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  • 151.
    Sadeghimeresht, Esmaeil
    et al.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Raman, Sudharshan
    Nanyang Technological University, Singapore.
    Markocsan, Nicolaie
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Joshi, Shrikant V.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Forskningsmiljön produktionsteknik(PTW).
    High Temperature Erosion-Corrosion behavior of HVAF- & HVOF-Sprayed Fe-based Coatings2017Konferensbidrag (Övrigt vetenskapligt)
  • 152.
    Sadeghimeresht, Esmaeil
    et al.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Reddy, Liam
    The University of Nottingham, Faculty of Engineering, Nottingham, United Kingdom.
    Hussain, Tanvir
    The University of Nottingham, Faculty of Engineering, Nottingham, United Kingdom.
    Huhtakangas, Matti
    M. H. Engineering AB, Karlskoga, Sweden.
    Markocsan, Nicolaie
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Joshi, Shrikant V.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Forskningsmiljön produktionsteknik(PTW).
    Influence of KCl and HCl on high temperature corrosion of HVAF-sprayed NiCrAlY and NiCrMo coatings2018Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 148, s. 17-29Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The oxidation performance of NiCrAlY and NiCrMo coatings thermally sprayed by high velocity air-fuel (HVAF) technique has been investigated in a chloridizing-oxidizing environment, with and without a KCl deposit, at 600 °C for up to 168 h. Both coatings protected the substrate in the absence of KCl due to formation of a dense Cr-rich oxide scale. In the presence of KCl, Cl−/Cl2 diffused through a non-protective and porous NiCr2O4 scale formed on NiCrAlY, leading to formation of volatile CrCl3. On the other hand, Mo in NiCrMo stimulated the formation of a more protective Cr-rich oxide scale which increased the corrosion resistance by reducing Cl−/Cl2 diffusion.

  • 153.
    Sadeghimeresht, Esmaeil
    et al.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Reddy, Liam
    The University of Nottingham, Faculty of Engineering, Nottingham, UK.
    Hussein, Tanvir
    The University of Nottingham, Faculty of Engineering, Nottingham, UK.
    Markocsan, Nicolaie
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Joshi, Shrikant V.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Chlorine-induced high temperature corrosion of HVAF-sprayed Ni-based alumina and chromia forming coatings2018Ingår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 132, nr March, s. 170-184Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Chlorine-induced corrosion of HVAF-sprayed Ni21Cr and Ni5Al coatings was investigated in 5 vol.% O2 + 500vppm HCl + N2 with and without KCl at 600 °C up to 168 h. Both coatings were protective in the absence of KCl. With KCl, Ni21Cr degraded through a two-stage mechanism: 1) formation of K2CrO4 followed by diffusion of Cl− through the oxide grain boundaries to yield chlorine and a non-protective oxide, and 2) inward diffusion of chlorine though defects in the non-protective oxide, leading to breakaway oxidation. Cl−/Cl2 could not diffuse through the protective alumina scale formed on Ni5Al, hence the corrosion resistance increased.

  • 154. Saha, B. P.
    et al.
    Kumar, V.
    Joshi, S. V.
    Balakrishnan, A.
    Martin, C. L.
    Investigation of compaction behavior of alumina nano powder2012Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 224, s. 90-95Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper investigates the impact of natural agglomerates on powder processing and consolidation through a comprehensive study of compaction of alumina powders of different particle size (ranging from 10 to 650 nm) and shape (spherical and irregular). The yield points of individual powders were determined from the green density-pressure relationship to ascertain the effect of initial particle size on agglomeration. The effect of surface modification by binder addition, which suppresses the significance of the initial particle size, was also studied. Diametral compression tests were carried out to estimate the green strength of the compacts. Results revealed that the green strength is strongly influenced not only by the initial particle size but also by the particle size distribution. The diametrically broken samples were subjected to fractographic studies followed by image analysis to calculate the agglomerate area fraction. The area fraction was found to be high for samples with low green strength and vice versa. (C) 2012 Elsevier B.V. All rights reserved.

  • 155. Saha, N. K.
    et al.
    Joshi, S. V.
    Performance evaluation of thin film composite polyamide nanofiltration membrane with variation in monomer type2009Ingår i: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 342, nr 1-2, s. 60-69Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work investigated the effect of variation in polyamide structure of thin film composite nanofiltration membranes resulting from variation in monomers on flux and rejection properties. Membranes from various combinations of monomers have been prepared including mixture of diamines or acid chlorides. The physicochemical characteristics of the membranes thus obtained were determined by infra-red spectroscopy, SEM, AFM, contact angle measurement and molecular model analysis. Attempts have been made to correlate the observed flux and rejection properties of the membranes with their physicochemical properties. It has been observed that polyamide structure influences flux and rejection of membranes to a great extent. (c) 2009 Elsevier B.V. All rights reserved.

  • 156. Saravanan, P.
    et al.
    Selvarajan, V.
    Joshi, S. V.
    Sundararajan, G.
    Experimental design and performance analysis of alumina coatings deposited by a detonation spray process2001Ingår i: Journal of Physics D: Applied Physics, Vol. 34, nr 1, s. 131-140Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The increasing demands for high-quality coatings has made it inevitable that the surface coating industry would put more effort into precisely controlling the coating process. Statistical design of experiments is an effective method for finding the optimum spray parameters to enhance thermal spray coating properties. In the present investigation, an attempt is made to produce high-quality alumina (Al2O3) coatings by optimizing the detonation spray process parameters following a (L16-24) factorial design approach. The process parameters that were varied include the fuel ratio, carrier gas flow rate, frequency of detonations and spray distance. The coating characteristics were quantified with respect to roughness, hardness and porosity. The performance of the coatings was quantitively evaluated using erosion, abrasion and sliding wear testing. Through statistical analysis of the experimental results, performed by the ANOVA method, the significance of each process parameter together with an optimal variable combination was obtained for the desired coating attributes. Confirmation experiments were conducted to verify the optimal spray parameter combination, which clearly showed the possibility of producing high-quality Al2O3 coatings.

  • 157. Saravanan, P.
    et al.
    Selvarajan, V.
    Rao, D. S.
    Joshi, S. V.
    Sundararajan, G.
    Influence of process variables on the quality of detonation gun sprayed alumina coatings2000Ingår i: Surface and Coatings Technology, Vol. 123, nr 1, s. 44-54Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Detonation gun (D-gun) spraying is one of the most promising thermal spray variants for depositing high quality wear resistant coatings. Of all the ceramic materials that can be D-gun sprayed, alumina (Al2O3) is the most widely established and these coatings have already gained industrial acceptance for diverse applications. The present study deals with a statistical design of experimental study of the D-gun spraying of Al2O3 powder. Coating experiments were conducted, using a Taguchi-full factorial (L16) design parametric study, to optimize the D-gun spray process parameters. Four selected important spraying parameters were considered in their upper and lower levels of the predefined range according to the test matrix, in order to display the range of processing conditions and their effect on the coating quality. Optical microscopy, scanning electron microscopy, X-ray diffraction, image analysis and hardness testing was used for characterization. Coating qualities are discussed with respect to surface roughness, hardness, porosity and microstructure. The attributes of the coatings are correlated with the changes in operating parameters and their relative importance and contribution ratios to overall variance are calculated. Detonation gun (D-gun) spraying is one of the most promising thermal spray variants for depositing high quality wear resistant coatings. Of all the ceramic materials that can be D-gun sprayed, alumina (Al2O3) is the most widely established and these coatings have already gained industrial acceptance for diverse applications. The present study deals with a statistical design of experimental study of the D-gun spraying of Al2O3 powder. Coating experiments were conducted, using a Taguchi-full factorial (L16) design parametric study, to optimize the D-gun spray process parameters. Four selected important spraying parameters were considered in their upper and lower levels of the predefined range according to the test matrix, in order to display the range of processing conditions and their effect on the coating quality. Optical microscopy, scanning electron microscopy, X-ray diffraction, image analysis and hardness testing was used for characterization. Coating qualities are discussed with respect to surface roughness, hardness, porosity and microstructure. The attributes of the coatings are correlated with the changes in operating parameters and their relative importance and contribution ratios to overall variance are calculated.

