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  • 151.
    Gustafsson, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Hornqvist, Magnus
    Volvo Aero Corporation.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Sharifimajd, Babak
    Siemens Industrial Turbomachinery AB.
    Fatigue crack growth behaviour of Inconel 718 with high temperature hold times2010In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 2, no 1, p. 1095-1104Article in journal (Refereed)
    Abstract [en]

    In this work, fatigue crack growth measurements have been made on center-cracked tension specimens of Inconel 718, where the focus has been to observe the effect of high temperature hold times on the fatigue crack growth behaviour of the material. The material testing has been done at three different temperatures, namely 450 degrees C, 550 degrees C and 650 degrees C. All testing were done in an isothermal LCF context with a standard test method for measuring the fatigue crack growth rates.

  • 152.
    Gustafsson, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Hornqvist, M
    Volvo Aero Corp.
    Mansson, T
    Volvo Aero Corp.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Influence of high temperature hold times on the fatigue crack propagation in Inconel 7182011In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 33, no 11, p. 1461-1469Article in journal (Refereed)
    Abstract [en]

    High temperature fatigue crack growth in Inconel 718 has been studied at the temperatures 450 degrees C, 500 degrees C, 550 degrees C and 650 degrees C. The tests were conducted both without hold times and with hold times of different lengths and with a mix of both. Focus has been on quantifying the effect the hold time has upon the crack growth rate and how much it damages the material. Furthermore, it has been investigated how this damage influences the actual cracking behavior, i.e. where in the loading cycle the damage contributes most to the crack growth. This damage is related to the concept of a damaged zone in front of the crack tip. The size of the damaged zone has been derived from the tests and a microscopy study to confirm the findings has also been carried out. It is found that the concept of a damaged zone can be a successful explanatory model for the observed crack growth behavior under high temperature hold time.

  • 153.
    Gustafsson, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Hörnqvist, Magnus
    Volvo Aero Corporation, Trollhättan.
    Månsson, Tomas
    Volvo Aero Corporation, Trollhättan.
    Sjöström, Sören
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics.
    Fatigue Crack Growth behaviour of Inconel 718 - the Concept of a Damaged Zone Caused by High Temperature Hold Times2011In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 10, p. 2821-2826Article in journal (Refereed)
    Abstract [en]

    Fatigue crack growth testing of Inconel 718 has been carried out at the temperatures 550 °C and 650 °C. The tests were conducted using a mix of hold times and pure cyclic loading, referred to as block tests. From the test results, the existence of an embrittled volume or damaged zone in the vicinity of the crack tip has been revealed. It has been found that the evolution of this damaged zone can be sufficiently well described using a power law function with an exponent n = 0.25.

  • 154.
    Gustafsson, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Modeling of the Constitutive Behavior of Inconel 718 at Intermediate Temperatures2011In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 133, p. 094501-1-094501-4Article in journal (Refereed)
    Abstract [en]

    Turbine disks are of large importance to turbine designers as theyare exposed to hot environment and subjected to high loads. Inorder to analyze such components with respect to fatigue crackinitiation, the work generally starts with a rigorous analysis of thefirst few cycles, during which an important stress redistributionwill always take place in an inelastic structure. In this work, thenonlinear kinematic hardening law by Ohno and Wang (1998,“Constitutive Modeling of Cyclic Plasticity With Emphasis onRatchetting,” Int. J. Mech. Sci., 40, pp. 251–261) has been used incombination with an isotropic softening law for describing theinitial stress-strain distribution for strain controlled uniaxial testsof the material Inconel 718. Focus has been placed on finding asimple model with few material parameters and to describe theinitial softening and the comparatively small mean stress relaxationobserved during the material testing. The simulation resultsobtained by using the model fit the experimental resultswell.

  • 155.
    Gärdsback, Magnus
    et al.
    Sandvik Materials Technology, Sandviken.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Hedström, David
    Sandvik Materials Technology, Sandviken.
    Persson, Katarina
    Sandvik Materials Technology, Sandviken.
    Influence of Strain Path on Work Hardening and Texture in an Austenitic Stainless Steel2014In: THERMEC 2013, Trans Tech Publications Inc., 2014, Vol. 783-786, p. 2567-2572Conference paper (Refereed)
    Abstract [en]

    The effect of strain path on work hardening and texture for a super austenitic stainless steel was investigated using both experiments and modeling. Compression deformation tests by stepwise changing loading direction in two and three dimensions were performed on cubic specimens at room temperature. The results were compared to uniaxial compression with equal accumulative strain, up to 20%, and uniaxial tension with equal final strain, up to 10% elongation of the longest side. The textures in all samples were analyzed using pole figures from EBSD analysis. Because of the high stacking fault energy of this super austenitic stainless steel, the texture was dominated by <110>-fiber texture in the compressive direction for the uniaxial compression, <111>- and <100>-fiber texture in the tensile direction for the uniaxial tensile test, and a combination of all these for the cube deformation. The density of the texture was much weaker for samples where the loading direction altered, if samples with equal accumulated strain were compared. The cube deformation was also modeled using a crystal plasticity model. The crystal plasticity model consists of a representative volume element (RVE) containing crystal grains with random orientations. The Taylor assumption was used for homogenization between the macro-and subscale. The material parameters in the crystal plasticity model were determined by calibration of its macroscopic response to experimental data. The simulated textures correspond rather well to the experimental results, but the work hardening should be completed to take into account kinematic hardening.

  • 156.
    Hallander, P.
    et al.
    SAAB AB, Linköping.
    Akermo, M,
    Aeuronautical and Vehicle Eng/Lightweigh Structures, KTH, Stockholm.
    Mattei, Christophe
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Petersson, M.
    SAAB AB, Linköping.
    Nyman, T
    SAAB AB, Linköping.
    An experimental study of mechanisms behind wrinkle development during forming of composite laminates2013In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 50, p. 54-64Article in journal (Refereed)
    Abstract [en]

    A general problem when forming quasi-isotropic, multilayer unidirectional (UD) prepreg over a double curved geometry is out-of-plane wrinkling. The presented study aims to show the existence of compression in the laminate in a recess area that is globally under tension during forming. Further it aims to investigate the influence of compression on the out-of-plane wrinkle development.

    An experimental study is performed with pre-stacked UD prepreg on a forming tool with varying cross section. Investigated parameters include lay-up sequence, prepreg ply thickness, inter-ply friction and prepreg ply impregnation. Experimental evaluation is performed on the out-of-plane defect height, type, location and number. Further, measurements are performed on the outer-ply deformation in the z-direction and inside the formed component using Micro CT. The study show that compression is to some degree always developed during forming of a recess area but that the lay-up sequence has a dominant effect on the wrinkling development.

  • 157. Hareland, Mathias
    et al.
    Hoel, Anders
    Jonsson, Stefan
    Liang, David
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Selection of Flapper Valve Steel for High Efficient Compressor2014Conference paper (Refereed)
  • 158.
    Hass, Ursula
    et al.
    Linköping University, Department of Medical and Health Sciences, Division of Health Care Analysis. Linköping University, Faculty of Health Sciences.
    Andersson, Agneta
    Linköping University, Department of Medical and Health Sciences, Social Medicine and Public Health Science. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Local Health Care Services in West Östergötland, Research & Development Unit in Local Health Care.
    Brodin, Håkan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Persson, Jan
    Linköping University, Department of Medical and Health Sciences, Division of Health Care Analysis. Linköping University, Faculty of Health Sciences.
    Assessment of computer-aided assistive technology: analysis of outcomes and costs1997In: Augmentative and Alternative Communication: AAC, ISSN 0743-4618, E-ISSN 1477-3848, Vol. 3, no 2, p. 125-135Article in journal (Refereed)
    Abstract [en]

    The objectives of this study were to identify and quantify outcomes related to implementation of computer-aided assistive technologies (CAAT) for individuals with communication disabilities and to analyze CAAT costs comprising the selected devices as well as the selection process. The study was designed as a pre/post, longitudinal study. Intermediate and global measures were used as outcome measures. Costs reflecting the resource consumption for the selected devices as well as the selection process were estimated. Individuals with communication disabilities who were referred to the regional CAAT centers were asked to participate in the study. Eighty-seven individuals were recruited. The study shows that usage of CAAT involves reasonable marginal costs for the selection process and equipment (on average SEK 14,800). Usage of CAAT diminishes disability and increases skills in handling computers. However, the outcomes are not entirely positive regarding handicap, health-related quality of life, and utility.

    Read More: http://informahealthcare.com/doi/abs/10.1080/07434619712331277928

  • 159.
    Isaksson, Claes
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sjögren, Anders
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Compressive failure on non-crimp fabric composites containing impact damage, holes and artificial defectsManuscript (preprint) (Other academic)
    Abstract [en]

    The present study concerns compressive failure of glass fibre NCF composite laminates. The objectives of the study are firstly to give insight into the mechanisms leading to failure, and secondly to provide guidelines for development of physically based engineering models.

