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  • 51.
    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. 

  • 52.
    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.

  • 53. 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, 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.

  • 54.
    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.

  • 55.
    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)
  • 56. Islavath, N.
    et al.
    Ramasamy, E.
    Das, D.
    Joshi, Shrikant. V.
    Spray coated seed layer for scalable synthesis of aligned ZnO nanowire arrays on FTO substrate and their photovoltaic properties2015In: Ceramics International, Vol. 41, no 3, p. 4118-4122Article in journal (Refereed)
    Abstract [en]

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

  • 57.
    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.

  • 58.
    Islavath, Nanaji
    et al.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Saroja, S.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Reddy, K Srinivas
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Harikesh, P.C.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Veerappan, G.
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Ramasamy, Easwaramoorthi
    Centre for Solar Energy Materials, International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad 500005, India.
    Effect of hole-transporting materials on the photovoltaic performance and stability of all-ambient-processed perovskite solar cells2017In: Journal of Energy Chemistry, ISSN 2095-4956, Vol. 26, no 3, p. 584-591Article in journal (Refereed)
    Abstract [en]

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

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

  • 59.
    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.

  • 60.
    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)
  • 61.
    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.

  • 62. 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.

  • 63. 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.

  • 64. 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.

  • 65. 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.

  • 66. 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.

  • 67. 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.

  • 68. 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.

  • 69. 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.

  • 70. 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.

  • 71. 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.

  • 72. 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.

  • 73. 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.

  • 74. 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.

  • 75. 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.

  • 76. Joshi, S. V.
    et al.
    Sundararajan, G.
    Bell, T.
    Surface engineering in India: On the upswing2004In: Surface Engineering, Vol. 20, no 2, p. 81-82Article in journal (Refereed)
  • 77. Joshi, S. V.
    et al.
    Thawari, G.
    Kumar, L. S.
    Sen, D.
    Sundararajan, G.
    Influence of Laser Glazing on the Characteristics and Tribological Performance of Plasma and Detonation Sprayed WC-Co Coatings2001In: Proceedings of the International Thermal Spray Conference, 2001, p. 583-592Conference paper (Refereed)
    Abstract [en]

    This paper deals with a comprehensive evaluation of the laser glazing or re-melting route as a possible means of specifically enhancing the performance of thermal sprayed WC-Co coatings. In the present study, a high-power continuous-wave 9kW CO2 laser was utilized for laser treatment of plasma sprayed as well as detonation sprayed WC-Co coatings. The influence of the two most important laser-related variables, namely laser power and scan speed, on the properties of the laser-treated layers was investigated. Both mere surface densification by melting a thin top layer of the coating as well as melting of the entire portion of the coated layer were targeted during laser treatment. In each case, the laser treated coatings were fully characterized by optical microscopy, scanning electron microscopy, and microhardness measurements. In addition, the influence of laser processing on the elemental distribution, phase constitution and extent of defects in the treated layers was investigated. The tribological performance of the laser-glazed coatings was also evaluated and compared against the performance of their as-sprayed counterparts. The study has revealed significant differences between the response of plasma and detonation sprayed WC-Co layers when subjected to laser treatment. The potential of plasma-sprayed coatings to match the performance of the inherently superior detonation sprayed coatings by adopting laser glazing as a post-processing step has also been assessed.

  • 78.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Coating formation by solution precursor plasma spraying and prospects for powder-solution hybrid processing2016Conference paper (Other academic)
  • 79.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Experiences of spraying fine powders dissolved in alcohol or water2016Conference paper (Other academic)
  • 80.
    Joshi, Shrikant V.
    et al.
    Defence Metallurgical Research Lab., Hyderabad, India.
    Ganguli, D.
    Central Glass and Ceramic Research Inst., Calcutta, India.
    Plasma spraying of ceramic powders produced by the sol-gel technique1992In: Metals Materials and Processes, ISSN 0970-423X, Vol. 4, no 1, p. 33-42Article in journal (Refereed)
    Abstract [en]