  • 158. Saravanan, P.
    et al.
    Selvarajan, V.
    Srinivasa Rao, D.
    Joshi, S. V.
    Sundararajan, G.
    Application of Taguchi method to the optimization of detonation spraying process2000Ingår i: Materials and Manufacturing Processes, Vol. 15, nr 1, s. 139-153Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present study deals with an application of the Taguchi method to the optimization of a detonation spray process for alumina coatings. Coating experiments were conducted using the Taguchi-fractional factorial (L8) design parametric study to optimize spray process parameters. The Taguchi design evaluated the effects of four detonation spray process parameters: acetylene to oxygen ratio, carrier gas flow rate, frequency of detonations and spray distance. The coating qualities evaluated were surface roughness, porosity, microhardness, and abrasion mass loss. The influence of process parameters on the as-sprayed coating qualities is discussed. The results of the study indicate that the higher fuel ratio and lower spray distance will result in higher hardness, lower porosity and lower abrasion mass loss. The Taguchi analysis employed in the present investigation led to optimized process parameters for the most abrasive wear resistant alumina coatings.

  • 159. Saravanan, P.
    et al.
    Selvarajan, V.
    Srivastava, M. P.
    Joshi, S. V.
    Sundararajan, G.
    Influence of spraying variables on structure and properties of plasma sprayed alumina coatings2000Ingår i: British Ceramic Transactions, Vol. 99, nr 6, s. 241-247Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An experimental statistical design study on the plasma spraying of alumina powder has been carried out.Coating experiments were conducted, using a Taguchi full factorial L16 design parametric approach, to study the effect of four key plasma processing variables on the coating quality, namely, primary gas flow rate, arc current, powder feed rate, and spray distance. Optical microscopy, scanning electron microscopy, XRD, image analysis, and hardness testing were used for characterization. The resulting as sprayed coating characteristics were quantified with respect to roughness, microhardness, porosity, and microstructure. Through statistical calculation (analysis of variance), the parameters that have significant influence on the structure and properties of the coatings were identified and their relative importance and contribution ratios to overall variance were studied. The Taguchi evaluation employed in the present investigation showed that an improvement in the coating properties could be achieved using an optimum combination of variables.

  • 160. Saravanan, P.
    et al.
    Selvarajan, V.
    Srivastava, M. P.
    Rao, D. S.
    Joshi, S. V.
    Sundararajan, G.
    Study of plasma- and detonation gun-sprayed alumina coatings using Taguchi experimental design2000Ingår i: Journal of Thermal Spray Technology, Vol. 9, nr 4, s. 505-512Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Atmospheric plasma spraying (APS) is a most versatile thermal spray method for depositing alumina (Al2O3) coatings, and detonation gun (D-gun) spraying is an alternative thermal spray technology for depositing such coatings with extremely good wear characteristics. The present study is aimed at comparing the characteristics of Al2O3 coatings deposited using the above techniques by using Taguchi experimental design. Alumina coating experiments were conducted using a Taguchi fractional-factorial (L8) design parametric study to optimize the spray process parameters for both APS and D-gun. The Taguchi design evaluated the effect of four APS and D-gun spray variables on the measured coating attributes. The coating qualities evaluated were surface roughness, porosity, microhardness, abrasion, and sliding wear. The results show that the coating quality is directly related to the corresponding coating microstructure, which is significantly influenced by the spray parameters employed. Though it is evident that the D-gun-sprayed coatings consistently exhibit dense and uniform microstructure, higher hardness, and superior tribological performance, the attainment of suitable plasma-sprayed coatings can be improved by employing the Taguchi analysis.

  • 161. Shariff, S. M.
    et al.
    Jain, V.
    Sundararajan, G.
    Joshi, S. V.
    Influence of laser glazing on properties of diffusion borided layers2003Ingår i: ICALEO 2003 - 22nd International Congress on Applications of Laser and Electro-Optics, Congress Proceedings, 2003, s. 1506-, artikel-id 1506Konferensbidrag (Refereegranskat)
    Abstract [en]

    Pack boriding of steels is known to possess numerous advantages over conventional techniques like carburizing and nitriding. The combination of high hardness coupled with low co-efficient of friction offered by the diffusion borided layers makes them a promising candidate for combating abrasive, adhesive and erosive wear. However, the boronizing treatment on steels is usually found to result in the formation of a porous, irregular top surface layer and often the borided layer comprises of FeB and Fe2B phases. Of the above, FeB formation is highly undesirable, as it is prone to induce cracking in the coating due to thermal expansion mismatch. While the brittle FeB layer in the boride coating can be eliminated by appropriate post heat treatment or by carefully manipulating the process parameters, porosity and structural irregularity, which play a vital role in tribological performance of the coating, continue to exist in the boride layer. The efficacy of laser post-treatment of the borided layer in overcoming the above problems has been investigated and forms the subject of this paper. A pulsed Nd: YAG laser, capable of delivering an average power of 400W, was utilized for irradiation of the borided layer. Prior to laser treatment, boronizing of En-8 steel samples was carried out by pack-boriding process using an indigenously developed boronizing mixture. The boronized layer was subjected to laser irradiation with varied laser power, under a nitrogen shroud and the laser-treated layers were extensively characterized for surface roughness, phase constitution, microstructure and hardness. Laser glazing resulted in complete densification of the irregular porous top region of the previously boronized layer. An increase in laser power was found to lead to an increase in boride layer depth with accompanying decrease in hardness and porosity. Depending on the laser power employed, distinct microstructures were noted in the treated layer and could be attributed to varying extents of dilution of the boronized layer by Fe from the substrate. Apart from analyzing the influence of laser power on the characteristics of the diffusion borided layer, tribological performance of the laser-treated layers was also evaluated and compared with that of the untreated boride layer. Results of abrasive wear tests indicated substantial improvement in tribological properties and strong dependence on the laser power employed.

  • 162. Shariff, S. M.
    et al.
    Jain, V.
    Sundararajan, G.
    Joshi, S. V.
    Property enhancement of diffusion borided layers by laser treatment2005Ingår i: Journal of Laser Applications, Vol. 17, nr 2, s. 100-109Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Tribological properties such as abrasion and erosion resistance of boride coatings on steels have been proven to be outstanding when compared with conventional hardening techniques, e.g., carburizing and nitriding. Pack boriding is a relatively simple and economical technique among all the methods available for boriding. A single phase Fe2B layer is desirable in the boride coating for its superior performance and this can be achieved in several ways. However, the boride coating is often associated with inherent porosity, especially near the surface and this is undesirable from the standpoint of structural integrity of the coating particularly for applications involving highly loaded parts. Laser-based postprocessing is an effective technique for eliminating these undesirable microstructural features without deteriorating the mechanical properties of the coating. In the present investigation, a low activity boronizing mixture was used for pack boriding of a medium carbon steel to obtain a single phase Fe2B layer. The coating was laser treated with a pulsed Nd-yttrium-aluminum-garnet laser at different laser powers to control the extent of melting of the boride layer. Characterization of both as-borided and laser treated coatings was carried out to examine changes in surface roughness, microstructural features, and microhardness profile and phases as a result of laser treatment. Testing of the coating under erosive and abrasive wear conditions was also carried out to ascertain the influence of laser treatment on tribological performance of the coating. It was found that, under controlled processing parameters, it is possible to improve the durability of coating properties through laser treatment. © 2005 Laser Institute of America.

