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  • 201.
    Freton, Pierre
    et al.
    Paul Sabatier University, Toulouse, France.
    Gonzales, Jean-Jacques
    Paul Sabatier University, Toulouse, France.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Mougenot, Jacques
    Paul Sabatier University, Toulouse, France.
    Discussion sur les différentes formulations des équations de l´énergie dans les modèles de plasmas thermiques à deux températures2013Conference paper (Other academic)
    Abstract [fr]

    Pour modéliser un plasma thermique à deux températures, les travaux de la littérature proposent en général de résoudre une équation pour l’énergie des électrons et une autre pour celle des lourds. Néanmoins, tous les auteurs ne sont pas d’accord sur une formulation et diverses écritures de ces deux équations de l'énergie peuvent être trouvées dans la littérature. Les principales différences concernent deux termes : le terme correspondant à l'énergie d'ionisation et le terme relatif à la part de conductivité thermique réactive. Suivant les auteurs ces deux termes peuvent être attribués, indifféremment à l’équation de l’énergie régissant la température des particules lourdes ou celle des électrons.

      Afin de nous positionner et éclaircir ce point, nous proposons de développer théoriquement les deux équations de l'énergie en repartant de l'équation de Boltzmann et de ses moments. Les résultats obtenus avec la formulation proposée sont alors comparés avec ceux obtenus avec les formulation de la littérature.

  • 202.
    Frodelius, Jenny
    et al.
    Linköping University, Thin Film Physics Division, Department of Physics.
    Sonestedt, Marie
    Chalmers University of Technology, Microscopy and Microanalysis, Department of Applied Physics.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Palmquist, Jens-Petter
    Kanthal AB, 734 27 Hallstahammar, Sweden.
    Stiller, Krystyna
    Chalmers University of Technology, Microscopy and Microanalysis, Department of Applied Physics.
    Högberg, Hans
    Linköping University, Thin Film Physics Division, Department of Physics.
    Hultman, Lars
    Linköping University, Thin Film Physics Division, Department of Physics.
    Ti2AlC coatings deposited by High Velocity Oxy-Fuel spraying2008In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 202, no 24, p. 5976-5981Article in journal (Refereed)
    Abstract [en]

    High Velocity Oxy-Fuel has been utilized to spray coatings from Ti2AlC (MAXTHAL 211®) powders. X-ray diffraction showed that the coatings consist predominantly of Ti2AlC with inclusions of the phases Ti3AlC2, TiC, and Al–Ti alloys. The fraction of Ti2AlC in coatings sprayed with a powder size of 38 μm was found to increase with decreasing power of the spraying flame as controlled by the total gas flow of H2 and O2. A more coarse powder (56 μm) is less sensitive to the total gas flow and retains higher volume fraction of MAX-phase in the coatings, however, at the expense of increasing porosity. X-ray pole figure measurements showed a preferred crystal orientation in the coatings with the Ti2AlC (000l) planes aligned to the substrate surface. Bending tests show a good adhesion to stainless steel substrates and indentation yields a hardness of 3–5 GPa for the coatings sprayed with a powder size of 38 μm.

  • 203.
    Ganvir, Ashish
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Design of Suspension Plasma Sprayed Thermal Barrier Coatings2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Thermal barrier coatings (TBCs) are widely used on gas turbine components to provide thermal insulation, which in combination with advanced cooling, can enable the gas turbine to operate at significantly higher temperatures even above the melting temperature of the metallic components. There is a permanent need,mainly due to environmental reasons, to increase the combustion temperature inturbines, hence new TBC solutions are needed. By using a liquid feedstock in thermal spraying, new types of TBCs can be produced. Suspension plasma/flame or solution precursor plasma spraying are examples of techniques that can be utilized for liquid feedstock thermal spraying. This approach of using suspension and solution feedstock, which is an alternative to the conventional solid powder feedstock spraying, is gaining increasing research interest since it has been shown to be capable of producing coatings withsuperior performance. The objective of this research work was to identify relationships between process parameters, coating microstructure, thermal conductivity and lifetime in suspension plasma sprayed TBCs. A further objective was to utilize these relationships to enable tailoring of the TBC microstructure for superior performance compared to state-of-the-art TBC used in industry today, i.e. solid feedstock plasma sprayed TBCs. Different spraying techniques, namely suspension high velocity oxy fuel, solution precursor plasma and suspension plasma spraying (with axial and radial feeding) were explored and compared to solid feedstock plasma spraying. A variety of microstructures, such as highly porous, vertically cracked and columnar, were produced and investigated. It was shown that there are strong relationships between microstructure, thermo-mechanical properties and performance of the coatings. Specifically, axial suspension plasma spraying wasshown as a very promising technique to produce various microstructures as wellas highly durable coatings. Based on the experimental results, a tailored columnar microstructure design for a superior TBC performance is also proposed.

  • 204.
    Ganvir, Ashish
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Microstructure and Thermal Conductivity of Liquid Feedstock Plasma Sprayed Thermal Barrier Coatings2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Thermal barrier coating (TBC) systems are widely used on gas turbine components to provide thermal insulation and oxidation protection. TBCs, incombination with advanced cooling, can enable the gas turbine to operate at significantly higher temperatures even above the melting temperature of the metallic materials. There is a permanent need mainly of environmental reasons to increase the combustion turbine temperature, hence new TBC solutions are needed.By using a liquid feedstock in thermal spraying, new types of TBCs can be produced. Suspension plasma/flame or solution precursor plasma spraying are examples of techniques that can be utilized for liquid feedstock thermal spraying.This approach of using suspension and solution feedstock, which is an alternative to the conventional solid powder feed stock spraying, is gaining increasing research interest, since it has been shown to be capable of producing coatings with superior coating performance.The objective of this research work was to explore relationships between process parameters, coating microstructure, thermal diffusivity and thermal conductivity in liquid feedstock thermal sprayed TBCs. A further aim was to utilize this knowledge to produce a TBC with lower thermal diffusivity and lower thermal conductivity compared to state-of-the-art in industry today, i.e. solid feed stock plasma spraying. Different spraying techniques, suspension high velocity oxy fuel,solution precursor plasma and suspension plasma spraying (with axial and radialfeeding) were explored and compared with solid feedstock plasma spraying.A variety of microstructures, such as highly porous, vertically cracked and columnar, were obtained. It was shown that there are strong relationships between the microstructures and the thermal properties of the coatings.Specifically axial suspension plasma spraying was shown as a very promising technique to produce various microstructures as well as low thermal diffusivity and low thermal conductivity coatings.

