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  • 101.
    Charles, Corinne
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Järvstråt, Niklas
    University West, Department of Engineering Science, Division of Production Engineering.
    Modelling Ti-6Al-4V microstructure by evolution laws implemented as finite element subroutines:: Application to TIG metal deposition2008In: 8 th International Conference on Trends in welding research,: Pine Mountain, Georgia, June 2-6, 2008Conference paper (Other academic)
  • 102.
    Charles Murgau, Corinne
    University West, Department of Engineering Science, Division of Welding Technology.
    Microstructure model for Ti-6Al-4V used in simulation of additive manufacturing2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is devoted to microstructure modelling of Ti-6Al-4V. The microstructure and the mechanical properties of titanium alloys are highly dependent on the temperature history experienced by the material. The developed microstructure model accounts for thermaldriving forces and is applicable for general temperature histories. It has been applied to study wire feed additive manufacturing processes that induce repetitive heating and cooling cycles.The microstructure model adopts internal state variables to represent the microstructure through microstructure constituents' fractions in finite element simulation. This makes it possible to apply the model efficiently for large computational models of general thermomechanical processes. The model is calibrated and validated versus literature data. It is applied to Gas Tungsten Arc Welding -also known as Tungsten Inert Gas welding-wire feed additive manufacturing process.Four quantities are calculated in the model: the volume fraction of phase, consisting of Widmanstätten, grain boundary, and martensite. The phase transformations during cooling are modelled based on diffusional theory described by a Johnson-Mehl-Avrami-Kolmogorov formulation, except for diffusionless martensite formation where the Koistinen-Marburger equation is used. A parabolic growth rate equation is used for the to transformation upon heating. An added variable, structure size indicator of Widmanstätten, has also been implemented and calibrated. It is written in a simple Arrhenius format.The microstructure model is applied to in finite element simulation of wire feed additive manufacturing. Finally, coupling with a physically based constitutive model enables a comprehensive and predictive model of the properties that evolve during processing.

  • 103.
    Charles Murgau, Corinne
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Lundbäck, Andreas
    Division of Mechanics of Solid Materials, Luleå University of Technology, 971 81 Luleå, Sweden .
    Åkerfeldt, Pia
    Division of Materials Science, Luleå University of Technology, 971 81 Luleå, Sweden .
    Pederson, Robert
    GKN Aerospace Engine Systems, 461 81 Trollhättan, Sweden .
    Temperature and microstructure evolution in Gas Tungsten Arc Welding wire feed additive manufacturing of Ti-6Al-4V2019In: Materials, E-ISSN 1996-1944, Vol. 12, no 21, article id E3534Article in journal (Refereed)
    Abstract [en]

    The Finite Element Method (FEM) is used to solve temperature field and microstructure evolution during GTAW wire feed additive manufacturing process.The microstructure of titanium alloy Ti-6Al-4V is computed based on the temperature evolution in a point-wise logic. The methodology concerning the microstructural modeling is presented. A model to predict the thickness of the Į lath morphology is also implemented. The results from simulations are presented togethe rwith qualitative and quantitative microstructure analysis.

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  • 104.
    Chazelas, Christophe
    et al.
    European Ceramic Center, SPCTS CNRS UMR 7315, University of Limoges, Limoges, France.
    Trelles, Juan Pablo
    Mechanical Engineering, University of Massachusetts Lowell, Lowell, USA.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Vardelle, Armelle
    European Ceramic Center, SPCTS CNRS UMR 7315, University of Limoges, Limoges, France.
    Main issues for a fully predictive plasma spray torch model and numerical considerations2017In: Plasma chemistry and plasma processing, ISSN 0272-4324, E-ISSN 1572-8986, Vol. 37, no 3, p. 627-651Article in journal (Refereed)
    Abstract [en]

    Plasma spray is one of the most versatile and established techniques for the deposition of thick coatings that provide functional surfaces to protect or improve the performance of the substrate material. However, a greater understanding of plasma spray torch operation will result in improved control of process and coating properties and in the development of novel plasma spray processes and applications. The operation of plasma torches is controlled by coupled dynamic, thermal, chemical, electromagnetic, and acoustic phenomena that take place at different time and space scales. Computational modeling makes it possible to gain important insight into torch characteristics that are not practically accessible to experimental observations, such as the dynamics of the arc inside the plasma torch. This article describes the current main issues in carrying out plasma spray torch numerical simulations at a high level of fidelity. These issues encompass the use of non-chemical and non-thermodynamic equilibrium models, incorporation of electrodes with sheath models in the computational domain, and resolution of rapid transient events, including the so-called arc reattachment process. Practical considerations regarding model implementation are also discussed, particularly the need for the model to naturally reproduce the observed torch operation modes in terms of voltage and pressure fluctuations.

  • 105.
    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.

  • 106.
    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.

  • 107.
    Choquet, Isabelle
    University West, Department of Engineering Science, Division of Welding Technology.
    Gas tungsten arc models including the physics of the cathode layer: remaining issues2018In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 62, no 1, p. 177-196Article in journal (Refereed)
    Abstract [en]

    A recent review pointed out that the existing models for gas tungsten arc coupling the electrode (a cathode) and the plasma are not yet complete enough. Their strength is to predict with good accuracy either the electric potential or the temperature field in the region delimited by the electrode and the workpiece. Their weakness is their poor ability to predict with good accuracy these two fields at once. However, both of these fields are important since they govern the heat flux to the workpiece through current density and temperature gradient. New developments have been made since then. They mainly concern the approaches addressing the electrode sheath (or space charge layer) that suffered from an underestimation of the arc temperature. These new developments are summarized and discussed, the modelling assumptions are examined, and important modelling issues that remain unexplored are underlined.

  • 108.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Johansson, J.
    Wigren, J.
    New powder port holder geometry to avoid lump formation in APS2005In: 17th international symposium on plasma chemistry (ISPC 17) :: Toronto, Canada, August 7th – 12th, 2005, 2005, p. OP7. 1-6Conference paper (Other academic)
    Abstract [en]

    A new geometry of the powder port ring holder used in atmospheric plasma spraying has recently been designed to avoid lump formation, and successfully tested for a set of process parameters associated with Ni-5Al powder used in production to form bond coat [1]. But with ZrO 2 powder used to made top coat, improvements were not enough satisfactory. Here, we investigate numerically the cause of the remaining defects, and further improve the ring geometry to prevent lump from forming in any part of the coating.

  • 109.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Johansson, Jimmy
    Volvo Aero Corporation, Trollhättan.
    Wigren, Jan
    Volvo Aero Corporation, Trollhättan.
    Clogging and lump formation during atmospheric plasma spraying with powder injection downstream the plasma gun2007In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 16, no 4, p. 512-523Article in journal (Refereed)
    Abstract [en]

    This study aimed to numerically and experimentally investigate lump formation during atmospheric plasma spraying with powder injection downstream the plasma gun exit. A first set of investigations was focused on the location and orientation of the powder port injector. It turned out impossible to keep the coating quality while avoiding lumps by simply moving the powder injector. A new geometry of the powder port ring holder was designed and optimized to prevent nozzle clogging, and lump formation using a gas screen. This solution was successfully tested for applications with Ni-5wt.%Al and ZrO2-7wt.%Y2O3 powders used in production. The possible secondary effect of plasma jet shrouding by the gas screen, and its consequence on powder particles prior to impact was also studied.