  • 163. Shariff, S. M.
    et al.
    Pal, T. K.
    Padmanabham, G.
    Joshi, S.
    Influence of chemical composition and prior microstructure on diode laser hardening of railroad steels2013Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 228, s. 14-26Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Diode laser surface treatment of three different railroad steels, namely pearlitic railroad-rail steel (PRS), ferritic-pearlitic railroad-wheel steel (FPRS) and bainitic railroad-rail steel (BRS), has been investigated. Power-ramping experiments, with in-situ surface temperature measurement, were initially carried out to assess surface temperature effects on treated layers. Influence of laser energy on characteristics of treated layers like surface topology, case-depth, microstructure and micro-hardness was comprehensively analyzed. Results revealed that the hardened layer depth is governed by both the process parameters as well as the nature of the substrate steel. With melting, significant reduction in hardness was noted owing to an increase in residual austenite and coarsening of martensitic microstructure. Unlubricated dry-sliding wear tests performed under close to real rail/wheel conditions revealed substantial improvement in wear resistance of hardened/melted rail steels compared to the parent substrates. The observed differences in characteristics of the laser-treated layers and their tribological behavior have been correlated with the chemistry and prior microstructure of the parent substrates. (C) 2013 Elsevier B.V. All rights reserved.

  • 164. Shariff, S. M.
    et al.
    Pal, T. K.
    Padmanabham, G.
    Joshi, S. V.
    Comparative Study on Dry Sliding Wear Behavior of Various Railroad Steels2011Ingår i: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 133, nr 2, s. 9-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Understanding the wear behavior of various railroad steels used in different components such as rails, wheels, crossings, and curves has a direct impact on the performance of the rail-wheel system in railroad technology. In the present investigation, the wear behavior of steels having varying microstructures (pearlite, ferrite-pearlite, austenite, and bainite) and different chemical compositions has been studied, utilizing a ball-on-disk sliding tribometer under prototypic load and dry conditions. Results indicate that the wear performance of the steel and the mechanism responsible for its wear are significantly governed by the microstructure as well as changes that occur in the contact region during sliding. The formation of tribo-particles comprising oxides of Fe and their possible smearing resulted in high wear resistance in pearlitic steels with considerable plastic deformation of ferrite lamellae compared with austenitic and bainitic steels. In the case of bainitic steel, the absence of any significant smearing of oxide debris, combined with the presence of some distributed tungsten from the ball, contributed to severe wear. On the other hand, in the case of austenitic steel, third-body abrasion by debris particles, comprising a mix of hard metallic and oxide particles, contributed to severe wear despite its high work-hardening ability. On the whole, the pearlitic steel exhibited superior wear resistance with a lower friction coefficient compared with the bainitic and austenitic steels. [DOI:10.1115/1.4003485]

  • 165. Shariff, S. M.
    et al.
    Pal, T. K.
    Padmanabham, G.
    Joshi, S. V.
    Sliding wear behaviour of laser surface modified pearlitic rail steel2010Ingår i: Surface Engineering, ISSN 0267-0844, E-ISSN 1743-2944, Vol. 26, nr 3, s. 199-208Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Improving wear resistance of rails has a direct impact on the performance of rail-wheel system in railroad technology. Enhancement of sliding wear resistance at curved track, where factors such as adhesion, high slip ratios and contact fatigue act at contact patch of rail-wheel system, is particularly desirable. In the present investigation, influence of laser surface modification on sliding wear performance of a pearlitic rail steel (used in Indian railways) under two different conditions, namely, laser hardening (without any melting involved) and laser melting (with thin surface layer melting), has been studied under laboratory conditions. Before sliding wear testing, the effect of laser scanning speed on the treated layer depth has been optimised, utilising a 9 kW CO2 laser system. Sliding wear tests were carried out using a pin-on-disc device, with laser treated and untreated pearlitic rail steel discs and sliding pins made of wheel steel material, tungsten carbide (WC) and high speed steel (HSS). The tests were performed under normal prototypic loads and unlubricated conditions. Microhardness in the laser melted layer was in the range of 830-900 HV as against 890-1070 HV in the hardened layer, and was found to depend on the laser scanning speed. Sliding wear resistance of both hardened and melted layers was found to be significantly improved compared to untreated rail steel. The coefficient of friction was also marginally reduced in the laser surface melted layers.

  • 166. Shariff, S. M.
    et al.
    Sundararajan, G.
    Joshi, S. V.
    Parametric influence on cut quality attributes and generation of processing maps for laser cutting1999Ingår i: Journal of Laser Applications, Vol. 11, nr 2, s. 54-63Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Laser cutting is an attractive alternative to conventional cutting methods due to its many inherent advantages. However, notwithstanding its promise for processing diverse categories of materials, the understanding of the subject is incomplete. Although numerous processes are known to significantly influence cutting quality, comprehensive data of practical utility - such as identification of processing regimes to achieve optimum cut surface attributes - remain yet to be generated. The present article establishes a methodology to develop such "processing maps" and illustrates their utility by using laser cutting of mild steel and commercially pure titanium as case studies. The processing maps can be constructed based on any chosen cut quality criteria and can be used to optimize the process on the basis of operational costs. Results reveal that, for achieving good quality cuts, such processing regimes constitute only a narrow region within the wide operating window for mere cuttability and vary substantially with material-assist gas combination. Typically, the operating window for inert gas-assisted cutting is narrower than that for oxygen-assisted cutting involving an exothermic oxidation reaction, which contributes significantly to the overall energy input to the cutting front. The influence of the two major process parameters, laser power and cutting speed, on cut quality attributes such as surface roughness, kerf width, heat affected zone, and cut surface morphology is also discussed in detail. The experimental results have also been compared with theoretical predictions of a scaling law for laser cutting. © 1999 Laser Institute of America.

  • 167.
    Sivakumar, G.
    et al.
    Center for Engineered Coatings, International Advanced Research Center for Powder Metallurgy and New Materials, Hyderabad, India.
    Banerjee, S.
    Indian Institute of Technology Bombay, Department of Metallurgical Engineering and Materials Science, Mumbai, India.
    Raja, V. S.
    Indian Institute of Technology Bombay, Department of Metallurgical Engineering and Materials Science, Mumbai, India.
    Joshi, Shrikant V.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Forskningsmiljön produktionsteknik(PTW).
    Hot corrosion behavior of plasma sprayed powder-solution precursor hybrid thermal barrier coatings2018Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 349, s. 452-461Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In recent times, plasma sprayed powder-solution precursor hybrid composite thermal barrier coatings have been developed to harness the dual benefits of both conventional atmospheric plasma spraying (APS) and solution precursor plasma spraying (SPPS) processes. In this study, hot corrosion behavior of plasma sprayed powder-solution precursor composite (PSP-SPC) YSZ TBCs in molten salt mixtures of 90 wt.% Na2SO4 + 5 wt.% V2O5 + 5 wt.% NaCl and 50 wt.% Na2SO4 + 50 wt.% V2O5 at 900 °C was investigated. The employed coating showed a bimodal microstructure comprising coarse splats derived from the powder feedstock as in the APS process and fine splats resulting from the solution precursor as typical of SPPS process. The PSP-SPC coatings showed a significantly higher resistance to spallation than APS, SPPS and EB-PVD coatings in both the salt environments. These coatings showed shorter life in vanadate environment compared to that of the chloride environments as the former promotes the formation of monoclinic ZrO2 and YVO4 phases more than the latter. © 2018