    The governing failure mechanism for laminates with impact damage, artificial delaminations as well as artificial delaminations and holes was delamination growth, while the governing failure mechanism for laminates with holes was fibre microbuckling and kink band formation. A single artificial dent in the specimens did not seem to reduce the compressive strength to any great extent, but when the dent was combined with artificial delaminations the compressive strength was substantially reduced and the specimens failed due to delamination growth.

  • 160.
    Isaksson, Claes
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sjögren, Anders
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Effects on through-the-thickness pressure on the compressive failure of non-crimp fabric compositesManuscript (preprint) (Other academic)
    Abstract [en]

    This paper presents results from an experimental investigation of the influence of a low through-the- thickness pressure on the compressive failure of glass fibre non-crimp fabric composite laminates. Specimens with holes and artificial delaminattons have been manufactured and tested both with and without through-the-thickness pressure, and based on the results obtained it is clear that fibre microbuckling and kinking governs final failure of laminates with open holes, while initiation and propagation of delaminations governs final failure of laminates with artificial delaminations. However, by applying a low through-the-thickness pressure, initiation and propagation of delaminations can be prevented, or at least postponed, and the compressive failure strength thereby substantially improved.

  • 161.
    Jia, N
    et al.
    Northeastern University.
    Nie, Z H
    Northeastern University.
    Ren, Y
    Argonne National Laboratory.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Wang, Y D
    Northeastern University.
    Zhao, X
    Northeastern University.
    Formation of Deformation Textures in Face-Centered-Cubic Materials Studied by In-Situ High-Energy X-Ray Diffraction and Self-Consistent Model2010In: METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, ISSN 1073-5623, Vol. 41A, no 5, p. 1246-1254Article in journal (Refereed)
    Abstract [en]

    The evolution of deformation textures in copper and alpha brass that are representative of fcc metals with different stacking fault energies (SFEs) during cold rolling is predicted using a self-consistent (SC) model. The material parameters used for describing the micromechanical behavior of each metal are determined from the high-energy X-ray (HEXRD) diffraction data. At small reductions, a reliable prediction of the evolution of the grain orientation distribution that is represented as the continuous increase of the copper and brass components is achieved for both metals when compared with the experimental textures. With increasing deformation, the model could characterize the textures of copper, i.e., the strengthening of the copper component, when dislocation slip is still the dominant mechanism. For alpha brass at moderate and large reductions, a reliable prediction of its unique feature of texture evolution, i.e., the weakening of the copper component and the strengthening of the brass component, could only be achieved when proper boundary conditions together with some specified slip/twin systems are considered in the continuum micromechanics mainly containing twinning and shear banding. The present investigation suggests that for fcc metals with a low SFE, the mechanism of shear banding is the dominant contribution to the texture development at large deformations.

  • 162.
    Jia, N
    et al.
    Northeastern University.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Brown, D W
    Los Alamos National Laboratory.
    Clausen, B
    Los Alamos National Laboratory.
    Wang, Y D
    Northeastern University.
    Tensile Deformation Behavior of Duplex Stainless Steel Studied by In-Situ Time-of-Flight Neutron Diffraction2008In: METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, ISSN 1073-5623, Vol. 39A, no 13, p. 3134-3140Article in journal (Refereed)
    Abstract [en]

    For a duplex alloy being subjected to deformation, the different mechanical behaviors of its constituent phases may lead to a nonuniform partition of stresses between phases. In addition, the grain-orientation-dependent elastic/plastic anisotropy in each phase may cause grain-to-grain interactions, which further modify the microscopic load partitioning between phases. In the current work, neutron diffraction experiments on the spectrometer for materials research at temperature and stress (SMARTS) were performed on an austenite-ferrite stainless steel for tracing the evolution of various microstresses during tensile loading, with particular emphasis on the load sharing among grains with different crystallographic orientations. The anisotropic elastic/plastic properties of the duplex steel were simulated using a visco-plastic self-consistent (VPSC) model that can predict the phase stress and the grain-orientation-dependent stress. Material parameters used for describing the constitutive laws of each phase were determined from the measured lattice strain distributions for different diffraction {hkl} planes as well as the laboratorial macroscopic stress-strain curve of the duplex steel. The present investigations provide in-depth understanding of the anisotropic micromechanical behavior of the duplex steel during tensile deformation.

  • 163.
    Jia, N
    et al.
    Key Laboratory for Anisotrooy and Testure of Materials Northeastern university, Shenyang, China.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Chai, G C
    Sandvik Materials Technology SFM Sandviken.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Wang, Y D
    Key Laboratory for Anisotropy and Texture of Materials Northeastern university, Shenyang, China.
    Direct experimental mapping of microscale deformation heterogeneity in duplex stainless steel2008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 491, no 1-2, p. 425-433Article in journal (Refereed)
    Abstract [en]

    In situ tensile test has been performed with the electron back-scattering diffraction (EBSD) technique for characterizing the deformation heterogeneity at microscopic level of a duplex stainless steel consisting of austenite and ferrite. It was observed that, as deformation proceeded, the fraction of low-angle boundaries continuously increased and strain gradient developed at some grain boundaries and twin boundaries, as well as in the interior of some grains. The in situ experiments quantitatively captured the change of grain-orientation-dependent plastic behavior in respective phases and the strain partition between duplex phases as a function of applied strain. Using a visco-plastic self-consistent (VPSC) model incorporating the accommodation of micromechanical properties of grains with different orientations in two phases, the evolution of microstresses/microstrains at various length scales was simulated and discussed in detailed within the material undergoing plastic deformation. The experimental observations are well explained by the VPSC model. The present investigations provide the in-depth understanding of anisotropic micromechanical behaviors of the duplex steel. © 2008 Elsevier B.V. All rights reserved.

  • 164.
    Jia, N
    et al.
    Key Lab for Anisotropy and Texture of Materials Northeastern University, Shenyang, China.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Wang, Y D
    Dept of Materials Science and Engineering University of Tennessee, Knoxville, USA.
    Johansson, Sten
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Liaw, P K
    Dept of Materials Science and Engineering University of Tennessee, Knoxville, USA.
    Micromechanical behavior and texture evolution of duplex stainless steel studied by neutron diffraction and self-consistent modeling2008In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 56, no 4, p. 782-793Article in journal (Refereed)
    Abstract [en]

    Microscopic incompatibility-induced stresses in a duplex stainless steel undergoing plastic deformation are elucidated using a visco-plastic self-consistent model. The model considers not only the grain-orientation-dependent stresses and phase-to-phase interactions, but also texture evolution during deformation. The parameters used for describing the micromechanical behavior of the two-phase polycrystalline material are directly derived from the neutron diffraction data. A reliable prediction of the evolution of grain orientation distributions for both phases at small deformations is achieved after considering various micromechanical interactions of the studied material. © 2007 Acta Materialia Inc.

  • 165.
    Jia, N
    et al.
    Key Laboratory for Anisotropy and Testure of Materials, Northeastern University, Shenyang, China.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Wang, Yandong
    Key Lab for Anisotropy & Texture of Mater., Northeastern Univ., Shenyang, China.
    Zhao, X
    School of Materials and Metallurgy, Northeastern University, Shenyang, China.
    Self-consistent modeling of rolling textures in an austenitic-ferritic duplex steel2011In: Materials Science and Engineering A, ISSN 0921-5093, Vol. 528, no 10-11, p. 3615-3624Article in journal (Refereed)
    Abstract [en]

    Rolling textures of the constituent phases in an austenitic–ferritic duplex stainless steel are measured by X-ray diffraction experiments, showing that the brass-type texture, typical of f.c.c. materials with low SFE, is developed in the austenitic phase, and the rotated-cube and brass-R textures are developed in the ferritic phase. On the basis of the experimental texture components and fibers at different reductions, rolling textures of the respective phases in the duplex steel are simulated using a self-consistent model. After considering various micromechanical interactions within the steel, a reliable prediction of the evolution of grain orientation distributions for the phases at small reductions is achieved. An attempt in modeling the brass-type texture for the f.c.c. metallic phase is also performed by incorporating the shear banding mechanism into the presented model.