  • 110.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Welding Technology.
    Nilsson, Håkan
    Chalmers University of Technology, Department of Applied Mechanics, Gothenburg, Sweden.
    A predictive model for gas tungsten arc heat source2016In: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings: 25th – 27th of October 2016, Lund: Swedish Production Academy , 2016, p. 1-10Conference paper (Refereed)
    Abstract [en]

    Gas tungsten arcs are used as heat sources in production processes such as welding and metal deposition.However, the most advanced of the existing gas tungsten arc models still lack predicting the arc temperature observed experimentally, unless imposing a priori the extent of the cathode arc attachment.Possible causes of this problem were investigated. It was concluded that the physical state of the arcing gas tungsten cathode was too simplified by the existing models. This oversimplification results in an overestimation of the cathode arc attachment area and an underestimation of the arc temperature field.An improved model was developed based only on physical criteria. It was tested by comparison with experimental measurements available in the literature. Good agreement with the temperature measured on the cathode surface and within the arc were obtained.

  • 111.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Production Engineering.
    Nilsson, Håkan
    Chalmers University of Technology.
    Electric welding arc modeling with the three-dimensional solver OpenFOAM: A comparison of different electromagnetic models2011In: 64 th Annual Assembly and International Conference of International Institute of Welding, 64th IWW: Chennai, 17-22 july, 2011. Working group 212, 2011, p. 212-1189-11-1-212-1189-11-16Conference paper (Other academic)
    Abstract [en]

    This study focuses on the modeling of a plasma arc heat source in the context ofelectric arc welding. The model was implemented in the open source CFD softwareOpenFOAM-1.6.x, coupling thermal fluid mechanics in three dimensions with electromagnetics.Different approaches were considered for modeling the electromagneticfields: i) the three-dimensional approach, ii) the two-dimensional axi-symmetric approach,iii) the electric potential formulation, and iv) the magnetic field formulation asdescribed by Ramírez et al. [1]. The underlying assumptions and the differencesbetween these models are detailed. The models i) to iii) reduce to the same quasione-dimensional limit for an axi-symmetric configuration with negligible radial currentdensity, contrary to the formulation iv). The models ii) to iv) cannot represent the samephysics when the radial current density is significant, such as for a short arc or anelectrode with a conical tip. The models i) to iii) were retained for doing numerical simulations.The corresponding solvers were tested against analytic solution for an infiniteelectric rod. Perfect agreement was obtained for all the models tested. The completesolver (thermal fluid coupled with electromagnetics) was tested against experimentalmeasurements for Gas Tungsten Arc Welding (GTAW). The shielding gas was argon,the arc was short (2mm), the electrode tip conical, and the configuration axi-symmetric.Anode and cathode were treated as boundary conditions. The models i) and ii) lead tothe same results, but not the formulation iii). It indeed neglects the radial current densitycomponent, resulting in a poor estimation of the magnetic field, and in turn of thearc velocity. Limitations of the complete solver were investigated changing also the gascomposition, and testing boundary conditions. These conditions, difficult to measureand to estimate a priori, significantly affect the simulation results.

  • 112.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Production Engineering.
    Nilsson, Håkan
    Chalmers University of Technology, Department of Applied Mechanics,412 96 Gothenburg, Sweden.
    On the choice of electromagnetic model for shorthigh-intensity arcs, applied to welding2012In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 20, p. 205203-Article in journal (Refereed)
    Abstract [en]

    Four different approaches were considered for modelling the electromagneticfields of high-intensity electric arcs: i) the three-dimensional model, ii) the twodimensionalaxi-symmetric model, iii) the electric potential formulation, and iv) themagnetic field formulation. The underlying assumptions and the differences betweenthese models are described in detail. Models i) to iii) reduce to the same limit for anaxi-symmetric configuration with negligible radial current density, contrary to modeliv). Models i) to iii) were retained and implemented in the open source CFD softwareOpenFOAM. The simulation results were first validated against the analytic solutionof an infinite electric rod. Perfect agreement was obtained for all the models tested.The electromagnetic models i) to iii) were then coupled with thermal fluid mechanicsin OpenFOAM, and applied to the calculation of an axi-symmetric Gas Tungsten ArcWelding (GTAW) test case with short arc (2mm) and truncated conical electrode tip.Models i) and ii) lead to the same simulation results, but not model iii). Model iii)is suited in the specific limit of long axi-symmetric arc, with negligible electrode tipeffect. For short axi-symmetric arc, the more general axi-symmetric formulation ofmodel ii) should instead be used.

  • 113.
    Choquet, Isabelle
    et al.
    University West, Department of Technology, Mathematics and Computer Science.
    Lucquin-Desreuw, B
    Hydrodynamic limit for an arc discharge at atmospheric pressure2005In: Journal of statistical physics, ISSN 0022-4715, E-ISSN 1572-9613, Vol. 119, no 1-2, p. 197-239Article in journal (Refereed)
    Abstract [en]

    In this paper we study a partially ionized plasma that corresponds to an arc discharge at atmospheric pressure. We derive an inviscid hydrodynamic/diffusion limit, characterized by two temperatures, from a system of Boltzmann type transport equations modelling that plasma problem. The original property of this system is that impact ionization is a leading order collisional process. As a consequence, the density of electrons is given in terms of the density of the other species (and its temperature) via a Saha law.

  • 114.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Nilsson, Håkan
    Chalmers University of Technology, Department of Applied Mechanics, Gothenburg.
    Analysis of the Influence of the Composition of the Shielding Gas on Pressure Force and Heat Fluxes in Arc Welding2014In: Proceedings of The 6th International Swedish Production Symposium 2014 / [ed] Johan Stahre, Björn Johansson,Mats Björkman, 2014, p. 1-8Conference paper (Refereed)
    Abstract [en]

    A main problem raised by arc welding manufacturing is the determination ofthe optimal process parameters to ensure weld quality as well as resource efficient andsustainable production. To address this problem a better process understanding is required.In this study thermal magneto hydrodynamic modeling of a welding arc is used to reacha deeper insight into the influence of the composition of the shielding gas on the pressureforce and the heat fluxes to a workpiece. The model was implemented in the open sourcesimulation software OpenFOAM. Four different shielding gas mixtures combining argonand carbon dioxide were studied. When increasing the fraction of carbon dioxide the resultsshow a significant increase of the arc velocity and temperature with constriction of thetemperature field, a decrease of the pressure force and a significant increase of the heatfluxes on the base metal.

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  • 115.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Nilsson, Håkan
    Chalmers University of Technology.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Production Engineering.
    Stenbacka, Nils
    University West, Department of Engineering Science, Division of Production Engineering.
    Numerical simulation of Ar-x%CO2 shielding gas and its effect on an electric welding arc2011In: IIW Commission XII Doc. XII-2017-11, 2011, p. 1-12Conference paper (Other academic)
    Abstract [en]

    This study focuses on the simulation of a plasma arc heat source in the context of electric arc welding. The simulation model was implemented in the open source CFD software OpenFOAM-1.6.x, in three space dimensions, coupling thermal fluid mechanics with electromagnetism. Two approaches were considered for calculating the magnetic field: i) the three-dimensional approach, and ii) the so-called axisymmetric approach. The electromagnetic part of the solver was tested against analytic solution for an infinite electric rod. Perfect agreement was obtained. The complete solver was tested against experimental measurements for Gas Tungsten Arc Welding (GTAW) with an axisymmetric configuration. The shielding gas was argon, and the anode and cathode were treated as boundary conditions. The numerical solutions then depend significantly on the approach used for calculating the magnetic field. The so-called axisymmetric approach indeed neglects the radial current density component, mainly resulting in a poor estimation of the arc velocity. Plasma arc simulations were done for various Ar-x%CO2 shielding gas compositions: pure argon (x=0), pure carbon dioxide (x=100), and mixturesof these two gases with x=1 and 10% in mole. The simulation results clearly show that the presence of carbon dioxide results in thermal arc constriction, and increased maximum arc temperature and velocity. Various boundary conditions were set on the anode and cathode (using argon as shielding gas) to evaluate their influence on the plasma arc. These conditions, difficult to measure and to estimate a priori, significantly affect the heat source simulation results. Solution of the temperature and electromagnetic fields in the anode and cathode will thus be included in the forthcoming developments.