  • 168. Sivakumar, G.
    et al.
    Dusane, R. O.
    Joshi, S. V.
    A novel approach to process phase pure α-Al2O3 coatings by solution precursor plasma spraying2013Ingår i: Journal of the European Ceramic Society, Vol. 33, nr 13-14, s. 2823-2829Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present work represents a significant new approach in the field of thermal spraying to deposit nanostructured phase-pure α-Al2O3 coatings in a single step. In order to understand the mechanism of coating formation, a detailed investigation of in flight formed particles and splat morphologies has been carried out. A plausible deposition mechanism has been proposed based on the understanding derived from the above studies that can form the basis for developing novel ceramic coatings employing the solution precursor plasma spray technique. © 2013 Elsevier Ltd.

  • 169. Sivakumar, G.
    et al.
    Ramakrishna, M.
    Dusane, R. O.
    Joshi, Shrikant V.
    Effect of SPPS Process Parameters on In-Flight Particle Generation and Splat Formation to Achieve Pure α-Al2O3 Coatings2015Ingår i: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 24, nr 7, s. 1221-1234Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present paper describes the role of process conditions in developing phase-pure α-Al<inf>2</inf>O<inf>3</inf> coatings using solution precursor plasma spraying. Different precursor combinations were employed and two key parameters, namely plasma power and substrate pre-heat temperature, were varied. Detailed studies of in-flight formed particles and splat characteristics were found to correlate well with the Al<inf>2</inf>O<inf>3</inf> coating characteristics. The Al<inf>2</inf>O<inf>3</inf>-forming precursor formulation was also found to be crucial in determining the phase constitution of the deposited coatings. © 2015 ASM International

  • 170. Sivakumar, R.
    et al.
    Joshi, Shrikant V.
    Protective Coatings by Plasma Spraying: A Review1991Ingår i: Transactions of the Indian Ceramic Society, ISSN 0371-750X (Print), 2165-5456 (Online), Vol. 50, nr 1, s. 1-14Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In recent years, the use of plasma-sprayed protective coatings has gained increasing acceptance for prolonging the service life of critical components exposed to aggressive environments during normal operation. This paper is aimed at providing an overview of the current state-of-the-art of the plasma coating technology. It includes a brief discussion of the various important aspects associated with the development of reliable protective coatings as well as their evaluation, and outlines some noteworthy advances made in the field of plasma spray materials and equipment in the past few years. The various factors influencing the coating quality are identified and the wide-ranging utility of plasma-sprayed coatings is also highlighted.

  • 171. Sivudu, K. S.
    et al.
    Mahajan, Y. R.
    Joshi, S. V.
    Nano-enabled tribological thin film coatings: Global patent scenario2014Ingår i: Recent Patents on Nanotechnology, Vol. 8, nr 2, s. 97-116Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this paper is to present current status and future prospects of nano-enabled tribological thin film coatings based on worldwide patent landscape analysis. The study also presents an overview of technological trends by carrying out state-of-the-art literature analysis, including survey of corporate websites. Nanostructured tribological coatings encompass a wide spectrum of nanoscale microstructures, including nanocrystalline, nanolayered, nano-multilayered, nanocomposite, nanogradient structures or their unique combinations, which are composed of single or multi-component phases. The distinct microstructural features of the coatings impart outstanding tribological properties combined with multifunctional attributes to the coated components. Their unique combination of remarkable properties make them ideal candidates for a wide range of applications in diverse fields such as cutting and metalworking tools, biomedical devices, automotive engine components, wear parts, hard disc drives etc. The patent landscape analysis has revealed that nano-enabled tribological thin film coatings have significant potential for commercial applications in view of the lion's share of corporate industry in patenting activity. The largest patent portfolio is held by Japan followed by USA, Germany, Sweden and China. The prominent players involved in this field are Mitsubishi Materials Corp., Sandvik Aktiebolag, Hitachi Ltd., Sumitomo Electric Industries Ltd., OC Oerlikon Corp., and so on. The outstanding potential of nanostructured thin film tribological coatings is yet to be fully unravelled and, therefore, immense opportunities are available in future for micro-structurally engineered novel coatings to enhance their performance and functionality by many folds. © 2014 Bentham Science Publishers.

  • 172. Soma Raju, K. R. C.
    et al.
    Faisal, N. H.
    Srinivasa Rao, D.
    Joshi, S. V.
    Sundararajan, G.
    Electro-spark coatings for enhanced performance of twist drills2008Ingår i: Surface and Coatings Technology, Vol. 202, nr 9, s. 1636-1644Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Surface engineering approaches are being increasingly employed for enhancing the effective life of twist drills with a view to reduce machining costs. The electro-spark coating (ESC) technique provides a promising means of depositing wear resistant coatings that can potentially enhance the performance of these tools. However, it is often necessary to also optimize the machining conditions for coated tools to achieve an enhanced tool life. In the present investigation, varying spindle speeds were employed at a fixed vertical feed to evaluate the performance of WC-8Co ESC coated HSS drills in comparison to bare HSS drills. The number of holes drilled before reaching a preset average flank wear (0.5 mm), or catastrophic failure of the drill, was taken as the measure of tool life. The drill flank wear, monitored at regular intervals, as well as the cutting torque and thrust measured for all holes, were considered to be the key criteria for optimizing the cutting conditions. Results indicate that the WC-8Co coated drill tool life can be increased by a factor of more than 5, depending on the machining conditions selected. Furthermore, flank wear of the drill was found to increase rapidly at the end of drill life. Cutting torque data was also found to provide a useful indicator for predicting the end of tool life. © 2007 Elsevier B.V. All rights reserved.

  • 173. Subrahmanyam, A.
    et al.
    Valleti, K.
    Joshi, S. V.
    Sundararajan, G.
    Effect of arc suppression on the physical properties of low temperature dc magnetron sputtered tantalum thin films2007Ingår i: Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films, Vol. 25, nr 2, s. 378-382Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Arcing is a common phenomenon in the sputtering process. Arcs and glow discharges emit electrons which may influence the physical properties of films. This article reports the properties of tantalum (Ta) thin films prepared by continuous dc magnetron sputtering in normal and arc-suppression modes. The substrate temperature was varied in the range of 300-673 K. The tantalum films were ∌1.8 ÎŒm thick and have good adherence to 316 stainless steel and single-crystal silicon substrates. The phase of the Ta thin film determines the electrical and tribological properties. The films deposited at 300 K using both methods were crystallized in a tetragonal structure (Β phase) with a smooth surface (grain size of ∌10 nm) and exhibited an electrical resistivity of ∌194 ÎŒ cm and a hardness of ∌20 GPa. When the substrate temperature was 473 K and higher, the arc-suppression mode appears to influence the films to crystallize in the α phase with a grain size of ∌40 nm, whereas the normal power mode gave mixed phases Β and α beyond 473 K, the arc-suppression mode yields larger grain sizes in the Ta thin films and the hardness decreases. These changes in the physical properties in arc-suppression mode are attributed to either the change in plasma characteristics or the energetic particle bombardment onto the substrate, or both. © 2007 American Vacuum Society.

