Change search
Refine search result
123 1 - 50 of 115
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Bahbou, M. Fouzi
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Choquet, Isabelle
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Nylén, Per
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Numerical and Experimental Study of Ni-Particle Impact On A Ti-Surface2007In: Proceedings of the International Thermal Spray Conference: May 2007, Beijing, China, ASM International , 2007, p. 219-224Conference paper (Refereed)
  • 2.
    Bahbou, M. Fouzi
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Nylén, Per
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    On-Line Measurement of Plasma-Sprayed Ni-Particles during Impact on a Ti-Surface: influence of Surface Oxidation2007In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 16, no 4, p. 506-511Article in journal (Refereed)
    Abstract [en]

    The objective of this study was to analyze the impact of plasma-sprayed Ni5%Al particles on polished and grit-blasted Ti6Al4V samples under oxidized and nonoxidized conditions. For this purpose, measurements of thermal radiation and velocity of individual plasma-sprayed particles were carried out. From the thermal radiation at impact, splat diameter during flattening and temperature evolution during cooling were evaluated. Characteristic parameters related to the quality of contact between the splat and the substrate were retrieved. The flattening speed was introduced to characterize wetting, while the cooling rate was used to characterize solidification. The idea was to get a signature of particle impact for a given surface roughness and oxidation state by identifying parameters which strongly affect the splat behavior. Sieved Ni5%Al powder in a narrow range (+65 −75 μm) was sprayed on four sets of titanium alloy surfaces, consisting of polished and grit-blasted samples, one set had a nonoxidized surface and the other one was oxidized in an oven at 600 °C for two hours. Resulting splats after impact were characterized by scanning electron microscopy, the splats on oxidized surface showed pores in their core and detached fingers at the periphery. The cooling rate and flattening degree significantly increased on the oxidized smooth surface compared to the nonoxidized one. This trend was not found in grit-blasted surfaces, which implies that impact phenomena are different on grit-blasted surfaces than on smooth surfaces thus further work is needed.

  • 3.
    Bahbou, M. Fouzi
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Nylén, Per
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    On-Line measurement of plasma-sprayed ni-particles during impact on a ti-surface: influence of surface oxidation2007In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 16, no 6, p. 506-511Article in journal (Refereed)
    Abstract [en]

    The objective of this study was to analyze the impact of plasma-sprayed Ni5%Al particles on polished and grit-blasted Ti6Al4V samples under oxidized and nonoxidized conditions. For this purpose, measurements of thermal radiation and velocity of individual plasma-sprayed particles were carried out. From the thermal radiation at impact, splat diameter during flattening and temperature evolution during cooling were evaluated. Characteristic parameters related to the quality of contact between the splat and the substrate were retrieved. The flattening speed was introduced to characterize wetting, while the cooling rate was used to characterize solidification. The idea was to get a signature of particle impact for a given surface roughness and oxidation state by identifying parameters which strongly affect the splat behavior. Sieved Ni5%Al powder in a narrow range (+65 −75 μm) was sprayed on four sets of titanium alloy surfaces, consisting of polished and grit-blasted samples, one set had a nonoxidized surface and the other one was oxidized in an oven at 600 °C for two hours. Resulting splats after impact were characterized by scanning electron microscopy, the splats on oxidized surface showed pores in their core and detached fingers at the periphery. The cooling rate and flattening degree significantly increased on the oxidized smooth surface compared to the nonoxidized one. This trend was not found in grit-blasted surfaces, which implies that impact phenomena are different on grit-blasted surfaces than on smooth surfaces thus further work is needed.

  • 4.
    Bahbou, M. Fouzi
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Nylén, Per
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Relationship between surface topgraphy parameters and adhesion strength for plasma spraying2005In: ITSC 2005: Thermal Spray connects: Explore its surfacing potential!, The Material Information Society , 2005, p. 1027-1031Conference paper (Refereed)
    Abstract [en]

    To achieve sufficient adhesion strength within thermal spraying, the surface to be coated has to be modified. Grit blasting is the most common way to generate a clean and roughened surface. The bonding mechanism between the grit-blasted substrate and the coating is assumed to be due to mechanical anchoring, why an optimal surface roughness is essential. The surface roughness is usually evaluated using Ra which cannot fully characterize the complex nature of the chaotic substrate topography. This study was performed in order to evaluate if Ra can be replaced by other surface characteristic parameters such us R.q, Rpk, Rpv, Rk…with higher correlation to adhesion strength. Average roughness was measured by a perthometer and with white light interferometry to get 3D images of the surface topography. Disc shaped substrate samples of Ti6Al4V (AMS 4928) were grit blasted with aluminium oxide grit and plasma sprayed with a Ni5%Al coating. Adhesion strength was determined according to the ASTM C633 standard. The correlation between a number of different surface-parameters and adhesion strength were evaluated and compared with Ra.

  • 5.
    Bahbou, M. Fouzi
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Nylén, Per
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Two-step grit blasting for enhanced adhesion of thermal spray coatings2004In: Surface modification technologies XVIII: proceedings of the eighteenth international conference on surface modification technologies held in Dijon, France November 15-17, 2004, 2004, p. 23-27Conference paper (Refereed)
  • 6.
    Bahbou, M. Fouzi
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Barbezat, G.
    Sulzer Metco, Wohlen, Switzerland .
    A parameter study of the Protal® Process to optimise the adhesion of Ni5Al Coatings2004In: Thermal Spray 2004 : Advances in technology and applications: Proceedings of the International Thermal Spray Conference 10-12 May 2004, Osaka, Japan Thermal Spray 2004, 2004, p. 898-902Conference paper (Refereed)
    Abstract [en]

    The Protal process combines surface preparation using a laser and thermal spraying in one production step. The laser preparation is based on a photomechanical reaction induced by the interaction between a laser of high instantaneous power and a polluted surface. The mechanism of bonding and the coating-substrate interface are then changed in comparison with grit blasting resulting in a significantly reduced substrate roughness. This study is aimed at finding the optimal Protal process parameters for the coating adhesion of a Ni5%Al sprayed on Ti6Al4V and IN718 alloys. The parameters investigated are laser beam intensity, the time delay between the laser impact and the spray impact, powder feed rate, substrate roughness and temperature. A test plan including these parameters is analysed by means of a fractional factorial design of experiment method. The adhesions of the coatings are measured using the ASTM C633 standard test. Data are analysed by a multiple linear regression model using a least squares fit. In addition, the coating/substrate interface is examined by optical and electron scanning microscopy (SEM) techniques as well as by Auger electron spectroscopy. Substrate roughness, substrate temperature and laser intensity are all shown to have a negative correlation with adhesion strength within the investigated range. Areas of diffusion are noticed at the coating/substrate interface.