  • 205.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Yao, Y.
    Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, 41296, Sweden.
    Vadali, S. V. S. S.
    University of Hyderabad, School of Engineering Sciences and Technology, Hyderabad, 500046, India.
    Klement, Uta
    Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, 41296, Sweden.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    A facile approach to deposit graphenaceous composite coatings by suspension plasma spraying2019In: Coatings, ISSN 2079-6412, Vol. 9, no 3, article id 171Article in journal (Refereed)
    Abstract [en]

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

  • 206.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Calinas, Rosa Filomena
    Innovnano Materials, Coimbra, Portugal.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Curry, Nicholas
    Treibacher Industries AG, Althofen, Austria.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Experimental visualization of microstructure evolution during suspension plasma spraying of thermal barrier coatings2019In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 39, no 2-3, p. 470-481Article in journal (Refereed)
    Abstract [en]

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

  • 207.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Curry, Nicholas
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Characterization of Microstructure and Thermal Properties of YSZ Coatings Obtained by Axial Suspension Plasma Spraying (ASPS)2015In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 24, no 7, p. 1195-1204Article in journal (Refereed)
    Abstract [en]

    The paper aims at demonstrating various microstructures which can be obtained using the suspension spraying technique and their respective significance in enhancing the thermal insulation property of a thermal barrier coating. Three different types of coating microstructures are discussed which were produced by the Axial Suspension Plasma Spraying. Detailed characterization of coatings was then performed. Optical and scanning electron microscopy were utilized for microstructure evaluations; x-ray diffraction for phase analysis; water impregnation, image analysis, and mercury intrusion porosimetry for porosity analysis, and laser flash analysis for thermal diffusivity measurements were used. The results showed that Axial Suspension Plasma Spraying can generate vertically cracked, porous, and feathery columnar-type microstructures. Pore size distribution was found in micron, submicron, and nanometer range. Higher overall porosity, the lower density of vertical cracks or inter-column spacing, and higher inter-pass porosity favored thermal insulation property of the coating. Significant increase in thermal diffusivity and conductivity was found at higher temperature, which is believed to be due to the pore rearrangement (sintering and pore coarsening). Thermal conductivity values for these coatings were also compared with electron beam physical vapor deposition (EBPVD) thermal barrier coatings from the literature and found to be much lower. © 2015 ASM International

  • 208.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Curry, Nicholas
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Govindarajan, Sivakumar
    International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), 500005 Hyderabad, India.
    Characterization of Thermal Barrier Coatings Produced by Various Thermal Spray Techniques Using Solid Powder, Suspension, and Solution Precursor Feedstock Material2016In: International Journal of Applied CeramicTechnology, ISSN 1546-542X, Vol. 13, no 2, p. 324-332Article in journal (Refereed)
    Abstract [en]

    Use of a liquid feedstock in thermal spraying (an alternative to the conventional solid powder feedstock) is receiving an increasing level of interest due to its capability to produce the advanced submicrometer/nanostructured coatings. Suspension plasma spraying (SPS) and solution precursor plasma spraying (SPPS) are those advanced thermal spraying techniques which help to feed this liquid feedstock. These techniques have shown to produce better performance thermal barrier coatings (TBCs) than conventional thermal spraying. In this work, a comparative study was performed between SPS- and SPPS-sprayed TBCs which then were also compared with the conventional atmospheric plasma-sprayed (APS) TBCs. Experimental characterization included SEM, porosity analysis using weight difference by water infiltration, thermal conductivity measurements using laser flash analysis, and lifetime assessment using thermo-cyclic fatigue test. It was concluded that SPS coatings can produce a microstructure with columnar type features (intermediary between the columnar and vertically cracked microstructure), whereas SPPS can produce vertically cracked microstructure. It was also shown that SPS coatings with particle size in suspension (D50) <3 μm were highly porous with lower thermal conductivity than SPPS and APS coatings. Furthermore, SPS coatings have also shown a relatively better thermal cyclic fatigue lifetime than SPPS.

  • 209.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Curry, Nicholas
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Joshi, Shrikant
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Vilemova, Monika
    IPP.
    Pala, Zdenek
    IPP.
    Influence of Microstructure on Thermal Properties of Axial Suspension Plasma-Sprayed YSZ Thermal Barrier Coatings2016In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 25, no 1-2, p. 202-212Article in journal (Refereed)
    Abstract [en]

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

  • 210.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Curry, Nicholas
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nylén, Per
    University West, Department of Engineering Science, Research Environment Production Technology West.
    Toma, Filofteia-Laura
    Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Comparative study of suspension plasma sprayed and suspension high velocity oxy-fuel sprayed YSZ thermal barrier coatings2015In: Surface and Coatings Technology, ISSN 0257-8972, Vol. 268, p. 70-76Article in journal (Refereed)
    Abstract [en]

    Suspension Thermal Spraying is a relatively new thermal spaying technique to produce advanced thermal barrier coatings. This technique enables the production of much different performance thermal barrier coatings than conventional thermal spraying which uses solid powder as a feedstock material. In this work a comparative study is performed on four different types of thermal barrier coatings sprayed with two different thermal spay processes, suspension high velocity oxy-fuel spraying (SHVOF) and suspension plasma spraying (SPS) using two different water-based suspensions. Tests carried out include microstructural analysis with SEM, porosity analysis using weight difference by water infiltration, thermal conductivity measurements using laser flash analysis and lifetime assessment using thermo-cyclic fatigue tests. The results showed that SPS coatings were much porous and hence showed lower thermal conductivity than SHVOF coatings produced with the same suspension. From the thermo-cycling tests it was observed that the SPS coatings showed a higher lifetime than the SHVOF ones.

  • 211.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Curry, Nicholas
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nylén, Per
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Vilemova, Monika
    IPP Prague, Czech Republic.
    Pala, Zdenek
    IPP Prague, Czech Republic.
    Influence of Microstructure on Thermal Properties of Columnar Axial Suspension Plasma Sprayed Thermal Barrier Coatings2015In: Proceedings of the International Thermal Spray Conference: International Thermal Spray Conference and Exposition, ITSC 2015; Long Beach; United States; 11 May 2015 through 14 May 2015 / [ed] A. McDonald, A. Agarwal, G. Bolelli, A. Concustell, Y.-C. Lau, F.-L. Toma, E. Turunen, C. Widener, ASM International, 2015, p. 498-505Conference paper (Refereed)
    Abstract [en]

    Suspension Plasma Spraying is a relatively new thermal spraying technique to produce advanced thermal barrier coatings. This technique enables the production of a variety of structures from highly dense, highly porous, segmented or columnar coatings. In this work a comparative study is performed on six different suspension plasma sprayed thermal barrier coatings which were produced using axial injection and different process parameters. The influence of coating morphology and porosity on thermal properties was of specific interest. Tests carried out include microstructural analysis with SEM, phase analysis using XRD, porosity calculation using Archimedes experimental setup, pore distribution analysis using mercury infiltration technique and thermal diffusivity/conductivity measurements using laser flash analysis. The results showed that columnar and cauliflower type coatings were produced by axial suspension plasma spraying process. Better performance coatings were produced with relatively higher overall energy input given during spraying. Coatings with higher energy input, lower thickness and wider range of submicron and nanometer sized pores distribution showed lower thermal diffusivity and hence lower thermal conductivity. Also, in-situ heat treatment did not show dramatic increase in thermal properties.