  • 174. Sudharshan Phani, P.
    et al.
    Srinivasa Rao, D.
    Joshi, S. V.
    Sundararajan, G.
    Effect of process parameters and heat treatments on properties of cold sprayed copper coatings2007Ingår i: Journal of Thermal Spray Technology, Vol. 16, nr 3, s. 425-434Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cold gas dynamic spraying or cold spray is specifically suitable to obtain high-conductivity copper coatings for a variety of applications. Copper coatings at different coating parameters were deposited and subjected to various post treatments. The effect of process parameters and the treatment conditions on coating properties such as electrical conductivity, porosity, microhardness etc., was studied. The as-coated specimens exhibited low conductivities and conductivity was found to improve with heat treatment. Treatments were carried out in vacuum at different temperatures and for different durations and conductivities close to bulk annealed copper were achieved. Good correlation was observed between the conductivity, porosity and hardness of the as-coated and heat-treated specimens. Similar correlations were observed between conductivity-porosity and hardness-porosity of the coatings and the relative influence of cold work and porosity on coating properties was determined. © ASM International 2007.

  • 175.
    Sundararajan, G.
    et al.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur PO, Hyderabad 500005, India.
    Joshi, Shrikant
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Forskningsmiljön produktionsteknik(PTW). International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur PO, Hyderabad 500005, India.
    Rama Krishna, L.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur PO, Hyderabad 500005, India.
    Engineered surfaces for automotive engine and power train components2016Ingår i: Current Opinion in Chemical Engineering, E-ISSN 2211-3398, Vol. 11, s. 1-6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present era where light weighting of vehicles to meet legislation driven emission norms has gathered much pace, the surface engineering approach has been attracting increasing attention as its adoption is deemed inevitable if light alloys of Al, Ti and Mg are to be inducted for harvesting the potential associated benefits of fuel saving and yet yield enhanced component life. This review article attempts to provide a glimpse of various engineered surfaces that are currently being pursued by the automotive industry to combat degradation due to phenomena such as wear, thermal, fretting, fatigue and corrosion. Since the field is vast and subject of considerable research attention globally, only examples from authors’ lab have been included to highlight the immense promise of engineering surface for the automotive industry.

  • 176. Sundararajan, G.
    et al.
    Mahajan, Y. R.
    Joshi, S. V.
    Thermal spraying in India: Status and prospects2009Ingår i: Proceedings of the International Thermal Spray Conference, 2009, s. 511-516Konferensbidrag (Refereegranskat)
    Abstract [en]

    Notwithstanding the fact that the thermal spray technologies have globally proliferated into virtually all major industry segments, the acceptance of these processes by the Indian industry had been historically sluggish. However, the scenario in the country with respect to the thermal spray technologies is rapidly changing. A meaningful indicator of the obvious growth of thermal spraying is the spurt in the number of job shops, equipped with the latest thermal spray variants and sophisticated job-handling capabilities, that can now offer coating service. The number of captive units meeting in-house coating needs has also increased markedly in recent years. The non-availability of indigenous sources for thermal spray equipment as well as feedstock materials had been one of the key factors hampering growth of the thermal spray industry in India. The increasing adoption of thermal spraying by the Indian industry has been spurred by the fact that home-grown Indian companies are manufacturing spray systems, handling equipment and performance evaluation test rigs that are already being exported to foreign countries. Research on frontier areas like Cold Gas Dynamic Spraying and Solution Precursor Plasma Spraying is also active in the country. The above factors, along with the healthy growth trends observed recently, suggest a very bright future for thermal spray technologies in India. This paper provides an overview of the country status, charting the growth of thermal spray coatings in India in recent times. Copyright © 2009 ASM International® All rights reserved.

  • 177. Sundararajan, G.
    et al.
    Prasad, K. U. M.
    Rao, D. S.
    Joshi, S. V.
    A Comparative Study of Tribological Behavior of Plasma and D-Gun Sprayed Coatings under Different Wear Modes1998Ingår i: Journal of Materials Engineering and Performance, Vol. 7, nr 3, s. 343-351Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In recent years, thermal sprayed protective coatings have gained widespread acceptance for a variety of industrial applications. A vast majority of these applications involve the use of thermal sprayed coatings to combat wear. While plasma spraying is the most versatile variant of all the thermal spray processes, the detonation gun (D-gun) coatings have been a novelty until recently because of their proprietary nature. The present study is aimed at comparing the tribological behavior of coatings deposited using the two above techniques by focusing on some popular coating materials that are widely adopted for wear resistant applications, namely, WC-12%Co, Al2O3, and Cr3C2-NiCr. To enable a comprehensive comparison of the above indicated thermal spray techniques as well as coating materials, the deposited coatings were extensively characterized employing microstructural evaluation, microhardness measurements, and XRD analysis for phase constitution. The behavior of these coatings under different wear modes was also evaluated by determining their tribological performance when subjected to solid particle erosion tests, rubber wheel sand abrasion tests, and pin-on-disk sliding wear tests. The results from the above tests are discussed here. It is evident that the D-gun sprayed coatings consistently exhibit denser microstructures and higher hardness values than their plasma sprayed counterparts. The D-gun coatings are also found to unfailingly exhibit superior tribological performance superior to the corresponding plasma sprayed coatings in all wear tests. Among all the coating materials studied, D-gun sprayed WC-12%Co, in general, yields the best performance under different modes of wear, whereas plasma sprayed Al2O3 shows least wear resistance to every wear mode.

  • 178.
    Tesar, Tomas
    et al.
    Institute of Plasma Physics CAS, v.v.i., Department of Materials Engineering, Za Slovankou 3, 182 00 Praha 8, Czech Republic; Czech Technical University in Prague, Faculty of Nuclear Science and Physical Engineering, Department of Materials, Trojanova 13, 120 00 Praha 2, Czech Republic .
    Musalek, Radek
    Institute of Plasma Physics CAS, v.v.i., Department of Materials Engineering, Za Slovankou 3, 182 00 Praha 8, Czech Republic.
    Lukac, Frantisek
    Institute of Plasma Physics CAS, v.v.i., Department of Materials Engineering, Za Slovankou 3, 182 00 Praha 8, Czech Republic.
    Medricky, Jan
    Institute of Plasma Physics CAS, v.v.i., Department of Materials Engineering, Za Slovankou 3, 182 00 Praha 8, Czech Republic.
    Cizek, Jan
    Institute of Plasma Physics CAS, v.v.i., Department of Materials Engineering, Za Slovankou 3, 182 00 Praha 8, Czech Republic.
    Rimal, Vaclav
    Charles University, Faculty of Mathematics and Physics, V Holesovickach 2, 180 00 Praha 8, Czech Republic.
    Joshi, Shrikant V.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Forskningsmiljön produktionsteknik(PTW).
    Chraska, Tomas
    Institute of Plasma Physics CAS, v.v.i., Department of Materials Engineering, Za Slovankou 3, 182 00 Praha 8, Czech Republic.
    Increasing α-phase content of alumina-chromia coatings deposited by suspension plasma spraying using hybrid and intermixed concepts2019Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 71, s. 298-311Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The novel method of hybrid suspension plasma spraying of dry coarse aluminum oxide powder with chromium oxide suspension using hybrid water/argon-stabilized (WSP-H 500) plasma torch was utilized for the deposition of coatings with very high α-phase content reaching up to 90%. The deposition mechanism and phase composition were compared with those of coatings deposited from i) intermixed alumina-chromia suspension and ii) alumina suspension doped with chromium nitrate nonahydrate solution. All deposition routes showed alternative ways of preparation of novel multimaterial coatings. It was demonstrated that the chromia addition and the deposition route play the crucial role in the pronounced formation of the thermodynamically stable α-phase. © 2019