  • 166.
    Jia, N
    et al.
    School of Materials and Metallurgy Northeastern University, Shenyang, PRC.
    Wang, Y D
    School of Materials and Metallurgy Northeastern university, Shenyang, PRC.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Micromechanical behaviors of duplex steel: in situ neutron diffraction measurements and simulations2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, p. 104259-104265Article in journal (Refereed)
  • 167.
    Jiang, Shuang
    et al.
    Northeastern Univ, Peoples R China.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Jia, Nan
    Northeastern Univ, Peoples R China.
    Zhao, Xiang
    Northeastern Univ, Peoples R China.
    Zuo, Liang
    Northeastern Univ, Peoples R China.
    Microstructural and textural evolutions in multilayered Ti/Cu composites processed by accumulative roll bonding2019In: Journal of Materials Science & Technology, ISSN 1005-0302, Vol. 35, no 6, p. 1165-1174Article in journal (Refereed)
    Abstract [en]

    Ti/Cu multilayered composites were fabricated via accumulative roll bonding (ARB). During co-deformation of the constituent metals, the hard Ti layers necked preferentially and then fragmented with the development of shear bands. Transmission electron microscopy showed that with increasing ARB cycles, grains in Ti were significantly refined even though dynamic recrystallization has occurred. For Cu the significant grain refinement was only found within the shear banded region when the composite was processed after five ARB cycles. Due to the diffusion of Cu atoms into Ti at the heterophase inter faces, amorphization with a width less than 10 nm was identified even in the composite processed by one cycle. At higher ARB cycles, the width of amorphous region increased and intermetallic compounds CuTi appeared from the region. The lattice defects introduced at the heterophase interfaces under roll bonding was responsible for the formation of the nano-scaled compounds. X-ray diffraction showed that an abnormal {11 (2) over bar0} fiber texture was developed in Ti layers, while significant brass-type textures were developed in Cu layers. Some orientations along the {11 (2) over bar0} fiber favored the prismatic amp;lt;aamp;gt; slip for Ti. Tensile tests revealed the elevated strength without a substantial sacrifice of ductility in the composites during ARB. The unique mechanical properties were attributed to the significantly refined grains in individual metals, the good bonding between the constituent metals, as well as the development of an abnormal {11 (2) over bar0} fiber texture in Ti layers. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science amp; Technology.

  • 168.
    Johansson, Sten
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Fitzpatrick, ME
    Linkoping Univ, Dept Mech Engn, Div Engn Mat, S-58183 Linkoping, Sweden Open Univ, Dept Mat Engn, Milton Keynes MK7 6AA, Bucks, England.
    Errors in crack closure measurements caused by flexure test fixture support effects2001In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 41, no 1, p. 47-51Article in journal (Refereed)
    Abstract [en]

    Flexural tests are sometimes used for the evaluation of fatigue and fracture properties, especially for thin cross sections such as plate material where compact tension specimens cannot be used, or where material thickness is limited in the direction required for data generation. The method is also useful for evaluation of crack closure provided the force transfer occurs correctly. This paper shows how the influence of incorrect test fixture supports, which are outside the standard testing arrangement for such test specimens, can affect the force-displacement curves as evidenced using the back-face strain method, The results show that incorrect test fixture supports may cause deviations in the force-displacement trace as an artifact of the testing conditions. This effect can severely influence crack closure measurements. The effect was also modeled with finite element analysis.

  • 169.
    Johansson, Sten
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Kanesund, Jan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Investigation of localized damage in single crystals subjected to thermalmechanical fatigue (TMF)2010In: Procedia Engineering, ISSN 1877-7058, Vol. 2, no 1, p. 657-666Article in journal (Refereed)
    Abstract [en]

    The deformation and damage mechanisms arising during thermalmechanical fatigue (TMF) of a CMSX-4 and high-Cr single crystal super alloy, SCA425 have been investigated and a completely new failure mechanism involving recrystallization and oxidation has been discovered. The primary deformation mechanism is slip along the {111} planes. The deformation is highly localised to a number of bands, where recrystallization eventually occur during the thermalmechanical fatigue process. When the final failure occurs along these recrystallized bands it is accompanied by the formation of voids due to the presence of grain boundaries. The damage process is further enhanced by oxidation, since recrystallization occurs more easily in the gamma depleted zone under the oxide scale. The macroscopic as well as the microscopic damage and fracture mechanisms are varying with alloy and heat treatment. The aim of this work is to further investigate, discuss the local damage mechanisms responsible for TMF damage. Of special interest is the localisation of damage into twins and extremely localized rafted deformation bands.

  • 170.
    Johansson, Sten
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Recent Applications of Scanning Electron Microscopy2013In: Practical Metallography, ISSN 0032-678X, Vol. 50, no 12, p. 810-820Article in journal (Refereed)
    Abstract [en]

    Scanning electron microscopy (SEM) has since it was commercially available in the sixties been used in the study of solid inorganic and organic materials at magnifications ranging from 10 to above 10000 times. Analysis tools are now including diffraction phenomena like EBSD for crystallographic studies The use of X-ray generated was early introduced and the performance of those EDS systems is enormous even if the basic principle of detection is almost the same. Even if the development of digital electronics is one important factor for todays performance of SEM, the most important factor for success is the generation of electron probe size with a small diameter to obtain as high resolving power as possible In addition to that the electron density plays a major role since the resolving power is dependent on peak to background ratio to get a sharp image, the development of bright guns is the most important factor.

  • 171.
    Johansson, Sten
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Viskari, Leif
    Chalmers University of Technology and SKF Sweden.
    Stiller, Krystina
    Chalmers University of Technology Sweden.
    Hörnqvist, Magnus
    Chalmers University of Technology and GKN Aerospace Engine Systems Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Fracture Mechanisms During Intergranular Hold Time Fatigue Crack Growth in Inconel 718 Superalloy2013Conference paper (Refereed)
  • 172.
    Jonnalagadda, Krisha Praveen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Failure mechanisms in APS and SPS thermal barrier coatings during cyclic oxidation and hot corrosion2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Thermal Barrier Coatings (TBCs) are advanced material systems that are being used in the hot sections of gas turbines such as combustor, turbine blades, and vanes. The top ceramic coating in TBCs provides insulation against the hot gases and the intermediate metallic bond coat provides oxidation and corrosion resistance to the underlying turbine components.

    Durability of thermal barrier coatings is very important for the overall performance of the gas turbine. TBCs can fail in several different ways and there is a combination of more than one failure mechanism in most situations. One of the most widely used TBC is atmospheric plasma sprayed (APS) yttria stabilized zirconia (YSZ). Both the deposition technique and the TBC material have certain limitations. The main aim of this research is to study new TBC materials and/or new deposition techniques and compare with the conventional YSZ and understand their failure mechanisms during cyclic oxidation and hot corrosion.

    Thermal cyclic oxidation of a newly developed high purity nano YSZ thermal barrier coating has been studied. Cross sectional analysis of exposed as well as completely failed samples showed a mixed-type failure caused by crack propagation parallel to the bond coat/top coat interface. The majority of the damage occurred towards the end of the coating life. A finite element model has been developed to study the probability of crack growth along different paths that leads to the final failure.

    Hot corrosion mechanism in suspension plasma sprayed two-layer gadolinium zirconate/YSZ, three-layer dense gadolinium zirconate/gadolinium zirconate/YSZ, and a single-layer YSZ has been studied in the presence of sodium sulfate and vanadium pentoxide. The test results showed that gadolinium zirconate coatings were more susceptible to corrosion compared to YSZ coatings despite gadolinium zirconate coatings having lower reactivity with the corrosive salts.

    Thermal cycling behavior of a high chromium bond coat has been studied. Cross-sectional analysis showed formation of sandwich type microstructure with chromium rich oxide and alumina as the top and the bottom layers.

    Inter-diffusion of minor elements between different MCrAlY coatings – substrate systems has been studied using, diffusion simulation software, DICTRA. The simulation results showed that the diffusion of minor elements in the coatings is dependent on the rate of β phase depletion in the beginning. After the depletion of β phase there was no clear dependence of the coating composition on the diffusion of minor elements.

    List of papers
    1. Hot Corrosion Mechanism in Multi-Layer Suspension Plasma Sprayed Gd2Zr2O7 /YSZ Thermal Barrier Coatings in the Presence of V2O5 + Na2SO4
    Open this publication in new window or tab >>Hot Corrosion Mechanism in Multi-Layer Suspension Plasma Sprayed Gd2Zr2O7 /YSZ Thermal Barrier Coatings in the Presence of V2O5 + Na2SO4
    Show others...
    2017 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 26, no 1, p. 140-149Article in journal (Refereed) Published
    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.

    Place, publisher, year, edition, pages
    New York: Springer, 2017
    Keywords
    gadolinium zirconatehot corrosionmulti-layer thermal barrier coatingssuspension plasma sprayingvanadium pentoxide + sodium sulfate
    National Category
    Corrosion Engineering Manufacturing, Surface and Joining Technology Materials Chemistry
    Identifiers
    urn:nbn:se:liu:diva-134375 (URN)10.1007/s11666-016-0486-5 (DOI)000392060300014 ()
    Note

    Funding agencies: Vinnova in Sweden

    Available from: 2017-02-08 Created: 2017-02-08 Last updated: 2019-02-26Bibliographically approved
    2. Thermal fatigue failure of thermal barrier coatings with a high-Cr MCrAIY bond coat
    Open this publication in new window or tab >>Thermal fatigue failure of thermal barrier coatings with a high-Cr MCrAIY bond coat
    Show others...
    2016 (English)In: Proceedings of the International Thermal Spray Conference (ITSC), 2016, Vol. 324, p. 273-278Conference paper, Published paper (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs) were air-plasma sprayed onto Hastelloy X substrates. The TBCs consisted of a high-Cr MCrAlY (M for Ni and Co) bond coat and a yttria-stabilized zirconia (YSZ) top coat. The TBC samples were thermally cycled between 100 ºC and 1100 ºC with 1 hour dwell time at 1100 ºC. The thermal fatigue failure of the TBCs was investigated via microstructure analyses. The final fatigue failure of the TBCs was caused by the formation of interface-parallel cracks in the YSZ top coat. The formation of the cracks was found to be strongly related to the oxidation behaviour of the MCrAlY bond coat. The development of the oxide layers was therefore studied in detail. A thermokinetic model was also used to deepen the understanding on the elemental diffusion behavior in the materials.