  • 212.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Vassen, Robert
    Forschungszentrum Jülich GmbH, IEK-1, Jülich, Germany.
    Tailoring columnar microstructure of axial suspension plasma sprayed TBCs for superior thermal shock performance2018In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 144, p. 192-208Article in journal (Refereed)
    Abstract [en]

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

  • 213.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Kumara, Chamara
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Nylen, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Thermal Conductivity in Suspension Sprayed Thermal Barrier Coatings: Modeling and Experiments2017In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 26, no 1-2, p. 71-82Article in journal (Refereed)
    Abstract [en]

    Axial suspension plasma spraying (ASPS) can generate microstructures with higher porosity and pores in the size range from submicron to nanometer. ASPS thermal barrier coatings (TBC) have already shown a great potential to produce low thermal conductivity coatings for gas turbine applications. It is important to understand the fundamental relationships between microstructural defects in ASPS coatings such as crystallite boundaries, porosity etc. and thermal conductivity. Object-oriented finite element (OOF) analysis has been shown as an effective tool for evaluating thermal conductivity of conventional TBCs as this method is capable of incorporating the inherent microstructure in the model. The objective of this work was to analyze the thermal conductivity of ASPS TBCs using experimental techniques and also to evaluate a procedure where OOF can be used to predict and analyze the thermal conductivity for these coatings. Verification of the model was done by comparing modeling results with the experimental thermal conductivity. The results showed that the varied scaled porosity has a significant influence on the thermal conductivity. Smaller crystallites and higher overall porosity content resulted in lower thermal conductivity. It was shown that OOF could be a powerful tool to predict and rank thermal conductivity of ASPS TBCs.

  • 214.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Kumara, Chamara
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Nylén, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Thermal conductivity in suspension sprayed thermal barrier coatings: Modelling and experiments2016In: Proceedings of the International Thermal Spray Conference, ASM International, 2016, Vol. 1, p. 368-374Conference paper (Refereed)
    Abstract [en]

    Axial Suspension Plasma spraying (ASPS) can generate microstructures with higher porosity and pores in the size range from submicron to nanometre. ASPS Thermal Barrier Coatings (TBCs) have already shown a great potential to produce low thermal conductivity coatings for gas turbine applications. It is important to understand the fundamental relationship between microstructural defects in the coating such as grain boundaries, porosity etc. and thermal conductivity. Object Oriented Finite element analysis (OOF) has been shown to be an effective tool for evaluating thermal conductivity for conventional TBCs as this method is capable of incorporating the inherent microstructure as an input to the model. The objective of this work was to analyse the thermal conductivity of ASPS TBCs using experimental techniques and also to evaluate a procedure where OOF can be used to predict and analyse the thermal conductivity for these coatings. Verification of the model was done using experimental thermal conductivity. Results showed that the varied scaled porosity has a significant influence on the thermal conductivity. Smaller grains, higher overall porosity content and lower columnar density resulted in lower thermal conductivity. It was shown that OOF could be a powerful tool to predict and rank thermal conductivity of ASPS TBCs.

  • 215.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Porosity analysis of axial suspension plasma sprayed thermal barrier coatings for gas turbine applications2016Conference paper (Other academic)
  • 216.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Calinas, R.
    Vitorino, N.
    Lukac, F.
    Ekberg, J.
    Chalmers University of Technology, Sweden.
    Influence of suspension characteristics on microstructure of axial suspension plasma-sprayed coatings2017Conference paper (Other academic)
  • 217.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Influence of Isothermal Heat Treatment on Porosity and Crystallite Size in Axial Suspension Plasma Sprayed Thermal Barrier Coatings for Gas Turbine Applications2017In: Coatings, ISSN 2079-6412, Vol. 7, no 1, p. 1-14, article id 4Article in journal (Refereed)
    Abstract [en]

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

  • 218.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Lukac, F.
    Pala, Z.
    Influence of microstructure on thermo-cyclic fatigue and thermal shock resistance of axial suspension plasma sprayed therm2016Conference paper (Other academic)
  • 219.
    Ganvir, Ashish
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Vaidhyanathan, Venkateswaran
    University West, Department of Engineering Science.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Pala, Zdenek
    Institute of Plasma Physics CAS, Za Slovankou 3, 182 00 Prague, Czech Republic.
    Lukac, Frantisek
    Institute of Plasma Physics CAS, Za Slovankou 3, 182 00 Prague, Czech Republic.
    Failure analysis of thermally cycled columnar thermal barrier coatings produced by high-velocity-air fuel and axial-suspension-plasma spraying: A design perspective2018In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 44, no 3, p. 3161-3172Article in journal (Refereed)
    Abstract [en]

    Axial-suspension-plasma spraying (ASPS) is a fairly recent thermal spray technology which enables production of ceramic top coats in TBCs, incorporating simultaneously the properties of both the conventional-plasma sprayed (highly insulating porous structures) and electron-beam-physical-vapor-deposited (strain-tolerant columnar structures) top coats. TBCs are required to insulate the hot components in a gas turbine engine against high temperature and harsh operating conditions. Periodic heating and cooling of turbine engines during operation can create severe thermal cyclic fatigue conditions which can degrade the performance of these coatings eventually leading to the failure. An in-depth experimental investigation was performed to understand the failure behavior of columnar TBCs subjected to thermal cyclic fatigue (TCF) test at 1100 C. The study revealed that the TCF performance was influenced to an extent, by the top coat microstructure, but was primarily affected by the severity of thermally grown oxide (TGO) growth at the bond coat-top coat interface. Mixed failure modes comprising crack propagation through the bond coat-TGO interface, through TGO and within the top coat were identified. Based on the analysis of the experimental results and thorough discussion a novel design of microstructure for the high TCF performance columnar TBC is proposed. © 2017 Elsevier Ltd and Techna Group S.r.l.