  • 116.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Nilsson, Håkan
    Chalmers University of Technology.
    Sass-Tisovskaya, Margarita
    University West, Department of Engineering Science, Division of Production Engineering.
    Modeling and simulation of a heat source in electric arc welding2011In: SPS11 : The 4th International Swedish Production Symposiom: Lund, 3-5 maj, 2011, 2011, p. 201-211Conference paper (Refereed)
    Abstract [en]

    This study focused on the modeling and simulation of a plasma heat source applied toelectric arc welding. The heat source was modeled in three space dimensions couplingthermal fluid mechanics with electromagnetism. Two approaches were considered forcalculating the magnetic field: i) three-dimensional, and ii) axi-symmetric. The anodeand cathode were treated as boundary conditions. The model was implemented in theopen source CFD software OpenFOAM-1.6.x. The electromagnetic part of the solverwas tested against analytic solution for an infinite electric rod. Perfect agreement wasobtained. The complete solver was tested against experimental measurements for GasTungsten Arc Welding (GTAW) with an axi-symmetric configuration. The shielding gaswas argon with thermodynamic and transport properties covering a temperature rangefrom 200 to 30 000 K. The numerical solutions then depend greatly on the approachused for calculating the magnetic field. The axi-symmetric approach indeed neglectsthe radial current density component, mainly resulting in a poor estimation of the arcvelocity. Various boundary conditions were set on the anode and cathode. Theseconditions, difficult to measure and to estimate a priori, significantly affect the plasmaheat source simulation results. Solution of the temperature and electromagnetic fieldsin the electrodes will thus be included in the forthcoming developments.

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    ElectricArc-SPS11
  • 117.
    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)
  • 118.
    Christiansson, Anna-Karin
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Danielsson, Fredrik
    University West, Department of Engineering Science, Division of Production Engineering.
    Heralic, Almir
    University West, Department of Engineering Science, Division of Production Engineering.
    Ottosson, Mattias
    University West, Department of Engineering Science, Division of Production Engineering.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Production Engineering.
    Automation of a robotised metal deposition system using laser melting of wire2008In: 18th International Conference on Flexible Automation and Intelligent Manufacturing (FAIM 2008): Skövde, 30 June-2 July, 2008, p. 122-129Conference paper (Other academic)
    Abstract [en]

    This paper presents a system for full automation of free-form-fabrication of fully dense metal structures using robotized laser melting of wire. The structure is built of beads of melted wire laid side by side and layer upon layer governed by synchronized robot motion. By full automation is here meant that the process starts with a product specification of a component, and ends in a geometrically validated dense metal component fulfilling industrial material requirements. Due to the complexity of this flexible manufacturing system, a number of different disciplines are involved. This paper discusses mainly the system design, which includes how off-line programming is used for automatic generation of code and how feedback control is used for on-line adjustment of parameters based on desired building properties. To meet industrial needs, the project is carried out in a close cooperation between research and development activities in academy and industry.

  • 119.
    Christiansson, Anna-Karin
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Ottosson, Mattias
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Sensor and control system for metal deposition using robotised laser welding.2006In: 16th International Conference on Computer Technology in Welding and Manufacturing: Kiev, Ukraine, 2006, p. 328-332Conference paper (Refereed)
  • 120.
    Coll Ferrari, Maria Teresa
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    On the evolution of tempering carbides in a modified H!# and a modified H11 when hardening at 1000°2013Conference paper (Refereed)
    Abstract [en]

    Hot- work tool steels require high austenitising temperature during hardening in order to yield the high tempering resistance that vanadium- rich carbides supply. Such grades, when offering high cleanness, are also used for plastic injection molding. The hardening temperature can then be lower, yielding a lower content of vanadium in the martensitic matrix and precipitating instead molybdenum-rich carbides, M2C- type, during tempering. M2C- type carbides are metastable and have high carbide/ matrix interface energy, which implies a greater driving force for coarsening than that in the MC- type. In this paper the carbide evolution in two hot- work grades hardened at 1000˚C, is studied after two and threetemperings. Type, size and distribution of tempering carbides were investigated with the help of TEM. Undissolved carbides were documented by SEM investigation and the microstructures classified by LOM. Hardness levels and Charpy V test results are also reported here.

  • 121.
    Coll Ferrari, Maria Teresa
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Andersson, J.
    Kvarnström, M.
    Influence of lowered austenitisation temperature during hardening on tempering resistance of modified H13 tool steel (Uddeholm Dievar)2013In: International Heat Treatment and Surface Engineering, ISSN 1749-5156, Vol. 7, no 3, p. 129-132Article in journal (Refereed)
    Abstract [en]

    The surface of large tools will be exposed to the hardening temperature for longer times than the core. This might in occasions, result in grain growth. In order to prevent this, it has become practice to lower the hardening temperature. This paper presents the effect of this practice on the precipitation of tempering carbides and the tempering resistance of Uddeholm Dievar. Composition of equilibrium austenite and the undissolved carbides at two different hardening temperatures were estimated by Thermo Calc simulations and the calculations predict that the balance between the amounts of molybdenum and vanadium in the austenite is shifted towards more molybdenum at the lower austenitising temperature. Since molybdenum stabilises M2C precipitates, it was predicted also that the tempering carbides would be almost only M2C in the sample with the lower austenitising temperature, whereas for the higher austenitising temperature, the subsequent tempering would yield a mixture of the much more stable MC together with M2C. Samples were hardened at the simulated temperatures and tempered. The existing carbides were investigated with help of SEM and TEM. The result shows that a lowered austenitisation temperature decreases the tempering resistance. However, the transmission electron microscopy reveals that both samples have the same mixture of tempering carbides, as the samples do not reach thermodynamical equilibrium during the holding time at the hardening temperature. The lower austenitising temperature gives less tempering carbides as less alloying elements are dissolved.