    National Category
    Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials Materials Chemistry Composite Science and Engineering
    Identifiers
    urn:nbn:se:liu:diva-134377 (URN)
    Conference
    International Thermal Spray Conference (ITSC), May 10-12, 2016, China
    Available from: 2017-02-08 Created: 2017-02-08 Last updated: 2017-02-16Bibliographically approved
  • 173.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Li, X. -H.
    Siemens Ind Turbomachinery AB, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Factors Affecting the Performance of Thermal Barrier Coatings in the Presence of V2O5 and Na2SO42016In: JOURNAL OF CERAMIC SCIENCE AND TECHNOLOGY, ISSN 2190-9385, Vol. 7, no 4, p. 409-415Article in journal (Refereed)
    Abstract [en]

    This study investigates the influence of temperature, salt concentration and thickness on the corrosion resistance of seven YSZ thermal barrier coatings in the presence of V2O5 and Na2SO4. For this study, a thick, high-porosity APS coating (670 gm) using hollow spherical powder (HOSP) and a thin, low-porosity APS coating (300 pm) using agglomerated and sintered (Aamp;S) powder were fabricated. Corrosion tests were conducted at 750 degrees C and 900 degrees C with a mixture of Na2SO4 and V2O5 for four hours. At each temperature, salt concentrations of 4,10 and 20 mg/cm(2) were used. SEM and XRD investigations after the corrosion tests revealed that a combination of low temperature and high salt concentration resulted in higher corrosion-induced damage to the thin TBC coatings. With regard to the thick TBC coatings, all except one sample failed during the corrosion test. This suggests that thick TBC coatings with higher porosity may not be suitable in corrosive environments.

  • 174.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Beijing Gen Research Institute Min and Met, Peoples R China.
    Li, Xin-Hai
    Siemens Ind Turbomachineiy AB, Sweden.
    Ji, Xiaojuan
    Beijing Gen Research Institute Min and Met, Peoples R China.
    Yu, Yueguang
    Beijing Gen Research Institute Min and Met, Peoples R China.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    A study of damage evolution in high purity nano TBCs during thermal cycling: A fracture mechanics based modelling approach2017In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 37, no 8, p. 2889-2899Article in journal (Refereed)
    Abstract [en]

    This work concerns the study of damage evolution in a newly developed high purity nano 8YSZ thermal barrier coating during thermal cyclic fatigue tests (TCF). TCF tests were conducted between 100 degrees C-1100 degrees C with a hold time of 1 hat 1100 degrees C, first till failure and later for interrupted tests. Cross section analysis along the diameter of the interrupted test samples revealed a mixed-type failure and that the most of the damage occurred towards the end of the coatings life. To understand the most likely crack growth mechanism leading to failure, different crack growth paths have been modelled using finite element analysis. Crack growing from an existing defect in the top coat towards the top coat/TGO interface has been identified as the most likely mechanism. Estimated damage by the model could predict the rapid increase in the damage towards the end of the coatings life. (C) 2017 Elsevier Ltd. All rights reserved.

  • 175.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Beijing General Reseach Institute of Mining and Metallurgy, Beijing, China.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Ji, Xiaojuan
    Beijing General Research Institute of Mining and Metallurgy, Beijing, China.
    Yu, Yueguang
    Beijing General Research Institute of Mining and Metallurgy, Beijing, China.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Comparison of Damage Evolution During Thermal Cycling in a High Purity Nano and Conventional Thermal Barrier Coating2017In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 332, p. 47-56Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs), consisting of a ceramic top coat and a metallic bond coat, offer resistance against high temperature degradation of turbine components. Cyclic oxidation of the bond coat, thermal stresses due to their thermal mismatches during cyclic operations, and sintering of the top coat are considered to be the common ways by which thermal barrier coatings fail. To reduce sintering, a nano structured high purity yttria stabilized zirconia (YSZ) was developed. The focus of this work is to compare the damage development of such high purity nano YSZ TBC during thermal cycling with a conventional YSZ TBC. Thermal cyclic fatigue (TCF) tests were conducted on both the TBC systems between 100 °C and 1100 °C with a 1 h hold time at 1100 °C. TCF test results showed that conventional YSZ TBC exhibited much higher life compared to the high purity nano YSZ TBC. The difference in the lifetime is explained by the use of microstructural investigations, crack length measurements along the cross-section and the difference in the elastic modulus. Furthermore, stress intensity factors were calculated in order to understand the difference(s) in the damage development between the two TBC systems.

  • 176.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Li, Xin-Hai
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Corrosion Mechanism in Thermal Barrier Coatings During Exposure to a Gas Mixture of N2-CO-CO2-SO22017Conference paper (Refereed)
  • 177.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Mahade, Satyapal
    Department of Engineering ScienceUniversity West, Trollhättan, Sweden.
    Curry, Nicholas
    Treibacher Industrie AG, Althofen, Austria.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Markocsan, Nicolaie
    Department of Engineering Science University West, Trollhättan, Sweden.
    Nylén, Per
    Department of Engineering Science University West, Trollhättan, Sweden.
    Björklund, Stefan
    Department of Engineering Science University West, Trollhättan, Sweden.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    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, 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.

  • 178.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Li, Xin-Hai
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Yu, Yueguang
    Modeling the Diffusion of Minor Elements in Different MCrAlY-Superalloy Coating/Substrates at High Temperature2017In: The Minerals, Metals & Materials Series., 2017Conference paper (Refereed)
  • 179.
    Jonnalagadda, Krisha Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Beijing Gen Research Institute Min and Met, Peoples R China.
    Li, Xin-Hai
    Siemens Ind Turbomachinery AB, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Yu, Yueguang
    Beijing Gen Research Institute Min and Met, Peoples R China.
    Modeling the Diffusion of Minor Elements in Different MCrAlY-Superalloy Coating/Substrates at High Temperature2017In: ENERGY MATERIALS 2017, SPRINGER INT PUBLISHING AG , 2017, p. 251-263Conference paper (Refereed)
    Abstract [en]

    As demands of energy supply have been increased continuously and at the same time the uses of fossil fuel are limited and the greenhouse effect should be minimized, the gas turbine industries have been making efforts to increase gas turbine efficiency and to reduce emissions for power generations. One of the efforts is a continuous development of high temperature capacity of ceramic thermal barrier coatings (TBCs) and metallic MCrAlY overlays. The MCrAlY overlays are used as both protective coatings and bond coats to TBCs on underlying superalloy components in the gas turbines. During high temperature exposure, elemental diffusion occurs between the bond coat and the substrate which can affect the overall coating performance. The present study investigates the diffusion of minor elements like Re, Ta, Si, Mo and Ti in various MCrAlY overlays and superalloy substrates. An oxidation-diffusion model has been used to study the elemental diffusion. The diffusion process contains two stages: beta depletion stage and the b depleted stage. In the stage when MCrAlY overlays exhibit gamma + beta microstructure, the diffusion of minor elements in the coatings was observed to be related to the b depletion rate. After that the diffusion of the minor elements did not show any clear dependence on the coating composition. The development principle of the elemental diffusion is discussed in detail.

  • 180.
    Jonnalagadda, Krishna Praveen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Thermal Barrier Coatings: Failure Mechanisms and Life Prediction2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Thermal barrier coatings (TBCs) use in the hot sections of gas turbine engine enables them to run at higher temperatures, and as a consequence, achieve higher thermal efficiency. For full operational exploitation of TBCs, understanding their failure and knowing the service life is essential. The broad objective of the current research is to study the failure mechanisms of new TBC materials and deposition techniques during corrosion and thermal cycling and to develop life models capable of predicting the final failure during thermal cycling.

    Yttria-stabilized zirconia (YSZ) has constraints such as limited operation temperature, despite being the current industry standard. Pyrochlores of A2B2O7 type have been suggested as a potential replacement for YSZ and were studied in this work. Additionally, improvements to the conventional YSZ in the form of nanostructured YSZ were also explored. The requirement for the new deposition process comes from the fact that the existing low-cost deposition processes, like atmospheric plasma spray (APS), generally exhibit lower strain tolerance. A relatively new technique, suspension plasma spray (SPS), known to be promising with better strain tolerance, has been studied in this work.