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

  • 81.
    Joshi, Shrikant V.
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Goel, Sneha
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Björklund, S.
    Wiklund, U.
    Hybrid powder-suspension Al2O3-ZrO2 coatings by axial plasma spraying: Processing, characteristics & tribological behavior2017Conference paper (Other academic)
  • 82. Joshi, Shrikant V.
    et al.
    Sivakumar, G.
    Hybrid Processing with Powders and Solutions: A Novel Approach to Deposit Composite Coatings2015In: Journal of Thermal Spray Technology, Vol. 24, no 7, p. 1166-1186Article in journal (Refereed)
    Abstract [en]

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

  • 83. Joshi, Shrikant V.
    et al.
    Sivakumar, R.
    An Analytical Approach to Plasma Spraying1993In: Plasma spraying: Theory and applications / [ed] Suryanarayanan, R., New Jersey: World Scientific, 1993, p. 121-137Chapter in book (Refereed)
  • 84. Joshi, Shrikant V.
    et al.
    Srivastava, P.
    Lifetime determining factors during thermal cycling of zirconia based thermal barrier coatings1995In: Surface Engineering, ISSN 0267-0844, E-ISSN 1743-2944, Vol. 11, no 3, p. 233-239Article in journal (Refereed)
    Abstract [en]

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

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

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

  • 86. Kaur, N.
    et al.
    Kumar, M.
    Sharma, S. K.
    Kim, D. Y.
    Kumar, S.
    Chavan, N. M.
    Joshi, Shrikant V.
    Singh, N.
    Singh, H.
    Study of mechanical properties and high temperature oxidation behavior of a novel cold-spray Ni-20Cr coating on boiler steels2015In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 328, p. 13-25Article in journal (Refereed)
    Abstract [en]

    In the current investigation, high temperature oxidation behavior of a novel cold-spray Ni-20Cr nano-structured coating was studied. The nanocrystalline Ni-20Cr powder was synthesized by the investigators using ball milling, which was deposited on T22 and SA 516 steels by cold spraying. The crystallite size based upon Scherrer's formula for the developed coatings was found to be in nano-range for both the substrates. The accelerated oxidation testing was performed in a laboratory tube furnace at a temperature 900 degrees C under thermal cyclic conditions. Each cycle comprised heating for one hour at 900 degrees C followed by cooling for 20 min in ambient air. The kinetics of oxidation was established using weight change measurements for the bare and the coated steels. The oxidation products were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) and X-ray mapping techniques. It was found from the results that the coating was successful in reducing the weight gain of SA213-T22 and SA 516-Grade 70 steel by 71% and 94%, respectively. This may be attributed to relatively denser structure, lower porosity and lower oxide content of the coating. Moreover, the developed nano-structured Ni-20Cr powder coating was found to perform better than its counterpart micron-sized Ni-20Cr powder coating, in terms of offering higher oxidation resistance and hardness. (C) 2014 Elsevier B.V. All rights reserved.

  • 87. Koppoju, S.
    et al.
    Shariff, S. M.
    Singh, A. K.
    Mantripragada, R.
    Gadhe, P.
    Joshi, S. V.
    Evolution of texture during laser surface treatment of an austenitic manganese steel2015In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 102, p. 29-34Article in journal (Refereed)
    Abstract [en]

    This work describes the evolution of microstructure and texture of an austenitic manganese steel (1.34C-13.6Mn-0.45Si-Fe, wt.%) during surface modification using a high power diode laser. Strong (002) texture has been observed on the surface of the steel with increase in interaction time. It has been found that columnar type dendrites are responsible for the strong texture which is favorably grown in the < 001 > direction perpendicular to the substrate plane. The growth of dendrites with specific crystallographic direction is governed by the interfacial energy anisotropy and thermal gradient direction. (C) 2015 Elsevier Inc. All rights reserved.