  • 122.
    Coll Ferrari, María Teresa
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Effect of austenitising temperature and cooling rate on microstructures of hot-work tool steels2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The average size of hot-work tools has gradually increased over the past years.This affects the effective temperature cycle tools experience during hardening,as large dimensions prevent uniform and rapid cooling, and thereby the resulting microstructures and properties. In order to avoid the formation of coarse structures or cracking during heat treatment it has become common practise to lower the austenitising temperature below that recommended by the steel manufacturer.In this work, therefore, the effects of austenitising at temperatures lower thancommonly recommended are investigated. Three 5% Cr hot-work tool steelsalloyed with Mo and V were heat treated, resulting microstructures andtempering carbides were studied and transformation characteristics determined for different austenitising temperatures and different cooling rates. The temperatures and cooling rates have been chosen to be representative for heat treatments of different sizes of tools. Bainite rather than martensite formed during slow cooling regardless of austenitising temperature. A lowered austenitising temperature produced largeramounts of both bainite and retained austenite while a higher caused graingrowth. Carbon partitioning during the bainitic transformation resulted in anincrease of the carbon content in the retained austenite of at least 0.3 wt.%. The austenitising temperature influences also the type and amount of tempering carbides that precipitate, which affects the properties of the steel. Higher austenitising temperatures favour the precipitation of MC carbides during tempering. The Mo rich M2C type carbides were proven to be more prone to coarsening during service at 560°C-600°C, while V rich MC carbides preserve their fine distribution. A best practice heat treatment needs to balance the increase of grain size with increasing austenitising temperatures, with the possibility to form more tempering carbides. Higher austenitising temperatures also give less retained austenite, which can affect dimensional stability and toughness negatively after tempering

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  • 123.
    Cruz-Crespo, Amado
    et al.
    Universidad Central "Marta Abreu" de Las Villas, Universidade Federal de Uberlandia.
    Gonzalez, Lorenzo Perdomo
    Anim Hlth & Vet Labs Agcy, VLA Lasswade Vet Labs Agcy Lasswade, King Abdulaziz University.
    Rafael, Quintana
    Universidad Central "Marta Abreu" de Las Villas.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Welding Technology. Universidade Federal de Uberlandia University West - Sweden Fed Univ Uberlandia UFU.
    Flux for Hardfacing by Submerged Arc Welding from Ferrochrome-manganese and Slag from the Simultaneous Reduction of Chromite and Pyrolusite2019In: Soldagem & Inspeção, ISSN 0104-9224, E-ISSN 1980-6973, Vol. 24, article id e2424Article in journal (Refereed)
    Abstract [en]

    The obtaining of a flux for hardfacing by Submerged Arc Welding (SAW), using ferrochrome-manganese and slag obtained from the simultaneous carbothermal reduction of chromite and pyrolusite is addressed. The ferrochrome-manganese and the slag were obtained, conceiving that both products satisfy the requirements of the components (alloy system and matrix) of an agglomerated flux for hardfacing. The fusion-reduction process to obtain the alloy and the slag was carried out in a direct current electric arc furnace. The pouring was carried out into water to facilitate the separation and grinding of the cast products. An experimental flux was manufactured, using the obtained alloy and slag. Deposits were obtained by SAW, which were characterized in terms of: chemical composition, microstructure and hardness. It was concluded that the flux obtained from ferrochrome-manganese and slag from the simultaneous carbothermal reduction of chromite and pyrolusite, allows to deposit an appropriate metal for work under abrasion conditions, characterized by significant carbon and chromium contents and a martensitic microstructure predominantly, with hardness of 63 HRc.

  • 124.
    Curry, Nicholas
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Design of Thermal Barrier Coating Systems2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Thermal barrier coatings (TBC’s) are used to provide both thermal insulation and oxidation protection to high temperature components within gas turbines. The development of turbines for power generation and aviation has led to designs where the operation conditions exceed the upper limits of most conventional engineering materials. As a result there has been a drive to improve thermal barrier coatings to allow the turbine to operate at higher temperatures for longer.

    The focus of this thesis has been to design thermal barrier coatings with lower conductivity and longer lifetime than those coatings used in industry today. The work has been divided between the development of new generation air plasma spray (APS) TBC coatings for industrial gas turbines and the development of suspension plasma spray (SPS) TBC systems.

    The route taken to achieve these goals with APS TBC’s has been twofold. Firstly an alternative stabiliser has been chosen for the zirconium oxide system in the form of dysprosia. Secondly, control of the powder morphology and spray parameters has been used to generate coating microstructures with favourable levels of porosity.

    In terms of development of SPS TBC systems, these coatings are relatively new with many of the critical coating parameters not yet known. The focus of the work has therefore been to characterise their lifetime and thermal properties when produced in a complete TBC system.

    Results demonstrate that dysprosia as an alternative stabiliser gives a reduction in thermal conductivity. While small at room temperature and in the as produced state; the influence becomes more pronounced at high temperatures and with longer thermal exposure time. The trade-off for this lowered thermal conductivity may be in the loss of high temperature stability. Overall, the greatest sustained influence on thermal conductivity has been from creating coatings with high levelsof porosity.

    In relation to lifetime, double the thermo-cyclic fatigue (TCF) life relative to the industrial standard was achieved using a coating with engineered porosity. Introducing a polymer to the spray powder helps to generate large globular pores within the coating together with a large number of delaminations. Such a structure was shown to be highly resistant to TCF testing.

    SPS TBC’s were shown to have much greater performance relative to their APS counterparts in thermal shock life, TCF life and thermal conductivity. Columnar SPS coatings are a prospective alternative for strain tolerant coatings in gas turbine engines.

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  • 125.
    Curry, Nicholas
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Design of Thermal Barrier Coating Systems2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Thermal barrier coatings (TBC’s) are used to provide both thermal insulation and oxidation protection to high temperature components within gas turbines. The development of turbines for power generation and aviation has led to designs where the operation conditions exceed the upper limits of most conventional engineering materials. As a result there has been a drive to improve thermal barrier coatings to allow the turbine to operate hotter for longer.

    The focus of this study has been the development of a new generation of TBC system for industrial implementation. The goal for these new coatings was to achieve lower conductivity and longer lifetime than those coatings used today. The route taken to achieve these goals has been twofold. Firstly an alternative stabiliser has been chosen for the zirconium oxide system in the form of dysprosia. Secondly, Control of the powder morphology and spray parameters has been used to generate coating microstructures with favourable levels of porosity.

    Samples have been heavily characterised using the laser flash technique for evaluation of thermal properties. Measurements were performed at room temperature and at intervals up to 1200°C. Samples have also been tested in their as produced state and after heat treatments of up to 200 hours.

    Lifetime evaluation has been performed using the thermo-cyclic fatigue test to expose coating systems to successive cycles of heating and cooling combined with oxidation of the underlying metallic coating.

    Microstructures have been prepared and analysed using SEM. An image analysis routine has been used to attempt to quantify changes in microstructure features between coating types or coating exposure times and to relate those changes to changes in thermal properties

    Results show that dysprosia as an alternative dopant gives a reduction in thermal conductivity. While small at room temperature and in the as produced state; the influence becomes more pronounced at high temperatures and with thermal exposure time. Overall, the greatest sustained influence on thermal conductivity has been from creating coatings with high levels of porosity.

    In relation to lifetime, the target of double the thermo-cyclic fatigue life was achieved using a coating with engineered porosity. Introducing a polymer to the spray powder helps to generate large globular pores within the coating together with a large number of delaminations. Such a structure has shown to be highly resistant to TCF testing.

  • 126.
    Curry, Nicholas
    University West, Department of Engineering Science, Division of Mechanical Engineering. University West, Department of Engineering Science, Research Enviroment Production Technology West. Treibacher AG, Austria.
    Feedstock for SPS and SPPS: Properties and Processing2016Conference paper (Other academic)
  • 127.
    Curry, Nicholas
    University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Suspension plasma spray: how suspension properties and spray parameters influence coating possibilities2016Conference paper (Other academic)
  • 128.
    Curry, Nicholas
    et al.
    University West, Department of Engineering Science.
    Donoghue, Jack
    University of Manchester.
    Evolution of thermal conductivity of dysprosia stabilised thermal barrier coating systems during heat treatment2012In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, ISSN 0257-8972, Vol. 209, p. 38-43Article in journal (Refereed)
    Abstract [en]

    Dysprosia stabilised zirconia coatings offer a potential reduction in thermal heat transfer for thermal barrier coating systems with the added benefit of being producible with existing equipment and spray knowledge. However, there is little information on the long term performance of such systems relative to the standard coatings. While a low thermal conductivity is important for a gas turbine; sintering resistance is important to maintain properties over the lifetime of a component.