  • 7.
    Bahbou, M. Fouzi
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Nylén, Per
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Wigren, J.
    Volvo Aero, Trollhättan.
    Effect of grit blasting and spraying angle on the adhesion strength of a plasma-sprayed coating2004In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 13, no 4, p. 508-514Article in journal (Refereed)
  • 8.
    Bolelli, G.
    et al.
    University of Modena and Reggio Emilia, Dipartimento di Ingegneria “Enzo Ferrari”, Via Pietro Vivarelli 10/1, I-41125 Modena (MO), Italy.
    Berger, L. -M
    Fraunhofer-Institut für Werkstoff- und Strahltechnik (IWS), Winterbergstr. 28, D-01277 Dresden, Germany.
    Börner, T.
    University of Modena and Reggio Emilia, Dipartimento di Ingegneria “Enzo Ferrari”, Via Pietro Vivarelli 10/1, I-41125 Modena (MO), Italy.
    Koivuluoto, H.
    Tampere University of Technology, Department of Materials Science, Korkeakoulunkatu 6, FI-33720 Tampere, Finland.
    Lusvarghi, L.
    University of Modena and Reggio Emilia, Dipartimento di Ingegneria “Enzo Ferrari”, Via Pietro Vivarelli 10/1, I-41125 Modena (MO), Italy.
    Lyphout, Christophe
    University West, Department of Engineering Science, Division of Production Engineering.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Matikainen, V.
    Tampere University of Technology, Department of Materials Science, Korkeakoulunkatu 6, FI-33720 Tampere, Finland.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Sassatelli, P.
    University of Modena and Reggio Emilia, Dipartimento di Ingegneria “Enzo Ferrari”, Via Pietro Vivarelli 10/1, I-41125 Modena (MO), Italy.
    Trache, R.
    Fraunhofer-Institut für Werkstoff- und Strahltechnik (IWS), Winterbergstr. 28, D-01277 Dresden, Germany.
    Vuoristo, P.
    Tampere University of Technology, Department of Materials Science, Korkeakoulunkatu 6, FI-33720 Tampere, Finland.
    Tribology of HVOF- and HVAF-sprayed WC-10Co4Cr hardmetal coatings: A comparative assessment2015In: Surface and Coatings Technology, ISSN 0257-8972, Vol. 265, p. 125-144Article in journal (Refereed)
    Abstract [en]

    his paper provides a comprehensive assessment of the sliding and abrasive wear behaviour of WC–10Co4Cr hardmetal coatings, representative of the existing state-of-the-art. A commercial feedstock powder with two different particle size distributions was sprayed onto carbon steel substrates using two HVOF and two HVAF spray processes.Mild wear rates of < 10-7 mm3/(Nm) and friction coefficients of ≈ 0.5 were obtained for all samples in ball-on-disk sliding wear tests at room temperature against Al2O3 counterparts. WC–10Co4Cr coatings definitely outperform a reference electrolytic hard chromium coating under these test conditions. Their wear mechanisms include extrusion and removal of the binder matrix, with the formation of a wavy surface morphology, and brittle cracking. The balance of such phenomena is closely related to intra-lamellar features, and rather independent of those properties (e.g. indentation fracture toughness, elastic modulus) which mainly reflect large-scale inter-lamellar cohesion, as quantitatively confirmed by a principal component analysis. Intra-lamellar dissolution of WC into the matrix indeed increases the incidence of brittle cracking, resulting in slightly higher wear rates. At 400 °C, some of the hardmetal coatings fail because of the superposition between tensile residual stresses and thermal expansion mismatch stresses (due to the difference between the thermal expansion coefficients of the steel substrate and of the hardmetal coating). Those which do not fail, on account of lower residual stresses, exhibit higher wear rates than at room temperature, due to oxidation of the WC grains.The resistance of the coatings against abrasive wear, assessed by dry sand–rubber wheel testing, is related to inter-lamellar cohesion, as proven by a principal component analysis of the collected dataset. Therefore, coatings deposited from coarse feedstock powders suffer higher wear loss than those obtained from fine powders, as brittle inter-lamellar detachment is caused by their weaker interparticle cohesion, witnessed by their systematically lower fracture toughness as well.

  • 9.
    Bolelli, G.
    et al.
    University of Modena and Reggio Emilia, Dipartimento di Ingegneria 'Enzo Ferrari', Via P. Vivarelli 10/1, Modena, MO, Italy .
    Berger, L.-M.
    Fraunhofer-Institut für Werkstoff- und Strahltechnik (IWS), Winterbergstr. 28, Dresden, Germany.
    Börner, T.
    Fraunhofer-Institut für Werkstoff- und Strahltechnik (IWS), Winterbergstr. 28, Dresden, Germany.
    Koivuluoto, H.
    Tampere University of Technology, Department of Materials Science, Korkeakoulunkatu 6, Tampere, Finland .
    Matikainen, V.
    Tampere University of Technology, Department of Materials Science, Korkeakoulunkatu 6, Tampere, Finland .
    Lusvarghi, L.
    University of Modena and Reggio Emilia, Dipartimento di Ingegneria 'Enzo Ferrari', Via P. Vivarelli 10/1, Modena, MO, Italy .
    Lyphout, Christophe
    University West, Department of Engineering Science, Division of Production Engineering.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylén, Per
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Sassatelli, P.
    University of Modena and Reggio Emilia, Dipartimento di Ingegneria 'Enzo Ferrari', Via P. Vivarelli 10/1, Modena, MO, Italy .
    Trache, R.
    Fraunhofer-Institut für Werkstoff- und Strahltechnik (IWS), Winterbergstr. 28, Dresden, Germany .
    Vuoristo, P.c
    Tampere University of Technology, Department of Materials Science, Korkeakoulunkatu 6, Tampere, Finlan.
    Sliding and abrasive wear behaviour of HVOF- and HVAF-sprayed Cr3C2-NiCr hardmetal coatings2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 358-359, p. 32-50Article in journal (Refereed)
    Abstract [en]