  • 220.
    Gaudiuso, Caterina
    et al.
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, Via Amendola 173, Bari, Italy.
    Giannuzzi, Giuseppe
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, Via Amendola 173, Bari, Italy.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Lugarà, Pietro Mario
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, Via Amendola 173, Bari, Italy.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems.
    Incubation effect in burst mode fs-laser ablation of stainless steel samples2018In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 10520, article id 105200AArticle in journal (Refereed)
    Abstract [en]

    We report on an experimental study of the incubation effect during irradiation of stainless steel targets with bursts of femtosecond laser pulses at 1030 nm wavelength and 100 kHz repetition rate. The bursts were generated by splitting the pristine 650-fs laser pulses using an array of birefringent crystals which provided time separations between sub-pulses in the range from 1.5 ps to 24 ps. We measured the threshold fluence in Burst Mode, finding that it strongly depends on the bursts features. The comparison with Normal Pulse Mode revealed that the existing models introduced to explain the incubation effect during irradiation with trains of undivided pulses has to be adapted to describe incubation during Burst Mode processing. In fact, those models assume that the threshold fluence has a unique value for each number of impinging pulses in NPM, while in case of BM we observed different values of threshold fluence for fixed amount of sub-pulses but different pulse splitting. Therefore, the incubation factor coefficient depends on the burst features. It was found that incubation effect is higher in BM than NPM and that it increases with the number of sub-pulses and for shorter time delays within the burst. Two-Temperature-Model simulations in case of single pulses and bursts of up to 4 sub-pulses were performed to understand the experimental results. © Copyright SPIE.

  • 221.
    Gaudiuso, Caterina
    et al.
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, via Amendola 173, Bari, Italy & Università degli Studi di Bari, Dipartimento Interuniversitario di Fisica, via Amendola 173, Bari, Italy .
    Giannuzzi, Giuseppe
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, via Amendola 173, Bari, Italy & Università degli Studi di Bari, Dipartimento Interuniversitario di Fisica, via Amendola 173, Bari, Italy.
    Volpe, Annalisa
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, via Amendola 173, Bari, Italy.
    Lugarà, Pietro Mario
    Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, via Amendola 173, Bari, Italy & Università degli Studi di Bari, Dipartimento Interuniversitario di Fisica, via Amendola 173, Bari, Italy.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Ancona, Antonio
    University West, Department of Engineering Science, Division of Production Systems. Istituto di Fotonica e Nanotecnologie (IFN)-CNR U.O.S. Bari, via Amendola 173, Bari, Italy.
    Incubation during laser ablation with bursts of femtosecond pulses with picosecond delays2018In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 4, p. 3801-3813Article in journal (Refereed)
    Abstract [en]

    Abstract: We report on an experimental investigation of the incubation effect during irradiation of stainless steel with bursts of ultrashort laser pulses. A series of birefringent crystals was used to split the pristine 650-fs pulses into bursts of up to 32 sub-pulses with time separations of 1.5 ps and 3 ps, respectively. The number of selected bursts was varied between 50 and 1600. The threshold fluence was measured in case of Burst Mode (BM) processing depending on the burst features, i.e. the number of sub-pulses and their separation time, and on the number of bursts. We found as many values of threshold fluence as the combinations of the number of bursts and of sub-pulses constituting the bursts set to give the same total number of impinging sub-pulses. However, existing incubation models developed for Normal Pulse Mode (NPM) return, for a given number of impinging pulses, a constant value of threshold fluence. Therefore, a dependence of the incubation coefficient with the burst features was hypothesized and experimentally investigated. Numerical solutions of the Two Temperature Model (TTM) in case of irradiation with single bursts of up to 4 sub-pulses have been performed to interpret the experimental results. © 2018 Optical Society of America.

  • 222.
    Glorieux, Emile
    et al.
    University West, Department of Engineering Science, Division of Production System.
    Franciosa, Pasquale
    University of Warwick, Warwick Manufacturing Group (WMG), Coventry, CV4 7AL, United Kingdom.
    Ceglarek, Dariusz
    University of Warwick, Warwick Manufacturing Group (WMG), Coventry, CV4 7AL, United Kingdom.
    Quality and productivity driven trajectory optimisation for robotic handling of compliant sheet metal parts in multi-press stamping lines2019In: Robotics and Computer-Integrated Manufacturing, ISSN 0736-5845, E-ISSN 1879-2537, Vol. 56, p. 264-275Article in journal (Refereed)
    Abstract [en]

    This paper investigates trajectory generation for multi-robot systems that handle compliant parts in order to minimise deformations during handling, which is important to reduce the risk of affecting the part’s dimensional quality. An optimisation methodology is proposed to generate deformation-minimal multi-robot coordinated trajectories for predefined robot paths and cycle-time. The novelty of the proposed optimisation methodology is that it efficiently estimates part deformations using a precomputed Response Surface Model (RSM), which is based on data samples generated by Finite Element Analysis (FEA) of the handled part and end-effector. The end-effector holding forces, plastic part deformations, collision-avoidance and multi-robot coordination are also considered as constraints in the optimisation model. The optimised trajectories are experimentally validated and the results show that the proposed optimisation methodology is able to significantly reduce the deformations of the part during handling, i.e. up to 12% with the same cycle-time in the case study that involves handling compliant sheet metal parts. This investigation provides insights into generating specialised trajectories for material handling of compliant parts that can systematically minimise part deformations to ensure final dimensional quality. © 2018

  • 223.
    Glorieux, Emile
    et al.
    University West, Department of Engineering Science, Division of Automation Systems.
    Svensson, Bo
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Danielsson, Fredrik
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Lennartson, Bengt
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying. University West, Department of Engineering Science, Division of Production Systems. Department of Signals and Systems, Chalmers University of Technology, Gothenburg, Sweden.
    A Constructive Cooperative Coevolutionary Algorithm Applied to Press Line Optimisation2014In: Proceedings of the 24th International Conference on Flexible Automation and Intelligent Manufacturing: Capturing Competitive Advantage via Advanced Manufacturing and Enterprise Transformation / [ed] F. Frank Chen, Lancaster, PA, USA: DEStech Publications, Inc. , 2014, p. 909-916Conference paper (Refereed)
    Abstract [en]

    Simulation-based optimisation often considers computationally expensive problems. Successfully optimising such large scale and complex problems within a practical time frame is a challenging task. Optimisation techniques to fulfil this need to be developed. A technique to address this involves decomposing the considered problem into smaller subproblems. These subproblems are then optimised separately. In this paper, an efficient algorithm for simulation-based optimisation is proposed. The proposed algorithm extends the cooperative coevolutionary algorithm, which optimises subproblems separately. To optimise the subproblems, the proposed algorithm enables using a deterministic algorithm, next to stochastic genetic algorithms, getting the flexibility of using either type. It also includes a constructive heuristic that creates good initial feasible solutions to reduce the number of fitness calculations. The extension enables solving complex, computationally expensive problems efficiently. The proposed algorithm has been applied on automated sheet metal press lines from the automotive industry. This is a highly complex optimisation problem due to its non-linearity and high dimensionality. The optimisation problem is to find control parameters that maximises the line’s production rate. These control parameters determine velocities, time constants, and cam values for critical interactions between components. A simulation model is used for the fitness calculation during the optimisation. The results show that the proposed algorithm manages to solve the press line optimisation problem efficiently. This is a step forward in press line optimisation since this is to the authors’ knowledge the first time a press line has been optimised efficiently in this way.