    In this study, four dysprosia stabilised zirconia coatings are compared with a standard yttria stabilised coating in present industrial use.

    Samples were exposed to isothermal furnace conditions at 1150 °C from 5 to 200 hours to observe the sintering resistance of the coating systems. Tests carried out include microstructural analysis with SEM, thermal conductivity measurements using laser flash analysis and porosity changes monitored using image analysis.

  • 129.
    Curry, Nicholas
    et al.
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Janikowski, Wysomir
    University of Manchester.
    Pala, Zdenek
    Academy of Sciences of the Czech Republic, Institute of Plasma Physics.
    Vilémová, Monica
    Academy of Sciences of the Czech Republic, Institute of Plasma Physics.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Impact of Impurity Content on the Sintering Resistance and Phase Stability of Dysprosia- and Yttria-Stabilized Zirconia Thermal Barrier Coatings2014In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 23, no 1-2, p. 160-169Article in journal (Refereed)
    Abstract [en]

    Dysprosia-stabilized zirconia (DySZ) is a promising candidate to replace yttria-stabilized zirconia (YSZ) as a thermal barrier coating due to its lower inherent thermal conductivity. It is also suggested in studies that DySZ may show greater stability to high temperature phase changes compared to YSZ, possibly allowing for coatings with extended lifetimes. Separately, the impurity content of YSZ powders has been proven to influence high-temperature sintering behavior. By lowering the impurity oxides within the spray powder, a coating more resistant to sintering can be produced. This study presents both high purity and standard purity dysprosia and YSZ coatings and their performance after a long heat treatment. Coatings were produced using powder with the same morphology and grain size; only the dopant and impurity content were varied. Samples have been heat treated for exposure times up to 400 h at a temperature of 1150 °C. Samples were measured for thermal conductivity to plot the evolution of coating thermal properties with respect to exposure time. Thermal conductivity has been compared to microstructure analysis and porosity measurement to track structural changes. Phase analysis utilizing x-ray diffraction was used to determine differences in phase degradation of the coatings after heat treatment. © 2013 ASM International.

  • 130.
    Curry, Nicholas
    et al.
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    Janikowski, Wyszomir
    University of Mancheste.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Impact of impurity content on the sintering resistance of dysprosia and yttria stabilised zirconia 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. 557-563Conference paper (Refereed)
    Abstract [en]

    Dysprosia stabilised zirconia (DySZ) is a promising candidate to replace yttria stabilised zirconia (YSZ) as a thermal barrier coating due to its lower inherent thermal conductivity. It is also suggested in studies that DySZ may show greater stability to high temperature phase changes compared to YSZ, possibly allowing for coatings with extended lifetimes. Separately, the impurity content of YSZ powders has been proven to influence high temperature sintering behaviour. By lowering the impurity oxides within the spray powder, a coating more resistant to sintering can be produced. This study presents both high purity and standard purity dysprosia and yttria stabilised zirconia coatings and their performance after a long heat treatment. Coatings were produced using powder with the same morphology and grain size; only the dopant and impurity content were varied. Samples have been heat treated for exposure times up to 400 hours at a temperature of 1150°C. Samples were subsequently measured for thermal conductivity to plot the evolution of coating thermal properties with respect to exposure time. Thermal conductivity has been compared to microstructure analysis and porosity measurement to track structural changes due to sintering.

  • 131.
    Curry, Nicholas
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Markocsan, Nicolaie
    University West, Department of Engineering Science.
    Goddard, Caroline
    Manchester University.
    Influence of Sensor contact on the Thermal Conductivity Values of Thermal Barrier Coatings: Part 1 Experimental2010In: Proceedings of the 24th International Conference on Surface Modification Technologies: 7-9 sept, Dresden, 2010, p. 317-327Conference paper (Refereed)
  • 132.
    Curry, Nicholas
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Li, Xin-Hai
    Siemens Turbomachinery.
    Tricoire, Aurelien
    Volvo Aero Corp.
    Dorfman, Mitch
    Sulzer Metco.
    Next Generation Thermal Barrier Coatings for the Gas Turbine Industry2010In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, ISSN 1059-9630, Vol. 20, no 1-2, p. 108-115Article in journal (Refereed)
    Abstract [en]

    The aim of this study is to develop the next generation of production ready air plasma sprayed thermalbarrier coating with a low conductivity and long lifetime. A number of coating architectures wereproduced using commercially available plasma spray guns. Modifications were made to powder chemistry,including high purity powders, dysprosia stabilized zirconia powders, and powders containingporosity formers. Agglomerated & sintered and homogenized oven spheroidized powder morphologieswere used to attain beneficial microstructures. Dual layer coatings were produced using the two powders.Laser flash technique was used to evaluate the thermal conductivity of the coating systems from roomtemperature to 1200 C. Tests were performed on as-sprayed samples and samples were heat treated for100 h at 1150 C. Thermal conductivity results were correlated to the coating microstructure using imageanalysis of porosity and cracks. The results show the influence of beneficial porosity on reducing thethermal conductivity of the produced coatings.

  • 133.
    Curry, Nicholas
    et al.
    University West, Department of Engineering Science, Division of Production Engineering. University West, Department of Engineering Science, Research Enviroment Production Technology West.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Li, Xin-Hai
    Tricoire, Aurelien
    Dorfman, Mitchell
    Next Generation Thermal Barrier Coatings for the Gas Turbine Industry2010In: Proceedings of the Thermal Spray: Global Solutions for Future Application (ITSC 2010) Conference: Singapore, May 3-5, 2010, 2010, p. 716-722Conference paper (Refereed)
  • 134.
    Curry, Nicholas
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Production Engineering.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspong, Sweden.
    Tricoire, Aurélien
    Volvo Aero, Trollhättan.
    Dorfman, Mitch
    Sulzer Metco, Westbury, United States.
    Next generation thermal barrier coatings for the gas turbine industry2011In: Journal of Thermal Spray Technology, Vol. 20, no 1-2, p. 108-115Article in journal (Refereed)
    Abstract [en]

    The aim of this study is to develop the next generation of production ready air plasma sprayed thermal barrier coating with a low conductivity and long lifetime. A number of coating architectures were produced using commercially available plasma spray guns. Modifications were made to powder chemistry, including high purity powders, dysprosia stabilized zirconia powders, and powders containing porosity formers. Agglomerated & sintered and homogenized oven spheroidized powder morphologies were used to attain beneficial microstructures. Dual layer coatings were produced using the two powders. Laser flash technique was used to evaluate the thermal conductivity of the coating systems from room temperature to 1200 °C. Tests were performed on as-sprayed samples and samples were heat treated for 100 h at 1150 °C. Thermal conductivity results were correlated to the coating microstructure using image analysis of porosity and cracks. The results show the influence of beneficial porosity on reducing the thermal conductivity of the produced coatings. © 2010 ASM International.