    At the gas turbine operating conditions, TBCs degrade and eventually fail. Common failure observed in gas turbines can be due to corrosion, thermal mismatch between the ceramic and the metallic layers, and bond coat oxidation during thermal cycling. SPS and APS TBCs were subjected to different test conditions to understand their corrosion behavior. A study on the multi-layered SPS TBCs in the presence of V2O5+Na2SO4 showed that YSZ based SPS coatings were less susceptible to corrosion damage compared to Gd2Zr2O7 SPS TBCs. A study on the influence of a sealing layer in multi-layered SPS TBCs in the presence of Na2SO4+NaCl showed that the sealing layer is ineffective if the material used for sealing is inert to the molten salts. A new study on the influence of corrosion, caused by a mixed-gas atmosphere, on the thermal cycling fatigue life of SPS TBCs was conducted. Results showed that corrosive products grew inside the top coat close to the bond coat/top coat interface along with accelerated growth of alumina. These, together, reduced the TCF life of corrosion exposed samples significantly. Finally, a study on the influence of salt concentration and temperature on a thin (dense) and a thick (porous) coating showed that thick and porous coatings have lower corrosion resistance than the thin and dense coatings. Additionally, a combination of low temperature and high salt concentration was observed to cause more damage.

    Thermal cycling studies were done with the objective of understanding the failure mechanisms and developing a life model. A life model based on fracture mechanics approach has been developed by taking into account different crack growth paths during thermal cycling, sintering of the top coat, oxidation of the bond coat and the thermal mismatch stresses. Validation of such a life model by comparing to the experimental results showed that the model could predict the TCF life reasonably well at temperatures of 1100 °C or below. At higher temperatures, the accuracy of the model became worse. As a further development, a simplified crack growth model was established. This simplified model was shown to be capable of predicting the TCF life as well as the effect of hold times with good accuracy.

    List of papers
    1. Hot Corrosion Mechanism in Multi-Layer Suspension Plasma Sprayed Gd2Zr2O7 /YSZ Thermal Barrier Coatings in the Presence of V2O5 + Na2SO4
    Open this publication in new window or tab >>Hot Corrosion Mechanism in Multi-Layer Suspension Plasma Sprayed Gd2Zr2O7 /YSZ Thermal Barrier Coatings in the Presence of V2O5 + Na2SO4
    Show others...
    2017 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 26, no 1, p. 140-149Article in journal (Refereed) Published
    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.

    Place, publisher, year, edition, pages
    New York: Springer, 2017
    Keywords
    gadolinium zirconatehot corrosionmulti-layer thermal barrier coatingssuspension plasma sprayingvanadium pentoxide + sodium sulfate
    National Category
    Corrosion Engineering Manufacturing, Surface and Joining Technology Materials Chemistry
    Identifiers
    urn:nbn:se:liu:diva-134375 (URN)10.1007/s11666-016-0486-5 (DOI)000392060300014 ()
    Note

    Funding agencies: Vinnova in Sweden

    Available from: 2017-02-08 Created: 2017-02-08 Last updated: 2019-02-26Bibliographically approved
    2. Failure of Multilayer Suspension Plasma Sprayed Thermal Barrier Coatings in the Presence of Na2SO4 and NaCl at 900 °C
    Open this publication in new window or tab >>Failure of Multilayer Suspension Plasma Sprayed Thermal Barrier Coatings in the Presence of Na2SO4 and NaCl at 900 °C
    Show others...
    2019 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, no 1-2, p. 212-222Article in journal (Refereed) Published
    Abstract [en]

    The current investigation focuses on understanding the influence of a columnar microstructure and a sealing layer on the corrosion behavior of suspension plasma sprayed thermal barrier coatings (TBCs). Two different TBC systems were studied in this work. First is a double layer made of a composite of gadolinium zirconate + yttria stabilized zirconia (YSZ) deposited on top of YSZ. Second is a triple layer made of dense gadolinium zirconate deposited on top of gadolinium zirconate + YSZ over YSZ. Cyclic corrosion tests were conducted between 25 and 900 °C with an exposure time of 8 h at 900 °C. 75 wt.% Na2SO4 + 25 wt.% NaCl were used as the corrosive salts at a concentration of 6 mg/cm2. Scanning electron microscopy analysis of the samples’ cross sections showed that severe bond coat degradation had taken place for both the TBC systems, and the extent of bond coat degradation was relatively higher in the triple-layer system. It is believed that the sealing layer in the triple-layer system reduced the number of infiltration channels for the molten salts which resulted in overflowing of the salts to the sample edges and caused damage to develop relatively more from the edge.

    Keywords
    columnar microstructure, composite of gadolinium zirconate and YSZ, hot corrosion, suspension plasma spray
    National Category
    Manufacturing, Surface and Joining Technology
    Research subject
    ENGINEERING, Manufacturing and materials engineering; Production Technology
    Identifiers
    urn:nbn:se:liu:diva-154778 (URN)10.1007/s11666-018-0780-5 (DOI)000456599500019 ()2-s2.0-85055998259 (Scopus ID)
    Funder
    VINNOVA
    Note

    This article is an invited paper selected from presentations at the 2018 International Thermal Spray Conference, held May 7-10, 2018, in Orlando, Florida, USA, and has been expanded from the original presentation.

    Available from: 2018-11-06 Created: 2019-02-26 Last updated: 2019-02-26
    3. Factors Affecting the Performance of Thermal Barrier Coatings in the Presence of V2O5 and Na2SO4
    Open this publication in new window or tab >>Factors Affecting the Performance of Thermal Barrier Coatings in the Presence of V2O5 and Na2SO4
    Show others...
    2016 (English)In: JOURNAL OF CERAMIC SCIENCE AND TECHNOLOGY, ISSN 2190-9385, Vol. 7, no 4, p. 409-415Article in journal (Refereed) Published
    Abstract [en]

    This study investigates the influence of temperature, salt concentration and thickness on the corrosion resistance of seven YSZ thermal barrier coatings in the presence of V2O5 and Na2SO4. For this study, a thick, high-porosity APS coating (670 gm) using hollow spherical powder (HOSP) and a thin, low-porosity APS coating (300 pm) using agglomerated and sintered (Aamp;S) powder were fabricated. Corrosion tests were conducted at 750 degrees C and 900 degrees C with a mixture of Na2SO4 and V2O5 for four hours. At each temperature, salt concentrations of 4,10 and 20 mg/cm(2) were used. SEM and XRD investigations after the corrosion tests revealed that a combination of low temperature and high salt concentration resulted in higher corrosion-induced damage to the thin TBC coatings. With regard to the thick TBC coatings, all except one sample failed during the corrosion test. This suggests that thick TBC coatings with higher porosity may not be suitable in corrosive environments.

    Place, publisher, year, edition, pages
    GOLLER VERLAG GMBH, 2016
    Keywords
    HOSP; agglomerated and sintered YSZ; hot corrosion; TBC
    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:liu:diva-134310 (URN)10.4416/JCST2016-00058 (DOI)000391246300013 ()
    Note

    Funding Agencies|Vinnova, Sweden

    Available from: 2017-02-06 Created: 2017-02-03 Last updated: 2019-02-26Bibliographically approved
    4. A study of damage evolution in high purity nano TBCs during thermal cycling: A fracture mechanics based modelling approach
    Open this publication in new window or tab >>A study of damage evolution in high purity nano TBCs during thermal cycling: A fracture mechanics based modelling approach
    Show others...
    2017 (English)In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 37, no 8, p. 2889-2899Article in journal (Refereed) Published
    Abstract [en]

    This work concerns the study of damage evolution in a newly developed high purity nano 8YSZ thermal barrier coating during thermal cyclic fatigue tests (TCF). TCF tests were conducted between 100 degrees C-1100 degrees C with a hold time of 1 hat 1100 degrees C, first till failure and later for interrupted tests. Cross section analysis along the diameter of the interrupted test samples revealed a mixed-type failure and that the most of the damage occurred towards the end of the coatings life. To understand the most likely crack growth mechanism leading to failure, different crack growth paths have been modelled using finite element analysis. Crack growing from an existing defect in the top coat towards the top coat/TGO interface has been identified as the most likely mechanism. Estimated damage by the model could predict the rapid increase in the damage towards the end of the coatings life. (C) 2017 Elsevier Ltd. All rights reserved.

    Place, publisher, year, edition, pages
    ELSEVIER SCI LTD, 2017
    Keywords
    Thermal cyclic fatigue; High purity nano YSZ; Crack growth modelling; Damage evolution
    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:liu:diva-137827 (URN)10.1016/j.jeurceramsoc.2017.02.054 (DOI)000400531500015 ()
    Note

    Funding Agencies|Vinnova in Sweden

    Available from: 2017-06-02 Created: 2017-06-02 Last updated: 2019-02-26
    5. Comparison of Damage Evolution During Thermal Cycling in a High Purity Nano and Conventional Thermal Barrier Coating
    Open this publication in new window or tab >>Comparison of Damage Evolution During Thermal Cycling in a High Purity Nano and Conventional Thermal Barrier Coating
    Show others...
    2017 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 332, p. 47-56Article in journal (Refereed) Published
    Abstract [en]

    Thermal barrier coatings (TBCs), consisting of a ceramic top coat and a metallic bond coat, offer resistance against high temperature degradation of turbine components. Cyclic oxidation of the bond coat, thermal stresses due to their thermal mismatches during cyclic operations, and sintering of the top coat are considered to be the common ways by which thermal barrier coatings fail. To reduce sintering, a nano structured high purity yttria stabilized zirconia (YSZ) was developed. The focus of this work is to compare the damage development of such high purity nano YSZ TBC during thermal cycling with a conventional YSZ TBC. Thermal cyclic fatigue (TCF) tests were conducted on both the TBC systems between 100 °C and 1100 °C with a 1 h hold time at 1100 °C. TCF test results showed that conventional YSZ TBC exhibited much higher life compared to the high purity nano YSZ TBC. The difference in the lifetime is explained by the use of microstructural investigations, crack length measurements along the cross-section and the difference in the elastic modulus. Furthermore, stress intensity factors were calculated in order to understand the difference(s) in the damage development between the two TBC systems.