    This paper provides a comprehensive characterisation of HVOF- and HVAF-sprayed Cr3C2–25 wt.% NiCr hardmetal coatings. One commercial powder composition with two different particle size distributions was processed using five HVOF and HVAF thermal spray systems.All coatings contain less Cr3C2 than the feedstock powder, possibly due to the rebound of some Cr3C2-rich particles during high-velocity impact onto the substrate.Dry sand-rubber wheel abrasive wear testing causes both grooving and pull-out of splat fragments. Mass losses depend on inter- and intra-lamellar cohesion, being higher (≥70 mg after a wear distance of 5904 m) for the coatings deposited with the coarser feedstock powder or with one type of HVAF torch.Sliding wear at room temperature against alumina involves shallower abrasive grooving, small-scale delamination and carbide pull-outs, and it is controlled by intra-lamellar cohesion. The coatings obtained from the fine feedstock powder exhibit the lowest wear rates (≈5x10−6 mm3/(Nm)). At 400 °C, abrasive grooving dominates the sliding wear behaviour; wear rates increase by one order of magnitude but friction coefficients decrease from ≈0.7 to ≈0.5. The thermal expansion coefficient of the coatings (11.08x10−6 °C−1 in the 30–400 °C range) is sufficiently close to that of the steel substrate (14.23x10−6 °C−1) to avoid macro-cracking

  • 10.
    Chen, Y.
    et al.
    University of Manchester, School of Materials, Manchester, United Kingdom.
    Zhao, X.
    Shanghai Jiao Tong University, Shanghai Key Laboratory of Advanced High-Temperature Materials and Precision Forming, Shanghai, China .
    Dang, Y.
    University of Manchester, School of Materials, Manchester, United Kingdom.
    Xiao, Ping
    University of Manchester, School of Materials, Manchester, United Kingdom.
    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, Division of Production Engineering.
    Characterization and understanding of residual stresses in a NiCoCrAlY bond coat for thermal barrier coating application2015In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 94, p. 1-14Article in journal (Refereed)
    Abstract [en]

    The residual stresses in a NiCoCrAlY bond coat deposited on a Ni-base superalloy substrate after oxidation at 1150 °C were studied by X-ray diffraction using the sin2Ψ technique. The stresses were found to be tensile; they first increased and then decreased with oxidation time. High temperature stress measurement indicated that the stress developed and built up upon cooling, predominantly within the temperature range from 1150 °C to 600 °C. Microstructural examination suggested that, due to the limited penetration depth into the bond coat, the X-ray only probed the stress in a thin surface layer consisting of the single γ-phase formed through Al depletion during oxidation. Quantitative high temperature X-ray diffraction analysis revealed that, above 600 °C, the volume fraction of the β-phase in the bond coat increased with decreasing temperature. The mechanisms of stress generation in the bond coat were examined and are discussed based on the experiments designed to isolate the contribution of possible stress generation factors. It was found that the measured bond coat stresses were mainly induced by the volume change of the bond coat associated with the precipitation of the β-phase upon cooling.

  • 11.
    Chen, Ying
    et al.
    University of Manchester,School of Materials, M13 9PL, Manchester, United Kingdom.
    Zhang, Xun
    University of Manchester,School of Materials, M13 9PL, Manchester, United Kingdom.
    Zhao, Xiaofeng
    Shanghai Jiao Tong University, Shanghai Key Laboratory of Advanced High-Temperature Materials and Precision Forming, Shanghai, 200240, China.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Nylén, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Xiao, Ping
    University of Manchester,School of Materials, M13 9PL, Manchester, United Kingdom; Shanghai Jiao Tong University, Shanghai Key Laboratory of Advanced High-Temperature Materials and Precision Forming, Shanghai, 200240, China.
    Measurements of elastic modulus and fracture toughness of an air plasma sprayed thermal barrier coating using micro-cantilever bending2019In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 374, p. 12-20Article in journal (Refereed)
    Abstract [en]

    The elastic modulus and fracture toughness of an air plasma sprayed thermal barrier coating (APS TBC) were measured using the micro-cantilever bending technique. The micro-cantilevers were machined by a focused ion beam with their central arms either parallel or normal to the bond coat/topcoat interface. Such orientations allowed direct measurements of both the in-plane and out-of-plane elastic moduli as well as mode I fracture toughness by bending. The calculated elastic modulus along the in-plane and out-of-plane direction is 144 GPa and 110 GPa, respectively, suggesting that the APS TBC is elastically anisotropic at microscale. The derived mode I fracture toughness along the plane parallel to the interface is 0.40 MPam. This relatively low toughness reflects the weak fracture resistance of the highly-flawed APS for short cracks at microscale. The measurements in this study can be incorporated into micromechanical life time prediction models of the APS TBCs. © 2019 Elsevier B.V.

  • 12.
    Choquet, Isabelle
    et al.
    University West, Department of Technology, Mathematics and Computer Science.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Wigren, J
    Deposition Rate Increase in APS Processes by Means of Multiple Injection Ports2004In: Thermal Spray 2004: Advances in Technology and Application: Proceedings of the International Thermal Spray Conference 10–12 May 2004, Osaka, Japan, 2004, p. 691-695Conference paper (Other academic)
  • 13.
    Clement, C.
    et al.
    National School of Engineers, University of Limoges, Limoges, 87280, France.
    Sadeghimeresht, Esmaeil
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Lyphout, Christophe
    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.
    Corrosion behavior of HVAF- and HVOF-sprayed high-chromium Fe-based coatings2015Conference paper (Refereed)
    Abstract [en]

    Fe-based coatings with three particular elemental compositions and two different powder particle size were prepared by high-velocity air fuel (HVAF) and high-velocity oxy fuel (HVOF) techniques. The corrosion behavior of which were comparatively studied in 3.5 wt.% NaCl solution. The results indicated that the coatings produced by HVAF process exhibited denser structure with lower porosity. Polarization and electrochemical impedance spectroscopy (EIS) tests indicated that the HVAF coatings provided better corrosion resistance than the HVOF coatings. The presence of defects was significant in HVOF coatings. The investigation illustrated that the corrosion paths initiated and grow through defects of the coating. Furthermore, adding Cr strongly improved the corrosion resistance of the coatings. The results confirmed that the cheap HVAF process could be a potential alternative to HVOF to fabricate Fe-based coatings for industrial applications.