  • 135.
    Curry, Nicholas
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Östergren, Lars
    Volvo Aero Corporation, Trollhättan.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery, Finspång.
    Dorfman, Mitch
    Sulzer Metco, Westbury, USA.
    Evaluation of the Lifetime and Thermal Conductivity of Dysprosia-Stabilized Thermal Barrier Coating Systems2013In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 22, no 6, p. 864-872Article in journal (Refereed)
    Abstract [en]

    The aim of this study was the further development of dysprosia stabilised zirconia coatings for gas turbine applications. The target for these coatings was a longer lifetime and higher insulating performance compared to today's industrial stan dard thermal barrier coating. Two morphologies of ceramic top coat were studied; one using a dual layer systems and the second using a polymer to generate porosity. Evaluations were carried out using laser flash technique to measure thermal properties. Lifetime testing was conducted using thermal shock testing and thermo-cyclic fatigue testing. Microstructure was assessed with SEM and Image analysis used to characterise porosity content. The results show that coatings with an engineered microstructure give performance twice that of the present reference coating.

  • 136.
    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)
  • 137.
    Curry, Nicholas
    et al.
    University West, Department of Engineering Science, Division of Mechanical Engineering.
    VanEvery, Kent
    Progressive Surface, Grand Rapids, MI 49512, USA .
    Snyder, Todd
    Progressive Surface, Grand Rapids, MI 49512, USA.
    Markocsan, Nicolaie
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Thermal Conductivity Analysis and Lifetime Testing of Suspension Plasma-Sprayed Thermal Barrier Coatings2014In: Coatings, ISSN 2079-6412, Vol. 4, no 3, p. 630-650Article in journal (Refereed)
    Abstract [en]

    Suspension plasma spraying (SPS) has become an interesting method for the production of thermal barrier coatings for gas turbine components. The development of the SPS process has led to structures with segmented vertical cracks or column-like structures that can imitate strain-tolerant air plasma spraying (APS) or electron beam physical vapor deposition (EB-PVD) coatings. Additionally, SPS coatings can have lower thermal conductivity than EB-PVD coatings, while also being easier to produce. The combination of similar or improved properties with a potential for lower production costs makes SPS of great interest to the gas turbine industry. This study compares a number of SPS thermal barrier coatings (TBCs) with vertical cracks or column-like structures with the reference of segmented APS coatings. The primary focus has been on lifetime testing of these new coating systems. Samples were tested in thermo-cyclic fatigue at temperatures of 1100 °C for 1 h cycles. Additional testing was performed to assess thermal shock performance and erosion resistance. Thermal conductivity was also assessed for samples in their as-sprayed state, and the microstructures were investigated using SEM

  • 138.
    Curry, Nicholas
    et al.
    University West, Department of Engineering Science, Division of Manufacturing Processes. Treibacher Industrie AG, Althofen 9330, Austria.
    VanEvery, Kent
    Progressive Surface, Grand Rapids, MI 49512, USA.
    Snyder, Todd
    Progressive Surface, Grand Rapids, MI 49512, USA.
    Susnjar, Johann
    Treibacher Industrie AG, Althofen 9330, Austria.
    Björklund, Stefan
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    Performance Testing of Suspension Plasma Sprayed Thermal Barrier Coatings Produced with Varied Suspension Parameters2015In: Coatings, ISSN 2079-6412, Vol. 5, no 3, p. 338-356Article in journal (Refereed)
    Abstract [en]

    Suspension plasma spraying has become an emerging technology for the production of thermal barrier coatings for the gas turbine industry. Presently, though commercial systems for coating production are available, coatings remain in the development stage. Suitable suspension parameters for coating production remain an outstanding question and the influence of suspension properties on the final coatings is not well known. For this study, a number of suspensions were produced with varied solid loadings, powder size distributions and solvents. Suspensions were sprayed onto superalloy substrates coated with high velocity air fuel (HVAF) -sprayed bond coats. Plasma spray parameters were selected to generate columnar structures based on previous experiments and were maintained at constant to discover the influence of the suspension behavior on coating microstructures. Testing of the produced thermal barrier coating (TBC) systems has included thermal cyclic fatigue testing and thermal conductivity analysis. Pore size distribution has been characterized by mercury infiltration porosimetry. Results show a strong influence of suspension viscosity and surface tension on the microstructure of the produced coatings.

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  • 139.
    da Silva, Leandro João
    et al.
    SENAI Innovation Institute for Manufacturing Systems and Laser Processing, Joinville, SC, Brazil; Federal University of Uberlândia (UFU), Laprosolda – Center for Research and Development of Welding,Processes, Uberlandia, MG, Brazil.
    Souza, Danielle Monteiro
    Federal University of Uberlândia (UFU), Laprosolda – Center for Research and Development of Welding,Processes, Uberlandia, MG, Brazil.
    de Araújo, Douglas Bezerra
    Federal University of Uberlândia (UFU), Laprosolda – Center for Research and Development of Welding,Processes, Uberlandia, MG, Brazil.
    Reis, Ruham Pablo
    Federal University of Uberlândia (UFU), Laprosolda – Center for Research and Development of Welding,Processes, Uberlandia, MG, Brazil.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Welding Technology. Federal University of Uberlândia (UFU), Laprosolda – Center for Research and Development of Welding,Processes, Uberlandia, MG, Brazil.
    Concept and validation of an active cooling technique to mitigate heat accumulation in WAAM2020In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 107, no 5-6, p. 2513-2523Article in journal (Refereed)
    Abstract [en]

    This work aimed at introducing and exploring the potential of a thermal management technique, named as near-immersion active cooling (NIAC), to mitigate heat accumulation in Wire + Arc Additive Manufacturing (WAAM). According to this technique concept, the preform is deposited inside a work tank that is filled with water, whose level rises while the metal layers are deposited. For validation of the NIAC technique, Al5Mg single-pass multi-layer linear walls were deposited by the CMT® process under different thermal management approaches. During depositions, the temperature history of the preforms was measured. Porosity was assessed as a means of analyzing the potential negative effect of the water cooling in the NIAC technique. The preform geometry and mechanical properties were also assessed. The results showed that the NIAC technique was efficient to mitigate heat accumulation in WAAM of aluminum. The temperature of the preforms was kept low independently of its height. There was no measurable increase in porosity with the water cooling. In addition, the wall width was virtually constant, and the anisotropy of mechanical properties tends to be reduced, characterizing a preform quality improvement. Thus, the NIAC technique offers an efficient and low-cost thermal management approach to mitigate heat accumulation in WAAM and, consequently, also to cope with the deleterious issues related to such emerging alternative of additive manufacturing.