    Place, publisher, year, edition, pages
    Elsevier, 2017
    Keywords
    High purity nano, damage evolution, thermal cycling fatigue, crack length measurement, conventional TBC
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-142311 (URN)10.1016/j.surfcoat.2017.09.069 (DOI)000418968100007 ()2-s2.0-85030751243 (Scopus ID)
    Note

    Funding agencies: Vinnova in Sweden [2015-06870]

    Available from: 2017-10-25 Created: 2017-10-25 Last updated: 2019-02-26Bibliographically approved
    6. Thermal barrier coatings: Life model development and validation
    Open this publication in new window or tab >>Thermal barrier coatings: Life model development and validation
    2019 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 362, p. 293-301Article in journal (Refereed) Published
    Abstract [en]

    The failure of thermal barrier coatings (TBCs) during thermal cyclic fatigue (TCF) tests depends mainly on the thermal mismatch between the coating and the substrate, the thermally grown oxides (TGO) at the top coat-bond coat interface, and the sintering of the top coat. Understanding the interplay between these factors is essential for developing a life model. The present work focuses on further development of a previously established fracture mechanics based life model and its validation by comparing with the experimental results. The life model makes use of a Paris' law type equation to estimate the cycles to failure based on micro-crack growth. The fitting parameters for the Paris' law were obtained from the experimentally measured crack lengths after the interruption of TCF tests at different cycles. An alternative approach to obtain the fitting parameters through video monitoring was also discussed. It is shown that regardless of the approach to obtain the fitting parameters, the life model in its current form is able to predict the TCF life at different temperatures with reasonable accuracy. However, at very high temperatures (1150 °C) the predictive capabilities of the model appeared to be poor.

    Keywords
    Thermal barrier coatings, Thermal cyclic fatigue, Life modeling, Life prediction
    National Category
    Manufacturing, Surface and Joining Technology
    Identifiers
    urn:nbn:se:liu:diva-154779 (URN)10.1016/j.surfcoat.2019.01.117 (DOI)000461526400035 ()
    Note

    Funding agencies: VINNOVA in Sweden

    Available from: 2019-02-26 Created: 2019-02-26 Last updated: 2019-04-03
    7. Fatigue life prediction of thermal barrier coatings using a simplified crack growth model
    Open this publication in new window or tab >>Fatigue life prediction of thermal barrier coatings using a simplified crack growth model
    2019 (English)In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 39, no 5, p. 1869-1876Article in journal (Refereed) Published
    Abstract [en]

    Models that can predict the life of thermal barrier coatings (TBCs) during thermal cycling fatigue (TCF) tests are highly desirable. The present work focuses on developing and validating a simplified model based on the relation between the energy release rate and the TCF cycles to failure. The model accounts for stresses due to thermal mismatch, influence of sintering, and the growth of TGO (alumina and other non-protective oxides). The experimental investigation of TBCs included; 1) TCF tests at maximum temperatures of 1050 °C, 1100 °C, 1150 °C and a minimum temperature of 100 °C with 1 h and 5 h (1100 °C) hold times. 2) Isothermal oxidation tests at 900, 1000 and 1100 °C for times up to 8000 h. The model was calibrated and validated with the experimental results. It has been shown that the model is able to predict the TCF life and effect of hold time with good accuracy.

    Keywords
    Thermal barrier coatings, Thermal cycling fatigue, Life prediction model, Energy release rate
    National Category
    Manufacturing, Surface and Joining Technology
    Identifiers
    urn:nbn:se:liu:diva-154780 (URN)10.1016/j.jeurceramsoc.2018.12.046 (DOI)000459950700016 ()
    Note

    Funding agencies: Vinnova in Sweden

    Available from: 2019-02-26 Created: 2019-02-26 Last updated: 2019-03-20
  • 181.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Arts and Sciences.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, 61283, Finspång, Sweden.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Fatigue life prediction of thermal barrier coatings using a simplified crack growth model2019In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 39, no 5, p. 1869-1876Article in journal (Refereed)
    Abstract [en]

    Models that can predict the life of thermal barrier coatings (TBCs) during thermal cycling fatigue (TCF) tests are highly desirable. The present work focuses on developing and validating a simplified model based on the relation between the energy release rate and the TCF cycles to failure. The model accounts for stresses due to thermal mismatch, influence of sintering, and the growth of TGO (alumina and other non-protective oxides). The experimental investigation of TBCs included; 1) TCF tests at maximum temperatures of 1050 °C, 1100 °C, 1150 °C and a minimum temperature of 100 °C with 1 h and 5 h (1100 °C) hold times. 2) Isothermal oxidation tests at 900, 1000 and 1100 °C for times up to 8000 h. The model was calibrated and validated with the experimental results. It has been shown that the model is able to predict the TCF life and effect of hold time with good accuracy.

  • 182.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Arts and Sciences.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, 61283 Finspång, Sweden.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Thermal barrier coatings: Life model development and validation2019In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 362, p. 293-301Article in journal (Refereed)
    Abstract [en]

    The failure of thermal barrier coatings (TBCs) during thermal cyclic fatigue (TCF) tests depends mainly on the thermal mismatch between the coating and the substrate, the thermally grown oxides (TGO) at the top coat-bond coat interface, and the sintering of the top coat. Understanding the interplay between these factors is essential for developing a life model. The present work focuses on further development of a previously established fracture mechanics based life model and its validation by comparing with the experimental results. The life model makes use of a Paris' law type equation to estimate the cycles to failure based on micro-crack growth. The fitting parameters for the Paris' law were obtained from the experimentally measured crack lengths after the interruption of TCF tests at different cycles. An alternative approach to obtain the fitting parameters through video monitoring was also discussed. It is shown that regardless of the approach to obtain the fitting parameters, the life model in its current form is able to predict the TCF life at different temperatures with reasonable accuracy. However, at very high temperatures (1150 °C) the predictive capabilities of the model appeared to be poor.

  • 183.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Mahade, Satyapal
    Department of Engineering Science, University West, Trollhättan, Sweden.
    Kramer, Stephanie
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Zhang, Pimin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Curry, Nicholas
    Treibacher Industrie AG, Althofen, Austria.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Failure of Multilayer Suspension Plasma Sprayed Thermal Barrier Coatings in the Presence of Na2SO4 and NaCl at 900 degrees C2019In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, no 1-2, p. 212-222Article in journal (Refereed)
    Abstract [en]

    The current investigation focuses on understanding the influence of a columnar microstructure and a sealing layer on the corrosion behavior of suspension plasma sprayed thermal barrier coatings (TBCs). Two different TBC systems were studied in this work. First is a double layer made of a composite of gadolinium zirconate+yttria stabilized zirconia (YSZ) deposited on top of YSZ. Second is a triple layer made of dense gadolinium zirconate deposited on top of gadolinium zirconate+YSZ over YSZ. Cyclic corrosion tests were conducted between 25 and 900 degrees C with an exposure time of 8h at 900 degrees C. 75wt.% Na2SO4+25wt.% NaCl were used as the corrosive salts at a concentration of 6mg/cm(2). Scanning electron microscopy analysis of the samples cross sections showed that severe bond coat degradation had taken place for both the TBC systems, and the extent of bond coat degradation was relatively higher in the triple-layer system. It is believed that the sealing layer in the triple-layer system reduced the number of infiltration channels for the molten salts which resulted in overflowing of the salts to the sample edges and caused damage to develop relatively more from the edge.