  • 88. Krishna, G. R.
    et al.
    Das, D. K.
    Singh, V.
    Joshi, S. V.
    Role of Pt content in the microstructural development and oxidation performance of Pt-aluminide coatings produced using a high-activity aluminizing process1998In: Materials Science and Engineering A, Vol. 251, no 1-2, p. 40-47Article in journal (Refereed)
    Abstract [en]

    The present study highlights the effect of Pt content on the microstructure of Pt-aluminide coatings produced using a single-step high-activity aluminizing process. The amount of Pt in the coating was varied by changing the thickness of the initial electroplated Pt layer between 1 and 15 μm. The aluminium uptake from the pack was found to be almost the same for all the coatings produced using a Pt layer of thickness 2.5 μm and above, with a somewhat lower uptake for the coating corresponding to a 1 μm thick Pt layer. The coating microstructure, which consisted of an outer two-phase (PtAl2 in a matrix of NiAl) layer, an intermediate NiAl layer and an interdiffusion layer, was also found to be independent of the Pt layer thickness when it was in the range 2.5-10 μm. In the case of the 1 μm Pt layer, however, the whole of the Pt remained in solid solution in the NiAl phase. For a Pt layer thickness exceeding 10 μm, on the other hand, a continuous surface layer of PtAl2 phase was observed. The above mentioned influence of the thickness of the Pt plated layer on the microstructure of the Pt-aluminide coatings observed in the present investigation could be explained in terms of the Pt concentration in the diffusion layer resulting from the interdiffusion between the Pt layer and the superalloy substrate during the pre-aluminizing diffusion treatment. Cyclic oxidation tests on these Pt-aluminide coatings reveal that the presence of Pt in aluminide coatings, in general, enhances oxidation resistance. However, in order to fully realize the beneficial effects of Pt on oxidation behaviour, a certain minimum Pt content in the coating was found to be necessary.

  • 89.
    Kumar, M.
    et al.
    CGC College of Engineering, Landran, India.
    Singh, H.
    Singh, N.
    Chavan, N.
    Kumar, S.
    Joshi, Shrikant
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Development of high-performance cols-sprayed nano-structured NI-20Cr coatings for hash environment of power plant boilers2017Conference paper (Other academic)
  • 90. Kumar, M.
    et al.
    Singh, H.
    Singh, N.
    Hong, S. M.
    Choi, I. S.
    Suh, J. Y.
    Chavan, N. M.
    Kumar, S.
    Joshi, S. V.
    Development of nano-crystalline cold sprayed Ni-20Cr coatings for high temperature oxidation resistance2015In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 266, p. 122-133Article in journal (Refereed)
    Abstract [en]

    In the current investigation a pre-synthesized nano-crystalline Ni-20Cr powder was deposited by cold-spray technique on SA 516 steel. The powder was synthesized by ball milling approach. The nano-crystallinity of the developed coating was established by crystallite size measurements from XRD profile, which was further endorsed by TEM analysis. High-temperature oxidation behavior of uncoated and coated samples was studied under cyclic isothermal conditions at 900 degrees C for 50 cycles in a laboratory tube furnace. The oxidation rates for the bare and coated steel were evaluated in terms of weight gain data. Different characterization techniques, such as X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), and transmission electron microscopy (TEM) analyses were utilized to characterize the oxide scale. The hardness and oxidation resistance of the steel increased after the application of coating. The reduction in oxidation rate of the base steel was 94%. Moreover, the developed nanostructured coating was observed to reduce weight gain by 64% in comparison with micron-sized Ni-20Cr cold spray coating thus offers a higher oxidation resistance. This may be attributed to relatively denser structure, lower porosity and lower oxide content of the nanostructured coating. (C) 2015 Elsevier B.V. All rights reserved.

  • 91. Kumar, M.
    et al.
    Singh, H.
    Singh, N.
    Joshi, Shrikant. V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Chavan, N.
    Kumar, S.
    Evaluation of high temperature oxidation behavior of a cold spray Ni-20Cr nano-structured coating2016Conference paper (Other academic)
  • 92.
    Kumar, Rajiv
    et al.
    IITB-Monash Research Academy, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
    Joardar, Joydip
    International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad, India.
    Raman, R.K. Singh
    Department of Mechanical and Aerospace Engineering, Monash University, VIC 3800 Australia.
    Raja, V.S.
    Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
    Joshi, Shrikant
    University West, Department of Engineering Science, Research Enviroment Production Technology West. International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad, India.
    Parida, S.
    Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
    Effect of chromium and aluminum addition on anisotropic and microstructural characteristics of ball milled nanocrystalline iron2016In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 671, p. 164-169Article in journal (Refereed)
    Abstract [en]