  • 179. Thawari, G.
    et al.
    Sundar, J. K. S.
    Sundararajan, G.
    Joshi, S. V.
    Influence of process parameters during pulsed Nd: YAG laser cutting of nickel-base superalloys2005Ingår i: Journal of Materials Processing Technology, Vol. 170, nr 1-2, s. 229-239Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Although CO2 lasers have been widely employed for commercial sheet metal cutting operations, increased recognition of the processing benefits afforded by pulsed Nd:YAG lasers has recently fuelled interest in the latter. Pulsed Nd:YAG laser cutting differs from conventional continuous wave laser cutting as it involves overlapping of a series of individual spots generated by each pulse. In this paper, a typical cutting regime for pulsed Nd:YAG laser cutting of 1 mm thick Hastelloy-X sheet has been constructed and explained in terms of extent of spot overlap. The characteristics of single holes drilled employing the same process parameters as those employed for cutting were investigated and correlated with the obtained processing regime. Additionally, the influence of key process parameters like pulse duration on the shift in the constructed processing regime was investigated. Cut quality attributes like kerf width, cut edge kerf profile and surface roughness were also studied and their dependence on process parameters has been discussed. © 2005 Elsevier B.V. All rights reserved.

  • 180. Thawari, G.
    et al.
    Sundarararjan, G.
    Joshi, S. V.
    Laser surface alloying of medium carbon steel with SiC(P)2003Ingår i: Thin Solid Films, Vol. 423, nr 1, s. 41-53Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Laser surface alloying (LSA) is increasingly recognised as a powerful surface modification tool to enhance the wear and corrosion resistance of engineering components. The present work deals with laser alloying of medium carbon steel with silicon carbide using a high-power CO2 laser. A processing regime, identifying an appropriate laser power-scan speed combination for achieving defect-free alloyed layers, has been established during the study. The influence of repetitive scans on the alloyed layer properties was also subsequently investigated in a comprehensive manner. Repetitive scanning was found to affect substantially the laser-alloyed zone (LAZ) and heat-affected zone dimensions, as well as the phase constitution of the laser-alloyed layers. The microstructure in the LSA layers was also observed to vary significantly with the number of scans, besides changing quite distinctly with depth in the LAZ. Tribological tests revealed considerable improvement in abrasive wear performance by laser surface alloying, and the results also emphasise the need to control the number of repetitive scans to achieve optimum performance. © 2002 Elsevier Science B.V. All rights reserved.

  • 181.
    Thomas, C.A.
    et al.
    ESS. Lund, Sweden.
    Hartl, M.A.
    ESS. Lund, Sweden.
    Lee, Y
    ESS. Lund, Sweden.
    Shea, T.J
    ESS. Lund, Sweden.
    Adli, E.
    University of Oslo, Oslo, Norway.
    Gjersdal, H.
    University of Oslo, Oslo, Norway.
    Jaekel, M.R.
    University of Oslo, Oslo, Norway.
    Rohne, O.
    University of Oslo, Oslo, Norway.
    Joshi, Shrikant V.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT). Högskolan Väst, Institutionen för ingenjörsvetenskap, Forskningsmiljön produktionsteknik(PTW).
    Preliminary Measurement On Potential Luminescent Coating Material For The Ess Target Imaging Systems: Transverse Profile Monitors2017Ingår i: Proceedings of IBIC2016, Barcelona, Spain, 2017, s. 559-562Konferensbidrag (Övrigt vetenskapligt)
  • 182. Valleti, K.
    et al.
    Jyothirmayi, A.
    Ramakrishna, M.
    Joshi, S. V.
    Influence of substrate temperature and bias voltage on properties of chromium nitride thin films deposited by cylindrical cathodic arc deposition2011Ingår i: Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films, Vol. 29, nr 5, artikel-id 051515Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Chromium nitride (CrN) thin films have been deposited on high speed steel (HSS) substrates using rotating cylindrical cathodic arc deposition technique and the influence of substrate temperature (TSub) and bias voltage (VSub) on the physical/mechanical and corrosion resistance properties of the films comprehensively investigated. An increase in TSub was found to significantly influence the phase composition of films, which changed from a mixture of Cr CrxN CrN to predominantly CrN. This was also accompanied by an increase in droplet formation and columnar grain size. With increase in TSub over the range investigated (230 °C to 500 °C), an increase in adhesion strength by nearly 30 was observed. In contrast, change in VSub from -50 to -150 V resulted in the growth of highly dense (111) oriented CrN thin films but with relatively little change in phase constitution, adhesion strength or microdroplet formation. A change in TSub from 230 °C to 500 °C was accompanied by a nearly 50 fall in corrosion resistance, plausibly due to the concomitant decrease in pure Cr phase content and increase in macroscopic defect concentration with increase in TSub. In view of the above, CrN thin films deposited using cylindrical cathodic arc deposition technique yield better corrosion resistance and mechanical properties when grown at low TSub. © 2011 American Vacuum Society.

  • 183. Valleti, K.
    et al.
    Murali Krishna, D.
    Joshi, S. V.
    Functional multi-layer nitride coatings for high temperature solar selective applications2014Ingår i: Solar Energy Materials and Solar Cells, Vol. 121, s. 14-21Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A solar-selective functional multi-layered coating for high temperature applications has been developed on copper and stainless steel substrates using an industrially viable cathodic arc physical vapor deposition technique. The selective coating was formulated in such a way that the constituent functional layers are mainly high temperature stable nitride materials which are also hard and capable of imparting protection against wear. A multi-layer structure comprising TiAlCrN as IR reflector, TiAlN as absorber and AlSiN as anti-reflective layer was found to exhibit promising results. The stacking of these three materials with appropriate thickness in a systematic manner, viz. Cu/TiAlCrN/TiAlN/AlSiN with high Cr and Al contents in TiAlCrN and TiAlN layers, respectively, yielded high absorptivity (αAM1.5=0.91) and low emissivity (ε=0.07) values corresponding to an attractive optical selectivity (α/ε) of 13. The open air high temperature performance of the optimized multi-layer structure was also investigated in the temperature range 27-700 C and the stability of the coatings at high temperatures with respect to optical properties was established. © 2013 Elsevier B.V.

  • 184. Valleti, K.
    et al.
    Rejin, C.
    Joshi, S. V.
    Factors influencing properties of CrN thin films grown by cylindrical cathodic arc physical vapor deposition on HSS substrates2012Ingår i: Materials Science and Engineering A, Vol. 545, s. 155-161Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present study deals with growth of well-adherent and tough CrN thin films by cylindrical cathodic arc physical vapor deposition. The influence of substrate preparation parameters and deposition variables on film properties has been systematically investigated. The adhesion strength, hardness and crack propagation resistance (CPR) of the films were evaluated for different processing conditions. High substrate hardness and low substrate surface roughness were found to be conducive for obtaining well-adherent films. Cr ion etching was found to yield superior film properties, with the duration of etching also being a key determining factor. The nitrogen partial pressure employed during film deposition was noted to significantly influence the phase combination of the CrN x films as well as the stress levels in the deposited films. In case of multilayer CrN x films, alternating high toughness-low toughness layers were found to yield encouraging properties, with CPR values markedly higher than those obtained in mono-layer CrN x films, with no compromise in either hardness or adhesion strength. © 2012 Elsevier B.V.