  • 14.
    Curry, Nicholas
    et al.
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Tang, Zhaolin
    Northwest Mettech Corp., Vancouver, Canada.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Influence of Bond Coat Surface Roughness on the Structure of Axial Suspension Plasma Spray Thermal Barrier Coatings - Thermal and Lifetime Performance2015In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 268, no April, p. 15-23Article in journal (Refereed)
  • 15.
    Ericsson, Mikael
    et al.
    University West, Department of Technology, Mathematics and Computer Science. University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Berglund, D.
    Nylén, Per
    University West, Department of Technology, Mathematics and Computer Science. University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Three Dimensional Simulation of Robot path, Heat Transfer and Residual Stresses of a TIG-welded Part with Complex Geometry2002In: Trends in Welding Research: Proceedings of the 6th International Conference: Phoenix, AZ, 15-19 April, 2002, 2002, p. 973-978Conference paper (Other academic)
    Abstract [en]

    In this paper a system is presented that combines a robot off-line programming software with a finite element model that predicts temperature-time histories and residual stress distributions. The objective is to develop a tool for the engineer where robot trajectories and welding process parameters can be optimized on parts with complex geometry. The system was evaluated on a stainless steel gas turbine component. Robot weld paths were defined off-line and automatically downloaded to the finite element program, where transient temperatures and residual stresses were predicted. Temperature dependent properties and phase change, were included in the analysis. Assumptions and principles behind the modeling techniques are presented together with predicted temperature histories, residual stresses, and fixture forces.

  • 16.
    Ericsson, Mikael
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Bolmsjö, Gunnar
    University West, Department of Engineering Science, Division of Automation Systems.
    Nylén, Per
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Three-dimensional simulation of robot path and heat transfer of a TIG-welded part with complex geometry2002In: 11th International Conferences on Computer Technology in Welding: Colombus, Ohio December 6-7, 2001, 2002, p. 309-316Conference paper (Other academic)
    Abstract [en]

    The application of commercial software (OLP) packages for robot simulation, and programming, use interactive computer graphics, provide powerful tools for creating welding paths off-line. By the use of such software, problems of robot reach, accessibility, collision and timing can be eliminated during the planning stage. This paper describes how such software can be integrated with a numerical model that predicts temperature-time histories in the solid material. The objective of this integration is to develop a tool for the engineer where robot trajectories and process parameters can be optimized on parts with complex geometry. Such a tool would decrease the number of weld trials, increase productivity and reduce costs. Assumptions and principles behind the modeling techniques are presented together with experimental evaluation of the correlation between modeled and measured temperatures.

  • 17.
    Ericsson, Mikael
    et al.
    University West, Department of Technology, Mathematics and Computer Science.
    Nylén, Per
    University West, Department of Technology, Mathematics and Computer Science.
    A look at the optimization of robot welding speed based on process modelling2007In: Welding Journal, ISSN 0043-2296, Vol. 86, no 8, p. 238-244Article in journal (Refereed)
    Abstract [en]

    Simulation tools to search for optimal process parameters are of great interest to reduce the number of experiments and thereby reduce cost and production time. In this paper, robot simulation has been used in combination with finite element simulations to optimize robot speed in order to minimize distortion while keeping complete joint penetration. In an earlier work performed by the authors, a finite element model was developed to predict heat transfer and residual stresses of parts with complex shapes. An interface between a robot simulation model and a finite element analysis model was also constructed. In this paper, an iterative method for robot speed optimization has been developed using MATLAB. The algorithm is designed to maintain complete joint penetration while maximizing productivity by utilizing the fastest weld speed. The method makes it possible to optimize the heat input to the component and thereby minimize component deformation for parts with complex shapes. The system was evaluated on stainless steel plates with varying thicknesses. Robot weld paths were defined off line and automatically downloaded to the finite element software where the optimization was performed. Simulations and experimental validations are presented.

  • 18.
    Ericsson, Mikael
    et al.
    University West, Department of Technology, Mathematics and Computer Science.
    Nylén, Per
    University West, Department of Technology, Mathematics and Computer Science.
    Berglund, D.
    Ling-Peng, R.
    Three dimensional simulation of robot path, heat transfer and residual stresses of a welded part with complex geometry2005In: International jourrnal for the joining of materials, ISSN 0905-6866, Vol. 17, no 2, p. 42-51Article in journal (Refereed)
    Abstract [en]

    In this article a simulation system is presented that combines computer aided robotics software used to define the welding operation, with a finite element model that predicts temperature-time histories and residual stress distributions for welding applications. The objective is to develop a tool for engineering processes in which robot trajectories and welding process parameters can be optimized off-line on parts with complex geometries. The system was evaluated on a stainless steel gas turbine component. Temperature dependent properties and phase change were included in the analysis. The turbine component was welded using an in-house TIG welding cell. The assumptions and principles that underpin the modeling techniques are presented together with predicted temperature histories, residual stresses, and fixture forces. Predicted residual stresses were compared with neutron diffraction measurements.

  • 19.
    Ericsson, Mikael
    et al.
    University West, Department of Technology, Mathematics and Computer Science.
    Nylén, Per
    University West, Department of Technology, Mathematics and Computer Science.
    Danielsson, Fredrik
    University West, Department of Technology, Mathematics and Computer Science.
    Carlsson, Henrik
    University West, Department of Technology, Mathematics and Computer Science.
    Off-line programming of robots for metal deposition2005In: Trends in welding research: Proceedings of the 7th international conference, May 16-20. Pine Mountain, Georgia, 2005, p. 629-634Conference paper (Other academic)
    Abstract [en]

    Metal Deposition (MD) is a rapid prototyping technique to build parts by depositing metal in a required fashion. When a complex-shaped part is to be built, a simulation tool is needed to define robot trajectories. Three different simulation-based methods for robot trajectory generation are introduced and compared in this study. The methods are; reversed milling, adapted rapid prototyping and application programming in a computer aided robotics software. All methods were shown capable of creating robot paths for complex shapes, with the CAR software approach being the most flexible. Using this method, the geometry to be built is automatically sliced into layers and a robot path is automatically generated. The method was tentatively evaluated and appears to provide a powerful technique in the design and optimisation of robot paths for MD. Experiments showed that it is possible to manufacture fully dense parts using an Nd-Yag laser.