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

  • 93.
    Kumar, Raju
    et al.
    Centre for Nanomaterials, International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad 500005, India.
    Govinadarajan, Sivakumar
    Centre for Engineered Coatings, International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad 500005, India.
    Janardhana, Reddy Kunda Siri Kiran
    Centre for Nanomaterials, International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad 500005, India.
    Rao, Tata Narasinga
    Centre for Nanomaterials, International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad 500005, India.
    Joshi, Shrikant
    University West, Department of Engineering Science, Research Enviroment Production Technology West. Centre for Engineered Coatings, International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad 500005, India.
    Anandan, Srinivasan
    Centre for Nanomaterials, International Advanced Research Centre for Powder Metallurgy and New Materials, Hyderabad 500005, India.
    Facile One-Step Route for the Development of in Situ Cocatalyst-Modified Ti3+ Self-Doped TiO2 for Improved Visible-Light Photocatalytic Activity2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 41, p. 27642-27653Article in journal (Refereed)
    Abstract [en]

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

  • 94.
    Kumar, S.
    et al.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur.Po, Hyderabad 500 005, India.
    Jyothirmayi, A.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur.Po, Hyderabad 500 005, India.
    Wasekar, Nitin
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur.Po, Hyderabad 500 005, India.
    Joshi, Shrikant
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Influence of annealing on mechanical and electrochemical properties of cold sprayed niobium coatings2016In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 296, p. 124-135Article in journal (Refereed)
    Abstract [en]

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

  • 95.
    Kumar, S.
    et al.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, India.
    Ramakrishna, M.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur Po, Hyderabad, 500 005, India.
    Chavan, N.M.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur Po, Hyderabad, 500 005, India.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur Po, Hyderabad, 500 005, India.
    Correlation of splat state with deposition characteristics of cold sprayed niobium coatings2017In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 130, p. 177-195Article in journal (Refereed)
    Abstract [en]

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

  • 96.
    Kumar, S.
    et al.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, India.
    Reddy, S.K.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, India.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Microstructure and performance of cold sprayed Al-SiC composite coatings with high fraction of particulates2017In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 318, p. 62-71Article in journal (Refereed)
    Abstract [en]

    Deposition of metal matrix composites (MMCs) through thermal spraying has traditionally presented problems associated with heterogeneity, porosity, and low wettability of particulates with matrix. Cold spray is a very rapid deposition process which is suitable for depositing a variety of ductile materials without any thermal degradation. Many researchers have attempted to deposit Al-SiC MMCs with 10–20% SiC using this technique. In the present study, three different powder compositions (FAl-23SiC, FAl-46SiC, FAl-71SiC) obtained by mixing Al and SiC powders were cold sprayed on aluminum substrates. The volume percentage and the average size of the SiC particulates in the cold sprayed coatings were estimated and found to be 23%, 47% and 52% for FAl-23SiC, FAl-46SiC and FAl-71SiC feedstocks, respectively. Effects of percentage and size of the SiC particulate retained in the composite coatings on the mechanical properties and the sliding wear performance were studied at different sliding conditions in the as-sprayed and heat treated conditions. The results were comprehensively analyzed and found to correlate well with the microstructure of the coatings.

  • 97.
    Kumar, S.
    et al.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, India.
    Vidyasagar, V.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad,India.
    Jyothirmayi, A.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, India.
    Joshi, Shrikant
    University West, Department of Engineering Science, Research Enviroment Production Technology West. International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, India.
    Effect of Heat Treatment on Mechanical Properties and Corrosion Performance of Cold-Sprayed Tantalum Coatings2016In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 25, no 4, p. 745-756Article in journal (Refereed)
    Abstract [en]

    The cold-spray technique is of significant interest to deposit refractory metals with relatively high melting point for a variety of demanding applications. In the present study, mechanical properties of cold-sprayed tantalum coatings heat treated at different temperatures were investigated using microtensile testing, scratch testing, and nanoindentation. The corrosion performance of heat-treated coatings was also evaluated in 1 M KOH solution, and potentiodynamic polarization as well as impedance spectroscopy studies were carried out. Assessment of structure–property correlations was attempted based on microstructure, porosity, and intersplat bonding state, together with mechanical and corrosion properties of the heat-treated cold-sprayed tantalum coatings. Coatings annealed at 1500 °C, which is very close to the recrystallization temperature of tantalum, were found to perform almost as bulk tantalum, with exciting implications for various applications.