  • 140.
    Dahat, Shubham
    et al.
    University West, Department of Engineering Science, Division of Welding Technology.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Welding Technology.
    Andersson, Joel
    University West, Department of Engineering Science, Division of Welding Technology.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Welding Technology.
    A Methodology to Parameterize Wire + Arc Additive Manufacturing: A Case Study for Wall Quality Analysis2020In: Journal of Manufacturing and Materials Processing, ISSN 2504-4494, Vol. 4, no 1, article id 4010014Article in journal (Refereed)
    Abstract [en]

    The objective of this work was the development of a methodology to parametrize wire + arc additive manufacturing (WAAM), aiming dimension repeatability, and tolerances. Parametrization of WAAM is a difficult task, because multiple parameters are involved and parameters are inter-dependent on each other, making overall process complex. An approach to study WAAM would be through operational maps. The choice of current (Im) and travel speed (TS) for the desirable layer width (LW) determines a parametrization that leads to either more material or less material to be removed in post-operations, which is case study chosen for this work. The work development had four stages. First stage, named ‘mock design’, had the objective of visualizing the expected map and reduce further number of experiments. At the second stage, ‘pre-requisite for realistic operational map’, the objective was to determine the operating limits of TS and Im with the chosen consumables and equipment. Within the ‘realistic operational map’ stage, a design for the experiments was applied to cover a parametric area (working envelope) already defined in the previous stage and long and tall walls were additively manufactured. Actual values of LW (external and effective layer width) were measured and an actual operating envelope was reached. According to the geometry-oriented case study, a surface waviness index (SWindex) was defined, determined, and overlapped in the envelope. It was observed that the walls with parameters near the travel speed limits presented higher SWindex. This operational map was further validated (fourth stage) by selecting a target LW and finding corresponding three parametric set (covering the whole range of operational map) to produce walls on which geometry characterization was carried out. After geometry characterization, obtained LW was compared with the target LW (the maximum values were very tied, with deviations from +0.3 to 0.5 mm), with a SWindex deviation at the order of 0.05. Both results evidence high reproductivity of the process, validating the proposed methodology to parametrize WAAM.

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  • 141. DAS, D.K.
    et al.
    Singh, Vakil
    Joshi, Shrikant V.
    High temperature oxidation behaviour of directionally solidified nickel base superalloy CM–247LC2003In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 19, no 6, p. 695-708Article in journal (Refereed)
    Abstract [en]

    The present paper describes the isothermal and cyclic oxidation behaviour of the technologically important nickel base directionally solidified superalloy CM-247LC in air in the temperature range 1000-1200°C. This superalloy behaves as a transition nickel base alloy under isothermal oxidation conditions and exhibits a fairly long transient oxidation period (~20 h at 1100°C). Irrespective of the temperature of exposure and nature of oxidation (isothermal or cyclic), a composite oxide scale develops on CM-247LC. While the outer portion of the oxide scale consists of either spinel (NiAl2O4) or a mixture of spinel and NiO, depending on oxidation temperature, the inner portion is always constituted of alumina. Beyond the transient period, the alloy is found to follow parabolic oxidation kinetics. The oxide layer that forms is invariably very non-uniform in thickness, and is dispersed with two types of oxide particles. While tantalum rich oxide particles are found scattered in the outer zone of the oxide layer, hafnium rich oxide particles lie close to the oxide/metal interface. Results also reveal that the nature of oxidation associated with the CM-247LC superalloy causes entrapment of metal islands in the oxide layer.

  • 142.
    Das, Kallol
    et al.
    University West, Department of Engineering Science.
    Eynian, Mahdi
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Wretland, Anders
    GKN Aerospace Engine Systems AB, Trollhättan, Sweden.
    Effect of tool wear on quality in drilling of titaniumalloy Ti6Al4V, Part II: Microstructure and Microhardness2017In: High speed machining, E-ISSN 2299-3975, Vol. 3, p. 11-22Article in journal (Refereed)
    Abstract [en]

    Drilling of Ti6Al4V with worn tools can introduce superficial and easily measured features such as increase of cutting forces, entry and exit burrs and surface quality issues and defects. Such issues were presented in the part I of this paper. In part II, subsurface quality alterations,such as changes of the microstructure and microhardness variation is considered by preparing metallographic sections and measurement, mapping of the depth of grain deformation, and microhardness in these sections. Drastic changes in the microstructure and microhardness were found in sections drilled with drills with large wear lands,particularly in the dry cutting tests. These measurements emphasize the importance of detection of tool wear and ensuring coolant flow in drilling of holes in titanium components.

  • 143. Davies, P.
    et al.
    Pederson, Robert
    University West, Department of Engineering Science, Division of Welding Technology. University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. Institute of Structural Materials, College of Engineering, Swansea University, Bay Campus, Fabian Way, Swansea SA1 8EN, United Kingdom.
    Coleman, M.
    Institute of Structural Materials, College of Engineering, Swansea University, Bay Campus, Fabian Way, Swansea SA1 8EN, United Kingdom.
    Birosca, S.
    Institute of Structural Materials, College of Engineering, Swansea University, Bay Campus, Fabian Way, Swansea SA1 8EN, United Kingdom.
    The hierarchy of microstructure parameters affecting the tensile ductility in centrifugally cast and forged Ti-834 alloy during high temperature exposure in air2016In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 117, p. 51-67Article in journal (Refereed)
    Abstract [en]

    Ductility regression is the main concern in using Ti-834 titanium alloy at temperatures above 500 °C for aerospace applications. The reduction of ductility in titanium alloys at high temperatures is strongly correlated to the exposure time. In the current study the effect of prolonged exposure at 500 °C on the tensile ductility of two differently processed Ti-834 alloys was investigated. In order to simulate actual Ti-834 processing routes, forged and centrifugally cast materials were used. The tensile tests were conducted on various specimens exposed at 500 °C for 100, 200 and 500 h to observe microstructure feature changes. Moreover, the effect of microstructure, microtexture, α-case, α2 and silicide precipitate coarsening during high temperature exposure was studied thoroughly. The cast alloy was found to have a minimum ductility and failed at 1.8% strain after exposure at 500 °C/500 h when the α-case layer was retained during testing, whilst, the ductility of the forged alloy was unaffected. The effects of individual microstructural parameters on the ductility regression in Ti-834 alloy were quantified. The results showed that 7.1% strain differences between the cast and forged alloy are related to microstructural variations including; morphology, lath widths, grain size and shape, grain orientations and microtexture. A total of 9.6% strain loss was observed in centrifugally cast Ti-834 after aging at 500°C/500 h and quantified as follow; 3.6% due to α-case formation during high temperature exposure, 0.2% due to α2-precipitates coarsening, 4.4% due to further silicide formation and coarsening, 1.4% due to additional microstructure changes during high temperature exposure. Furthermore, silicide coarsening on α/β phase boundaries caused large void formation around the precipitates. A theoretical model supported by experimental observations for silicide precipitation in fully colony and duplex microstructures was established. The element partitioning during exposure caused Al and Ti depletion in the vicinity of the β phase in the lamellae, i.e., αs area. This resulted in lowering the strength of the alloy and facilitated the formation of Ti3(SiZr)2 precipitates. The Al depletion and nano-scale partitioning observed at the αs/β boundaries resulted in easy crack initiation and promoted propagation in the centrifugally cast colony microstructure and reduced the basal slip τcrss. Furthermore, silicides were not formed in αp (high Al, Ti and low Zr areas) in the forged duplex microstructure that promoted superior mechanical performance and ductility over the cast alloy.

    Graphical abstract

  • 144.
    De Backer, Jeroen
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Robotic Friction Stir Welding for Flexible Production2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Friction Stir Welding (FSW) is a modern welding process that joins materials by frictional heat, generated by a rotating tool. Unlike other welding processes, the material never melts, which is beneficial for the weld properties. FSW is already widely adopted in several industries but the applications are limited to simple geometries like straight lines or circular welds, mostly in aluminium. The welding operation is performed by rigid FSW machines, which deliver excellent welds but puts limitations on the system in terms of flexibility and joint geometries. Therefore, several research groups are working on the implementation of the FSW process on industrial robots. A robot allows welding of three-dimensional geometries and increases the flexibility of the whole system. The high process forces required for FSW, in combination with the limited stiffness of the robot brings some extra complexity to the system.  The limitations of the robot system are addressed in this licentiate thesis.