  • 184.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Management and Engineering, Linköping, Sweden.
    Mahade, Satyapal
    Högskolan Väst, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT).
    Kramer, Stephanie
    Linköping University, Department of Management and Engineering. Linköping University, Faculty of Science & Engineering.
    Zhang, Pimin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Curry, Nicholas
    Treibacher Industrie AG, Althofen, Austria.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB,Finspång,Sweden.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Failure of Multilayer Suspension Plasma Sprayed Thermal Barrier Coatings in the Presence of Na2SO4 and NaCl at 900 °C2019In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, no 1-2, p. 212-222Article in journal (Refereed)
    Abstract [en]

    The current investigation focuses on understanding the influence of a columnar microstructure and a sealing layer on the corrosion behavior of suspension plasma sprayed thermal barrier coatings (TBCs). Two different TBC systems were studied in this work. First is a double layer made of a composite of gadolinium zirconate + yttria stabilized zirconia (YSZ) deposited on top of YSZ. Second is a triple layer made of dense gadolinium zirconate deposited on top of gadolinium zirconate + YSZ over YSZ. Cyclic corrosion tests were conducted between 25 and 900 °C with an exposure time of 8 h at 900 °C. 75 wt.% Na2SO4 + 25 wt.% NaCl were used as the corrosive salts at a concentration of 6 mg/cm2. Scanning electron microscopy analysis of the samples’ cross sections showed that severe bond coat degradation had taken place for both the TBC systems, and the extent of bond coat degradation was relatively higher in the triple-layer system. It is believed that the sealing layer in the triple-layer system reduced the number of infiltration channels for the molten salts which resulted in overflowing of the salts to the sample edges and caused damage to develop relatively more from the edge.

  • 185.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Beijing Gen Res Inst Min and Met, Peoples R China.
    Li, Xin-Hai
    Siemens Ind Turbomachinery AB, Sweden.
    Ji, Xiaojuan
    Beijing Gen Res Inst Min and Met, Peoples R China.
    Yu, Yueguang
    Beijing Gen Res Inst Min and Met, Peoples R China.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Influence of Top Coat and Bond Coat Pre-Oxidation on the Corrosion Resistance of Thermal Barrier Coatings in the Presence of SO22018In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBOMACHINERY TECHNICAL CONFERENCE AND EXPOSITION, 2018, VOL 6, AMER SOC MECHANICAL ENGINEERS , 2018, article id V006T24A018Conference paper (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs) degradation due to corrosion is one of the commonly observed failure types in land-based gas turbines due to the usage of low grade fuels. Sulfur in its gaseous form, as SO2, can attack the TBC system and result in the degradation of both the coating and the turbine component. The present study aims to understand the difference in the corrosion induced damage caused by SO2 gas mixture in different coating architectures. Corrosion tests were conducted at 780 degrees C in a tube furnace for a period of 168h. The inlet test gas had a composition of 1SO(2)-0.1CO-20CO(2)-N-2 (bal.) in vol. %. The coating architectures consisted of 1) an overlay coating, 2) a single-side bond coat TBC, 3) an all-side bond coat TBC, 4) an all-side bond coat TBC subjected to pre-oxidation prior to the corrosion tests. The results from the corrosion tests showed that the damage was the most severe for the overlay followed by single-side bond coat TBC. Between the other two systems, the TBC subjected to pre-oxidation had relatively lower corrosion damage. The corrosion damage started from the edges for the overlay and single-side bond coat TBC and as well as through the penetration of the gas through the coating. For the coatings with bond coat on all sides, the edge damage appeared to be considerably reduced and the damage is predominantly through the gas infiltration.

  • 186.
    Jonnalagadda, Krishna Praveen
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Zhang, Pimin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Gupta, Mohit
    Department of Engineering Science, University West, Trollhättan.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Hot gas corrosion and its influence on the thermal cycling performance of suspension plasma spray TBCs2019In: Proceedings of ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition, New York, NY: American Society of Mechanical Engineers , 2019Conference paper (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs) manufactured with suspension plasma spray (SPS) are promising candidates for use in gas turbines due to their high strain tolerance during thermal cyclic fatigue (TCF). However, corrosion often occurs alongside thermal fatigue and coating durability under these conditions is highly desirable. The current study focuses on understanding the corrosion behavior and its influence on the thermal cyclic fatigue life of SPS TBCs. Corrosion tests were conducted at 780 OC using a mixed-gas (1SO2-0.1CO-20CO2-N2(bal.) in vol. %) for 168h. They were later thermally cycled between 100-1100 ⁰C with a 1h hold time at 1100 ⁰C. Corrosion test results indicated that the damage predominantly started from the edges and a milder damage was observed at the center. Nickel sulfide was observed on top of the top coat and also in the columnar gaps of the top coat. Chromium oxides were observed inside the top coat columnar gaps but close to the bond coat/top coat interface. They were believed to reduce the strain tolerance of SPS TBCs to an extent and also amplify the thermal mismatch stresses during TCF tests. This, together with a fast growth of alumina during the TCF, resulted in a significant drop in the TCF life compared to the standard TCF tests.

  • 187.
    Kahl, S.
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sapa Technology, Sweden.
    Osikowicz, W.
    Sapa Technology, Sweden.
    Composite Aluminum-Copper Sheet Material by Friction Stir Welding and Cold Rolling2013In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 22, no 8, p. 2176-2184Article in journal (Refereed)
    Abstract [en]

    An aluminum alloy and a pure copper material were butt-joined by friction stir welding and subsequently cold rolled. The cold-rolling operation proved to be very advantageous because small voids present after friction stir welding were closed, the interface area per material thickness was enlarged, a thin intermetallic layer was partitioned, and the joint was strengthened by strain hardening. Tensile test specimens fractured in the heat-affected zone in the aluminum material; tensile strengths of the joints exceeded the tensile strengths of the base materials and were as high as 335 MPa. During soft annealing of the composite material, a 6-8-μm-thick intermetallic layer was grown at the interface. Nevertheless, tensile fracture still occurred in the heat-affected zone of the aluminum material. Electrical resistivity of the joint was smaller than resistivity of the aluminum material. Production of such composite material would result in coiled sheet material that could be subjected to further treatments such as electroplating and forming operations in an efficient and economically viable manner. The new composite material is promising for emerging automotive and industrial electrical applications.

  • 188.
    Kahl, Sören
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sapa Heat Transfer Technology, Finspång, Sweden .
    Ekström, Hans-Erik
    Sapa Technology, Finspång, Sweden .
    Mendoza, Jesus
    Sapa Technology, Finspång, Sweden .
    Tensile, Fatigue and Creep Properties of Aluminum Heat Exhanger Tube Alloys for Temperatures from 293 K to 573 K (20°C to 300°C)2014In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, ISSN 1073-5623, Vol. 45A, no 2, p. 663-681Article in journal (Refereed)
    Abstract [en]

    Since automotive heat exchangers are operated at varying temperatures and under varying pressures, both static and dynamic mechanical properties should be known at different temperatures. Tubes are the most critical part of the most heat exchangers made from aluminum brazing sheet. We present tensile test, stress amplitude-fatigue life, and creep–rupture data of six AA3XXX series tube alloys after simulated brazing for temperatures ranging from 293 K to 573 K (20 °C to 300 °C). While correlations between several mechanical properties are strong, ranking of alloys according to one property cannot be safely deduced from the known ranking according to another property. The relative reduction in creep strength with increasing temperature is very similar for all six alloys, but the general trends are also strong with respect to tensile and fatigue properties; an exception is one alloy that exhibits strong Mg-Si precipitation activity during fatigue testing at elevated temperatures. Interrupted fatigue tests indicated that the crack growth time is negligible compared to the crack initiation time. Fatigue lifetimes are reduced by creep processes for temperatures above approximately 423 K (150 °C). When mechanical properties were measured at several temperatures, interpolation to other temperatures within the same temperature range was possible in most cases, using simple and well-established equations.

  • 189.
    Kahl, Sören
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Gränges Technology, Gränges AB, Finspång, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Calmunger, Mattias
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Olsson, Björn
    Sapa Technology, Sapa AB, Finspång, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    In Situ EBSD During Tensile Test of Aluminum AA3003 Sheet2014In: Micron, ISSN 0968-4328, E-ISSN 1878-4291, ISSN 0968-4328, Vol. 58, p. 15-24Article in journal (Refereed)
    Abstract [en]

    Miniature tensile-test specimens of soft-annealed, weakly textured AA3003 aluminum sheet in 0.9 mm thickness were deformed until fracture inside a scanning electron microscope. Tensile strength measured by the miniature tensile test stage agreed well with the tensile strength by regular tensile testing. Strain over the microscope field of view was determined from changes in positions of constituent particles. Slip lines were visible in secondary electron images already at 0.3% strain; activity from secondary slip systems became apparent at 2% strain. Orientation rotation behavior of the tensile load axis with respect to the crystallographic axes agreed well with previously reported trends for other aluminum alloys. Start of the fracture and tensile crack propagation were documented in secondary electron images. The region of fracture nucleation included and was surrounded by many grains that possessed high Schmid factors at zero strain. Crystal lattice rotation angles in the grains surrounding the initial fracture zone were higher than average while rotations inside the initial fracture zone were lower than average for strains from zero to 31%. The orientation rotation behavior of the tensile load axes of the grains around the fracture zone deviated from the average behavior in this material.