  • 98.
    Kumara, Chamara
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Segerstark, Andreas
    GKN Aerospace Engine Systems AB, Trollhättan, SE-461 81, Sweden.
    Hanning, Fabian
    Chalmers University of Technology, Department of Industrial and Materials Science, 412 96 Gothenburg, Sweden.
    Dixit, Nikhil
    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.
    Moverare, Johan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Division of Engineering Materials, Department of Management and Engineering, Linköping University, SE-58183 Linköping, Sweden.
    Nylén, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Microstructure modelling of laser metal powder directed energy deposition of alloy 7182019In: Additive Manufacturing, ISSN 2214-8604, Vol. 25, p. 357-364Article in journal (Refereed)
    Abstract [en]

    A multi-component and multi-phase-field modelling approach, combined with transformation kinetics modelling, was used to model microstructure evolution during laser metal powder directed energy deposition of Alloy 718 and subsequent heat treatments. Experimental temperature measurements were utilised to predict microstructural evolution during successive addition of layers. Segregation of alloying elements as well as formation of Laves and δ phase was specifically modelled. The predicted elemental concentrations were then used in transformation kinetics to estimate changes in Continuous Cooling Transformation (CCT) and Time Temperature Transformation (TTT) diagrams for Alloy 718. Modelling results showed good agreement with experimentally observed phase evolution within the microstructure. The results indicate that the approach can be a valuable tool, both for improving process understanding and for process development including subsequent heat treatment.

  • 99. Lohia, A.
    et al.
    Sivakumar, G.
    Ramakrishna, M.
    Joshi, S. V.
    Deposition of Nanocomposite Coatings Employing a Hybrid APS + SPPS Technique2014In: Journal of Thermal Spray Technology, Vol. 23, no 7, p. 1054-1064Article in journal (Refereed)
    Abstract [en]

    A novel approach hybridizing the conventional atmospheric plasma spraying and the solution precursor plasma spraying techniques has been explored to develop nanocomposite coatings. The above hybrid processing route involves simultaneous feeding of an appropriate solution precursor and commercially available spray-grade powder feedstock to realize microstructures comprising nanostructured and micron-sized features, which are unique in thermal spraying. The attractive prospects offered by this hybrid technique for deposition of nanocomposite coatings are specifically highlighted in this paper through a case study. Plasma sprayed Mo-alloy coatings are known for their good tribological characteristics and widely used in many applications. Further augmentation in performance of these coatings is expected through incorporation of distributed nanostructured oxide phases in the microstructure. Successful development of such coatings using a spray-grade Mo-alloy powder and a suitable oxide-forming solution precursor has been demonstrated. Splat formation under varied processing conditions has been comprehensively investigated and related to microstructure and tribological behavior of the coatings to assess the efficacy of the above nanocomposite coatings for wear resistant applications. © 2014, ASM International.

  • 100. Mandati, S.
    et al.
    Sarada, B. V.
    Dey, S. R.
    Joshi, S. V.
    CuIn1-xGaxSe2 thin-film absorber layers for solar photovoltaics fabricated by two-stage pulsed current electrodeposition2014In: Materials Letters, Vol. 118, p. 158-160Article in journal (Refereed)
    Abstract [en]

    Single phase polycrystalline Copper Indium Gallium Diselenide (CIGS) thin-films for solar photovoltaic applications were fabricated by an economical two-stage method of Pulsed Current (PC) electrodeposition. Cu, Ga and Se were first co-deposited onto a Mo foil followed by deposition of In. The as-deposited films were annealed in Argon atmosphere at 550 C for 30 min and were further characterized to study their morphology, phase constitution, and optical absorption. The results revealed that the films have a compact morphology and are comprised of a crystalline chalcopyrite single phase CIGS. The bandgap of the CIGS films was found to be 1.27 eV from absorption studies. The photoelectrochemical studies revealed the p-type nature of CIGS films with improved photocurrent over that obtained for one-stage PC electrodeposited CIGS thin-films. © 2013 Elsevier B.V.

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