  • 224.
    Goel, Sneha
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Post-treatment of Alloy 718 produced by electron beam melting2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Electron beam melting (EBM), a metal additive manufacturing (AM) process, has received considerable industrial attention for near net shape manufacture of complex geometries with traditionally difficult-to-machine materials. This has fuelled considerable academic interest in investigating EBM of Alloy 718, a nickel ironbased superalloy possessing an exciting combination of good mechanical behaviour and cost effectiveness. EBM production of Alloy 718 is particularly promising for aerospace and other sectors which value rapid production of components with large scope for design flexibility. The EBM builds are characterized by presence of inevitable defects and, anisotropy within a build is also a concern. Consequently, as-built Alloy 718 has to be subjected to post-build thermal-treatments (post-treatments) to ensure that the parts eventually meet the critical service requirements. Not withstanding the above, limited knowledge is available about optimal post-treatments for EBM-built Alloy 718. Therefore, the main focus of the work presented in this thesis was to systematically investigate the response of EBM-built material to post-treatments, which include hotisostatic pressing (HIPing), solution treatment (ST), and aging.

    HIPing of EBM-built Alloy 718 led to more than an order of magnitude reduction in defect content, which was reduced from as high as 17% to < 0.2% in samples built with intentionally introduced porosity to investigate limits of defect closure achievable through HIPing. In addition, HIPing also caused complete dissolution of δ and γ" phases present in the as-built condition, with the latter causing dropin hardness of the material. HIPing had no effect on the carbides and inclusions such as TiN, Al2O3 present in the built material. The evolution of microstructure during ST and aging was systematically investigated. Growth of potentially beneficial grain boundary δ phase precipitates was found to cease after a certain duration of ST, with samples subjected to prior-HIPing exhibiting lesser precipitation of the δ phase during ST. While the specimen hardness increased onaging, it was observed to plateau after a duration significantly shorted than the specified ASTM 'standard' aging cycle. Therefore, prima facie there are promising prospects for shortening the overall heat treatment duration. A combination of HIPing, ST, and aging treatments in a single uninterrupted cycle was also explored. Future work involving incorporation of a shortened heat treatment schedule in a combined cycle can have significant industrial implications.

  • 225.
    Goel, Sneha
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Ahlfors, Magnus
    Quintus Technologies AB, Västerås, Sweden.
    Bahbou, Fouzi
    ARCAM AB, Mölndal, Sweden.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Effect of Different Post-treatments on the Microstructure of EBM-Built Alloy 7182019In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 28, no 2, p. 673-680Article in journal (Refereed)
    Abstract [en]

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

  • 226.
    Goel, Sneha
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Curry, Nicholas
    Treibacher Ind AG, Althofen, Austria.
    Wiklund, U.
    Uppsala Univ, Dept Technol, Mat Sci Div, S-75121 Uppsala, Swede.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Axial suspension plasma spraying of Al2O3 coatings for superior tribological properties2017In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 315, p. 80-87Article in journal (Refereed)
    Abstract [en]

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

  • 227.
    Goel, Sneha
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Joshi, Shrikant
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Deposition of Novel Composite Coatings by Suspension-Powder Hybrid Plasma Spraying2016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, p. 1-8Conference paper (Refereed)
    Abstract [en]

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

  • 228.
    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. 

  • 229.
    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.

  • 230.
    Goel, Sneha
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Sittiho, Anumat
    University of Idaho, Department of Chemical and Materials Engineering, Moscow, ID 83844, United States.
    Charit, Indrajit
    University of Idaho, Department of Chemical and Materials Engineering, Moscow, ID 83844, United States.
    Klement, Uta
    Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, Sweden.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Effect of post-treatments under hot isostatic pressure on microstructural characteristics of EBM-built Alloy 7182019In: Additive Manufacturing, ISSN 2214-8604, Vol. 28, p. 727-737Article in journal (Refereed)
    Abstract [en]

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

  • 231.
    Gopal, Vasanth
    et al.
    Department of Physics, School of Advanced Sciences, VIT, Vellore 632014, India Centre for Biomaterials, Cellular and Molecular Theranostics, VIT, Vellore 632014, India.
    Goel, Sneha
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Manivasagam, Geetha
    Centre for Biomaterials, Cellular and Molecular Theranostics, VIT, Vellore 632014, India.
    Joshi, Shrikant V.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Performance of Hybrid Powder-Suspension Axial Plasma Sprayed Al2O3-YSZ Coatings in Bovine Serum Solution2019In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 12, article id E1922Article in journal (Refereed)
    Abstract [en]

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

  • 232.
    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.

  • 233.
    Gruber, H.
    et al.
    Chalmers University of Technology, Department of Industrial and Materials Science, Division of Materials and Manufacture, Gothenburg, SE-412 96, Sweden.
    Karimi Neghlani, Paria
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Hryha, E.
    Chalmers University of Technology, Department of Industrial and Materials Science, Division of Materials and Manufacture, Gothenburg, SE-412 96, Sweden.
    Nyborg, L.
    Chalmers University of Technology, Department of Industrial and Materials Science, Division of Materials and Manufacture, Gothenburg, SE-412 96, Sweden.
    Effect of Powder Recycling on the Fracture Behavior of Electron Beam Melted Alloy 7182018In: Powder Metallurgy Progress, ISSN 1335-8987, Vol. 18, no 1, p. 40-48Article in journal (Other academic)
    Abstract [en]

    Understanding the effect of powder feedstock alterations during multicycle additive manufacturing on the quality of built components is crucial to meet the requirements on critical parts for aerospace engine applications. In this study, powder recycling of Alloy 718 during electron beam melting was studied to understand its influence on fracture behavior of Charpy impact test bars. High resolution scanning electron microscopy was employed for fracture surface analysis on test bars produced from virgin and recycled powder. For all investigated samples, an intergranular type of fracture, initiated by non-metallic phases and bonding defects, was typically observed in the regions close to or within the contour zone. The fracture mode in the bulk of the samples was mainly moderately ductile dimple fracture. The results show a clear correlation between powder degradation during multi-cycle powder reuse and the amount of damage relevant defects observed on the fracture surfaces. In particular, samples produced from recycled powder show a significant amount of aluminum-rich oxide defects, originating from aluminum-rich oxide particulates on the surface of the recycled powder. © 2018 H. Gruber et al., published by Sciendo.