    One part of the thesis studies the effect of robot deflections on the weld quality. A sensor-based solution is presented that measures the path deviation and compensates this deviation by modifying the robot trajectory. The tool deviation is reduced to an acceptable tolerance and root defects in the weld are hereby eliminated. The sensor-based method provided better process understanding, leading to a new strategy that uses existing force-feedback for path compensations of the tool. This method avoids extra sensors and makes the system less complex. Another part of this work focuses on the extra complexity to maintain a stable welding process on more advanced geometries. A model is presented that allows control of the heat input in the process by control of the downforce. Finally, the robot’s limitations in terms of maximal hardness of the materials to be welded are investigated. Parameter tuning and implementation of preheating are proposed to allow robotic FSW of superalloys.

  • 145.
    De Backer, Jeroen
    et al.
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Bolmsjö, Gunnar
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Thermoelectric method for temperature measurement in friction stir welding2013In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 18, no 7, p. 541-550Article in journal (Refereed)
    Abstract [en]

    Previous research within friction stir welding (FSW) has demonstrated that online control of welding parameters can improve the mechanical properties and is necessary for certain applications to guarantee a consistent weld quality. One approach to control the process is by adapting the heat input to maintain a stable welding temperature, within the specified operating boundaries. This requires accurate in-process temperature measurements. This paper presents a novel method to measure the temperature at the interface of the FSW tool and workpiece. The method is based on the thermoelectric effect between dissimilar materials. The measurements are compared to thermocouple measurements and to a physical model and show good correspondence to each other. Experiments demonstrate that the method can quickly detect temperature variations, due to geometrical variations of the workpiece or due to parameter changes. This allows use of the method for online control of robotic FSW.

  • 146.
    De Backer, Jeroen
    et al.
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Bolmsjö, Gunnar
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Temperature control of robotic friction stir welding using the thermoelectric effect2014In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 70, no 1-4, p. 375-383Article in journal (Refereed)
    Abstract [en]

    Friction stir welding (FSW) of non-linear joints receives an increasing interest from several industrial sectors like automotive, urban transport and aerospace. A force-controlled robot is particularly suitable for welding complex geometries in lightweight alloys. However, complex geometries including three-dimensional joints, non-constant thicknesses and heat sinks such as clamps cause varying heat dissipation in the welded product. This will lead to changes in the process temperature and hence an unstable FSW process with varying mechanical properties. Furthermore, overheating can lead to a meltdown, causing the tool to sink down into the workpiece. This paper describes a temperature controller that modifies the spindle speed to maintain a constant welding temperature. A newly developed temperature measurement method is used which is able to measure the average tool temperature without the need for thermocouples inside the tool. The method is used to control both the plunging and welding operation. The developments presented here are applied to a robotic FSW system and can be directly implemented in a production setting.

  • 147.
    De Backer, Jeroen
    et al.
    University West, Department of Engineering Science, Division of Automation Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Automation Systems.
    Surface Quality and Strength in Robotic Friction Stir Welding of Thin Automotive Aluminium Alloys2011In: The 4th International Swedish Production Symposium / [ed] Jan-Eric Ståhl, The Swedish Production Academy , 2011, p. 554-562Conference paper (Refereed)
    Abstract [en]

    Friction Stir Welding (FSW) is a novel method for joining materials without using consumablesand without melting the materials. It uses a rotating tool that creates frictionalheat and mixes the materials mechanically together. Robotic application of FSW allowsthree-dimensional welding of light-weight metals in e.g. the automotive industry. TheStiRoLight project is driven by Saab Automobile AB and performed at University Westfor investigation of robotic FSW of three-dimensional welding seams. It aims to introduceFSW in the automotive production line. This paper describes the effect of penetrationdepth of the FSW tool during force controlled robotic welding of thin (< 2 mm) aluminium inoverlap configuration. The influence of pin length on strength of welded aluminium sheetsis investigated using tensile and peel tests. The main limiting factor for penetration depthis the surface quality on the backside of the weld, which often is important in automotiveapplications. Further, the roughness of the plates on the backside is measured and relatedto pin length and backing bar properties. This paper shows a relation between penetrationdepth and tensile strength, and suggests an optimal pin length to guarantee a good weldquality while maintaining an acceptable surface quality. The influence of sheet thicknesstolerance is also discussed. Knowledge is fed back to designers and manufacturingengineers to facilitate for use in production with guaranteed product quality.

  • 148.
    De Backer, Jeroen
    et al.
    University West, Department of Engineering Science, Division of Production System. TWI Ltd, Cambridge, UK.
    Martin, Jonathan
    TWI Ltd, Cambridge, UK.
    Wei, Sam
    TWI Ltd, Cambridge, UK.
    Robotic Stationary Shoulder FSW: benefits and limitations2016In: Conference proceedings of the 11th International Symposium on Friction Stir Welding, 2016Conference paper (Refereed)
  • 149.
    De Backer, Jeroen
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Soron, Mikael
    ESAB Welding AB .
    Ilar, Torbjörn
    University West, Department of Engineering Science, Division of Production Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Process and Product Development.
    Friction stir welding with robot for light vehicle design2010In: Proceedings from the 8th International Friction Stir Welding Symposium: Timmendorfer Strand, Germany 18-20 May 2010, The Welding Institute , 2010Conference paper (Other academic)
    Abstract [en]

    Reducing weight is one of the enablers to design more environmentally friendly vehicles. Friction Stir Welding (FSW) supports low weight design through its capability to join different combinations of light weight materials, e.g. different aluminium alloys, but also through its possibilities in producing continuous joints. StiRoLight is a recently started project for robotised FSW for joining of light weight materials emphasising on the vehicle industry, an industry with a long-time experience of robotic welding. The first task involves investigation of force feedback for maintaining the desired contact force. Another important aspect in robotised FSW is the compliance of the robot, which may result in deviations from the pre-programmed path as a result of the high process forces experienced during the welding operation. The further exploration of three-dimensional FSW seams and definition of the process windows will be part of further research within this project.

  • 150.
    de Souza Amaral, Thiago
    et al.
    CBMM, Araxá, MG, Brasil.
    Carboneri Carboni, Marcelo
    CBMM, São Paulo, SP, Brasil.
    Scotti, Americo
    University West, Department of Engineering Science, Division of Welding Technology. Universidade Federal de Uberlândia – UFU, Uberlândia, MG, Bras.
    Avaliação da Aplicação de um Atlas de Soldagem de um Aço Bainítico Microligado ao Nióbio: Application Assessment of a Welding Atlas of a Niobium Microalloyed Bainitic Steel2017In: Soldagem & Inspeção, ISSN 0104-9224, E-ISSN 1980-6973, Vol. 22, no 2, p. 163-173Article in journal (Refereed)
    Abstract [en]

    Niobium microalloyed steels have shown to be an excellent solution for fabrication of structural beams, employing concepts already developed for the oil and gas industry. However, the definition of the actual welding related needs of this family of bainite steels is not well described in the welding standards mostly used in the structural construction sector. This paper demonstrates the construction and assessment of a Welding Atlas, built from using physical simulations (Gleeble and dilatrometry) and mechanical tests of the simulated specimens. The objective is to have the Atlas as a guiding tool to improve the parametrization for welding this class of steels. The proposal methodology was applied to a HSLA bainitic steel class 65 ksi. It was possible to determine with more accuracy the recommended energy range of the weld, including the need or not of preheating, and show that they were comparable with actual welds. The methodology shows benefits including a safer parametrization and cost savings resulting from unnecessary preheating elimination.

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