  • 190.
    Kahl, Sören
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Gränges Technology, Gränges AB, Finspång.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Tensile Failure of Thin Aluminium Sheet Observed by In-Situ EBSD2015In: 17TH INTERNATIONAL CONFERENCE ON TEXTURES OF MATERIALS (ICOTOM 17), IOP Publishing , 2015, Vol. 82Conference paper (Refereed)
    Abstract [en]

    Tensile tests on two similar 75-μm-thick aluminium sheet materials were carried out inside a scanning electron microscope equipped with an electron backscatter detector. The materials were subjected to simulated brazing prior to the test because this type of material is used for fins in automotive heat exchangers. Grain sizes were large relative to sheet thickness and ND-rotated cube and P texture components dominated the recrystallization textures; their volume fractions differed strongly in the two different materials, though. Strains over the microscope image fields were determined from positions of constituent particles or from grain sizes; the two methods gave consistent results. Grains with high Schmid factors accumulated significantly more deformation than grains with low Schmid factors. Cracks nucleated in high-Schmid factor grains, or in groups of such grains, at the specimen edges. When only low-Schmid factor grains were present at the specimen edges, the crack nucleated inside the specimen. The subsequent crack growth was intragranular and occurred at approximately 90° relative to the load direction.

  • 191.
    Kahl, Sören
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Zajac, Jozefa
    Sapa Technology, Finspång.
    Ekström, Hans-Erik
    Sapa Technology, Finspång.
    Mechanical Properties of Heat Exchanger Tube Materials at Elevated Temperatures2012Conference paper (Other academic)
  • 192.
    Kahlin, Magnus
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Saab AB, Aeronaut, SE-58188 Linkoping, Sweden.
    Ansell, Hans
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering. Saab AB, Aeronaut, SE-58188 Linkoping, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Fatigue behaviour of additive manufactured Ti6Al4V, with as-built surfaces, exposed to variable amplitude loading2017In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 103, p. 353-362Article in journal (Refereed)
    Abstract [en]

    Additive Manufacturing (AM) allows for great design freedom compared to conventional manufacturing. This is very attractive for the aerospace industry in which AM could contribute to lightweight designs and thereby reduce fuel consumption, increase payload and extend flight range. The fatigue behaviour for rough as-built AM surfaces has previously been characterized with constant amplitude testing but in aerospace applications, most parts are exposed to variable amplitude loading. The fatigue behaviour for variable amplitude is not always consistent with the behaviour for constant amplitude due to effects of overloads and local plastic deformations. Therefore, variable amplitude loading behaviour of laser sintered and electron beam melted Ti6Al4V, with rough as-built surfaces have been investigated in this study using the Short-FALSTAFF (Fighter Aircraft Loading STAndard For Fatigue) load sequence. The predicted and the experimental fatigue life was overall consistent even though most experimental results exceeded the predicted life, especially for the laser sintered material. These findings show that conventional cumulative damage fatigue life predictions give reliable predictions for AM materials with rough as-built surfaces for the type of tension dominated load sequence used. (C) 2017 Elsevier Ltd. All rights reserved.

  • 193.
    Kahlin, Magnus
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials.
    Ansell, Hans
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Fatigue Behaviour of Notched Additive Manufactured Ti6Al4V with As-built Surfaces2017In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, no 101, p. 51-60Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing (AM) allows the manufacturer to produce parts with complex geometries that are difficult to produce with conventional production methods. Generally, AM is considered to have great potential for the aerospace industry by contributing to reduced weight and lower costs. There are a number of challenges to be solved before AM can be fully utilized in the aerospace industry, and the understanding of fatigue behaviour is one of the major challenges. Although the fatigue properties of flat additive manufactured specimens with rough as-built surfaces already have been widely studied, in practice, few aerospace components have a simple flat geometry with no corners or radii that would act as stress concentrations. Therefore, the combined effect on fatigue life of a rough as-built surface and a geometrical notch needs to be established. In this study, the fatigue properties of both laser sintered and electron beam melted Ti6Al4V have been investigated and a combined effect of a rough as-built surface and a geometrical notch has been determined. In addition, hot isostatic pressing was found to have no impact on fatigue life for rough as-built surfaces. These findings can be directly applied to predict fatigue behaviour of an AM industrial component.

  • 194.
    Kahlin, Magnus
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Saab AB, Aeronautics, Linköping.
    Sjögren, Torsten
    RISE - Research Institutes of Sweden, Borås, Sweden.
    Ansell, Hans
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering. Saab AB, Aeronautics, Linköping.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Thickness Dependent Fatigue Properties of Additive Manufactured Ti6Al4V with As-Built Surface2017Conference paper (Refereed)
  • 195.
    Kanesund, Jan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Brodin, Håkan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Siemens Ind Turbomachinery AB, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Hot corrosion influence on deformation and damage mechanisms in turbine blades made of IN-792 during service2019In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 96, p. 118-129Article in journal (Refereed)
    Abstract [en]

    The deformation and damage mechanisms of a gamma-prime hardened superalloy is investigated in the current paper. Two turbine blades made of precision cast polycrystalline superalloy IN-792 have been examined after service exposure under engine conditions typical for industrial gas turbines. This study is compared to a previous study with focus on deformation and damage mechanisms in IN-792 during thermal mechanical fatigue testing performed under laboratory conditions. The failure of the two turbine blades is explained as a combination of two damage mechanisms, mechanical and chemical damage. In the current investigation, type I hot corrosion and creep are the two dominant damage mechanisms. The type I hot corrosion is confirmed by the presence of Ti-sulfides and sulfur in free form at the grain boundaries, which has caused embrittlement and loss of resistance to crack growth. In turn, this has shortened the turbine blade life dramatically and intercrystalline failure is the dominant damage mechanism. Almost all cracks have propagated intercrystalline in the two turbine blades. In the previous study, mechanical damage mechanism is the dominant mechanism and for the highest temperature also oxidation give is contribution. In the previous study, almost all cracks propagated transcrystalline. When exposed to laboratory conditions, the areas around cracks are more plastically deformed compared to the area around the cracks in the turbine blades. In the two studies, dynamic recrystallization has occurred at the grain boundaries.

  • 196.
    Kanesund, Jan
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    A Study of the Influence of Plastic Pre Strain in Different Directions Before Ageing of Extruded and Hydro Formed Material on the Mechanical Properties of AA60632012Conference paper (Refereed)
  • 197.
    Kanesund, Jan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Deformation and damage mechanisms in IN792 during thermomechanical fatigue2011In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 528, no 13-14, p. 4658-4668Article in journal (Refereed)
    Abstract [en]

    The deformation and damage mechanisms arising during thermomechanical fatigue (TMF) of the polycrystallinesuperalloy IN792 have been investigated. The TMF cycles used in this study are in-phase(IP) and out-of-phase (OP). The minimum temperature used in all TMF-tests is 100 ◦C while the maximumtemperature is 500 or 750 ◦C in the IP TMF-tests and 750, 850 or 950 ◦C in the OP TMF-tests. Themajority of the cracks are transcrystalline, except for the IP TMF-test at 750 ◦C, where some tendencyto intercrystalline crack growth can be seen. In all tests, the cracks were initiated and propagated inlocations where deformation structures such as deformation bands have formed in the material. In thetemperature interval 750–850 ◦C, twins were formed in both IP and OP TMF-tests and this behaviouris observed to be further enhanced close to a crack. Twins are to a significantly lesser extent observedfor tests with a lower (500 ◦C) and a higher (950 ◦C) maximum temperature. Recrystallization at grainboundaries, around particles and within the deformation structures have occurred in the OP TMF-testswith a maximum temperature of 850 and 950 ◦C and this is more apparent for the higher temperature.Void formation is frequently observed in the recrystallized areas even for the case of compressive stressesat high temperature.

  • 198.
    Kanesund, Jan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    The Deformation and Damage Mechanisms During Thermomechanical Fatigue (TMF) in IN7922011In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 10, p. 189-194Article in journal (Refereed)
    Abstract [en]

    The deformation and damage mechanisms arising during thermomechanical fatigue (TMF) of the polycrystalline superalloy IN792 have been investigated. The TMF cycles used in this study are in-phase (IP) and out-of-phase (OP). The minimum temperature used in all TMF-tests is 100 °C while the maximum temperature is 750 °C in the IP TMF-tests and 850° or 950 °C in the OP TMF-tests. Most cracks have propagated transgranularly through the material and this holds for all temperatures used in this study. In all tests, the cracks have initiated and propagated in locations where deformation structures such as deformation bands have formed in the material. In the temperature interval 750°-850 °C, twins are formed in both IP and OP TMF-tests and this behaviour is observed to be further enhanced close to a crack. Twins are to a significantly lesser extent observed for tests with a higher (950 °C) maximum temperature. Recrystallization at grain boundaries, around particles and within the deformation structures have occurred in the OP TMF-tests with a maximum temperature of 850° and 950 °C and this is more apparent for the higher temperature.

  • 199.
    Kangas, Pasi
    et al.
    Sandvik Materials Technology, Sandviken.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Duplex Stainless Steels for Oil & Gas Applications2016Conference paper (Refereed)
  • 200.
    Kaouache, Belkhiri
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials.
    Bäckström, Daniel
    Ahmad, Maqsood
    Vuoristo, Taina
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    To Increase Fatigue Strength of Grey Iron By Shot Peening2015Conference paper (Refereed)
1234567 151 - 200 of 427
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