  • 234.
    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)
  • 235.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Design of Microstructures in Thermal Barrier Coatings: A Modelling Approach2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Plasma sprayed Thermal Barrier Coating systems (TBCs) are commonly used for thermal protection of components in modern gas turbine application such as power generation, marine and aero engines. The material that is most commonly used in these applications is Yttria Stabilized Zirconia (YSZ) because of this ceramic’s favourable properties, such as low thermal conductivity, phase stability to high temperature, and good erosion resistance. The coating microstructures in YSZ coatings are highly heterogeneous, consisting of defects such as pores and cracks of different sizes which determine the coating’s final thermal and mechanical properties, and the service lives of the coatings. Determination of quantitative microstructure–property correlations is of great interest as experimental procedures are time consuming and expensive.

    This objective of this thesis work was to investigate the relationships between coating microstructure and thermal-mechanical properties of TBCs, and to utilise these relationships to design an optimised microstructure to be used for next generation TBCs. Simulation technique was used to achieve this goal. Important microstructural parameters influencing the performance of TBCs were identified and coatings with the identified microstructural parameters were designed, modelled and experimentally verified. TBCs comprising of large globular pores with connected cracks inherited within the coating microstructure were shown to have significantly enhanced performance. Low thermal conductivity, low Young‘s modulus and high lifetime were exhibited by these coatings. The modelling approach described in this work can be used as a powerful tool to design new coatings as well as to achieve optimised microstructures.

  • 236.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Design of Thermal Barrier Coatings: A modelling approach2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Atmospheric plasma sprayed (APS) thermal barrier coatings (TBCs) are commonly used for thermal protection of components in modern gas turbine application such as power generation, marine and aero engines. TBC is a duplex material system consisting of an insulating ceramic topcoat layer and an intermetallic bondcoat layer. TBC microstructures are highly heterogeneous, consisting of defects such as pores and cracks of different sizes which determine the coating's final thermal and mechanical properties, and the service lives of the coatings. Failure in APS TBCs is mainly associated with the thermo-mechanical stresses developing due to the thermally grown oxide (TGO) layer growth at the topcoat-bondcoat interface and thermal expansion mismatch during thermal cycling. The interface roughness has been shown to play a major role in the development of these induced stresses and lifetime of TBCs.The objective of this thesis work was two-fold for one purpose: to design an optimised TBC to be used for next generation gas turbines. The first objective was to investigate the relationships between coating microstructure and thermal-mechanical properties of topcoats, and to utilise these relationships to design an optimised morphology of the topcoat microstructure. The second objective was to investigate the relationships between topcoat-bondcoat interface roughness, TGO growth and lifetime of TBCs, and to utilise these relationships to design an optimal interface. Simulation technique was used to achieve these objectives. Important microstructural parameters influencing the performance of topcoats were identified and coatings with the feasible identified microstructural parameters were designed, modelled and experimentally verified. It was shown that large globular pores with connected cracks inherited within the topcoat microstructure significantly enhanced TBC performance. Real topcoat-bondcoat interface topographies were used to calculate the induced stresses and a diffusion based TGO growth model was developed to assess the lifetime. The modelling results were compared with existing theories published in previous works and experiments. It was shown that the modelling approach developed in this work could be used as a powerful tool to design new coatings and interfaces as well as to achieve high performance optimised morphologies.

  • 237.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Design of Thermal Barrier Coatings: A Modelling Approach2015Book (Other academic)
    Abstract [en]

    This book details the relationships between microstructure, interface roughness, and properties of thermal barrier coatings. The author proposes a method for the reduction of the thermal conductivity of the ceramic layer in order to increase the lifetime of thermal barrier coatings. He includes models for the optimization of ceramic layer microstructure and interface roughness.

  • 238.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Spraying of solid oxide fuel cells2016Conference paper (Other academic)
  • 239.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Curry, Nicholas
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Vaßen, Robert
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Design of Next Generation Thermal Barrier Coatings- Experiments and Modelling2013In: Surface and Coatings Technology, ISSN 0257-8972, Vol. 220, p. 20-26Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coating (TBC) systems have been used in the gas turbine industry since the 1980's. The future needs of both the air and land based turbine industry involve higher operating temperatures with longer lifetime on the component so as to increase power and efficiency of gas turbines. The aim of this study was to meet these future needs by further development of zirconia coatings. The intention was to design a coating system which could be implemented in industry within the next three years. Different morphologies of ceramic topcoat were evaluated; using dual layer systems and polymers to generate porosity. Dysprosia stabilised zirconia was also included in this study as a topcoat material along with the state-of-the-art yttria stabilised zirconia (YSZ). High purity powders were selected in this work. Microstructure was assessed with scanning electron microscope and an in-house developed image analysis routine was used to characterise porosity content. Evaluations were carried out using the laser flash technique to measure thermal conductivity. Lifetime was assessed using thermo-cyclic fatigue testing. Finite element analysis was utilised to evaluate thermal-mechanical material behaviour and to design the morphology of the coating with the help of an artificial coating morphology generator through establishment of relationships between microstructure, thermal conductivity and stiffness. It was shown that the combined empirical and numerical approach is an effective tool for developing high performance coatings. The results show that large globular pores and connected cracks inherited within the coating microstructure result in a coating with best performance. A low thermal conductivity coating with twice the lifetime compared to the industrial standard today was fabricated in this work.

