plasma-particle systems, and incorporates the Knudsen discontinuum effects on both heat and momentum transfer. The significance of these factors is illustrated through some example calculations performed under typical plasma spraying conditions. Comparison with experimental data reveals that the present method, although simple and easy to use, enables accurate predictions to be made and can be a very useful tool in the model assisted development of various plasma-particle processing systems.

  • 97. Joshi, S. V.
    et al.
    Srivastava, M. P.
    On the thermal cycling life of plasma-sprayed yttria-stabilized zirconia coatings1993In: Surface and Coatings Technology, Vol. 56, no 3, p. 215-224Article in journal (Refereed)
    Abstract [en]

    The influence of various factors on the thermal shock resistance of plasma-sprayed yttria-stabilized zirconia (YSZ) coatings was investigated. The coatings, formed using different spraying conditions, were repeatedly exposed to a thermal cycle involving a 30 minute heating period at 1200°C followed by a water quench during this study. The results suggest that, for any given YSZ powder, there exists an optimum plasma arc current for obtaining coatings that best endure such severe temperature cycling conditions. Other coating variables, such as spray distance and powder feed rate, are also observed to effect coating durability. Furthermore, the YSZ overlayer thickness and the bond coat material employed are found to be important coating life determining factors. © 1993.

  • 98. Joshi, S. V.
    et al.
    Srivastava, M. P.
    Chatterjee, M.
    Ray, J.
    Chatterjee, A.
    Ganguli, D.
    Plasma spraying of an indigenous yttria stabilized zirconia powder prepared by the sol-gel technique1993In: Bulletin of Materials Science, Vol. 16, no 1, p. 19-28Article in journal (Refereed)
    Abstract [en]

    An indigenous sol-gel derived yttria-partially stabilized zirconia (Y-PSZ) powder has been characterized and its suitability for plasma spraying applications evaluated. The powder, determined to have about 5·1% yttria content, predominantly consisted of spherical particles with an average equivalent particle diameter close to 25 μm. Furthermore, it was found that the powder did not contain any particles >50 μm, which is considered the ideal upper size limit for spray-grade ceramic powders in order to ensure complete melting during spraying. The sol-gel produced powder exhibited good flow characteristics and the plasma sprayed coatings developed using this powder were also found to have excellent thermal shock resistance. The corresponding results obtained using an imported Y-PSZ powder are also presented for the purpose of comparison. © 1993 Indian Academy of Sciences.

  • 99. Joshi, S. V.
    et al.
    Srivastava, M. P.
    Pal, A.
    Pal, S.
    Plasma spraying of biologically derived hydroxyapatite on implantable materials1993In: Journal of Materials Science: Materials in Medicine, Vol. 4, no 3, p. 251-255Article in journal (Refereed)
    Abstract [en]

    Plasma spraying of hydroxyapatite (HA) coatings on human implants is considered to provide a promising means of enhancing their biocompatibility and improving tissue growth. This paper briefly describes a method of extracting HA powder from a biological source, namely human teeth. The physical and chemical characteristics of the derived powder are studied and the suitability of this powder for plasma spraying applications is ascertained. The deposited coatings are found to retain the chemistry characteristic of the apatite. Typical results of metallographic and scanning electron microscopy (SEM) studies and hardness measurements on the sprayed HA coatings are presented. © 1993 Chapman & Hall.

  • 100. Joshi, S. V.
    et al.
    Srivastava, M. P.
    Sundararajan, G.
    Evidence of accelerated thermal cycling test schedules influencing the ranking of zirconia-base thermal barrier coatings1995In: Journal of Thermal Spray Technology, Vol. 4, no 3, p. 275-279Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs) often encounter temperature cycling in the course of normal operation. In the absence of actual or simulated engine test facilities, accelerated furnace thermal cycling experiments are frequently devised to evaluate the response of various TBCs. This study, which deals with yttria-stabilized and magnesia-stabilized zirconia systems, shows that the performance of a TBC is significantly governed by the severity of the time-temperature schedule employed. More importantly, the ranking of the two zirconia-base TBCs also is influenced by the adopted thermal cycling test schedule. These findings have ramifications in the design of suitable accelerated tests for TBC evaluation.

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