  • 185. Valleti, K.
    et al.
    Subrahmanyam, A.
    Joshi, S. V.
    Growth of nano crystalline near α phase tantalum thin films at room temperature using cylindrical magnetron cathode2008Ingår i: Surface and Coatings Technology, Vol. 202, nr 14, s. 3325-3331Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The much desired α (bcc) Tantalum (Ta) thin films are grown at room temperature using a newly designed cylindrical magnetron cathode (with rotating magnets geometry) with pulsing power. The new design has facilitated oblique incidence of adatoms. The electron temperature of the plasma has been enhanced due to the pulsing frequency (100 kHz). These two factors: oblique incidence of adatoms and enhanced electron temperature are presumed to be responsible for the formation of α phase Ta thin films at room temperature. The volume fractions of α and β phases have been evaluated from the X-ray data. The effect of pulsing (0-100 kHz) on the structural, electrical and mechanical properties of Ta thin films has also been studied. With the pulsing frequency, the lattice spacing in the Ta thin films increases (due to the incorporated argon) resulting in an increase in the compressive stress. Up to 75 kHz of the pulsing frequency, the Ta films formed are in the β phase (tetragonal) with ~ 13 nm grain size. At 100 kHz pulsing, the change in the surface morphology also indicates the phase change in the film. © 2008 Elsevier B.V. All rights reserved.

  • 186. Valleti, K.
    et al.
    Subrahmanyam, A.
    Joshi, S. V.
    Phani, A. R.
    Passacantando, M.
    Santucci, S.
    Studies on phase dependent mechanical properties of dc magnetron sputtered TaN thin films: Evaluation of super hardness in orthorhombic Ta4N phase2008Ingår i: Journal of Physics D: Applied Physics, Vol. 41, nr 4, artikel-id 045409Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanical hardness of the different phases of tantalum nitride (TaNx, x ≀ 1) thin films grown by the reactive planar dc magnetron sputtering technique at 300 °C have been evaluated. The different phases have been prepared by varying the nitrogen (N2) to argon (Ar) gas ratio R in the range 0.04-0.30. The phases present in each sample and their volume fractions are obtained from x-ray diffraction and Ta 4f7/2 binding energy x-ray photoelectron spectra, respectively. The grown TaN thin films are found to contain mainly cubic-TaN0.1, orthorhombic-Ta 4N, orthorhombic-Ta6N2.5, hexagonal-TaN 0.8 and cubic-TaN phases. The hardness corresponding to each phase has been derived from the experimental hardness values using ’rule of mixtures’. A super hardness of ∌61.9 GPa is observed in orthorhombic Ta4N phase. With increase in R, a decrease in the surface oxidation of TaN has been observed. The reduced surface oxidation is attributed to the formation of stoichiometric TaN thin films. The surface morphology is found to change considerably with increase in R. © 2008 IOP Publishing Ltd.

  • 187.
    Valleti, Krishna
    et al.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur P.O., Hyderabad, India.
    Krishna, D. Murali
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur P.O., Hyderabad, India.
    Reddy, P. Mohan
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur P.O., Hyderabad, India.
    Joshi, Shrikant
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Forskningsmiljön produktionsteknik(PTW). International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur P.O., Hyderabad, India.
    High temperature stable solar selective coatings by cathodic arc PVD for heat collecting elements2016Ingår i: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 145, nr 3, s. 447-453Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A functionally multilayered Cr/CrTiAlN-G/TiAlN/AlSiN/AlSiO coating configuration, suitable for enhancing solar selectivity of stainless steel substrates used in concentrated solar power (CSP) systems, has been formulated using cathodic arc physical vapor deposition (CAPVD) technique. The sequence of functional layers was decided based on their refractive index values and their relative thickness was optimized to achieve maximum solar selectivity. The optimized coating exhibits encouraging values of solar absorptivity (α) – 0.95 and thermal emissivity (ε) – 0.09 to 0.14 up to 600 °C. Further, the solar selectivity factor (α/ε) for the coating is found to be comparable with the best selective coatings currently available for elevated temperature operation. The coatings were also studied for their long term stability and found to be stable up to 500 °C, although considerable change in optical properties was observed on increasing the temperature to 600 °C. The noted properties make the present coating a promising candidate as a high temperature solar selective coating on stainless steel substrates.

  • 188.
    Valleti, Krishna
    et al.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, India.
    Puneet, C.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, India.
    Rama Krishna, L.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, India.
    Joshi, Shrikant
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Forskningsmiljön produktionsteknik(PTW).
    Studies on cathodic arc PVD grown TiCrN based erosion resistant thin films2016Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 34, nr 4, s. 1-7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Titanium chromium nitride (TiCrN) coatings with varying Cr content in two configurations, mono- and multilayer, were deposited on high speed steel substrates using a cylindrical cathodic arc physical vapor deposition technique. The physical, mechanical, and erosion behavior of the coatings were investigated. Among the monolayer coatings, the thicker Ti0.48Cr0.52N coatings yielded the best erosion resistance property. But with the increase in thickness, a considerable increase in residual stress is observed. Toward minimizing the stress accumulation, the effect of multilayering with periodic in situ heat treatment (after each 1 μm film growth) was studied by growing films in Ti0.52Cr0.48N/Ti0.40Cr0.60N bilayer configuration. A new approach based on % area of erosion damage for measuring relative wear rate of thin films has been proposed and implemented. The multilayer coatings exhibited superior erosion performance compared to the well-known erosion resistant TiN coatings that are in use for compressor blades from past few decades. Further, the erosion failure mechanisms in TiCrN coatings were also studied and found to be clearly different for mono- and multilayer configurations. The results reveal that the thicker multilayer TiCrN coatings (20 μm) exhibit promising choice for erosion resistance applications.

  • 189.
    Venkatesh, L.
    et al.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur, Hyderabad 500005, India. .
    Pitchuka, Suresh Babu
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur, Hyderabad 500005, India.
    Sivakumar, G.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur, Hyderabad 500005, India.
    Gundakaram, Ravi C.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur, Hyderabad 500005, India.
    Joshi, Shrikant V.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Forskningsmiljön produktionsteknik(PTW). Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Samajdar, I.
    Department of Metallurgical Engineering & Materials Science, IIT Bombay, Powai, Mumbai 400076, India.
    Microstructural response of various chromium carbide based coatings to erosion and nano impact testing2017Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 386-387, s. 72-79Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, we demonstrate the microstructure dependency of erosion behaviour of laser clad, detonation sprayed and atmospheric plasma sprayed chromium carbide based coatings. The final chromium carbide content in all the coatings was a strong function of rapid solidification rate associated with the processes. In the laser clad coating majority of the chromium carbides re-solidified while in the thermally sprayed coatings chromium carbide re-solidification was hindered to a large extent. Hence, the final chromium carbide content in the thermally sprayed coating decreased with increased extent of particle melting during spraying. Decarburisation and oxidation during thermal spraying lead to the formation of chromium carbides with lower carbon content and chromium oxide(s). Laser clad and detonation sprayed coatings, with higher chromium carbide content, showed lower erosion rates and exhibited fewer brittle erosion events. Embrittlement due to excessive dissolution of chromium carbides into the matrix and poor splat bonding were found to be the reasons for higher erosion rate of the plasma sprayed coating. Scanning electron microscopy and quantification of single erodent impact events clearly established ductile material removal in the laser clad and detonation sprayed coating and brittle material removal in the plasma sprayed coating as the dominant mechanism(s). A good agreement was found between solid particle erosion testing and nano impact testing results.