  • 240.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Dwivedi, Gopal
    Stony Brook University, USA.
    Nylén, Per
    University West, Department of Engineering Science, Research Environment Production Technology West.
    Vackel, Andrew
    Stony Brook University, USA.
    Sampath, Sanjay
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    An Experimental Study of Microstructure: Property Relationships in Thermal Barrier Coatings2013In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 22, no 5, p. 659-670Article in journal (Refereed)
    Abstract [en]

    The thermal-mechanical properties of thermal barrier coatings are highly influenced by the defects present in coating microstructure. The aim of this study was to meet the future needs of the gas turbine industry by further development of zirconia coatings through the assessment of microstructure-property relationships. A design of experiments was conducted for this purpose with current, spray distance, and powder feed rate as the varied parameters. Microstructure was assessed with SEM and image analysis was used to characterize porosity content. Evaluations were carried out using laser flash technique to measure thermal properties. A bi-layer beam curvature technique in conjunction with controlled thermal cycling was used to assess the mechanical properties, in particular their nonlinear elastic response. Coating lifetime was evaluated by thermo-cyclic fatigue testing. Relationships between microstructure and coating properties are discussed. Dense vertically cracked microstructure and highly porous microstructure with large globular pores were also fabricated. Correlations between parameters obtained from nonlinear measurements and lifetime based on a priori established microstructural analysis were attempted in an effort to develop and identify a simplified strategy to assess coating durability following sustained long-term exposure to high temperature thermal cycling.

  • 241.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Kuhn, J.
    Kesler, O.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Influence of Process Parameters on Microstructure and Permeability of Axial Suspension Plasma Sprayed Electrolytes in SOFCs2016Conference paper (Other academic)
  • 242.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Kumara, Chamara
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Nylén, Per
    University West, Department of Engineering Science, Research Enviroment Production Technology West. University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Bilayer Suspension Plasma-Sprayed Thermal Barrier Coatings with Enhanced Thermal Cyclic Lifetime: Experiments and Modeling2017In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 26, no 6, p. 1038-1051Article in journal (Refereed)
    Abstract [en]

    Suspension plasma spraying (SPS) has been shown as a promising process to produce porous columnar strain tolerant coatings for thermal barrier coatings (TBCs) in gas turbine engines. However, the highly porous structure is vulnerable to crack propagation, especially near the topcoat-bondcoat interface where high stresses are generated due to thermal cycling. A topcoat layer with high toughness near the topcoat-bondcoat interface could be beneficial to enhance thermal cyclic lifetime of SPS TBCs. In this work, a bilayer coating system consisting of first a dense layer near the topcoat-bondcoat interface followed by a porous columnar layer was fabricated by SPS using Yttria-stabilised zirconia suspension. The objective of this work was to investigate if the bilayer topcoat architecture could enhance the thermal cyclic lifetime of SPS TBCs through experiments and to understand the effect of the column gaps/vertical cracks and the dense layer on the generated stresses in the TBC during thermal cyclic loading through finite element modeling. The experimental results show that the bilayer TBC had significantly higher lifetime than the single-layer TBC. The modeling results show that the dense layer and vertical cracks are beneficial as they reduce the thermally induced stresses which thus increase the lifetime.

  • 243.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Li, X. -H
    Siemens Turbomachinery, Finspång, Sweden.
    Kjellman, B.
    GKN Aerospace, Trollhättan, Sweden.
    Influence of bondcoat surface characteristics on lifetime in suspension plasma sprayed thermal barrier coatings2017In: Proceedings of the International Thermal Spray Conference & Exposition (ITSC 2017), New York: Curran Associates, Inc , 2017, Vol. 2, p. 883-887Conference paper (Refereed)
    Abstract [en]

    Development of TBCs allowing higher combustion temperatures in gas turbines is of high commercial interest since it results in higher fuel efficiency and lower emissions. It is well known that TBCs produced by suspension plasma spraying (SPS) have lower thermal conductivity as compared to conventional systems due to their very fine porous microstructure. Moreover, columnar structured SPS TBCs are significantly cheaper to produce as compared to the conventionally used electron beam - physical vapour deposition (EB-PVD). However, SPS TBCs have not yet been commercialised due to low reliability and life expectancy of the coatings. Lifetime of a TBC system is significantly dependent on topcoat-bondcoat interface topography. The objective of this work was to study the effect of topcoat-bondcoat interface in SPS TBCs by changing bondcoat spray parameters and bondcoat surface heat treatment High velocity air fuel (HVAF) spraying was used for bondcoat deposition while axial-SPS was used for topcoat deposition. Same topcoat spray parameters were used for all samples. Lifetime was examined by thermal cyclic fatigue and thermal shock testing. The influence of surface roughness on lifetime has been discussed. The results show that HVAF could be a suitable process for bondcoat deposition to achieve long lifetime SPS TBCs. 

  • 244.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Li, X. -H
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Östergren, Lars
    GKN Aerospace, Trollhättan, Sweden.
    Influence of Bondcoat Spray Process on Lifetime of Suspension Plasma-Sprayed Thermal Barrier Coatings2018In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 27, no 1-2, p. 84-97Article in journal (Refereed)
    Abstract [en]

    Development of thermal barrier coatings (TBCs) manufactured by suspension plasma spraying (SPS) is of high commercial interest as SPS has been shown capable of producing highly porous columnar microstructures similar to the conventionally used electron beam–physical vapor deposition. However, lifetime of SPS coatings needs to be improved further to be used in commercial applications. The bondcoat microstructure as well as topcoat–bondcoat interface topography affects the TBC lifetime significantly. The objective of this work was to investigate the influence of different bondcoat deposition processes for SPS topcoats. In this work, a NiCoCrAlY bondcoat deposited by high velocity air fuel (HVAF) was compared to commercial vacuum plasma-sprayed NiCoCrAlY and PtAl diffusion bondcoats. All bondcoat variations were prepared with and without grit blasting the bondcoat surface. SPS was used to deposit the topcoats on all samples using the same spray parameters. Lifetime of these samples was examined by thermal cyclic fatigue testing. Isothermal heat treatment was performed to study bondcoat oxidation over time. The effect of bondcoat deposition process and interface topography on lifetime in each case has been discussed. The results show that HVAF could be a suitable process for bondcoat deposition in SPS TBCs.