     

  • 20.
    Eriksson, Robert
    et al.
    Siemens AG, Large Gas Turbines, Huttenstr. 12, 10553, Berlin, Germany.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Broitman, Esteban
    Linköping University. IFM, 58183, Linköping, Sweden.
    Jonnalagadda, Krishna Praveen
    Linköping University, IEI, 58183, Linköping, Sweden.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Lin Peng, Ru
    Linköping University, IEI, 58183, Linköping, Sweden.
    Stresses and Cracking During Chromia-Spinel-NiO Cluster Formation in TBC Systems2015In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 24, no 6, p. 1002-1014Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBC) are used in gas turbines to reduce the temperatures in the underlying substrate. There are several mechanisms that may cause the TBC to fail; one of them is cracking in the coating interface due to extensive oxidation. In the present study, the role of so called chromia-spinel-NiO (CSN) clusters in TBC failure was studied. Such clusters have previously been found to be prone to cracking. Finite element modeling was performed on a CSN cluster to find out at which stage of its formation it cracks and what the driving mechanisms of cracking are. The geometry of a cluster was obtained from micrographs and modeled as close as possible. Nanoindentation was performed on the cluster to get the correct Young’s moduli. The volumetric expansion associated with the formation of NiO was also included. It was found that the cracking of the CSN clusters is likely to occur during its last stage of formation as the last Ni-rich core oxidizes. Furthermore, it was shown that the volumetric expansion associated with the oxidation only plays a minor role and that the main reason for cracking is the high coefficient of thermal expansion of NiO. © 2015 ASM International

  • 21. Eriksson, Robert
    et al.
    Gupta, Mohit Kumar
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Broitman, Esteban
    Linköping University.
    Jonnalagadda, Krishna Praveen
    Linköping University.
    Nylén, Per
    University West, Department of Engineering Science, Research Environment Production Technology West.
    Peng, Ru Lin
    Linköping University.
    Stress and Cracking during Chromia-Spinel-NiO Cluster Formation in Thermal Barrier Coating Systems2015In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 24, no 6, p. 1002-1014Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBC) are used in gas turbines to reduce the temperatures in the underlying substrate. There are several mechanisms that may cause the TBC to fail; one of them is cracking in the coating interface due to extensive oxidation. In the present study, the role of so called chromia-spinel-NiO (CSN) clusters in TBC failure was studied. Such clusters have previously been found to be prone to cracking. Finite element modeling was performed on a CSN cluster to find out at which stage of its formation it cracks and what the driving mechanisms of cracking are. The geometry of a cluster was obtained from micrographs and modeled as close as possible. Nanoindentation was performed on the cluster to get the correct Young's moduli. The volumetric expansion associated with the formation of NiO was also included. It was found that the cracking of the CSN clusters is likely to occur during its last stage of formation as the last Ni-rich core oxidizes. Furthermore, it was shown that the volumetric expansion associated with the oxidation only plays a minor role and that the main reason for cracking is the high coefficient of thermal expansion of NiO.

  • 22.
    Fasth, Angelica
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylen, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Choi, B.
    Center for Theraml Spray Research, Stony Brook, New York.
    Klement, Uta
    Chalmers University.
    A Comparative studey of Mechanical Properties Between HVOF-spryed Maxphase Materials and Plasma Sprayed MCrAIY Coatings2009In: Surface Modification Technologies XXII: Proceedings of the Twenty Second International Conference on Surface Modification Technologies Held at University West, Trollhättan, Sweden September 22-24 2008 / [ed] T.S. Sudarshan & Per Nylen, VALAR Docs , 2009, p. 149-156Conference paper (Other academic)
  • 23.
    Fasth, Angelica
    et al.
    University West, Department of Engineering Science.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Markocsan, Nicolaie
    University West, Department of Engineering Science.
    Musalek, Radek
    Characterization of thermo-mechanical properties for thermal sprayed NiCoCrAlY coatings2010In: Proceedings of the Thermal Spray: Global Solutions for Future Application (ITSC 2010) Conference: Singapore, May 3-5, 2010, 2010, p. 431-435Conference paper (Refereed)
  • 24.
    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

  • 25.
    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.

  • 26.
    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.

  • 27.
    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.

  • 28.
    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.

  • 29.
    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.

  • 30.
    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.

  • 31.
    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.

  • 32.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Eriksson, Robert
    Linköping University, Linköping, Sweden.
    Sand, Ulf
    EDR Medeso, Västerås, Sweden.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    A Diffusion-based Oxide Layer Growth Model using Real Interface Roughness in Thermal Barrier Coatings for Lifetime Assessment2015In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 271, no June, p. 181-191Article in journal (Refereed)
    Abstract [en]

    The development of thermo-mechanical stresses during thermal cycling can lead to the formation of detrimental cracks in Atmospheric Plasma Sprayed (APS) Thermal Barrier Coatings systems (TBCs). These stresses are significantly increased by the formation of a Thermally Grown Oxide (TGO) layer that forms through the oxidation of mainly aluminium in the bondcoat layer of the TBC. As shown in previous work done by the authors, the topcoat-bondcoat interface roughness plays a major role in the development of the stress profile in the topcoat and significantly affects the lifetime of TBCs. This roughness profile varies as the TGO layer grows and changes the stress profile in the topcoat leading to crack propagation and thus failure.

    In this work, a two-dimensional TGO growth model is presented, based on oxygen and aluminium diffusion-reaction equations, using real interface profiles extracted from cross-section micrographs. The model was first validated by comparing the TGO profiles artificially created by the model to thermally cycled specimens with varying interface roughness. Thereafter, stress profiles in the TBC system, before and after the TGO layer growth, were estimated using a finite element modelling model described in previous work done by the authors. Three experimental specimens consisting of the same chemistry but with different topcoat-bondcoat interface roughness were studied by the models and the stress state was compared to the lifetimes measured experimentally. The combination of the two models described in this work was shown to be an effective approach to assess the stress behaviour and lifetime of TBCs in a comparative way.

  • 33.
    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.