  • 190. Venkatesh, L.
    et al.
    Samajdar, I.
    Tak, M.
    Gundakaram, R. C.
    Joshi, S. V.
    Process parameter impact on microstructure of laser clad inconel-chromium carbide layers2012Ingår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 702-703, s. 963-966Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Chromium carbide based metal matrix composite (MMC) coatings are ideally suited for high temperature erosive-corrosive applications. Laser cladding of such MMCs, with Inconel as the ductile matrix instead of the usual NiCr alloy, has been attempted in the present study. The relative hardness of the laser clad layers was observed to drop with increase in laser power. The reduction in hardness was attributed to retention of lower amounts of chromium carbides in the clad layer at higher laser powers. Use of chemically assisted scans with electron diffraction allowed extraction of effective micro-textural information on the coatings. © (2012) Trans Tech Publications, Switzerland.

  • 191.
    Venkatesh, Lakshmi Narayanan
    et al.
    Int Adv Res Ctr Powder Met & New Mat ARCI, Hyderabad 500005, Andhra Pradesh, India.
    Babu, Pitchuka Suresh
    Int Adv Res Ctr Powder Met & New Mat ARCI, Hyderabad 500005, Andhra Pradesh, India.
    Gundakaram, Ravi Chandra
    Int Adv Res Ctr Powder Met & New Mat ARCI, Hyderabad 500005, Andhra Pradesh, India.
    Doherty, Roger D.
    Drexel Univ, Dept Mat Engn, Philadelphia, PA 19104 USA.
    Joshi, Shrikant V.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Samajdar, Indradev
    Indian Inst Technol, Dept Met Engn & Mat Sci, Mumbai 400076, Maharashtra, India.
    Morphology-Dependent Hardness of Cr7C3-Ni-Rich Alloy Composite vs Orientation Independent Hardness of Cr7C3 Primary Phase in a Laser Clad Microstructure2017Ingår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, nr 4, s. 1534-1539Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Microstructural evolution with superheating was studied in chromium carbide-nickel coatings deposited by laser cladding. At lower superheating, selective growth of aOE (c) 0001 > direction from the high density of Cr7C3 grains nucleated resulted in a columnar structure with (0001) texture. Increased superheating lead to the loss of columnar structure as well as the (0001) texture. The hexagonal Cr7C3 showed an unusual isotropic nanoindentation hardness evidently correlated with its low c/a ratio. However, the rod-like morphology of the carbide dendrites resulted in significant anisotropy in the hardness of the composite.

  • 192.
    Venkatesh, Lakshmi Narayanan
    et al.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur, Hyderabad 500005, India; Department of Metallurgical Engineering & Materials Science, IIT Bombay, Powai, Mumbai 400076, India.
    Venkataraman, B.
    Defence Metallurgical Research Laboratory (DMRL), Kanchanbagh, Hyderabad 500058, India.
    Tak, Manish
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur, Hyderabad 500005, India.
    Sivakumar, Ganapathy S.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur, Hyderabad 500005, India.
    Gundakaram, Ravi C.
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur, Hyderabad 500005, India.
    Joshi, Shrikant V.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Forskningsmiljön produktionsteknik(PTW).
    Samajdar, Indradev S.
    Department of Metallurgical Engineering & Materials Science, IIT Bombay, Powai, Mumbai 400076, India.
    Room temperature and 600 °C erosion behaviour of various chromium carbide composite coatings2019Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 422-423, s. 44-53Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, the erosion behaviour of laser clad chromium carbide-Ni rich alloy composite coatings with a wide range of carbide contents at room temperature and 600 °C were investigated. The variation in carbide content of the coatings was due to dilution from the substrate and the high cooling rate in the laser cladding process preventing re-solidification of the molten carbides. Erosion rate was observed to be a function of carbide content alone and was significantly higher at 600 °C as compared to room temperature. Erosion wear ratio (E90/E30) was also dependent on carbide content but decreased at higher temperature and higher carbide contents. A comparison of erosion behaviour with detonation and plasma sprayed counterparts showed the superior performance of laser clad coatings at 600 °C. The poor erosion performance of the detonation and plasma sprayed coatings was due to weak splat bonding. Thick oxide layer formed on the steel substrate after pre-oxidation resulted in its poor erosion performance.

  • 193.
    Zhang, Pimin
    et al.
    Linköping University, Department of Management and Engineering, Linköping, SE-58183, Sweden.
    Sadeghi, Esmaeil
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Chen, Shula
    Linköping University, Department of Physics, Chemistry, and Biology, Linköping, SE-58183, Sweden.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, SE-61283, Sweden.
    Markocsan, Nicolaie
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Joshi, Shrikant V.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Forskningsmiljön produktionsteknik(PTW).
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry, and Biology, Linköping, SE-58183, Sweden.
    Buyanova, Irina A.
    Linköping University, Department of Physics, Chemistry, and Biology, Linköping, SE-58183, Sweden.
    Peng, Ru L.in
    Linköping University, Department of Management and Engineering, Linköping, SE-58183, Sweden.
    Effects of surface finish on the initial oxidation of HVAF-sprayed NiCoCrAlY coatings2019Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 364, s. 43-56Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Oxide scale formed on HVAF-sprayed NiCoCrAlY coatings and the effect of surface treatment were investigated by a multi-approach study combining photo-stimulated luminescence, microstructural observation and mass gain. The initial oxidationbehaviour of as-sprayed, polished and shot-peened coatings at 1000 °C is studied. Both polished and shot-peened coatings exhibited superior performance due to rapid formation of α-Al2O3 fully covering the coating and suppressing the growth of transient alumina, assisted by a high density of α-Al2O3 nuclei on surface treatment induced defects. Moreover, the fast development of a two-layer alumina scale consisting of an inward-grown inner α-Al2O3 layer and an outer layer transformed from outward-grown transient alumina resulted in a higher oxide growth rate of the as-sprayed coating.

  • 194.
    Zhang, Pimin
    et al.
    Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Sadeghimeresht, Esmaeil
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Markocsan, Nicolaie
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Joshi, Shrikant
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Isothermal oxidation behavior of HVAF-sprayed NiCoCrAlY coatings: Effect of surface treatment2017Ingår i: Proceedings of the International Thermal Spray Conference & Exposition (ITSC 2017), New York: Curran Associates, Inc , 2017, Vol. 1, s. 456-461Konferensbidrag (Refereegranskat)
    Abstract [en]

    NiCoCrAlY coatings are widely used as bond coats for ceramic thermal barrier coatings (TBCs) andoxidation and corrosion protective overlay coatings in industrial gas turbines. High temperature oxidation behaviour of NiCoCrAlYs has a great influence on the coating performance and lifetime of TBCs. A promising route to decrease the oxidation rate of such coatings is post-coating surface modification which can facilitate formation of a uniform alumina scale with a considerably slower growth rate compared to the as-sprayed coatings. In this work, the effect of surface treatment by means of shot peening and laser surface melting (LSM) on the oxidation resistance of high velocity air-fuel (HVAF) sprayed NiCoCrAlY coatings was studied. Isothermal oxidation was carried out at 1000⁰C for 1000h. Results showed that the rough surface of as-sprayed HVAF sprayed coatings was significantly changed after shot peening and LSM treatment, with a compact and smooth appearance. After the exposure, the oxide scales formed on surface-treated NiCoCrAlY coatings showed different morphology and growth rate compared to those formed on as-sprayed coating surface. The oxidation behaviour of surface treated HVAF-sprayed NiCoCrAlY coatings were revealed and discussed.

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