  • 245.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Li, X.
    Kjellman, B.
    Effect of bondcoat and substrate chemistry on oxide growth and lifetime in suspension plasma sprayed thermal barrier coatings2017Conference paper (Other academic)
  • 246.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Li, X-H
    Influence of topcoat-bondcoat interface on lifetime in suspension sprayed therma barrier coatings2016Conference paper (Other academic)
  • 247.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Li, Xin-Hai
    Siemens Turbomachinery AB, Finspång, Sweden.
    Kjellman, Björn
    GKN Aerospace, Trollhättan, Sweden.
    Development of bondcoats for high lifetime suspension plasma sprayed thermal barrier coatings2019In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 371, no SI, p. 366-377Article in journal (Refereed)
    Abstract [en]

    Fabrication of thermal barrier coatings (TBCs) by suspension plasma spraying (SPS) seems to be a promising alternative for the industry as SPS TBCs have the potential to provide lower thermal conductivity and longer lifetime than state-of-the-art allowing higher engine efficiency. Further improvements in lifetime of SPS TBCs and fundamental understanding of failure mechanisms in SPS TBCs are necessary for their widespread commercialisation. In this study, the influence of varying topcoat-bondcoat interface topography and bondcoat microstructure on lifetime was investigated. The objective of this work was to gain fundamental understanding of relationships between topcoat-bondcoat interface topography, bondcoat microstructure, and failure mechanisms in SPS TBCs. Seven sets of samples were produced in this study by keeping same bondcoat chemistry but varying feedstock particle size distributions and bondcoat spray processes. The topcoat chemistry and spray parameters were kept identical in all samples. Three-dimensional surface measurements along with scanning electron microscopy images were used to characterise bondcoat surface topography. The effect of varying interface topography and bondcoat microstructure on thermally grown oxide formation, stresses and lifetime was discussed. The results showed that varying bondcoat powder size distribution and spray process can have a significant effect on lifetime of SPS TBCs. Smoother bondcoats seemed to enhance the lifetime in case of SPS TBCs in case of same bondcoat chemistry and similar bondcoat microstructures. When considering the samples investigated in this study, samples with high velocity air-fuel (HVAF) bondcoats resulted in higher lifetime than other samples indicating that HVAF could be a suitable process for bondcoat deposition in SPS TBCs. © 2018 Elsevier B.V.

  • 248.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspong, Sweden.
    Peng, Ru Lin
    Linköping University, Linköping, Sweden.
    Improving the lifetime of suspension plasma sprayed thermal barrier coatings2017In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 332, p. 550-559Article in journal (Refereed)
    Abstract [en]

    Development of thermal barrier coating systems (TBCs) for gas turbine applications allowing higher combustion temperatures is of high interest since it results in higher fuel efficiency and lower emissions. TBCs produced by suspension plasma spraying (SPS) have been shown to exhibit significantly lower thermal conductivity as compared to conventional systems due to their very fine porosity microstructure. However they have not been commercialised yet due to low reliability and life expectancy of the coatings. In addition to the initial topcoat microstructure and its sintering resistance, lifetime of a TBC system is highly dependent on bondcoat chemistry as it influences the growth rate of thermally grown oxide (TGO) layer. To enhance the lifetime of SPS TBCs, fundamental understanding of relationships between topcoat microstructure and its evolution with time, bondcoat chemistry, TGO growth rate, and lifetime is essential. The objective of this work was to study the effect of topcoat microstructure evolution and TGO growth rate on lifetime in SPS TBC systems. Experimental MCrAlY bondcoat powders with different aluminium activities were investigated and compared to a commercial bondcoat powder. High velocity air fuel spraying was used for bondcoat deposition while axial-SPS was used for yttria stabilized zirconia topcoat deposition. Lifetime was examined by thermal cyclic fatigue testing. Isothermal heat treatment was performed to study TGO evolution with time. The changes in microstructure of SPS coatings due to sintering under long term exposure at high temperatures were investigated. Different failure modes in SPS TBCs were also examined. The bondcoat with higher aluminium activity resulted in a significantly higher thermal cyclic lifetime of the corresponding TBC as it could have promoted protective alumina layer growth for a longer period of time. The results indicate that the significant changes in topcoat microstructure due to sintering as observed in this work could have a detrimental effect on TBC lifetime. © 2017 Elsevier B.V.

  • 249.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery, Finspång, Sweden.
    Östergren, Lars
    GKN Aerospace, Trollhättan, Sweden.
    Development of bondcoat layer for long lifetime suspension plasma sprayed thermal barrier coatings2017In: Proceedings of the International Thermal Spray Conference & Exposition (ITSC 2017), New York: Curran Associates, Inc , 2017, Vol. 2, p. 1158-1163Conference paper (Refereed)
    Abstract [en]

    Development of thermal barrier coatings (TBCs) manufactured by suspension plasma spraying (SPS) is of high commercial interest as SPS has been shown capable to produce columnar microstructures similar to the conventionally used electron beam – physical vapour deposition (EB-PVD) process. Moreover, SPS is a significantly cheaper process and can also produce more porous coatings than EB-PVD. However, lifetime of SPS coatings needs to be improved further for them to be applicable in commercial applications.The bondcoat microstructure as well as topcoat-bondcoat interface topography affect the TBC lifetime significantly. The objective of this work was to investigate the feasibility of different bondcoat deposition process for SPS TBCs. In this work, a NiCoCrAlY bondcoat deposited by high velocity air fuel (HVAF) was compared to commercial NiCoCrAlY and PtAl bondcoats. All bondcoat variations were prepared with and without grit blasting the bondcoat surface. SPS was used to deposit the topcoats on all samples using the same spray parameters. Lifetime of these samples was examined by thermal cyclic fatigue and thermal shock testing. The effect of bondcoat deposition process and interface topography on lifetime in each case has been discussed. The results show that HVAF could be a suitable process for bondcoat deposition in SPS TBCs.

  • 250.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Rocchio-Heller, R.
    Oerlikon Metco, Westbury, USA.
    Liu, J.
    Oerlikon Metco, Westbury, USA.
    Li, X. -H
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Östergren, L.
    GKN Aerospace, Trollhättan, Sweden.
    Failure Analysis of Multilayered Suspension Plasma-Sprayed Thermal Barrier Coatings for Gas Turbine Applications2018In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 27, no 3, p. 402-411-Article in journal (Refereed)
    Abstract [en]

    Improvement in the performance of thermal barrier coatings (TBCs) is one of the key objectives for further development of gas turbine applications. The material most commonly used as TBC topcoat is yttria-stabilized zirconia (YSZ). However, the usage of YSZ is limited by the operating temperature range which in turn restricts the engine efficiency. Materials such as pyrochlores, perovskites, rare earth garnets are suitable candidates which could replace YSZ as they exhibit lower thermal conductivity and higher phase stability at elevated temperatures. The objective of this work was to investigate different multilayered TBCs consisting of advanced topcoat materials fabricated by suspension plasma spraying (SPS). The investigated topcoat materials were YSZ, dysprosia-stabilized zirconia, gadolinium zirconate, and ceria–yttria-stabilized zirconia. All topcoats were deposited by TriplexPro-210TM plasma spray gun and radial injection of suspension. Lifetime of these samples was examined by thermal cyclic fatigue and thermal shock testing. Microstructure analysis of as-sprayed and failed specimens was performed with scanning electron microscope. The failure mechanisms in each case have been discussed in this article. The results show that SPS could be a promising route to produce multilayered TBCs for high-temperature applications.

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