  • 34.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    A modelling approach to design of microstructures in thermal barrier coatings2013In: Journal of Ceramic Science and Technology, ISSN 2190-9385, Vol. 4, no 2, p. 85-92Article in journal (Refereed)
    Abstract [en]

    Thermo-mechanical properties of TBCs are strongly influenced by coating defects, such as delaminations and pores, thus making it essential to have a fundamental understanding of microstructure-property relationships in TBCs to produce a desired coating. Object-Oriented Finite element analysis (OOF) has been shown previously as an effective tool for evaluating thermal and mechanical material behaviour, as this method is capable of incorporating the inherent material microstructure as an input to the model. In this work, OOF was used to predict the thermal conductivity and effective Young's modulus of TBC topcoats. A Design of Experiments (DoE) was conducted by varying selected spray parameters for spraying Yttria Stabilized Zirconia (YSZ) topcoat. Microstructure was assessed with SEM and image analysis was used to characterize porosity content. The relationships between microstructural features and properties predicted by modelling are discussed. The microstructural features having the most beneficial effect on properties were sprayed with another spray gun so as to verify the results obtained from modelling. Characterisation of the coatings included microstructure evaluation, thermal conductivity and lifetime measurements. The modelling approach in combination with experiments undertaken in this study was shown to be an effective way in achieving coatings with optimised thermo-mechanical properties.

  • 35.
    Gupta, Mohit Kumar
    et al.
    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.
    Design of Low Thermal Conductivity Thermal Barrier Coatings by Finite Element Modelling2011In: Surface Modification Technologies XXIV: SMT24, Dresden, September 7-9, 2010 / [ed] T. S. Sudarshan, Eckhard Beyer, and Lutz-Michael Berger, 2011, p. 353-365Conference paper (Refereed)
    Abstract [en]

    Fundamental understanding of relationships between coating microstructure and thermal conductivity is important to be able to understand the influence of coating defects, such as delaminations and pores, on heat insulation in thermal barrier coatings (TBC). Object Oriented Finite element analysis (OOF) has recently been shown as an effective tool for evaluating thermo-mechanical material behaviour as this method is capable of incorporating the inherent material microstructure as an input to the model. The objective of this work was to evaluate a procedure where this technique is combined with Tbctool, a plasma-sprayed TBC like morphology generator, thus enabling development of low thermal conductivity coatings by simulation. Input parameters for Tbctool were computed from SEM images of sprayed microstructures using the image analysis software, Aphelion. Microstructures for as-sprayed as well as heat treated samples were evaluated. The thermal conductivities of the artificially generated microstructures were determined using OOF. Verification of the modelling procedure was performed by comparing predicted values by OOF with corresponding measured values using the laser flash technique. The results, although tentative in nature, indicate that the proposed simulation approach can be a powerful tool in the development of new low conductivity coatings.

  • 36.
    Gupta, Mohit Kumar
    et al.
    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.
    Structure-property Relationships in Thermal Barrier Coatings by Finite Element Modelling2012In: Surface Modification Technologies XXV : proceedings of the Twenty Fifth International Conference on Surface Modification Technologies: SMT25, Trollhättan, June 20-22, 2011 / [ed] T. S. Sudarshan, and P. Nylén, [Chennai]: Valardocs , 2012, p. 175-184Conference paper (Refereed)
    Abstract [en]

    The thermal and mechanical properties of Thermal Barrier Coating systems (TBCs) are strongly influenced by coating defects, such as delaminations and pores, thus making it essential to have a fundamental understanding of microstructure-property relationships in TBCs, to produce a desired coating. Object-Oriented Finite element analysis (OOF) has been shown previously as an effective tool for evaluating thermal and mechanical material behaviour, as this method is capable of incorporating the inherent material microstructure as an input to the model. In this work, OOF was used to predict the thermal conductivity and effective Young’s modulus of TBC topcoats. A Design of Experiments (DoE) was conducted by varying selected spray parameters for spraying Yttria Partially Stabilized Zirconia (YPSZ) topcoat. Characterisation of the coatings included microstructure, porosity and crack content and thermal conductivity measurements. The relationships between microstructural features, thermal conductivity and Young’s modulus are discussed.

  • 37.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Skogsberg, Kristoffer
    University West, Department of Engineering Science.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Influence of topcoat-bondcoat interface roughness on stresses and lifetime in Thermal Barrier Coatings2013In: Proceedings of the International Thermal Spray Conference / [ed] Editor: Rogerio S. Lima, Arvind Agarwal, Margaret M. Hyland, Yuk-Chiu Lau, Georg Mauer, André McDonald, and Filofteia-Laura, ASM International, 2013, p. 596-601Conference paper (Refereed)
    Abstract [en]

    Failure in Atmospheric Plasma Sprayed (APS) Thermal Barrier Coatings (TBCs) is associated with the thermomechanical stresses developing due to the Thermally Grown Oxide (TGO) layer growth 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. Modeling has been shown as an effective tool to understand the effect of interface roughness on induced stresses. In previous work done by the research group, it was observed that APS bondcoats performed better than the bondcoats sprayed with High Velocity OxyFuel (HVOF) process which is contrary to the present literature data. The objective of this work was to understand this observed difference in life-time with the help of finite element modeling by using real surface topographies. Different TGO layer thicknesses were evaluated. The modeling results were also compared with existing theories established on simplified sinusoidal profiles published in earlier works. It was shown that modeling can be used as an effective tool to understand the stress behavior in TBCs with different roughness profiles.

  • 38.
    Gupta, Mohit Kumar
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Skogsberg, Kristoffer
    University West, Department of Engineering Science.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Influence of Topcoat-Bondcoat Interface Roughness on Stresses and Lifetime inThermal Barrier Coatings2014In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 23, no 1-2, p. 170-181Article in journal (Refereed)
    Abstract [en]

    Failure in Atmospheric Plasma Sprayed (APS) Thermal Barrier Coatings (TBCs) is associated with the thermo-mechanical stresses developing due to the Thermally Grown Oxide (TGO) layer growth 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. Modeling has been shown as an effective tool to understand the effect of interface roughness on induced stresses. In previous work done by our research group, it was observed that APS bondcoats performed better than the bondcoats sprayed with High Velocity Oxy-Fuel (HVOF) process which is contrary to the present literature data. The objective of this work was to understand this observed difference in lifetime with the help of finite element modeling by using real surface topographies. Different TGO layer thicknesses were evaluated. The modeling results were also compared with existing theories established on simplified sinusoidal profiles published in earlier works. It was shown that modeling can be used as an effective tool to understand the stress behavior in TBCs with different roughness profiles.

  • 39.
    Jiang, Janna
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Fasth, Angelica
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylen, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Choi, W.B.
    Center for Thermal Spray Research, Stony Brook, NY, USA.
    Microindentation and Inverse Analysis to Characterize Elastic-Plastic Properties for Thermal Sprayed Ti2AlC and NiCoCrAlY2009In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 18, no 2, p. 194-200Article in journal (Refereed)
    Abstract [en]

    Elastic-plastic material properties for HVOF sprayed Ti2AlC (sprayed with Maxthal 211 powder) and plasma sprayed NiCoCrAlY coatings were investigated using modeling and experimental Berkovich microindentation. Optical microstructure evaluations were also performed. The theories of Hertz, Oliver and Pharr were combined with finite element analysis for extracting the material properties. Empirically based material models for both thermal sprayed Ti2AlC and NiCoCrAlY coatings are proposed.

  • 40.
    Jiang, Janna
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Fasth, Angelica
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Choi, W. B.
    Center for Thermal Spray Research, Stony Brook, NY, United States.
    Microindentation and inverse analysis to characterize elastic-plastic properties for thermal sprayed Ti2AlC and NiCoCrAlY2009In: Surface Modification Technologies XXII: Proceedings of the 22nd International Conference on Surface Modification Technologies SMT22 / [ed] T.S. Sudarshan & Per Nylen, VALAR Docs , 2009, Vol. 18, no 2, p. 177-186Conference paper (Refereed)
  • 41.
    Jiang, Janna
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Numerical modelling of the compression behaviour of single-crystalline MAX-phase materials2010In: Advanced materials research, ISSN 1022-6680, Vol. 89-91, p. 262-267Article in journal (Refereed)
    Abstract [en]

    In this article a numerical model to describe the mechanical behaviour of nanophased singlecrystalline Ti3SiC2 is proposed. The approach is a two dimensional finite element periodic unit cell consisting of an elastic matrix interlayered with shear deformable slip planes which obey the Hill's yield criterion. The periodic unit cell is used to predict compression material behaviour of Ti3SiC2 crystals with arbitrary slip plane orientations. Stress strain relationships are derived for Ti 3SiC2, and the effect of slip plane volume fraction as well as orientation of the slip planes are investigated. The two main deformation mechanisms of the material namely; ordinary slip and so called kinking are considered in the study.

  • 42.
    Jiang, Janna
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Nylén, Per
    University West, Department of Engineering Science, Division of Production Engineering.
    Object-oriented finite element analysis to simulate microindentation of thermal sprayed MAX-phase coatings2009In: Proceedings - 2009 International Conference on Computer Modeling and Simulation, ICCMS 2009, 2009, p. 337-341Conference paper (Other (popular science, discussion, etc.))
  • 43.
    Jonnalagadda, K.P.
    et al.
    Linköping University.
    Mahade, Satyapal
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Curry, Nicholas
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Li, X-H.
    Siemens Industrial Turbomachinary, Finspång, Sweden.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Nylen, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Peng, R.L.
    Trebacher Indiustrie, Austria.
    Hot corrosion behavior of multi-layer suspension plasma sprayed Gd2Zr2O7 /YSZ thermal barrier coatings2016In: Thermal Spray 2016: Proceedings from the International Thermal Spray Conference in Shanghai, P.R China, May 10-12, 2016, DVS Media GmbH , 2016, Vol. 324, p. 261-266Conference paper (Refereed)
  • 44.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Mahade, Satyapal
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Curry, Nicholas
    Treibacher Ind AG, Althofen, Austria.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Nylen, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Hot Corrosion Mechanism in Multi-Layer Suspension Plasma Sprayed Gd2Zr2O7 /YSZ Thermal Barrier Coatings in the Presence of V2O5 + Na2SO42017In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 26, no 1-2, p. 140-149Article in journal (Refereed)
    Abstract [en]

    This study investigates the corrosion resistance of two-layer Gd2Zr2O7/YSZ, three-layer dense Gd2Zr2O7/ Gd2Zr2O7/YSZ, and a reference single-layer YSZ coating with a similar overall top coat thickness of 300-320 µm. All the coatings were manufactured by suspension plasma spraying resulting in a columnar structure except for the dense layer. Corrosion tests were conducted at 900 °C for 8 h using V2O5 and Na2SO4 as corrosive salts at a concentration of approximately 4 mg/cm2. SEM investigations after the corrosion tests show that Gd2Zr2O7-based coatings exhibited lower reactivity with the corrosive salts and the formation of gadolinium vanadate (GdVO4), accompanied by the phase transformation of zirconia was observed. It is believed that the GdVO4 formation between the columns reduced the strain tolerance of the coating and also due to the fact that Gd2Zr2O7 has a lower fracture toughness value made it more susceptible to corrosion-induced damage. Furthermore, the presence of a relatively dense layer of Gd2Zr2O7 on the top did not improve in reducing the corrosion-induced damage. For the reference YSZ coating, the observed corrosion-induced damage was lower probably due to combination of more limited salt penetration, the SPS microstructure and superior fracture toughness of YSZ.

  • 45.
    Jonnalagadda, Krishna Praveen
    et al.
    Linkoping University, Department of Manangement and Engineering,Linkoping, Sweden.
    Peng, Ru Lin
    Linkoping University, Department of Manangement and Engineering,Linkoping, Sweden.
    Mahade, Satyapal
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Nylén, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Curry, Nicholas
    Treibacher Industrie AG, Austria.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspang, Sweden.
    Hot corrosion behavior of multi-layer suspension plasma sprayed Gd2Zr2O7/YSZ thermal barrier coatings2017In: InterCeram: International Ceramic Review, ISSN 0020-5214, Vol. 66, no 5, p. 180-184Article in journal (Refereed)
    Abstract [en]

    This study investigates the corrosion resistance of double layer Gd2Zr2O7/YSZ, triple layer dense Gd2Zr2O7 / Gd2Zr2O7/YSZ and a reference single layer YSZ coating with a similar overall top coat thickness of 300-320 Όm. All the coatings were manufactured by suspension plasma spraying (SPS), resulting in a columnar structure. Corrosion tests were conducted at 900°C for 8 hours using vanadium pentoxide and sodium sulphate as corrosive salts at a concentration of 4 mg/cm2. SEM investigations after the corrosion tests show that Gd2Zr2O7 coatings exhibited lower corrosion resistance than the reference material, YSZ. Reaction between the corrosive salts and Gd2Zr2O7 results in the formation of gadolinium vanadate ( GdVO4) along the top surface and between the columns. While the stresses due to phase transformation of zirconia can be relieved to some extent by realigning of the columns in the top coat, it is believed that GdVO4 formation between the columns, along with low fracture toughness of Gd2Zr2O7 had resulted in lower corrosion resistance. Furthermore, the presence of a relatively dense layer of Gd2Zr2O7 on the top, as a preventive layer for salt infiltration, did not improve the corrosion resistance.

  • 46.
    Joshi, Shrikant V.
    et al.
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Nylén, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Advanced Coatings by Thermal Spray Processes2019In: Technologies, Vol. 7, no 4, article id 79Article in journal (Refereed)
    Abstract [en]

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

  • 47.
    Karimi Neghlani, Paria
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Sadeghimeresht, Esmaeil
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Deng, D.
    Linköping University, Division of Engineering Materials, Department of Management and Engineering, Linköping, 581 83, Sweden.
    Gruber, H.
    University of Chalmers, Division of Materials and Manufacture, Industrial and Materials Science, Gothenburg, 412 96, Sweden.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Nylen, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Influence of build layout and orientation on microstructural characteristics of electron beam melted Alloy 7182018In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 99, no S1, p. 2903-2913Article in journal (Refereed)
    Abstract [en]

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

  • 48.
    Kumara, Chamara
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Deng, Dunyong
    Linköping University, Division of Engineering Materials, Department of Management and Engineering, Linköping, 58183, Sweden.
    Hanning, Fabian
    Chalmers University of Technology, Department of Industrial and Materials Science, Göteborg, 412 96, Sweden.
    Raanes, Morten
    NTNU, Department of Materials Science and Engineering, IMA, Alfred Getz vei 2, Trondheim, 7491, Norway.
    Moverare, Johan
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Linköping University, Division of Engineering Materials, Department of Management and Engineering, Linköping, 58183, Sweden.
    Nylén, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Predicting the Microstructural Evolution of Electron Beam Melting of Alloy 718 with Phase-Field Modeling2019In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50A, no 5, p. 527-2537Article in journal (Refereed)
    Abstract [en]

    Electron beam melting (EBM) is a powder bed additive manufacturing process where a powder material is melted selectively in a layer-by-layer approach using an electron beam. EBM has some unique features during the manufacture of components with high-performance superalloys that are commonly used in gas turbines such as Alloy 718. EBM has a high deposition rate due to its high beam energy and speed, comparatively low residual stresses, and limited problems with oxidation. However, due to the layer-by-layer melting approach and high powder bed temperature, the as-built EBM Alloy 718 exhibits a microstructural gradient starting from the top of the sample. In this study, we conducted modeling to obtain a deeper understanding of microstructural development during EBM and the homogenization that occurs during manufacturing with Alloy 718. A multicomponent phase-field modeling approach was combined with transformation kinetic modeling to predict the microstructural gradient and the results were compared with experimental observations. In particular, we investigated the segregation of elements during solidification and the subsequent "in situ" homogenization heat treatment at the elevated powder bed temperature. The predicted elemental composition was then used for thermodynamic modeling to predict the changes in the continuous cooling transformation and time-temperature transformation diagrams for Alloy 718, which helped to explain the observed phase evolution within the microstructure. The results indicate that the proposed approach can be employed as a valuable tool for understanding processes and for process development, including post-heat treatments. © 2019, The Author(s).

  • 49.
    Kumara, Chamara
    et al.
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Deng, Dunyong
    Linköping University, Division of Engineering Materials, Department of Management and Engineering, Linköping, Sweden.
    Moverare, Johan
    Linköping University, Division of Engineering Materials, Department of Management and Engineering, Linköping, Sweden.
    Nylén, Per
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Modelling of anisotropic elastic properties in alloy 718 built by electron beam melting2018In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 34, no 5, p. 529-537Article in journal (Refereed)
    Abstract [en]

    Owing to the inherent nature of the process, typically material produced via electron beam melting (EBM) has a columnar microstructure. As a result of that, the material will have anisotropic mechanical properties. In this work, anisotropic elastic properties of EBM built Alloy 718 samples at room temperature were investigated by using experiments and modelling work. Electron backscatter diffraction data from the sample microstructure was used to predict the Young’s modulus. The results showed that the model developed in the finite element software OOF2 was able to capture the anisotropy in the Young’s modulus. The samples showed transversely isotropic elastic properties having lowest Young’s modulus along build direction. In addition to that, complete transversely isotropic stiffness tensor of the sample was also calculated. © 2018 Institute of Materials, Minerals and Mining.

  • 50.
    Kumara, Chamara
    et al.
    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.
    Effect of columnar cracks and dense layer in suspension plasma sprayed thermal barrier coatings on the coating stresses under thermal shock loadings: A modelling approach2016In: 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 Spraying (SPS) has been shown as a promising process to produce porous columnar strain tolerant coatings for thermal barrier coating applications in gas turbine engines. However, the highly porous structure is vulnerable to crack propagation, especially near the top coat-bond coat interface, where high stresses are generated due to thermal shock conditions that occur during engine operation. These stresses directly influence the coating lifetime. A topcoat layer with high toughness near the top coat-bond coat interface could thus be beneficial to withstand the stresses. In this work, a bilayer coating system was fabricated by SPS using yttria stabilised zirconia. The bilayer coating consisted of a dense topcoat layer near the top coat-bond coat interface which could provide the necessary toughness followed by a porous columnar structured layer which contains columnar cracks which could provide the necessary strain tolerance. The objective of this work is to study the effect of the columnar/vertical crack features on the generated stresses in the thermal barrier coating during thermal cyclic loading. A finite element modelling approach has been used for this purpose. The results show that the bilayer coating structure reduces the thermally induced stresses and could thus increase the lifetime.

123 1 - 50 of 115
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf