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  • 301.
    Polák, Jaroslav
    et al.
    Institute of Physics of Materials, Academy of Sciences of Czech Republic, Brno.
    Petrás, Roman
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Skorik, Viktor
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Surface Profile Evolution adn Fatigue Crack Initiation in Sanicro 25 Steel at Room Temperature2016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 658, p. 221-228Article in journal (Refereed)
    Abstract [en]

    Evolution of the surface profile in room temperature cyclic loading has been studied in high alloy austenitic Sanicro 25 stainless steel. The localization of the cyclic plastic strain into persistent slip bands in the volume of the material leads to the formation of the specific surface relief in the form of persistent slip markings (PSMs) consisting of extrusions and intrusions. Evolution of the shape of PSMs was studied during interruption of cycling using SEM and FIB techniques. Three-dimensional information about the PSMs profiles was obtained. The profiles of both extrusions and intrusions and their evolution during cyclic loading were assessed. Generally extrusions grow, intrusions deepen and fatigue cracks initiate from the tip of the deepest intrusions. The experimental observations were compared and discussed in relation to existing physical models of surface relief formation and fatigue crack initiation.

  • 302.
    Polák, Jaroslav
    et al.
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno, Czech Republic.
    Petrás, Roman
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno, Czech Republic.
    Heczko, Milan
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno, Czech Republic.
    Kruml, Tomás
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno, Czech Republic.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
    Analysis of Cyclic Plastic Response of Heat Resistant Sanicro 25 Steel at Ambient and Elevated Temperatures2014In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, no 74, p. 68-73Article in journal (Refereed)
    Abstract [en]

    Austenitic heat resistant steel Sanicro 25 developed for high temperature applications in power generation industry has been subjected to selected low cycle fatigue tests at ambient and at elevated temperature. Saturated hysteresis loops at both temperatures were analyzed to deduce the probability density distribution of the internal critical stresses and to estimate the contribution of the effective stress for different strain amplitudes. The internal structure of the material at room and elevated temperature was studied using transmission electron microscopy and the results were discussed in relation to the cyclic stress- strain response

  • 303.
    Polák, Jaroslav
    et al.
    Institute of Physics of Materials, Academy of Sicences of Czech Republic, Brno.
    Petrás, Roman
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Heczko, Milan
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Kruml, Tomás
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Sandvik Materials Technology, Sandviken, Sweden.
    Evolution of the Cyclic Plastic Response of Sanicro 25 Steel Cycled at Ambient and Elevated Temperatures2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 83, no 1, p. 75-83Article in journal (Refereed)
    Abstract [en]

    Cyclic plastic response of the austenitic heat resistant steel Sanicro 25 has been studied during strain controlled low cycle fatigue tests performed at ambient and at elevated temperature. Simultaneously with the cyclic hardening/softening curves hysteresis loops during cyclic loading were analyzed using generalized statistical theory of the hysteresis loop. The probability density distribution function of the internal critical stresses, the effective saturated stress and their evolution during cycling were derived for various strain amplitudes. The internal dislocation structure and the surface relief at room and at elevated temperature were studied and correlated with the cyclic stress–strain response and the evolution of the probability density function of the internal critical stresses.

  • 304. Polák, Jaroslav
    et al.
    Petrás, Romas
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Heczko, Milan
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Kubena, Ivo
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Kruml, Tomás
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Low Cycle Fatigue Behavior of Sanicro25 Steel at Room and at Elevated Temperature2014In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 615, p. 175-182Article in journal (Refereed)
    Abstract [en]

    Austenitic heat resistant Sanicro 25 steel developed for high temperature applications in power generation industry has been subjected to strain controlled low cycle fatigue tests at ambient and at elevated temperature in a wide interval of strain amplitudes. Fatigue hardening/softening curves, cyclic stress–strain curves and fatigue life curves were evaluated at room temperature and at 700 °C. The internal dislocation structures of the material at room and at elevated temperature were studied using transmission electron microscopy. High resolution surface observations and FIB cuts revealed early damage at room temperature in the form of persistent slip bands and at elevated temperature as oxidized grain boundary cracks. Dislocation arrangement study and surface observations were used to identify the cyclic slip localization and to discuss the fatigue softening/hardening behavior and the temperature dependence of the fatigue life.

  • 305.
    Reed, Roger
    et al.
    Dept of Metallurgy and Materials, University of Birmingham, UK.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sato, Atsushi
    Dept of Metallurgy and Materials, University in Birmingham, UK.
    Karlsson, Fredrik
    Siemens Industrial Turbomachinery AB Materials Technology, Finspång.
    Hasselqvist, Magnus
    Siemens Industrial Turbomachinery, Finspång.
    A New Single Crystal Superalloy for Power Generation Applications2012In: Superalloys 2012: 12:th International Symposium on Superalloys / [ed] E.S. Huron et al, The Minerals, Metals, and Materials Society, 2012, p. 197-204Conference paper (Refereed)
    Abstract [en]

    The properties of a newly developed single crystal super alloy-known as STAL-15 - is described which is suitable for use in first stage blades of industrial gas turbines (IGTs). With 15 wt.% Cr and 4.55 wt.% Al, the alloy combines good corrosion and oxidation resistance with sufficient creep and fatigue performance. Traditionally, polycrystalline alloys such as IN792 and 1N738LC or the single crystal alloy PWA-1483 have been used for this application; unfortunately they display only limited resistance to environmental degradation. The new alloy does not display this weakness and is therefore highly optimised for IGT applications. The new alloy is shown to be an alumina (Al2O3) former; the mechanisms behind the Al 2O3-formation process are studied and the effects arising from changes in the chemical composition have been modelled. In addition, the mechanical properties in terms of creep and fatigue resistance are demonstrated together and the alloy stability evaluated during long term (up to 10,000 hours) exposure. For such applications, the new alloy is superior to existing nickel-based single crystal superalloys designed for aeroengine applications and which are optimised for very high creep resistance. The absence of Re contributes to a lower cost of alloy stock, and enhanced castability.

  • 306.
    Saarimäki, Jonas
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Cracks in superalloys2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Gas turbines are widely used in industry for power generation and as a power source at hard to reach locations where other possibilities for electrical power supplies are insufficient. New ways of producing greener energy is needed to reduce emission levels. This can be achieved by increasing the combustion temperature of gas turbines. High combustion temperatures can be detrimental and degrade critical components. This raises the demands on the high temperature performance of the superalloys used in gas turbine components. These components are frequently subjected to different cyclic loads combined with for example dwell-times and overloads at elevated temperatures, which can influence the crack growth. Dwell-times have been shown to accelerate crack growth and change cracking behaviour in both Inconel 718, Haynes 282 and Hastelloy X. On the other hand, overloads at the beginning of a dwell-time cycle have been shown to retard the dwell-time effect on crack growth in Inconel 718. More experiments and microstructural investigations are needed to better understand these effects.

    The work presented in this thesis was conducted under the umbrella of the research program Turbo Power; "High temperature fatigue crack propagation in nickel-based superalloys", where I have mainly looked at fatigue crack growth mechanisms in superalloys subjected to dwell-fatigue, which can have a devastating effect on crack propagation behaviour. Mechanical testing was performed under operation-like cycles in order to achieve representative microstructures and material data for the subsequent microstructural work. Microstructures were investigated using light optical microscopy and scanning electron microscopy (SEM) techniques such as electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD). 

    The outcome of this work has shown that there is a significant increase in crack growth rate when dwell-times are introduced at maximum load (0 % overload) in the fatigue cycle. With the introduction of a dwell-time there is also a shift from transgranular to intergranular crack growth for both Inconel 718 and Haynes 282. The crack growth rate decreases with increasing overload levels in Inconel 718 when an overload is applied prior to the dwell-time. At high temperature, intergranular crack growth was observed in Inconel 718 as a result of oxidation and the creation of nanometric voids. Another observed growth mechanism was crack advance along δ-phase boundaries with subsequent oxidation of the δ-phase. 

    This thesis comprises two parts. Part I gives an introduction to the field of superalloys and the acting microstructural mechanisms related to fatigue and crack propagation. Part II consists of five appended papers, which report the work completed as part of the project.

    List of papers
    1. Influence of Overloads on Dwell Time Fatigue Crack Growth in Inconel 718
    Open this publication in new window or tab >>Influence of Overloads on Dwell Time Fatigue Crack Growth in Inconel 718
    2014 (English)In: Materials Science and Engineering: A, Vol. 612, p. 398-405Article in journal (Refereed) Published
    Abstract [en]

    Inconel 718 is one of the most commonly used superalloys for high temperature applications in gasturbines and aeroengines and is for example used for components such as turbine discs. Turbine discs can be subjected to temperatures up to ~700 °C towards the outer radius of the disc. During service, the discs might start to develop cracks due to fatigue and long dwell times. Additionally, temperature variations during use can lead to large thermal transients during start-up and shutdown which can lead to overload peaks in the normal dwell time cycle. In this study, tests at 550 °C with an overload prior to the start of each dwell time, have been performed. The aim of the investigation was to get a better understanding of the effects of overloads on the microstructure and crack mechanisms. The microstructure was studied using electron channelling contrast imaging (ECCI). The image analysis toolbox in Matlab was used on cross sections of the cracks to quantify: crack length, branch length, and the number of branches in each crack. It was found that the amount of crack branching increases with an increasing overload and that the branch length decreases with an increasing overload. When the higher overloads were applied, the dwell time effect was almost cancelled out. There is a strong tendency for an increased roughness of the crack path with an increasing crack growth rate.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    Keywords
    nickel based superalloys, fatigue, fracture, mechanical charcterization, electron microscopy
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-109348 (URN)10.1016/j.msea.2014.06.068 (DOI)000340331300049 ()
    Available from: 2014-08-14 Created: 2014-08-14 Last updated: 2018-01-18Bibliographically approved
    2. Time- and Cycle-Dependent Crack Propagation in Haynes 282
    Open this publication in new window or tab >>Time- and Cycle-Dependent Crack Propagation in Haynes 282
    2016 (English)In: Journal of Materials Science and Engineering: A, ISSN 2161-6213, Vol. 658, p. 463-471Article in journal (Refereed) Published
    Abstract [en]

    Haynes 282 is a promising superalloy candidate for several high-temperature applications in both aero and land-based gas turbine engines. To study the crack growth behaviour under time-dependent conditions relevant to such applications, a test program was carried out at room temperature up to 700 °C with conditions ranging from pure cyclic to sustained tensile loading. At 650 °C and high stress intensity factors the crack growth was fully time-dependent for dwell-times of 90 s and longer. At lower stress intensities, the behaviour was mainly controlled by the cyclic loading, even under dwell conditions. The behaviour under dwell-fatigue conditions was well described by a liner superposition model.

    Place, publisher, year, edition, pages
    Elsevier, 2016
    Keywords
    Nickel based superalloys, fatigue, fracture, mechanical characterisation, electron microscopy
    National Category
    Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-126922 (URN)10.1016/j.msea.2016.01.111 (DOI)000372560800054 ()
    Note

    At the time for thesis presentation publication was in status: Manuscript

    Name of manuscript was: Time-dependent crack propagation in Haynes 282

    Funding agencies: Agora Materiae, graduate school, Faculty grant SFO-MAT-LiU [2009-00971]; Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through the Swedish research program TURBO POWER

    Available from: 2016-04-07 Created: 2016-04-07 Last updated: 2018-01-18Bibliographically approved
    3. Anisotropy Effects During Dwell-fatigue Caused by δ-phase Orientation in Forged Inconel 718
    Open this publication in new window or tab >>Anisotropy Effects During Dwell-fatigue Caused by δ-phase Orientation in Forged Inconel 718
    2017 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, no 692, p. 174-181Article in journal (Refereed) Published
    Abstract [en]

    Inconel 718 is a commonly used superalloy for turbine discs in the gas turbine industry. Turbine discs are often subjected to dwell-fatigue as a result of long constant load cycles. The effect of anisotropy on dwell-fatigue cracking in forged turbine discs have not yet been thoroughly investigated. Crack propagation behaviour was characterised using compact tension (CT) samples cut in different orientations from a real turbine disc forging. Samples were also cut in two different thicknesses in order to investigate the influence of plane strain and plane stress condition on the crack propagation rates. The samples were subjected to dwell-fatigue tests at 550 °C with 90 s or 2160 s dwell-times at maximum load. Microstructure characterisation was done using scanning electron microscopy (SEM) techniques such as electron channelling contrast imaging (ECCI), electron backscatter diffraction (EBSD), and light optical microscopy (LOM). The forged alloy exhibits strong anisotropic behaviour caused by the non-random δ-phase orientation. When δ-phases were oriented perpendicular compared to parallel to the loading direction, the crack growth rates were approximately ten times faster. Crack growth occurred preferably in the interface between the γ-matrix and the δ-phase.

    Place, publisher, year, edition, pages
    Elsevier, 2017
    Keywords
    Anisotropy, Nickel-based superalloys, Fatigue, Mechanical characterisation, Scanning electron microscopy
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-135825 (URN)10.1016/j.msea.2017.03.063 (DOI)000400718400021 ()
    Note

    Funding agencies: Agora Materiae, graduate school, Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU 2009-00971]; Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Sy

    Available from: 2017-03-24 Created: 2017-03-24 Last updated: 2018-01-18
    4. Grain Size Depending Dwell-Fatigue Crack Growth in Inconel 718
    Open this publication in new window or tab >>Grain Size Depending Dwell-Fatigue Crack Growth in Inconel 718
    2018 (English)In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, article id 1700930Article in journal (Refereed) Published
    Abstract [en]

    Inconel 718 is a commonly used superalloy for turbine discs in the gas turbine industry. Turbine discs are normally subjected to dwell-fatigue as a result of long constant load cycles. Dwell-times have been shown to give rise to increased crack propagation rates in superalloys at elevated temperatures. Dwell-time crack propagation behavior in Inconel 718 has been tested at 550 °C using Kb test samples with 2160 s dwell-times at maximum load and “pure fatigue” tests. The dwell-time effect has been studied for differently processed Inconel 718, that is, fine grained bar, grain enlarged bar, and cast material. This has been done in order to investigate the effect of grain size on crack propagation. Microstructure characterization is conducted using scanning electron microscopy techniques such as electron channeling contrast imaging and electron backscatter diffraction. Time dependent crack propagation rates are strongly affected by grain size. Propagation rates increase with decreasing grain size, whereas crack tip blunting increased with increasing grain size.

    Place, publisher, year, edition, pages
    Wiley-VCH Verlagsgesellschaft, 2018
    Keywords
    electron microscopy, fatigue, fracture, mechanical characterzation, nickel base superalloys
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-144395 (URN)10.1002/adem.201700930 (DOI)000435928600009 ()
    Note

    Funded by Swedish Energy Agency Siemens Industrial Turbomachinery ABGKN Aerospace Engine Systems Royal Institute of Technology through the Swedish research program TURBO POWER

    Available from: 2018-01-18 Created: 2018-01-18 Last updated: 2018-08-30
  • 307.
    Saarimäki, Jonas
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Effect of Dwell-times on Crack Propagation in Superalloys2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Gas turbines are widely used in industry for power generation and as a power source at "hard to reach" locations where other possibilities for electrical supply are insufficient. There is a strong need for greener energy, considering the effect that pollution has had on global warming, and we need to come up with ways of producing cleaner electricity. A way to achieve this is by increasing the combustion temperature in gas turbines. This increases the demand on the high temperature performance of the materials used e.g. superalloys in the turbine. These high combustion temperatures can lead to detrimental degradation of critical components. These components are commonly subjected to cyclic loading of different types e.g. combined with dwell-times and overloads at elevated temperatures, which influence the crack growth. Dwell-times have shown to accelerate crack growth and change the cracking behaviour in both Inconel 718 and Haynes 282. Overloads at the beginning of the dwell-time cycle have shown to retard the dwell time effect on crack growth in Inconel 718. To understand these effects more microstructural investigations are needed.

    The work presented in this licentiate thesis was conducted under the umbrella of the research program Turbo Power; "High temperature fatigue crack propagation in nickel-based superalloys", concentrating on fatigue crack growth mechanisms in superalloys during dwell-times, which have shown to have a devastating effect on the crack propagation behaviour. Mechanical testing was performed under operation-like conditions in order to achieve representative microstructures and material data for the subsequent microstructural work. The microstructures were microscopically investigated in a scanning electron microscope (SEM) using electron channeling contrast imaging (ECCI) as well as using light optical microscopy.

    The outcome of this work has shown that there is a significant increase in crack growth rate when dwell-times are introduced at the maximum load (0% overload) in the fatigue cycle. With the introduction of a dwell-time there is also a shift from transgranular to intergranular crack growth for both Inconel 718 and Haynes 282. When an overload is applied prior to the dwell-time, the crack growth rate decreases with increasing overload levels in Inconel 718. At high temperature crack growth in Inconel 718 took place as intergranular crack growth along grain boundaries due to oxidation and the creation of nanometric voids. Another observed growth mechanism was crack advance along phase boundaries with subsequent severe oxidation of the phase.

    This thesis comprises two parts. The first giving an introduction to the field of superalloys and the acting microstructural mechanisms that influence fatigue during dwell times. The second part consists of two appended papers, which report the work completed so far in the project.

    List of papers
    1. Influence of Overloads on Dwell Time Fatigue Crack Growth in Inconel 718
    Open this publication in new window or tab >>Influence of Overloads on Dwell Time Fatigue Crack Growth in Inconel 718
    2014 (English)In: Materials Science and Engineering: A, Vol. 612, p. 398-405Article in journal (Refereed) Published
    Abstract [en]

    Inconel 718 is one of the most commonly used superalloys for high temperature applications in gasturbines and aeroengines and is for example used for components such as turbine discs. Turbine discs can be subjected to temperatures up to ~700 °C towards the outer radius of the disc. During service, the discs might start to develop cracks due to fatigue and long dwell times. Additionally, temperature variations during use can lead to large thermal transients during start-up and shutdown which can lead to overload peaks in the normal dwell time cycle. In this study, tests at 550 °C with an overload prior to the start of each dwell time, have been performed. The aim of the investigation was to get a better understanding of the effects of overloads on the microstructure and crack mechanisms. The microstructure was studied using electron channelling contrast imaging (ECCI). The image analysis toolbox in Matlab was used on cross sections of the cracks to quantify: crack length, branch length, and the number of branches in each crack. It was found that the amount of crack branching increases with an increasing overload and that the branch length decreases with an increasing overload. When the higher overloads were applied, the dwell time effect was almost cancelled out. There is a strong tendency for an increased roughness of the crack path with an increasing crack growth rate.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    Keywords
    nickel based superalloys, fatigue, fracture, mechanical charcterization, electron microscopy
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-109348 (URN)10.1016/j.msea.2014.06.068 (DOI)000340331300049 ()
    Available from: 2014-08-14 Created: 2014-08-14 Last updated: 2018-01-18Bibliographically approved
    2. Time- and Cycle-Dependent Crack Propagation in Haynes 282
    Open this publication in new window or tab >>Time- and Cycle-Dependent Crack Propagation in Haynes 282
    2016 (English)In: Journal of Materials Science and Engineering: A, ISSN 2161-6213, Vol. 658, p. 463-471Article in journal (Refereed) Published
    Abstract [en]

    Haynes 282 is a promising superalloy candidate for several high-temperature applications in both aero and land-based gas turbine engines. To study the crack growth behaviour under time-dependent conditions relevant to such applications, a test program was carried out at room temperature up to 700 °C with conditions ranging from pure cyclic to sustained tensile loading. At 650 °C and high stress intensity factors the crack growth was fully time-dependent for dwell-times of 90 s and longer. At lower stress intensities, the behaviour was mainly controlled by the cyclic loading, even under dwell conditions. The behaviour under dwell-fatigue conditions was well described by a liner superposition model.

    Place, publisher, year, edition, pages
    Elsevier, 2016
    Keywords
    Nickel based superalloys, fatigue, fracture, mechanical characterisation, electron microscopy
    National Category
    Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-126922 (URN)10.1016/j.msea.2016.01.111 (DOI)000372560800054 ()
    Note

    At the time for thesis presentation publication was in status: Manuscript

    Name of manuscript was: Time-dependent crack propagation in Haynes 282

    Funding agencies: Agora Materiae, graduate school, Faculty grant SFO-MAT-LiU [2009-00971]; Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through the Swedish research program TURBO POWER

    Available from: 2016-04-07 Created: 2016-04-07 Last updated: 2018-01-18Bibliographically approved
  • 308.
    Saarimäki, Jonas
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Mechanical Properties of Mix Joint TIG Welded Hastelloy X2017Conference paper (Refereed)
  • 309.
    Saarimäki, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Hörnqvist Colliander, Magnus
    Dept of Applied Physics, Chalmers University of Technology, Gothenburg and GKN Aerospace engine Systems, R&T Centre, Trollhättan.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Anisotropy Effects During Dwell-fatigue Caused by δ-phase Orientation in Forged Inconel 7182017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, no 692, p. 174-181Article in journal (Refereed)
    Abstract [en]

    Inconel 718 is a commonly used superalloy for turbine discs in the gas turbine industry. Turbine discs are often subjected to dwell-fatigue as a result of long constant load cycles. The effect of anisotropy on dwell-fatigue cracking in forged turbine discs have not yet been thoroughly investigated. Crack propagation behaviour was characterised using compact tension (CT) samples cut in different orientations from a real turbine disc forging. Samples were also cut in two different thicknesses in order to investigate the influence of plane strain and plane stress condition on the crack propagation rates. The samples were subjected to dwell-fatigue tests at 550 °C with 90 s or 2160 s dwell-times at maximum load. Microstructure characterisation was done using scanning electron microscopy (SEM) techniques such as electron channelling contrast imaging (ECCI), electron backscatter diffraction (EBSD), and light optical microscopy (LOM). The forged alloy exhibits strong anisotropic behaviour caused by the non-random δ-phase orientation. When δ-phases were oriented perpendicular compared to parallel to the loading direction, the crack growth rates were approximately ten times faster. Crack growth occurred preferably in the interface between the γ-matrix and the δ-phase.

  • 310.
    Saarimäki, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Lundberg, Mattias
    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.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Dwell-fatigue crack propagation in additive manufactured Hastelloy X2018In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 722, p. 30-36Article in journal (Refereed)
    Abstract [en]

    Additively manufactured Hastelloy X by laser-powderbed fusion is a superalloy used in for example burners and non-rotating parts in gas turbines. Turbines are often subjected to dwell-fatigue as a result of an operating profile including load cycles with long constant power output. The effect of building direction and heat treatments on dwell-fatigue crack propagation in additively manufactured Hastelloy X has not yet been thoroughly investigated. Crack propagation behaviour was characterized using compact tension samples cut from as-built and heat treated material blocks. Samples were machine with the notch parallel and perpendicular to the building direction enabling the investigation of building direction on crack behaviour and crack propagation rates. The samples were subjected to dwell-fatigue tests at 700 degrees C with 90 s or 2160 s dwell-times at maximum load. Microstructural characterization was conducted using light optical microscopy and scanning electron microscopy techniques such as electron channelling contrast imaging and electron backscatter diffraction. The additively manufactured alloy exhibits anisotropic behaviour caused by the directionally solidified microstructure. Cracks propagated intergranularly and preferably through streaks of topologically dose-packed phases.

  • 311.
    Saarimäki, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Lundberg, Mattias
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Grain Size Depending Dwell-Fatigue Crack Growth in Inconel 7182018In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, article id 1700930Article in journal (Refereed)
    Abstract [en]

    Inconel 718 is a commonly used superalloy for turbine discs in the gas turbine industry. Turbine discs are normally subjected to dwell-fatigue as a result of long constant load cycles. Dwell-times have been shown to give rise to increased crack propagation rates in superalloys at elevated temperatures. Dwell-time crack propagation behavior in Inconel 718 has been tested at 550 °C using Kb test samples with 2160 s dwell-times at maximum load and “pure fatigue” tests. The dwell-time effect has been studied for differently processed Inconel 718, that is, fine grained bar, grain enlarged bar, and cast material. This has been done in order to investigate the effect of grain size on crack propagation. Microstructure characterization is conducted using scanning electron microscopy techniques such as electron channeling contrast imaging and electron backscatter diffraction. Time dependent crack propagation rates are strongly affected by grain size. Propagation rates increase with decreasing grain size, whereas crack tip blunting increased with increasing grain size.

  • 312.
    Saarimäki, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Lundberg, Mattias
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Brodin, Håkan
    Linköping University, Department of Management and Engineering. Linköping University, Faculty of Science & Engineering. Siemens Industrial Turbomachinery AB, Finspång.
    3D Residual Stresses in Selective Laser Melted Hastelloy X2017In: Residual Stresses 2016: ICRS-10, Materials Research Proceedings 2 (2016), 2017, Vol. 2, p. 73-78Conference paper (Refereed)
    Abstract [en]

    3D residual stresses in as manufactured EOS NickelAlloy HX, produced by laser powder bed additive manufacturing, are analysed on the surface closest to the build-plate. Due to the severe thermal gradient produced during the melting and solidification process, profound amounts of thermal strains are generated. Which can result in unwanted geometrical distortion and effect the mechanical properties of the manufactured component. Measurements were performed using a four-circle goniometer Seifert X-ray machine, equipped with a linear sensitive detector and a Cr-tube. Evaluation of the residual stresses was conducted using sin2ψ method of the Ni {220} diffraction peak, together with material removal technique to obtain in-depth profiles. An analysis of the material is reported. The analysis reveals unwanted residual stresses, and a complicated non-uniform grain structure containing large grains with multiple low angle grain boundaries together with nano-sized grains. Grains are to a large extent, not equiaxed, but rather elongated.

  • 313.
    Saarimäki, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Lundberg, Mattias
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    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 Industrial Turbomachinery AB, Finspång, Sweden.
    Characterization of Hastelloy X Produced by Laser Powder Bed Additive Manufacturing2016In: World PM2016 Proceedings, EPMA , 2016, p. 1-6Conference paper (Refereed)
    Abstract [en]

    The grain structure of the selective laser melting (SLM) material is complicated and cannot easily be resolved by etching of the as-manufactured surface. One method to reveal the true morphology is by performing an electron backscatter diffraction (EBSD) analysis of the material. An analysis of the SLM material is reported. The analysis reveals that the grain structure is very complicated and the grain size is non-uniform. The microstructure contains large grains with multiple low angle grain boundaries together with small grains that approach nanometre size in the smallest size range. Grains are to a large extent, not equiaxed, but rather elongated.

    Varying degrees of texture in different regions of the material have been observed. The degree of texture coincides with material volumes manufactured with different process parameter settings. Also areas with and without indications of texture have shown to exhibit different hardness. This is an indication of variation in mechanical properties in the different material volumes. Thin-walled areas, surface regions of solid material and lattices constitutes one group with similar microstructure indicating one class of material and secondly the bulk material with another microstructure would constitute the other material class

  • 314.
    Saarimäki, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    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 Industrial Turbomachinery AB, Finspång, Sweden.
    Damage Development in Thin Walled Selective Laser Melted Structures2016In: Materials Science and Technology 2016 (MS&T16): Proceedings, Warrendale, PA: Materials Science & Technology , 2016, p. 79-86Conference paper (Refereed)
    Abstract [en]

    Additive manufacturing has gained vast interest in e.g., aeronautical industry. The large number of superalloys available in powder form has enabled the utilization of the technology for hot gas turbine parts, leading to ground breaking design changes, in fuselage parts of large aircraft, and turbines.

    Different lattice truss structures were manufactured with the SLM process in parallel with solid SLM bars were produced. Hollow rectangular tubes and composites of tubes with an interior of lattice truss structures were also manufactured. Hot rolled material of Hastelloy X was included for reference. Mechanical testing was performed in tension showing that the SLM material is highly anisotropic and that the material has many advantages compared to the traditionally manufactured Hastelloy X alloy. Tests also show that fracture is promoted along certain planes in the lattice truss structure.

    lattice truss structures were analysed using digital imaging. At small deformations, the deformation in both the lattice and hybrid specimen is homogeneous. The deformation at onset of failure in the hybrid test bar is mainly a shearing of the lattice struts along a preferred plane, while the deformation map for the hybrid material still shows a planar deformation front perpendicular to the loading direction.

  • 315.
    Saarimäki, Jonas
    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. Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Eriksson, Robert
    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.
    Influence of Overloads on Dwell Time Fatigue Crack Growth in Inconel 7182014In: Materials Science and Engineering: A, Vol. 612, p. 398-405Article in journal (Refereed)
    Abstract [en]

    Inconel 718 is one of the most commonly used superalloys for high temperature applications in gasturbines and aeroengines and is for example used for components such as turbine discs. Turbine discs can be subjected to temperatures up to ~700 °C towards the outer radius of the disc. During service, the discs might start to develop cracks due to fatigue and long dwell times. Additionally, temperature variations during use can lead to large thermal transients during start-up and shutdown which can lead to overload peaks in the normal dwell time cycle. In this study, tests at 550 °C with an overload prior to the start of each dwell time, have been performed. The aim of the investigation was to get a better understanding of the effects of overloads on the microstructure and crack mechanisms. The microstructure was studied using electron channelling contrast imaging (ECCI). The image analysis toolbox in Matlab was used on cross sections of the cracks to quantify: crack length, branch length, and the number of branches in each crack. It was found that the amount of crack branching increases with an increasing overload and that the branch length decreases with an increasing overload. When the higher overloads were applied, the dwell time effect was almost cancelled out. There is a strong tendency for an increased roughness of the crack path with an increasing crack growth rate.

  • 316.
    Saarimäki, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Hörnqvist Colliander, Magnus
    Chalmers University of Technology, Department of Applied Physics, Göteborg, Sweden; GKN Aerospace Engine Systems, R&T Centre, Trollhättan, Sweden.
    Time- and Cycle-Dependent Crack Propagation in Haynes 2822016In: Journal of Materials Science and Engineering: A, ISSN 2161-6213, Vol. 658, p. 463-471Article in journal (Refereed)
    Abstract [en]

    Haynes 282 is a promising superalloy candidate for several high-temperature applications in both aero and land-based gas turbine engines. To study the crack growth behaviour under time-dependent conditions relevant to such applications, a test program was carried out at room temperature up to 700 °C with conditions ranging from pure cyclic to sustained tensile loading. At 650 °C and high stress intensity factors the crack growth was fully time-dependent for dwell-times of 90 s and longer. At lower stress intensities, the behaviour was mainly controlled by the cyclic loading, even under dwell conditions. The behaviour under dwell-fatigue conditions was well described by a liner superposition model.

  • 317.
    Sadeghimeresht, Esmaeil
    et al.
    Univ West, Sweden.
    Karimi, Paria
    Univ West, Sweden.
    Zhang, Pimin
    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.
    Andersson, Joel
    Univ West, Sweden.
    Pejryd, Lars
    Örebro Univ, Sweden.
    Joshi, Shrikant
    Univ West, Sweden.
    Isothermal Oxidation Behavior of EBM-Additive Manufactured Alloy 7182018In: PROCEEDINGS OF THE 9TH INTERNATIONAL SYMPOSIUM ON SUPERALLOY 718 and DERIVATIVES: ENERGY, AEROSPACE, AND INDUSTRIAL APPLICATIONS, SPRINGER INTERNATIONAL PUBLISHING AG , 2018, p. 219-240Conference paper (Refereed)
    Abstract [en]

    Oxidation of Alloy 718 manufactured by electron beam melting (EBM) process has been undertaken in ambient air at 650, 700, and 800 degrees C for up to 168 h. At 800 degrees C, a continuous external chromia oxide enriched in (Cr, Ti, Mn, Ni) and an internal oxide that was branched structure of alumina formed, whereas at 650 and 700 degrees C, a continuous, thin and protective chromia layer was detected. The oxidation kinetics of the exposed EBM Alloy 718 followed the parabolic rate law with an effective activation energy of similar to 248 +/- 22 kJ/mol in good agreement with values in the literature for conventionally processed chromia-forming Ni-based superalloys. The oxide scale formed on the surface perpendicular to the build direction was slightly thicker, and more adherent compared to the scale formed on the surface along the build direction, attributed to the varied grain texture in the two directions of the EBM-manufactured specimens. The increased oxygen diffusion and high Cr depletion found on the surface along the build direction were attributed to the fine grains and formation of vacancies/voids along this grain orientation.

  • 318.
    Sadrossadat, Mohsen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    On the Residual Stresses and Microstructure Formation of Aluminum-Silicon Cast Alloys2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Cast aluminum-silicon alloys are being increasingly used in automotive and aerospace industries for critical structure applications because of their excellent castability, low density, acceptable mechanical properties and low cost. Different casting and heat treatment parameters largely affect the microstructure and residual stress of the components, which in turn, has a great impact on their mechanical properties. In cast components, residual stresses are those stresses which may remain in the casting after it has been removed from the mould. The magnitude and distribution of the residual stresses can be critical to performance and should be considered in the design of a component. This work has been devoted to study the microstructure formation, residual stresses, and mechanical properties of aluminum-silicon castings.

    The effects of casting parameters on the microstructure of the selected alloys were investigated by means of optical and scanning electron microscopes. With the help of EDS, WDS, EBSD, and quantitative analysis techniques, it was found that solidification rate, modification, superheat, casting temperature can significantly affect the nucleation and growth, morphology and chemical composition of different phases. Based on the performed microsegregation analysis, a clear correlation between the concentration of silicon in the primary phase and cooling rate was found.

    Tensile tests at room and elevated temperatures in addition to microhardness experiments were performed to analyse the behaviour of the alloys under mechanical loads. The results showed that elongation to fracture, modulus of elasticity, and ultimate tensile strength of the tested alloys are temperature dependent. Moreover, the obtained information was used to establish a good model for simulating the behaviour of the cast alloys, as well as the mechanical properties and residual stresses.

    The type and magnitude of residual stresses were mainly evaluated by strain gauge, sectioning, thermal analysis methods, and was also simulated by finite element analysis using Abaqus software. It was found that casting parameters such as superheat, mould hardness, casting temperature, modification, and the casting geometry, can influence the accumulated residual stress in the component. The thermal treatment experiments also indicated that the base temperature of the cast part before fast cooling, maximum temperature difference within the component, and cooling water flow can influence the residual stress. Extensive simulation work done by Abaqus showed that the results obtained by simulation are in a reasonable relationship with the experimental measurements, considering the linearly elastic/linearly isotropically hardening plastic model.

    List of papers
    1. EBSD investigation of the effect of the solidification rate on the nucleation behavior of eutectic components in a hypoeutectic Al-Si-Cu alloy
    Open this publication in new window or tab >>EBSD investigation of the effect of the solidification rate on the nucleation behavior of eutectic components in a hypoeutectic Al-Si-Cu alloy
    2012 (English)In: Metals and Materials International, ISSN 1598-9623, E-ISSN 2005-4149, Vol. 18, no 3, p. 405-411Article in journal (Refereed) Published
    Abstract [en]

    This article is devoted to a study of the influence of solidification rate on the crystallographic orientation of eutectic components with respect to primary α-Al in the tested hypoeutectic alloy. Electron backscattering diffraction (EBSD) patterns were produced from Al-Si cast specimens, solidified with different cooling rates, and prepared by ion etch polishing as a complementary method after mechanical polishing. Results indicated a strong orientation relationship between the primary α-Al and eutectic aluminum phase at all cooling rates. It is also found that the silicon eutectic flakes are nucleated heterogeneously in the interdendritic eutectic liquid. Increasing the cooling rate from 2 to 80 mm/min is observed to be effective in lowering the intensity of relationship between the primary α-Al and eutectic aluminum phase and changing the misorientation angle clustering between primary α-Al and eutectic silicon phase in the interval 41-60 to lower angle intervals.

    Keywords
    EBSD, Pole figure analysis, Al-Si alloy, Nucleation, Orientation relationship
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-70096 (URN)10.1007/s12540-012-3004-4 (DOI)000305689900004 ()
    Available from: 2011-08-18 Created: 2011-08-18 Last updated: 2017-12-08Bibliographically approved
    2. Elemental Distribution, Morphological Analysis, and Hardness Measurement of an Al-Si Alloy, as Affected by Cooling Rate
    Open this publication in new window or tab >>Elemental Distribution, Morphological Analysis, and Hardness Measurement of an Al-Si Alloy, as Affected by Cooling Rate
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The effects of cooling rate on the as-cast microstructure and hardness of an Al - Si alloy was studied. To obtain different cooling rates, a special gradient casting furnace was designed and built. The microstructural analysis was carried out on as-cast samples to investigate the morphology (size, shape, and distribution) of the present phases. By using an analytical scanning electron microscope, the microsegregation of different alloying elements in the centre of aluminium dendrites was investigated. To study the effect of cooling rate on the mechanical properties, hardness of the samples and microhardness of the primary α-Al dendrites were measured. The results showed that the morphology of the silicon eutectic, refinement of the intermetallics, and the size of primary dendrites are cooling rate dependent. Moreover, a clear correlation between the concentration of silicon concentration in the centre of the aluminium dendrites and cooling rate was found.

    Keywords
    Elemental distribution, morphological analysis, hardness, Al-Si alloy
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-70097 (URN)
    Available from: 2011-08-18 Created: 2011-08-18 Last updated: 2011-08-19Bibliographically approved
    3. Experimental realization and finite element simulation of residual stresses in Al-Si water sprayed cast components
    Open this publication in new window or tab >>Experimental realization and finite element simulation of residual stresses in Al-Si water sprayed cast components
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    In this study, experiments were carried out to develop insights into  and understanding of the residual stresses that can arise during different thermal treatments of Al-Si components. The study consisted of two steps: experimental measurement of the residual stresses accumulated in the components and simulation of the results by finite element analysis. A special cooling apparatus was designed and built in order to perform selective cooling of the component. In the simulation step, the tensile behavior and parameters such as Young’s modulus values determined by tensile tests at different temperatures and the recorded cooling curves in the first step were used as input for the Abaqus software. The experimental results obtained by thermal analysis and residual stress measurement showed that by choosing a specific holding temperature before quenching, the value of residual stress increases linearly with flow rate of water spray coolant. On the other hand, for a constant value of cooling water flow rate, the maximum temperature difference between the middle and side bars of the test specimen (ΔTmax) and residual stress level decrease when the value of starting temperature of cooling decreases. It was shown that the strain gage method and thermal analysis are reliable techniques for measuring thermal residual stresses and prediction of residual strains in Al-Si components, respectively. It was also shown that the results obtained by simulation are reasonably in acceptable agreement with the experimentally measurements.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-70098 (URN)
    Available from: 2011-08-18 Created: 2011-08-18 Last updated: 2011-08-19Bibliographically approved
    4. The effects of casting parameters on residual stresses and microstructure variations of an Al-Si cast alloy
    Open this publication in new window or tab >>The effects of casting parameters on residual stresses and microstructure variations of an Al-Si cast alloy
    2009 (English)In: Advances in X-Ray Analysis (CD-ROM), ISSN 1097-0002, Vol. 52, p. 553-560Article in journal (Refereed) Published
    Abstract [en]

    Different casting parameters can change the microstructure and residual stresses of castings. The microstructure of Al-Si cast alloys is influenced by the morphology of silicon particles (shape, size and distribution), aluminum grain size and dendrite parameters. Dimensional changes resulting from casting caused by residual stresses can particularly affect the quality of near net shape castings. In this research, the influence of casting process parameters such as modification, superheat temperature, mould hardness and mould design on residual stresses and microstructure of an Al-Si-Mn alloy have been investigated. Experiments were conducted with different superheat, mould hardness, modification with Al-10Sr and two different casting designs. The micro structural changes associated with these parameters have been studied by optical microscopy, scanning electron microscopy and image analysis. The type and extent of residual stresses of all samples were determined using the sectioning method. The results show that all of the mentioned casting parameters have clear effects on residual stresses. The residual stresses decrease with lowered superheat, temperature and mould hardness. It was found that the residual stress increases both with adding a eutectic modifier and with change of casting design. It wasalso found that microstructure and mechanical properties are  influenced significantly by the mentioned parameter.

    Place, publisher, year, edition, pages
    Newton Square, PA, United States: International Centre for Diffraction Data (ICCD), 2009
    National Category
    Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-60908 (URN)
    Conference
    57th Annual Conference on Applications of X-ray Analysis Denver X-ray Conference (DXC), Denver, Colorado, USA, 4–8 August 2008
    Available from: 2010-10-29 Created: 2010-10-29 Last updated: 2016-02-17Bibliographically approved
    5. The effects of solidification conditions and heat treatment on the microstructure and mechanical properties of EN-AC 44400 alloy
    Open this publication in new window or tab >>The effects of solidification conditions and heat treatment on the microstructure and mechanical properties of EN-AC 44400 alloy
    2010 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 649, p. 505-510Article in journal (Refereed) Published
    Abstract [en]

    Improved mechanical and physical properties of an Al-Si alloy as a well-known casting alloy is strongly dependent upon the morphology of silicon particles, Al grains and also type of intermetallics which are in turn a function of alloy composition, solidification rate and heat treatment. This study aims at investigating the influence of the different solidification conditions (high pressure die, gradient and sand cast) and heat treatment on the microstructure (dendrite parameters, silicon particle morphology, intermetallic compounds), mechanical properties and fracture surface appearance of Al- 9Si- 4Mn alloy. To identify the features of microstructure and fracture surface analysis, a combination of optical metallography, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) have been employed. The results show that the cooling rate has a strong effect on the evolution of intermetallics, morphology of the silicon and dendrite parameters.

    Place, publisher, year, edition, pages
    Switzerland: Trans Tech Publications, 2010
    Keywords
    solidfication conditions, microstructure, mechanical properties, intermetallics, heat treatment
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-54536 (URN)10.4028/www.scientific.net/MSF.649.505 (DOI)
    Available from: 2010-03-22 Created: 2010-03-22 Last updated: 2017-12-12Bibliographically approved
    6. The influence of casting geometry on the tensile properties and residual stresses in aluminium castings
    Open this publication in new window or tab >>The influence of casting geometry on the tensile properties and residual stresses in aluminium castings
    2010 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 652, p. 174-179Article in journal (Refereed) Published
    Abstract [en]

    The soundness and the performance of castings are significantly affected by generation and accumulation of residual stresses. This has been proven that mechanical properties and residual stresses level of the casting components are affected by thermal gradient across the casting component during cooling and some intrinsic physical properties of the material. In the present work, microstructural development, mechanical properties, residual stress evolution and cooling curves associated with different legs of a mixed–section grid castings have been investigated employing scanning electron microscope, optical microscope, 3D measurement equipment, computerized thermal data acquisition instrument and tensile testing machine. Experimental results show that the accumulated residual stress in circular, triangular and rectangular grid shapes is increasing respectively. From the results it can be seen that there are clear influences of grid’s geometry on the microstructure and mechanical properties. The geometrical stiffness can affect a lot the residual stress level and the casting modulus has a big influence on the microstructure and mechanical properties.

    Place, publisher, year, edition, pages
    Switzerland: Trans Tech Publications, 2010
    National Category
    Engineering and Technology Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-60910 (URN)10.4028/www.scientific.net/MSF.652.174 (DOI)
    Available from: 2010-10-29 Created: 2010-10-29 Last updated: 2017-12-12Bibliographically approved
    7. The effect of heat treatment on the mechanical properties and residual stresses in a HPDC component of Al-Si-Mn alloy
    Open this publication in new window or tab >>The effect of heat treatment on the mechanical properties and residual stresses in a HPDC component of Al-Si-Mn alloy
    2007 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    This study aims at investigating the influence of the heat treatment process on microstructure, mechanical properties and residual stresses in a high pressure die cast (HPDC) of an aluminum alloy component. Two series of high pressure die cast components containing mainly Al -Si 8.4- Mn 0.43 were tested. The first group of components was as cast and the second heat treated. X-ray diffraction, quantitative metallography and mechanical testing methods were used to determine the residual stresses, microstructural features and mechanical properties respectively. Results indicate that the amount of residual stresses varies depending on heat treatment process. The selected heat treatment process can also change the microstructure and mechanical properties.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-39193 (URN)47126 (Local ID)47126 (Archive number)47126 (OAI)
    Conference
    5th International Conference on Mechanical Stress Evaluation by Neutrons and Synchrotron Radiation, September 24-26, Vienna, Austria
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2011-08-24Bibliographically approved
  • 319.
    Sadrossadat, Mohsen
    et al.
    Linköping University, Department of Management and Engineering. Linköping University, The Institute of Technology.
    Brodin, Håkan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering. Linköping University, The Institute of Technology.
    Experimental realization and finite element simulation of residual stresses in Al-Si water sprayed cast componentsManuscript (preprint) (Other academic)
    Abstract [en]

    In this study, experiments were carried out to develop insights into  and understanding of the residual stresses that can arise during different thermal treatments of Al-Si components. The study consisted of two steps: experimental measurement of the residual stresses accumulated in the components and simulation of the results by finite element analysis. A special cooling apparatus was designed and built in order to perform selective cooling of the component. In the simulation step, the tensile behavior and parameters such as Young’s modulus values determined by tensile tests at different temperatures and the recorded cooling curves in the first step were used as input for the Abaqus software. The experimental results obtained by thermal analysis and residual stress measurement showed that by choosing a specific holding temperature before quenching, the value of residual stress increases linearly with flow rate of water spray coolant. On the other hand, for a constant value of cooling water flow rate, the maximum temperature difference between the middle and side bars of the test specimen (ΔTmax) and residual stress level decrease when the value of starting temperature of cooling decreases. It was shown that the strain gage method and thermal analysis are reliable techniques for measuring thermal residual stresses and prediction of residual strains in Al-Si components, respectively. It was also shown that the results obtained by simulation are reasonably in acceptable agreement with the experimentally measurements.

  • 320.
    Sadrossadat, Mohsen
    et al.
    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 Effect of Heat Treatment on the Mechanical Properties and Residual Stresses in a HPDC Component of Al-Si-Mn Alloy2007Conference paper (Refereed)
  • 321.
    Sadrossadat, Mohsen
    et al.
    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 effects of casting parameters on residual stresses and microstructure variations of an Al-Si cast alloy2009In: Advances in X-Ray Analysis (CD-ROM), ISSN 1097-0002, Vol. 52, p. 553-560Article in journal (Refereed)
    Abstract [en]

    Different casting parameters can change the microstructure and residual stresses of castings. The microstructure of Al-Si cast alloys is influenced by the morphology of silicon particles (shape, size and distribution), aluminum grain size and dendrite parameters. Dimensional changes resulting from casting caused by residual stresses can particularly affect the quality of near net shape castings. In this research, the influence of casting process parameters such as modification, superheat temperature, mould hardness and mould design on residual stresses and microstructure of an Al-Si-Mn alloy have been investigated. Experiments were conducted with different superheat, mould hardness, modification with Al-10Sr and two different casting designs. The micro structural changes associated with these parameters have been studied by optical microscopy, scanning electron microscopy and image analysis. The type and extent of residual stresses of all samples were determined using the sectioning method. The results show that all of the mentioned casting parameters have clear effects on residual stresses. The residual stresses decrease with lowered superheat, temperature and mould hardness. It was found that the residual stress increases both with adding a eutectic modifier and with change of casting design. It wasalso found that microstructure and mechanical properties are  influenced significantly by the mentioned parameter.

  • 322.
    Sadrossadat, Mohsen
    et al.
    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 effects of solidification conditions and heat treatment on the microstructure and mechanical properties of EN-AC 44400 alloy2010In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 649, p. 505-510Article in journal (Refereed)
    Abstract [en]

    Improved mechanical and physical properties of an Al-Si alloy as a well-known casting alloy is strongly dependent upon the morphology of silicon particles, Al grains and also type of intermetallics which are in turn a function of alloy composition, solidification rate and heat treatment. This study aims at investigating the influence of the different solidification conditions (high pressure die, gradient and sand cast) and heat treatment on the microstructure (dendrite parameters, silicon particle morphology, intermetallic compounds), mechanical properties and fracture surface appearance of Al- 9Si- 4Mn alloy. To identify the features of microstructure and fracture surface analysis, a combination of optical metallography, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) have been employed. The results show that the cooling rate has a strong effect on the evolution of intermetallics, morphology of the silicon and dendrite parameters.

  • 323.
    Sadrossadat, Mohsen
    et al.
    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 influence of casting geometry on the tensile properties and residual stresses in aluminium castings2010In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 652, p. 174-179Article in journal (Refereed)
    Abstract [en]

    The soundness and the performance of castings are significantly affected by generation and accumulation of residual stresses. This has been proven that mechanical properties and residual stresses level of the casting components are affected by thermal gradient across the casting component during cooling and some intrinsic physical properties of the material. In the present work, microstructural development, mechanical properties, residual stress evolution and cooling curves associated with different legs of a mixed–section grid castings have been investigated employing scanning electron microscope, optical microscope, 3D measurement equipment, computerized thermal data acquisition instrument and tensile testing machine. Experimental results show that the accumulated residual stress in circular, triangular and rectangular grid shapes is increasing respectively. From the results it can be seen that there are clear influences of grid’s geometry on the microstructure and mechanical properties. The geometrical stiffness can affect a lot the residual stress level and the casting modulus has a big influence on the microstructure and mechanical properties.

  • 324.
    Sadrossadat, Mohsen
    et al.
    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.
    Lin Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    EBSD investigation of the effect of the solidification rate on the nucleation behavior of eutectic components in a hypoeutectic Al-Si-Cu alloy2012In: Metals and Materials International, ISSN 1598-9623, E-ISSN 2005-4149, Vol. 18, no 3, p. 405-411Article in journal (Refereed)
    Abstract [en]

    This article is devoted to a study of the influence of solidification rate on the crystallographic orientation of eutectic components with respect to primary α-Al in the tested hypoeutectic alloy. Electron backscattering diffraction (EBSD) patterns were produced from Al-Si cast specimens, solidified with different cooling rates, and prepared by ion etch polishing as a complementary method after mechanical polishing. Results indicated a strong orientation relationship between the primary α-Al and eutectic aluminum phase at all cooling rates. It is also found that the silicon eutectic flakes are nucleated heterogeneously in the interdendritic eutectic liquid. Increasing the cooling rate from 2 to 80 mm/min is observed to be effective in lowering the intensity of relationship between the primary α-Al and eutectic aluminum phase and changing the misorientation angle clustering between primary α-Al and eutectic silicon phase in the interval 41-60 to lower angle intervals.

  • 325.
    Sadrossadat, Mohsen
    et al.
    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.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Analysis of residual stress development during thermal processing of Al-Si alloys2010Conference paper (Refereed)
    Abstract [en]

    Residuals stresses can be present in almost every industrial component. Manufacturing processes such as casting, welding, and heat treatment are the most common causes of residual stresses. Thermal residual stresses could be developed in a component during heat treatment process as a result of non-uniform heating or cooling operations. In this study, experiments were carried out to develop insights into and understanding of the residual stresses that can arise during thermal treatments of Al-Si components. Due to the complexity of residual stresses analysis in real components, a common mixed-section casting was employed. In order to fulfill the requirements of performing different thermal treatments, a special cooling apparatus was designed and built. A number of the casting components of an Al-Si alloy were annealed for stress relief, and then removed from the furnace and cooled with different water flow rates. Then, the amount of accumulated residual stresses in the components was measured relaxation of stress using cutting. Thermal analysis and residual stress measurement for different thermal treatment regimes showed that by choosing a specific holding temperature before direct cooling, the value of residual stress increases linearly with flow rate of cooling. On the other hand, for a constant value of cooling water flow, ∆Tmax and residual stress level decreases when the value of base temperature of furnace decreases. Moreover, the cutting method can be a suitable method for measuring thermal residual stresses in Al-Si components and thermal analysis is a powerful technique to predict residual stresses.

  • 326.
    Sato, Atsushi
    et al.
    Dept of Metallurgy and Materials, University in Birmingham, UK.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Hasselqvist, Magnus
    Siemens Industrial Turbomachinery AB, Finspång.
    Reed, Roger
    Dept of Metallurgy and Materials, University of Birmingham, UK.
    On The Oxidation Resistance of Nickel-Based Superalloys2011In: Advanced Materials Research, ISSN 1022-6680, E-ISSN 1662-8985, Vol. 278, p. 174-179Article in journal (Refereed)
    Abstract [en]

    In this paper, the factors influencing the oxidation resistance of superalloys are studied. A model is proposed by which the Al2O3-forming properties of a given composition can be estimated, based upon the thermodynamic and kinetic factors influencing scale growth. The numerical modelling is tested by experimental work on a number of compositional variants of the newly-developed SCA425+ superalloy, which contains appreciable quantities of Cr. The modelling is shown to be in broad agreement with experiment. The effects of Al, Cr and Si on the oxidation resistance of this class of alloy have been rationalised.

  • 327.
    Sato, Atsushi
    et al.
    University of Birmingham, United Kingdom.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Hasselqvist, Magnus
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Reed, Roger C.
    University of Birmingham, United Kingdom.
    On the Mechanical Behavior of a New Single-Crystal Superalloy for Industrial Gas Turbine Applications2012In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 43A, no 7, p. 2302-2315Article in journal (Refereed)
    Abstract [en]

    The mechanical behavior of a new single-crystal nickel-based superalloy for industrial gas turbine (IGT) applications is studied under creep and out-of-phase (OP) thermomechanical fatigue (TMF) conditions. Neutron diffraction methods and thermodynamic modeling are used to quantify the variation of the gamma prime (γ′) strengthening phase around the γ′ solvus temperature; these aid the design of primary aging heat treatments to develop either uniform or bimodal microstructures of the γ′ phase. Under creep conditions in the temperature range 1023 K to 1123 K (750 °C to 850 °C), with stresses between 235 to 520 MPa, the creep performance is best with a finer and uniform γ′ microstructure. On the other hand, the OP TMF performance improves when the γ′ precipitate size is larger. Thus, the micromechanical degradation mechanisms occurring during creep and TMF are distinct. During TMF, localized shear banding occurs with the γ′ phase penetrated by dislocations; however, during creep, the dislocation activity is restricted to the matrix phase. The factors controlling TMF resistance are rationalized.

  • 328.
    Schlauer, C.
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials .
    Simonsson, K.
    Linköping University, Department of Management and Engineering, Solid Mechanics .
    Moverare, J.
    Linköping University, Department of Management and Engineering, Engineering Materials .
    The effect of machining on residual stresses and low cycle fatigue life of Inconel 718 gas turbine discs2002Report (Other academic)
  • 329.
    Schlauer, Christian
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    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.
    The effect of machining on residual stresses and low cycle fatigue life of Inconel 718 gas turbine discs2002Report (Other academic)
  • 330.
    Schmidt, Pål
    et al.
    Volvo Group Trucks Technology, Göteborg.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Davydov, Vadim
    Paul Shcerrer Institute, Spallation Neutron Source SINQ, Villinge PSI, Switzerland.
    Lundberg, Mattias
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Ahmad, Maqsood
    Volvo Group Trucks Technology, Göteborg.
    Vuoristo, Taina
    Testing Methods and Testing, Scania CV AB, Södertälje.
    Bäckström, Daniel
    Testing Methods and Testing, Scania CV AB, Södertälje.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Analysis of Residual Stress in Stres Harps of Grey Iron by Experiment and Simulation2014Conference paper (Refereed)
  • 331.
    Segersäll, Mikael
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Nickel-Based Single-Crystal Superalloys: the crystal orientation influence on high temperature properties2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Superalloys are a group of materials that are used in high temperature applications, for example gas turbines and aero engines. Gas turbines are most commonly used for power generation, and it is only the very critical components which are exposed to the most severe conditions within the turbine, which are made from superalloy material.

    Today, energy consumption in many parts of the world is very high and is tending to increase. This implies that all power generating sources, including gas turbines, must aim for higher efficiency. For the gas turbine industry, it is a continuous challenge to develop more energy-efficient turbines. One way to do this is to increase the temperature within the hot stage of the turbine. However, increased temperature in the hot stage also challenges the materials that are used there. Today’s materials are already pushed to the limit, i.e. they cannot be exposed to the temperatures which are required to further increase the turbine efficiency. To solve this problem, research which later can lead to better superalloys that can withstand even higher temperatures, has to be conducted within the area of superalloys.

    The aim of this licentiate thesis is to increase our knowledge about  deformation and damage mechanisms that occur in the microstructure in superalloys when they are subjected to high temperatures and loads. This knowledge can later be used when developing new superalloys. In addition, increased knowledge of what is happening within the material when it is exposed to those severe conditions, will facilitate the development of material models. Material models are used for FEM simulations, when trying to predict life times in gas turbine components during the design process.

    This licentiate thesis is based on results from thermomechanical fatigue (TMF) testing of Ni-based single-crystal superalloys. Results show that the deformation within the microstructure during TMF is localized to several deformation bands. In addition, the deformation mechanisms are mainly twinning and shearing of the microstructure. Results also indicate that TMF cycling seems to influence the creep rate of single-crystal superalloys.

    List of papers
    1. Deformation and Damage Mechanisms During Thermomechanical Fatigue of a Single-crystal Superalloy in the <001> and <011> Directions
    Open this publication in new window or tab >>Deformation and Damage Mechanisms During Thermomechanical Fatigue of a Single-crystal Superalloy in the <001> and <011> Directions
    2012 (English)In: Superalloy 2012: 12th International Symposium on Superalloys / [ed] Eric S. Huron, Roger C. Reed, Mark C. Hardy, Michael J. Mills, Rick E. Montero, Pedro D. Portella and Jack Telesman, The Minerals, Metals, and Materials Society, 2012, p. 215-223Conference paper, Oral presentation only (Refereed)
    Abstract [en]

    The purpose of this paper is to investigate the differences in mechanical response and microstructural behavior when the single-crystal Ni-based superalloy CMSX-4 is subjected to thermomechanical fatigue (TMF) in two different crystallographic directions, <001> and <011>. An out-of-phase (OP) straincontrolled TMF cycle with R=-∞ in the temperature range 100 to 850 °C was used. As expected, the material exhibited, when loaded in the <001> direction, a higher number of cycles to failure compared to the <011> direction, when equivalent strain ranges were compared. High strain ranges led to crystallographic fractures along one of the {111} planes while low strain ranges led to non-crystallographic fractures. This result was valid for both <001> and <011> directions. Specimens with random fractures also showed recrystallization close to the fracture surface. Twinning was found to be a major deformation mechanism for most specimens. A change in deformation mechanism from twinning to shearing was found in specimens subjected to loading in the <011> direction when going from low to high strain ranges. This investigation also indicated that crack propagation is a consequence of recrystallization and not the other way around.

    Place, publisher, year, edition, pages
    The Minerals, Metals, and Materials Society, 2012
    Keywords
    singel-crystal supearlloy, thermomechanical fatigue, deformation mechanisms, twinning, shearing
    National Category
    Engineering and Technology Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-81528 (URN)978-0-470-94320-5 (ISBN)
    Conference
    Superalloy 2012: 12th International Symposium on Superalloys, September 9-13 2012, Seven Springs, USA
    Available from: 2012-09-18 Created: 2012-09-18 Last updated: 2014-10-27Bibliographically approved
    2. Crystallographic Orientation Influence on the Serrated Yielding Behavior of a Single-Crystal Superalloy
    Open this publication in new window or tab >>Crystallographic Orientation Influence on the Serrated Yielding Behavior of a Single-Crystal Superalloy
    2013 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 6, no 2, p. 437-444Article in journal (Refereed) Published
    Abstract [en]

    Since Ni-based single-crystal superalloys are anisotropic materials, their behavior in different crystal orientations is of great interest. In this study, the yielding behavior in both tension and compression for 〈001〉, 〈011〉 and 〈111〉 oriented materials at 500 °C has been investigated. The 〈011〉 direction showed a serrated yielding behavior, a great tension/compression asymmetry in yield strength and visible deformation bands. However, the 〈001〉 and 〈111〉 directions showed a more homogeneous yielding, less tension/compression asymmetry in yield strength and no deformation bands. Microstructure investigations showed that the serrated yielding behavior of the 〈011〉 direction can be attributed to the appearance of dynamic strain aging (DSA) and that only one slip system is active in this direction during plastic deformation.

    Place, publisher, year, edition, pages
    Basel: MDPI AG, 2013
    Keywords
    single.crystals; superalloy; yield phenomena; tension/compression asymmetry; dynamic strain aging
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-88406 (URN)10.3390/ma6020437 (DOI)000315398600004 ()
    Available from: 2013-03-26 Created: 2013-02-05 Last updated: 2017-12-06Bibliographically approved
    3. Creep and Stress Relaxation Anisotropy of a Single-Crystal Superalloy
    Open this publication in new window or tab >>Creep and Stress Relaxation Anisotropy of a Single-Crystal Superalloy
    2014 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 45, no 5, p. 2532-2544Article in journal (Refereed) Published
    Abstract [en]

    In this study, the TMF stress relaxation and creep behavior at 1023 K and 1223 K (750 °C and 950 °C) have been investigated for a Ni-based single-crystal superalloy. Specimens with three different crystal orientations along their axes were tested; 〈001〉, 〈011〉, and 〈111〉, respectively. A highly anisotropic behavior during TMF stress relaxation was found where the 〈111〉 direction significantly shows the worst properties of all directions. The TMF stress relaxation tests were performed in both tension and compression and the results indicate a clear tension/compression asymmetry for all directions where the greatest asymmetry was observed for the 〈001〉 direction at 1023 K (750 °C); here the creep rate was ten times higher in compression than tension. This study also shows that TMF cycling seems to influence the creep rate during stress relaxation temporarily, but after some time it decreases again and adapts to the pre-unloading creep rate. Creep rates from the TMF stress relaxation tests are also compared to conventional constant load creep rates and a good agreement is found.

    Place, publisher, year, edition, pages
    Springer, 2014
    Keywords
    Single-crystal superalloy, thermomechanical fatigue, creep, stress relaxation, deformation mechanism
    National Category
    Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-89949 (URN)10.1007/s11661-014-2198-0 (DOI)000334428000026 ()
    Note

    On the day of the defense data of the Licentiate Thesis the status of this article was Manuscript.

    Available from: 2013-03-12 Created: 2013-03-12 Last updated: 2017-12-06Bibliographically approved
  • 332.
    Segersäll, Mikael
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    On Thermomechanical Fatigue of Single-Crystal Superalloys2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Thanks to their excellent mechanical and chemical properties at temperatures up to 1000 °C, nickel-based superalloys are used in critical components in high-temperature applications such as gas turbines and aero engines. One of the most critical components in a gas turbine is the turbine blade, and to improve the creep and fatigue properties of this component, it is sometimes cast in single-crystal form rather than in the more conventional poly-crystalline form. Gas turbines are most commonly used for power generation and the turbine efficiency is highly dependent on the performance of the superalloys.

    Today, many gas turbines are used as a complement for renewable energy sources, for example when the wind is not blowing or when the sun is not shining. This means that the turbine runs differently compared to earlier, when it ran for longer time periods with a lower number of start-ups and shut-downs. This new way of running the turbine, with an increased number of start-ups and shut-downs, results in new conditions for critical components, and one way to simulate these conditions is to perform thermomechanical fatigue (TMF) testing in the laboratory. During TMF, both mechanical strain and temperature are cycled at the same time, and one fatigue cycle corresponds to the conditions experienced by the turbine blade during one start-up and shutdown of the turbine engine.

    In the work leading to this PhD thesis, TMF testing of single-crystal superalloys was first performed in the laboratory and this was then followed microstructure investigations to study the occurring deformation and damage mechanisms. Specimens with different crystallographic directions have been tested in order to investigate the anisotropic behaviour shown by these materials. Results show a significant orientation dependence during TMF, in which specimens with a low elastic stiffness perform better. However, it is also shown that specimens with a higher number of active slip planes perform better during TMF compared to specimens with less active slip systems. This is because a higher number of active slip systems results in a more widespread deformation and seems to be beneficial for the TMF life. Further, microscopy shows that the deformation during TMF is localised to several deformation bands and that different deformation and damage mechanisms prevail according to in which crystal orientation the material is loaded. Deformation twinning is shown to be a major deformation mechanism during TMF, and the interception of twins seems to trigger recrystallization. This work also studies the effects of alloying a single-crystal superalloy with Si or Re, and results show a significant Si-effect where the TMF life increases by a factor of 2 when Si is added to the alloy.

    Finally, this research results in an increased knowledge of the mechanical response as well as a deeper understanding of the deformation and damage mechanisms that occur in single-crystal superalloys during TMF. It is believed that in the long-term, this can contribute to a more efficient and reliable power generation by gas turbines.

    List of papers
    1. Crystallographic Orientation Influence on the Serrated Yielding Behavior of a Single-Crystal Superalloy
    Open this publication in new window or tab >>Crystallographic Orientation Influence on the Serrated Yielding Behavior of a Single-Crystal Superalloy
    2013 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 6, no 2, p. 437-444Article in journal (Refereed) Published
    Abstract [en]

    Since Ni-based single-crystal superalloys are anisotropic materials, their behavior in different crystal orientations is of great interest. In this study, the yielding behavior in both tension and compression for 〈001〉, 〈011〉 and 〈111〉 oriented materials at 500 °C has been investigated. The 〈011〉 direction showed a serrated yielding behavior, a great tension/compression asymmetry in yield strength and visible deformation bands. However, the 〈001〉 and 〈111〉 directions showed a more homogeneous yielding, less tension/compression asymmetry in yield strength and no deformation bands. Microstructure investigations showed that the serrated yielding behavior of the 〈011〉 direction can be attributed to the appearance of dynamic strain aging (DSA) and that only one slip system is active in this direction during plastic deformation.

    Place, publisher, year, edition, pages
    Basel: MDPI AG, 2013
    Keywords
    single.crystals; superalloy; yield phenomena; tension/compression asymmetry; dynamic strain aging
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-88406 (URN)10.3390/ma6020437 (DOI)000315398600004 ()
    Available from: 2013-03-26 Created: 2013-02-05 Last updated: 2017-12-06Bibliographically approved
    2. Low-Cycle Fatigue Behaviour of a Ni-Based Single-Crystal Superalloy
    Open this publication in new window or tab >>Low-Cycle Fatigue Behaviour of a Ni-Based Single-Crystal Superalloy
    2014 (English)In: Advanced Materials Research, ISSN 1022-6680, E-ISSN 1662-8985, Vol. 891-892, p. 416-421Article in journal (Refereed) Published
    Abstract [en]

    In this study, low-cycle fatigue (LCF) tests at 500 degrees C in the < 001 >, < 011 > and < 111 > directions have been performed for the Ni-based single-crystal superalloy MD2. All tests were carried out in strain control with R-is an element of = -1. The < 001 > direction has the lowest stiffness of the three directions and also shows the best fatigue properties in this study followed by the < 011 > and < 111 > directions, respectively. It is well recognised that Ni-based single-crystal superalloys show a tension/compression asymmetry in yield strength and this study shows that a tension/compression asymmetry is also present during LCF conditions. At mid-life, the < 001 > direction generally has a higher stress in tension than in compression, while the opposite is true for the < 011 > direction. For the < 111 > direction the asymmetry is found to be strain range dependent. The < 011 > and < 111 > directions show a cyclic hardening behaviour when comparing cyclic stress-strain curves with monotonic stress-strain curves. In addition, the < 011 > and < 111 > directions show a serrated yielding behaviour for a number of cycles while the yielding of the < 001 > direction is more stable.

    Place, publisher, year, edition, pages
    Trans Tech Publications Inc., 2014
    Keywords
    Ni-based single-crystal superalloy, LCF, tension/compression asymmetry, serrated yielding
    National Category
    Engineering and Technology Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-104750 (URN)10.4028/www.scientific.net/AMR.891-892.416 (DOI)000337767700064 ()
    Conference
    Fatigue 2014, 11th International Fatigue Congress, Melbourne Cricket Ground, Melbourne, Australia, 2-7 March 2014.
    Available from: 2014-02-25 Created: 2014-02-25 Last updated: 2017-12-05
    3. In- and Out-of Phase Thermomechanical Fatigue of a Ni-Based Single-Crystal Superalloy
    Open this publication in new window or tab >>In- and Out-of Phase Thermomechanical Fatigue of a Ni-Based Single-Crystal Superalloy
    2014 (English)In: 2014 EUROSUPERALLOYS 2014 – 2nd European Symposium on Superalloys and their Applications / [ed] J. Y. Guédou and J. Choné, EDP Sciences, 2014, Vol. 14, p. Article no. 19003-Conference paper, Published paper (Refereed)
    Abstract [en]

    In this study, the difference between in-phase (IP) and out-of-phase (OP) thermomechanical fatigue (TMF) cycling from 100 to 750 °C has been investigated for the Ni-based single-crystal superalloy MD2. In addition, two different crystal orientations were studied, the ⟨001⟩ and ⟨011⟩ orientations respectively. When comparing IP and OP TMF lives, a strain range dependency is found for the ⟨001⟩ direction. For high strain ranges, IP cycling leads to a higher number of cycles to failure compared to OP. However at lower strain ranges, OP cycling leads to a higher number of cycles to failure compared to IP. Microstructure investigation shows that for the ⟨001⟩ direction, deformation twinning within the γ/γ′-microstructure is much more pronounced during OP conditions compared to IP. However for the ⟨011⟩ direction, the opposite is observed; twinning is more pronounced during IP TMF. From the microstructure investigation it is also visible that intersections between twins seems to trigger formation of TCP phases and recrystallization. These intersections also work as initiation points for TMF damage.

    Place, publisher, year, edition, pages
    EDP Sciences, 2014
    Series
    MATEC Web of Conferences, ISSN 2261-236X ; 14
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-111066 (URN)10.1051/matecconf/20141419003 (DOI)000351930400073 ()
    Conference
    EUROSUPERALLOYS 2014 – 2nd European Symposium on Superalloys and their Applications, 12-16 May 2014, Giens, France
    Available from: 2014-10-06 Created: 2014-10-06 Last updated: 2016-05-26Bibliographically approved
    4. Deformation and Damage Mechanisms During Thermomechanical Fatigue of a Single-crystal Superalloy in the <001> and <011> Directions
    Open this publication in new window or tab >>Deformation and Damage Mechanisms During Thermomechanical Fatigue of a Single-crystal Superalloy in the <001> and <011> Directions
    2012 (English)In: Superalloy 2012: 12th International Symposium on Superalloys / [ed] Eric S. Huron, Roger C. Reed, Mark C. Hardy, Michael J. Mills, Rick E. Montero, Pedro D. Portella and Jack Telesman, The Minerals, Metals, and Materials Society, 2012, p. 215-223Conference paper, Oral presentation only (Refereed)
    Abstract [en]

    The purpose of this paper is to investigate the differences in mechanical response and microstructural behavior when the single-crystal Ni-based superalloy CMSX-4 is subjected to thermomechanical fatigue (TMF) in two different crystallographic directions, <001> and <011>. An out-of-phase (OP) straincontrolled TMF cycle with R=-∞ in the temperature range 100 to 850 °C was used. As expected, the material exhibited, when loaded in the <001> direction, a higher number of cycles to failure compared to the <011> direction, when equivalent strain ranges were compared. High strain ranges led to crystallographic fractures along one of the {111} planes while low strain ranges led to non-crystallographic fractures. This result was valid for both <001> and <011> directions. Specimens with random fractures also showed recrystallization close to the fracture surface. Twinning was found to be a major deformation mechanism for most specimens. A change in deformation mechanism from twinning to shearing was found in specimens subjected to loading in the <011> direction when going from low to high strain ranges. This investigation also indicated that crack propagation is a consequence of recrystallization and not the other way around.

    Place, publisher, year, edition, pages
    The Minerals, Metals, and Materials Society, 2012
    Keywords
    singel-crystal supearlloy, thermomechanical fatigue, deformation mechanisms, twinning, shearing
    National Category
    Engineering and Technology Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-81528 (URN)978-0-470-94320-5 (ISBN)
    Conference
    Superalloy 2012: 12th International Symposium on Superalloys, September 9-13 2012, Seven Springs, USA
    Available from: 2012-09-18 Created: 2012-09-18 Last updated: 2014-10-27Bibliographically approved
    5. Creep and Stress Relaxation Anisotropy of a Single-Crystal Superalloy
    Open this publication in new window or tab >>Creep and Stress Relaxation Anisotropy of a Single-Crystal Superalloy
    2014 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 45, no 5, p. 2532-2544Article in journal (Refereed) Published
    Abstract [en]

    In this study, the TMF stress relaxation and creep behavior at 1023 K and 1223 K (750 °C and 950 °C) have been investigated for a Ni-based single-crystal superalloy. Specimens with three different crystal orientations along their axes were tested; 〈001〉, 〈011〉, and 〈111〉, respectively. A highly anisotropic behavior during TMF stress relaxation was found where the 〈111〉 direction significantly shows the worst properties of all directions. The TMF stress relaxation tests were performed in both tension and compression and the results indicate a clear tension/compression asymmetry for all directions where the greatest asymmetry was observed for the 〈001〉 direction at 1023 K (750 °C); here the creep rate was ten times higher in compression than tension. This study also shows that TMF cycling seems to influence the creep rate during stress relaxation temporarily, but after some time it decreases again and adapts to the pre-unloading creep rate. Creep rates from the TMF stress relaxation tests are also compared to conventional constant load creep rates and a good agreement is found.

    Place, publisher, year, edition, pages
    Springer, 2014
    Keywords
    Single-crystal superalloy, thermomechanical fatigue, creep, stress relaxation, deformation mechanism
    National Category
    Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-89949 (URN)10.1007/s11661-014-2198-0 (DOI)000334428000026 ()
    Note

    On the day of the defense data of the Licentiate Thesis the status of this article was Manuscript.

    Available from: 2013-03-12 Created: 2013-03-12 Last updated: 2017-12-06Bibliographically approved
    6. Modelling of Thermomechanical Fatigue Stress Relaxation in a Single-Crystal Nickel-Base Superalloy
    Open this publication in new window or tab >>Modelling of Thermomechanical Fatigue Stress Relaxation in a Single-Crystal Nickel-Base Superalloy
    2014 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 90, p. 61-70Article in journal (Refereed) Published
    Abstract [en]

    The thermomechanical fatigue (TMF) stress relaxation of the single-crystal nickel-base superalloy MD2 has been analysed and modelled in this paper. In-phase and out-of-phase TMF experiments in the nominal [001],[011] and [111] crystal orientations have been performed. The TMF cycle consists of two loadings each with a 100 h long hold-time. A simple crystallographic creep model, based on Norton’s creep law, has been developed and used in conjunction with a crystal plasticity model. The model takes anisotropy and tension/compression asymmetry into account, where the anisotropic behaviour is based on the crystallographic stress state. The values of the creep parameters in the anisotropic expression were determined by inverse modelling of the conducted TMF experiments, a parameter optimisation were performed. The developed model predicts the stress relaxation seen in the TMF experiments with good correlation.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    Keywords
    single-crystal superalloy, thermomechanical fatigue, creep, stress relaxation, anisotropy, parameter optimisation
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-107983 (URN)10.1016/j.commatsci.2014.04.009 (DOI)000336656200009 ()
    Available from: 2014-06-24 Created: 2014-06-24 Last updated: 2017-12-05Bibliographically approved
    7. Influence of crystal orientation on the thermomechanical fatigue behaviour in a single-crystal superalloy
    Open this publication in new window or tab >>Influence of crystal orientation on the thermomechanical fatigue behaviour in a single-crystal superalloy
    2015 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 623, no 19, p. 68-77Article in journal (Refereed) Published
    Abstract [en]

    In this study, the influuence from crystal orientation on the thermomehanical fatigue (TMF) behaviour of the recently developed single-rystal superalloy STAL-15 is considered, both from an experimental and a nite element (FE) perspective. Experimental results show that there is a strong inuence from the elastic stiffness, with respect to the loading direction, on the TMF life. However, the results also indicate that the number of active slip planes duringdeformation inuence the TMF life, where specimens with a higher number of active slip planes are favoured compared to specimens with fewer active slip planes. The higher number of active slip planes results in a more widespread deformation compared to a more conentrated deformation when only one slip plane is active. Deformation bands with smeared and elongated  γ-precipitates together with deformation twinning were found to be major deformation mechanisms, where the twins primarily were observed in specimens with several active slip planes. From an FE-perspective, therystal orientation with respect to the loading direction is quantied and adopted into a framework which makes it possible to describe the internal crystallographic arrangement and its entities in a material model. Further, a material model which incorporates the crystalorientation is able to predict the number of slip planes observed from microstructural observations, as well as the elasticstiness of the material with respect to the loading direction.

    Place, publisher, year, edition, pages
    Elsevier, 2015
    Keywords
    Single-crystal superalloy, Crystal orientation dependence, Thermome hanical fatigue, Deformation mechanisms, Finite element
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-111639 (URN)10.1016/j.msea.2014.11.026 (DOI)000349063100009 ()
    Note

    On the day of the defence day the status of this article was Manuscript.

    The work has been financially supported by Siemens Industrial Turbomachinery AB in Finspang, Sweden, and the Swedish Energy Agency, via the Research Consortium of Materials Technology for Thermal Energy Processes, Grant no. KME-702. In addition, the support from the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU #2009-00971) is also acknowledged.

    Available from: 2014-10-27 Created: 2014-10-27 Last updated: 2017-12-05Bibliographically approved
    8. Thermal-­Mechanical Fatigue Behaviour of a New Single Crystal Superalloy: Effects of Si and Re Alloying
    Open this publication in new window or tab >>Thermal-­Mechanical Fatigue Behaviour of a New Single Crystal Superalloy: Effects of Si and Re Alloying
    Show others...
    2015 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 95, p. 456-467Article in journal (Refereed) Published
    Abstract [en]

    The mechanical behaviour of a new single crystal superalloy suitable for power generation applications is considered. Effects of alloying with either Si or Re are elucidated. Out-of-phase thermal-mechanical fatigue is emphasised, although to clarify the effects arising some static creep deformation tests are also carried out. A significant Si-effect is found: a modest addition of 0.25 wt. % Si increases the TMF life by a factor of 2. Thinner deformation bands which traverse the γ'-phase are promoted by Si alloying, with a concomitant greater resistance to recrystallization and cracking along them. Alloying with Re, whilst improving the creep behaviour more markedly than Si, does not have such a strong effect on TMF life. The results provide insights into the composition/performance relationships relevant to the TMF performance of single crystal superalloys.

    Place, publisher, year, edition, pages
    Elsevier, 2015
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-111640 (URN)10.1016/j.actamat.2015.03.060 (DOI)000358626200046 ()
    Note

    On the day of the defence date the status of this article was Manuscript.

    The work has been supported financially by Siemens Industrial Turbomachinery AB in Finspang, Sweden and the Swedish Energy Agency, via the Research Consortium of Materials Technology for Thermal Energy Processes, Grant No. KME-702. In addition, the support from the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU #2009-00971) is also acknowledged. Funding from the Engineering and Physical Sciences Research Council (EPSRC) of the UK is acknowledged under Grant EP/J013501/1 'Multifunctional High Performance Alloys for Extreme Environments'.

    Available from: 2014-10-27 Created: 2014-10-27 Last updated: 2017-12-05Bibliographically approved
  • 333.
    Segersäll, Mikael
    et al.
    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.
    Norman, Viktor
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Fredriksson, Claes
    Student Reactions to CES EduPack in an Undergraduate Materials Selection Course2015Conference paper (Refereed)
  • 334.
    Segersäll, Mikael
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Kontis, Paraskevas
    Department of Materials, University of Oxford, Oxford, United Kingdom.
    Pedrazzini, Stella
    Department of Materials, University of Oxford, United Kingdom.
    Bagot, Paul A.J.
    Department of Materials, University of Oxford, Oxford, United Kingdom.
    Moody, Michael P.
    Department of Materials, University of Oxford, Oxford, United Kingdom.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Reed, Roger C.
    Department of Materials, University of Oxford, Oxford, United Kingdom.
    Thermal-­Mechanical Fatigue Behaviour of a New Single Crystal Superalloy: Effects of Si and Re Alloying2015In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 95, p. 456-467Article in journal (Refereed)
    Abstract [en]

    The mechanical behaviour of a new single crystal superalloy suitable for power generation applications is considered. Effects of alloying with either Si or Re are elucidated. Out-of-phase thermal-mechanical fatigue is emphasised, although to clarify the effects arising some static creep deformation tests are also carried out. A significant Si-effect is found: a modest addition of 0.25 wt. % Si increases the TMF life by a factor of 2. Thinner deformation bands which traverse the γ'-phase are promoted by Si alloying, with a concomitant greater resistance to recrystallization and cracking along them. Alloying with Re, whilst improving the creep behaviour more markedly than Si, does not have such a strong effect on TMF life. The results provide insights into the composition/performance relationships relevant to the TMF performance of single crystal superalloys.

  • 335.
    Segersäll, Mikael
    et al.
    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.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Influence of crystal orientation on the thermomechanical fatigue behaviour in a single-crystal superalloy2015In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 623, no 19, p. 68-77Article in journal (Refereed)
    Abstract [en]

    In this study, the influuence from crystal orientation on the thermomehanical fatigue (TMF) behaviour of the recently developed single-rystal superalloy STAL-15 is considered, both from an experimental and a nite element (FE) perspective. Experimental results show that there is a strong inuence from the elastic stiffness, with respect to the loading direction, on the TMF life. However, the results also indicate that the number of active slip planes duringdeformation inuence the TMF life, where specimens with a higher number of active slip planes are favoured compared to specimens with fewer active slip planes. The higher number of active slip planes results in a more widespread deformation compared to a more conentrated deformation when only one slip plane is active. Deformation bands with smeared and elongated  γ-precipitates together with deformation twinning were found to be major deformation mechanisms, where the twins primarily were observed in specimens with several active slip planes. From an FE-perspective, therystal orientation with respect to the loading direction is quantied and adopted into a framework which makes it possible to describe the internal crystallographic arrangement and its entities in a material model. Further, a material model which incorporates the crystalorientation is able to predict the number of slip planes observed from microstructural observations, as well as the elasticstiness of the material with respect to the loading direction.

  • 336.
    Segersäll, Mikael
    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.
    Crystallographic Orientation Influence on the Serrated Yielding Behavior of a Single-Crystal Superalloy2013In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 6, no 2, p. 437-444Article in journal (Refereed)
    Abstract [en]

    Since Ni-based single-crystal superalloys are anisotropic materials, their behavior in different crystal orientations is of great interest. In this study, the yielding behavior in both tension and compression for 〈001〉, 〈011〉 and 〈111〉 oriented materials at 500 °C has been investigated. The 〈011〉 direction showed a serrated yielding behavior, a great tension/compression asymmetry in yield strength and visible deformation bands. However, the 〈001〉 and 〈111〉 directions showed a more homogeneous yielding, less tension/compression asymmetry in yield strength and no deformation bands. Microstructure investigations showed that the serrated yielding behavior of the 〈011〉 direction can be attributed to the appearance of dynamic strain aging (DSA) and that only one slip system is active in this direction during plastic deformation.

  • 337.
    Segersäll, Mikael
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan J.
    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.
    Creep and Stress Relaxation Anisotropy of a Single-Crystal Superalloy2014In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 45, no 5, p. 2532-2544Article in journal (Refereed)
    Abstract [en]

    In this study, the TMF stress relaxation and creep behavior at 1023 K and 1223 K (750 °C and 950 °C) have been investigated for a Ni-based single-crystal superalloy. Specimens with three different crystal orientations along their axes were tested; 〈001〉, 〈011〉, and 〈111〉, respectively. A highly anisotropic behavior during TMF stress relaxation was found where the 〈111〉 direction significantly shows the worst properties of all directions. The TMF stress relaxation tests were performed in both tension and compression and the results indicate a clear tension/compression asymmetry for all directions where the greatest asymmetry was observed for the 〈001〉 direction at 1023 K (750 °C); here the creep rate was ten times higher in compression than tension. This study also shows that TMF cycling seems to influence the creep rate during stress relaxation temporarily, but after some time it decreases again and adapts to the pre-unloading creep rate. Creep rates from the TMF stress relaxation tests are also compared to conventional constant load creep rates and a good agreement is found.

  • 338.
    Segersäll, Mikael
    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. Siemens Industrial Turbomachinery AB, Finspång, Sweden .
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    In- and Out-of Phase Thermomechanical Fatigue of a Ni-Based Single-Crystal Superalloy2014In: 2014 EUROSUPERALLOYS 2014 – 2nd European Symposium on Superalloys and their Applications / [ed] J. Y. Guédou and J. Choné, EDP Sciences, 2014, Vol. 14, p. Article no. 19003-Conference paper (Refereed)
    Abstract [en]

    In this study, the difference between in-phase (IP) and out-of-phase (OP) thermomechanical fatigue (TMF) cycling from 100 to 750 °C has been investigated for the Ni-based single-crystal superalloy MD2. In addition, two different crystal orientations were studied, the ⟨001⟩ and ⟨011⟩ orientations respectively. When comparing IP and OP TMF lives, a strain range dependency is found for the ⟨001⟩ direction. For high strain ranges, IP cycling leads to a higher number of cycles to failure compared to OP. However at lower strain ranges, OP cycling leads to a higher number of cycles to failure compared to IP. Microstructure investigation shows that for the ⟨001⟩ direction, deformation twinning within the γ/γ′-microstructure is much more pronounced during OP conditions compared to IP. However for the ⟨011⟩ direction, the opposite is observed; twinning is more pronounced during IP TMF. From the microstructure investigation it is also visible that intersections between twins seems to trigger formation of TCP phases and recrystallization. These intersections also work as initiation points for TMF damage.

  • 339.
    Segersäll, Mikael
    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, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics.
    High Temperature Stress Relaxation of a Ni-based Single-Crystal Superalloy2013Conference paper (Refereed)
  • 340.
    Segersäll, Mikael
    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.
    Low-Cycle Fatigue Behaviour of a Ni-Based Single-Crystal Superalloy2014In: Advanced Materials Research, ISSN 1022-6680, E-ISSN 1662-8985, Vol. 891-892, p. 416-421Article in journal (Refereed)
    Abstract [en]

    In this study, low-cycle fatigue (LCF) tests at 500 degrees C in the < 001 >, < 011 > and < 111 > directions have been performed for the Ni-based single-crystal superalloy MD2. All tests were carried out in strain control with R-is an element of = -1. The < 001 > direction has the lowest stiffness of the three directions and also shows the best fatigue properties in this study followed by the < 011 > and < 111 > directions, respectively. It is well recognised that Ni-based single-crystal superalloys show a tension/compression asymmetry in yield strength and this study shows that a tension/compression asymmetry is also present during LCF conditions. At mid-life, the < 001 > direction generally has a higher stress in tension than in compression, while the opposite is true for the < 011 > direction. For the < 111 > direction the asymmetry is found to be strain range dependent. The < 011 > and < 111 > directions show a cyclic hardening behaviour when comparing cyclic stress-strain curves with monotonic stress-strain curves. In addition, the < 011 > and < 111 > directions show a serrated yielding behaviour for a number of cycles while the yielding of the < 001 > direction is more stable.

  • 341.
    Segersäll, Mikael
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    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.
    Deformation and Damage Mechanisms During Thermomechanical Fatigue of a Single-crystal Superalloy in the <001> and <011> Directions2012In: Superalloy 2012: 12th International Symposium on Superalloys / [ed] Eric S. Huron, Roger C. Reed, Mark C. Hardy, Michael J. Mills, Rick E. Montero, Pedro D. Portella and Jack Telesman, The Minerals, Metals, and Materials Society, 2012, p. 215-223Conference paper (Refereed)
    Abstract [en]

    The purpose of this paper is to investigate the differences in mechanical response and microstructural behavior when the single-crystal Ni-based superalloy CMSX-4 is subjected to thermomechanical fatigue (TMF) in two different crystallographic directions, <001> and <011>. An out-of-phase (OP) straincontrolled TMF cycle with R=-∞ in the temperature range 100 to 850 °C was used. As expected, the material exhibited, when loaded in the <001> direction, a higher number of cycles to failure compared to the <011> direction, when equivalent strain ranges were compared. High strain ranges led to crystallographic fractures along one of the {111} planes while low strain ranges led to non-crystallographic fractures. This result was valid for both <001> and <011> directions. Specimens with random fractures also showed recrystallization close to the fracture surface. Twinning was found to be a major deformation mechanism for most specimens. A change in deformation mechanism from twinning to shearing was found in specimens subjected to loading in the <011> direction when going from low to high strain ranges. This investigation also indicated that crack propagation is a consequence of recrystallization and not the other way around.

  • 342.
    Seifeddine, Salem
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Characteristics of cast aluminium-silicon alloys: microstructures and mechanical properties2006Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Applications of aluminium alloys are spreading in many industrial fields due to the excellent combination of castability, mechanical performance and lightness assured by such material. This project aims to establish a methodology in bringing the foundry process closer to the casting designer, and thereby leading to a more reliable and more optimised design. Improvement in the degree of integration between processing, metallurgical and mechanical properties of cast aluminium alloys will lead to a shorter lead-time from the very first design attempt, and sounder components, both of which strengthen the competitiveness of the material and the foundry industry.

    The microstructural features and mechanical properties of cast aluminium alloys are sensitive to composition, melt treatment, the casting process and formation of defects during mould filling, solidification and post-solidification treatment. The microstructural characteristics and the mechanical properties of A1-Si based alloys have been investigated by studies on various different commercial cast components and through systematically designed casting experiments with alloys containing various Si, Mg, Cu, Fe and Mn concentrations solidified under a wide range of cooling conditions. In this work, a gradient solidification thechnique has been employed, providing samples with a low content of oxide films and few porosity defects and with a well-fed and homogenous microstructure. In such samples the alloy's mechanical properties are determined by the microstructure constituents and not by any defects. The influence of the casting process on the microstructural formations and tensile properties has been thoroughly elucidated. Furthermore, relationships between microstructure characteristics and mechanical properties are assessed and discussed. The results indicate that Mg and Cu, due to the formation of A12Cu and Mg2Si have a significant role on the alloy strength, especially after thermal treatment. Significant advances have been mead in understanding the relationship between Fe and Mn levels and their contribution to the tensile strength. While Fe and its compounds, particularly the A15FeSi-needles, adversely influence the ultimate tensile strength and ductility, Mn has been found to not fully neutralize the deleterious character of iron, and especially the influence it has on ductility.

    Algorithms to predict the micorstructural parameters such as porosity, grain size, the volume fraction of different phases, especially A12Cu and Mg2Si, and their influence on the tensile strength, have been developed. The relationships developed between process, microstructure and mechanical properties have been implemented in commercial simulation software.

  • 343.
    Seifeddine, Salem
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Johansson, Sten
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Svensson, Ingvar L
    Komponentteknologi Ingenjörshögskolan i Jönköping.
    The influence of cooling rate and manganese content on the beta-Al5FeSi phase formation and formation and mechanical properties of Al-Si based alloys2008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 490, no 39845, p. 385-390Article in journal (Refereed)
    Abstract [en]

    The present study investigates the influence of manganese level and cooling rate on the formation of iron compounds and mechanical properties of Al–9%Si alloys containing 0.3%Fe. It has been established that high cooling rates and Mn additions are not able to totally nullify the formation of β-Al5FeSi-needles onto α-Al15(Fe,Mn)3Si2-Chinese scripts even at Mn:Fe ratio of 2:1, but produces improvement in tensile strength unlike the ductility which suffers a loss with the increment of Mn concentrations.

  • 344.
    Selegård, Linnéa
    et al.
    Saab Aeronautics, Linköping.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Billenius, Annethe
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Petersén, Gert
    Saab Aeronautics, Linköping.
    Ess, Markus
    Jonsson, Mattias
    Saab Aeronautics, Linköping.
    Residual Stresses in Dengeling-Treated Aluminum Alloy AA 70502017In: Residual Stresses 2016: ICRS-10, Materials Research Proceedings 2 (2017), Materials Research Foum , 2017, Vol. 2, p. 425-430Conference paper (Refereed)
    Abstract [en]

    Dengeling is a new method for mechanical surface treatment of metallic parts to enhance fatigue properties. The treatment produces consecutive lines of indents by a spherical indenter, resulting in compressive residual stresses in a surface layer. This paper investigated residual stresses, surface roughness and near surface deformation, in specimens of AA 7050 T7451 after different dengeling treatments. The effect of indent overlap (0%, 25% and 50%) and indenter size (∅3 and ∅8 mm) were studied. X-Ray diffraction measurements revealed that plastic deformation and compressive residual stresses were generated in a surface layer of about 1 mm by treatments using the ∅3 mm indenter and about 1.2 mm by treatment using the ∅8 mm indenter. Anisotropic residual stress fields were observed with higher compressive residual stresses (-360 MPa for 50% indent overlap, independent of indenter size) perpendicular to indent lines and lower (max -270 MPa for all the treatments) parallel to indent lines. Increasing the overlap between indents gave higher subsurface compressive residual stresses only in the transverse direction of indent lines. It also reduced the surface roughness. Best surface finish (Ra below 1 μm) was obtained when using the ∅8 mm indenter and 50% indent overlap.

  • 345.
    Sezavar, Arezoo
    et al.
    Ferdowsi Univ Mashhad, Iran.
    Sajjadi, Seyed Abdolkarim
    Ferdowsi Univ Mashhad, Iran.
    Babakhani, Abolfazl
    Ferdowsi Univ Mashhad, Iran.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Thermal Cyclic Fatigue Behavior of Nanostructured YSZ/NiCrAlY Compositionally Graded Thermal Barrier Coatings2019In: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 92, no 1-2, p. 89-107Article in journal (Refereed)
    Abstract [en]

    In this research, thermal cyclic fatigue (TCF) behavior of a compositionally graded layer (CGL) nanostructured coating was investigated and compared with the TCF behavior of a micro-CGL coating. The layers, as a thermal barrier coating (TBC), were made from nanostructured and/or conventional micro-sized yttria-stabilized zirconia (YSZ) and NiCrAlY powders. According to the composition of each layer, a certain ratio of YSZ/NiCrAlY powder was mixed and deposited by air plasma spray process on IN 738-LC as a substrate. In order to investigate the effect of temperature on the lifetime of coatings, TCF tests were conducted at two different high temperatures (900 and 1100 degrees C). These tests were done by holding the samples at the mentioned temperatures for 1h and then fast cooling to 100 degrees C by compressed air for 10min. Microstructural evaluation showed that there were some differences between the damage mechanisms of these two groups of compositionally graded TBCs. The results also showed that the average thermal cyclic lifetime of nanostructured compositionally graded TBCs is approximately 1.6 times higher than that of the micro-one. Moreover, it was indicated that the presence of much more spinel oxide regions formed at higher temperature has a remarkable effect on the lifetime of compositionally graded TBCs. [GRAPHICS] .

  • 346.
    Sezavar, Arezoo
    et al.
    Ferdowsi Univ Mashhad, Iran.
    Sajjadi, Seyed Abdolkarim
    Ferdowsi Univ Mashhad, Iran.
    Babakhani, Abolfazl
    Ferdowsi Univ Mashhad, Iran.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Beijing Engn Technol Res Ctr Surface Strengthenin, Peoples R China.
    Oxidation behavior of a nanostructured compositionally graded layer (CGL) thermal barrier coating (TBC) deposited on IN-738LC2019In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 374, p. 374-382Article in journal (Refereed)
    Abstract [en]

    In the present study, isothermal oxidation behavior of nanostructured compositionally graded layer (CGL) thermal barrier coatings (TBC) has been investigated. Moreover, the property of the produced coating was compared with that of a micro CGL, as well as a conventional bilayer TBC. For this purpose, nanostructured and micro Y2O3-stabilized ZrO2 (YSZ) were used as ceramic-powder feedstocks and three coatings were deposited by air plasma spray (APS) procedure on IN-738LC superalloy. The first TBC consisted of 100 wt% NiCrAlY as the bond coat, NiCrAlY and nanostructured YSZ in the weight ratio of 50:50 as the graded layer, and 100 wt% YSZ as the top coat. In the second coating a micro YSZ feedstock, instead of the nanostructured one, was used. The third coating was a conventional bilayer coating consisted of a bond coat and top coat. Isothermal oxidation was carried out at 1100 degrees in an atmospheric furnace for 10, 50, 100 and 150 h to investigate the kinetic of growth of thermally grown oxide (TGO). Microstructure evaluation, elemental and phase analysis, and hardness test were performed using field emission scanning electron microscopy, X-ray diffraction and Vickers hardness test. The results showed that nanostructured compositionally graded layer TBC has the lowest TGO growth rate compared with the other coatings. The hardness values of this kind of coating increased rapidly after 10 h exposure at 1100 degrees C, and then increased slightly to a certain constant value. Nanostructured coating showed different sintering effect due to its bimodal structure. Upon isothermally oxidation, XRD peaks were shifted slightly and tetragonal phase with a higher c/a ratio was appeared.

  • 347.
    Shen, Rickard R
    et al.
    Dept of Solid Mechanics, KTH Royal Institute of Technology, Stockholm.
    Zhou, Zhiliang
    Sandvik Materials Technology, Sandviken.
    Ping, Liu
    Sandvik Materials Technology, Sandviken.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Effect of PWHT on the Microstructure and Mechanical proerties of ERNiCrFe-7 All-Weld Metal2015In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 59, no 3, p. 317-323Article in journal (Refereed)
    Abstract [en]

    The effects on the microstructure and room temperature mechanical properties of the nickel-based filler metal ERNiCrFe-7 due to a post weld heat treatment (PWHT) at 610 °C have been studied. It was shown that PWHT caused an increase in yield strength and ultimate tensile strength, but at the cost of reduced ductility and impact toughness. Crack tip opening displacement (CTOD) fracture toughness tests revealed an initial increase in maximum CTOD when a short PWHT was given, but declined with prolonged PWHT. The PWHT also caused a transition in fracture mechanism from microvoid coalescence to quasi-cleavage in room temperature air. Chromium-rich M23C6 type grain boundary carbides were present already in the as-welded weld metal, and were observed to coarsen during the PWHT. Intragranular M23C6 carbides were not observed in the as-welded state, but were precipitated during the 610 °C PWHT. Precipitation of these intragranular carbides is believed to be the main reason for the changes in mechanical properties.

  • 348.
    Shen, Yong-Feng
    et al.
    Northeastern University, Shenyang, China.
    Wang, Yandong
    Northeastern University, Shenyang, China.
    Liu, Xiao-Peng
    Northeastern University, Shenyang, China.
    Sun, Xin
    Pacific Northwest National Laboratory, Richland, USA.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Zhang, Shu-Yan
    ISIS Facility, CCLRC Rutherford Appleton laboratory, Didcot, UK.
    Zuo, Liang
    Northeastern University, Shenyang, China.
    Liaw, Peter K.
    University of Tennessee, Knoxville, USA.
    Deformation mechanisms of a 20Mn TWIP steel investigated by in situ neutron diffraction and TEM2013In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 61, no 16, p. 6093-6106Article in journal (Refereed)
    Abstract [en]

    The deformation mechanisms and associated microstructure changes during tensile loading of an annealed twinning-induced plasticity steel with chemical composition Fe-20Mn-3Si-3Al-0.045C (wt.%) were systematically investigated using in situ time-of-flight neutron diffraction in combination with post mortem transmission electron microscopy (TEM). The initial microstructure of the investigated alloy consists of equiaxed gamma grains with the initial alpha'-phase of similar to 7% in volume. In addition to dislocation slip, twinning and two types of martensitic transformations from the austenite to alpha'- and epsilon-martensites were observed as the main deformation modes during the tensile deformation. In situ neutron diffraction provides a powerful tool for establishing the deformation mode map for elucidating the role of different deformation modes in different strain regions. The critical stress is 520 MPa for the martensitic transformation from austenite to alpha'-martensite, whereas a higher stress (>600 MPa) is required for actuating the deformation twin and/or the martensitic transformation from austenite to epsilon-martensite. Both epsilon- and alpha'-martensites act as hard phases, whereas mechanical twinning contributes to both the strength and the ductility of the studied steel. TEM observations confirmed that the twinning process was facilitated by the parent grains oriented with < 1 1 1 > or < 1 1 0 > parallel to the loading direction. The nucleation and growth of twins are attributed to the pole and self-generation formation mechanisms, as well as the stair-rod cross-slip mechanism.

  • 349.
    Sjögren, Torsten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Influences of the Graphite Phase on Elastic and Plastic Deformation Behaviour of Cast Irons2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The amount and morphology of the graphite phase largely controls the resulting properties of cast iron. For instance, in flake graphite cast irons the mechanical properties are low while the thermal conductivity is high. This is in contrast with spheroidal graphite cast irons where the mechanical properties are high and the thermal conductivity is low. These differences are due to the different graphite morphologies and must be accounted for in the design work and material selection of cast iron components. In this work the influence of the graphite phase on the elastic and plastic deformation behaviour of cast irons has been studied.

    The material grades studied originate from castings for marine diesel engine piston rings with different chemical analyses. Two groups of pearlitic cast iron materials were studied; one with differences in graphite morphology and one with grey irons that differed in graphite content. For these different material grades the mechanical properties were correlated to microstructural parameters. In addition to standard uniaxial tensile tests, acoustic emission measurements were used for the study of deformation.

    When studying the modulus of elasticity of the cast iron it was found that the modulus of elasticity of the inherent graphite phase depends on the roundness of the graphite particles and is due to the strong anisotropy of the graphite phase. A linear correlation between nodularity and the modulus of elasticity of the graphite phase was derived. This correlation made it possible to account for the anisotropy of the graphite phase in the model used. By applying the linear function when modelling the effective modulus of elasticity, a high accuracy between experimental and theoretical values was achieved.

    Another factor affecting the elastic response when subjecting a cast iron component to tensile load was found to be the plastic deformation that actually occurs at very low strains for all of the studied cast iron grades. It was observed that the plastic deformation in the low strain elastic region, quantified by using acoustic emission measurements, increased linearly with decreasing modulus of elasticity. These measurements showed that the amount of plastic deformation in the elastic region was largely controlled by the graphite morphology. It was concluded that as the roundness of the graphite particles increases, the plastic deformation activity in the elastic region decreases.

    The plastic deformation activity continued linearly into the pronounced plastic region of the tensile tests. A decrease in roundness or increase in graphite fraction resulted in an increase of the amount of plastic deformation and the strain hardening exponent. A

    dependence between strength coefficient and graphite fraction was observed. Models for the flow curves for pearlitic cast irons were developed and shown to accurately reproduce the observed experimental curves.

    The surveys performed and conclusions from this thesis will be helpful in the design of new cast iron materials.

    List of papers
    1. High Performance Piston Rings for Two-Stroke Marine Diesel Engines
    Open this publication in new window or tab >>High Performance Piston Rings for Two-Stroke Marine Diesel Engines
    2004 (English)In: Proceedings // 24th CIMAC World Congress on Combustion Engine Technology, 2004Conference paper, Published paper (Other academic)
    Abstract [en]

    The piston ring is a key component in a marine combustion engine. High mechanical loads, relatively high temperatures and corrosive gases and liquids influence its performance in terms of sealing capacity, wear of cylinder liner and the ring itself. Base material of the ring, coating technology and ring geometry design are discussed in the article.

    When tailoring cast iron materials suitable as piston ring base material two parameters are of importance; the morphology of the graphite and the constituents of the matrix. To optimize the properties of the cast iron a compromise is needed to achieve a satisfactory performance of the piston rings.

    Daros Piston Rings AB is currently developing a second generation of chromium-ceramic coating the so called Z-chrome. The objective of this project has been to increase the maximum operating temperature of the coating and leave the other characteristics of the coating unaffected. The difference between the commercial Daros coating Tritor® and the Z-chrome is the ceramic component included in the coated layer.

    Insufficient conformability of piston ring and liner geometry may produce a large local cylinder wall pressure which will destroy the oil film leading to uncontrolled wear and scuffing. Lack of conformability can also produce leakage paths for the combustion gases. Therefore a correct ring shape is of utmost importance. A new design philosophy designated OPCORE® has been developed and is presented here.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14415 (URN)
    Conference
    24th CIMAC World Congress on Combustion Engine Technology, June 7-11, Kyoto, Japan
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    2. Comparison of Mechanical Properties in Flake Graphite and Compacted Graphite Cast Irons for Piston Rings
    Open this publication in new window or tab >>Comparison of Mechanical Properties in Flake Graphite and Compacted Graphite Cast Irons for Piston Rings
    2004 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 17, no 2, p. 65-71Article in journal (Refereed) Published
    Abstract [en]

    Cast iron is often used as the piston ring material in marine diesel engines. The mechanical properties of cast irons are to a great extent governed by the size, distribution and shape of the incorporated graphite particles. In a set of experiments, the mechanical properties of a pearlitic grey cast iron and a pearlitic compacted graphite cast iron are compared. Both cast iron grades have a eutectic composition. The experiments confirm the importance of micro-yielding of the matrix at the tip of the graphite particles on the macroelastic behaviour of the studied cast irons. This applies especially for the flake graphite cast iron where the graphite tip is sharper and the matrix bridges between the graphite particles are shorter than in the case of the compacted graphite cast iron resulting in micro-yielding at the graphite tip at a very low macro-stress and macro-strain. The high local stresses at the graphite tips also result in the opening of the graphite cavities which is much more severe in the flake graphite cast iron than in the compacted graphite cast iron. The mechanical properties of the eutectic flake graphite cast iron are largely affected by the size and amount of the graphite particles. The smaller the graphite particles (faster solidification) in the microstructure, the lower the values of the mechanical properties. In compacted graphite cast iron, the macro-elastic behaviour is influenced by the matrix and the overall coarseness of the microstructure to a greater extent and the effect of the incorporated graphite particle size is much less pronounced.

    Keywords
    Mechanical properties, Eutectic pearlitic cast iron, Graphite shape, compacted graphite, Flake graphite, Micro-yelding
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14416 (URN)10.1179/136404604225017474 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    3. Modelling the Effect of Graphite Morphology on the Modulus of Elasticity in Cast Irons
    Open this publication in new window or tab >>Modelling the Effect of Graphite Morphology on the Modulus of Elasticity in Cast Irons
    2004 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 17, no 5, p. 271-279Article in journal (Refereed) Published
    Abstract [en]

    Nine grades of pearlitic cast iron containing different graphite morphologies (from flake, compacted and spheroidal) have been studied. The parameters investigated include the graphite aspect ratio, nodularity, graphite size and modulus of elasticity. These parameters have been correlated and compared with different existing bound and model equations. It has been found that the modulus of elasticity of the graphite phase increases as the aspect ratio and nodularity of the graphite increases, i.e.flake graphite gives a lower modulus of elasticity than spheroidal graphite. The experimental values of the modulus of elasticity show good agreement to bound and model equations, although flake graphite cast irons show higher deviation from the modelled values. An equation for the correlation between the graphite modulus of elasticity and the nodularity is presented. Introducing this linear correlation into an existing model for the determination of the effective modulus of elasticity gives a continuous function, including all grades of cast irons, with a very good agreement with experimental values. The modulus of elasticity of cast irons can be accurately predicted from both bound and especially model equations, using the aspect ratio and nodularity of the contained graphite particles. The fit is improved by using a modulus of elasticity of the graphite phase that is based on the graphite morphology, considering that the modulus of elasticity of the graphite is different in the basal and prismatic planes.

    Keywords
    Cast iron, Modulus of elasticity, Graphite morphology, Graphite aspect ratio, Compacted graphite, Flake graphite, Spheroidal graphite, Modelling
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14417 (URN)10.1179/136404604225022694 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    4. Studying Elastic Deformation Behaviour of Cast Irons by Acoustic Emission
    Open this publication in new window or tab >>Studying Elastic Deformation Behaviour of Cast Irons by Acoustic Emission
    2005 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 18, no 4, p. 249-256Article in journal (Refereed) Published
    Abstract [en]

    The deformation of metallic materials includes both an elastic and a plastic deformation. In the case of cast irons, the elastic region becomes less pronounced as the graphite changes from spheroidal to flake shaped, as observed in nodular and grey cast iron, respectively. The present study aims to correlate the shape of the graphite phase with the deformation behaviour, where the plastic deformation and other strain accommodating events are quantified by measurements of the acoustic emission events occurring in the interior of the material at loading. It also aims to explain how the appearance of cast iron stress–strain curves depends on the graphite morphology where, for instance, spheroidal graphite cast irons exhibit a seemingly linear elastic behaviour in contrast to flake graphite cast irons. The present study includes a series of pearlitic cast iron material grades with differences in nodularity and carbon equivalent, respectively. It is shown that as the roundness of the graphite phase increases, the ability to absorb energy increases. The measured acoustic emission indicates that plastic deformation occurs in the seemingly linear elastic region regardless of the cast iron grade, i.e. no cast iron grade exhibits perfect linear elasticity. The plastic deformation rate in the elastic region increases as the roundness of the graphite decreases and as the carbon equivalent increases. It is shown that the plastic deformation governs the resulting modulus of elasticity in all kind of cast irons, i.e. the modulus of elasticity decreases as the yielding of the material increases. The present study improves the understanding of the deformation behaviour in the elastic region of different cast irons. The survey shows that acoustic emission testing is a useful method when studying the deformation behaviour of cast irons.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14418 (URN)10.1179/136404605225023117 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    5. The Effect of Graphite Fraction and Morphology on the Plastic Deformation of Cast Irons
    Open this publication in new window or tab >>The Effect of Graphite Fraction and Morphology on the Plastic Deformation of Cast Irons
    2007 (English)In: Metallurgical and materials transactions. A, ISSN 1073-5623, Vol. 38, no 4, p. 840-847Article in journal (Refereed) Published
    Abstract [en]

    The plastic deformation behavior of cast irons, covering the majority of graphite morphologies, has not been comprehensively studied previously. In this investigation, the effect of graphite morphology and graphite fraction on the plastic deformation behavior of pearlitic cast irons has been evaluated. The investigation is based on tensile tests performed on various different cast iron grades, where the graphite morphology and volume fraction have been varied. Pearlitic steel with alloying levels corresponding to the cast irons were also studied to evaluate how the cast iron matrix behaves in tension without the effects of the graphite phase. It is concluded that as the roundness of the graphite phase increases, the strain hardening exponent decreases. This demonstrates that the amount of plastic deformation is higher in the matrix of lamellar cast iron grades compared to compacted and nodular cast iron grades. Furthermore, this study shows that the strength coefficient in flake graphite cast irons increases as the graphite fraction decreases due to the weakening effect of the graphite phase. This study presents relationships between the strain hardening exponent and the strength coefficient and the roundness and fraction of the graphite phase. Using these correlations to model the plastic part of the stress-strain curves of pearlitic cast irons, we were able to calculate curves in good agreement with experimentally determined curves, especially for gray cast irons and ductile iron.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14419 (URN)10.1007/s11661-007-9115-8 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2010-05-31
    6. Modelling the Effect of Graphite Morphology on the Deformation Behaviour of Cast Irons
    Open this publication in new window or tab >>Modelling the Effect of Graphite Morphology on the Deformation Behaviour of Cast Irons
    2006 (English)In: Eighth International Symposium on Science and Processing of Cast Iron, SPCI8, October 16-19, Beijing, China, 2006Conference paper, Published paper (Other academic)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14420 (URN)
    Available from: 2007-04-20 Created: 2007-04-20
    7. Modeling and Simulation of Elastic Properties in Cast Compacted Graphite Iron Engine Block
    Open this publication in new window or tab >>Modeling and Simulation of Elastic Properties in Cast Compacted Graphite Iron Engine Block
    2006 (English)In: MCWASP Conference XI, May 28-June 2, Opio, France, 2006Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14421 (URN)
    Available from: 2007-04-20 Created: 2007-04-20
    8. Study of the Mechanical and Thermal Properties of Pearlitic and Ferritic Cast Iron Matrices
    Open this publication in new window or tab >>Study of the Mechanical and Thermal Properties of Pearlitic and Ferritic Cast Iron Matrices
    2007 (English)In: GiessereiforschungArticle in journal (Refereed) Submitted
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14422 (URN)
    Available from: 2007-04-20 Created: 2007-04-20
  • 350.
    Sjögren, Torsten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Modelling the Effect of Graphite Morphology on the Modulus of Elasticity in Cast Irons2004In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 17, no 5, p. 271-279Article in journal (Refereed)
    Abstract [en]

    Nine grades of pearlitic cast iron containing different graphite morphologies (from flake, compacted and spheroidal) have been studied. The parameters investigated include the graphite aspect ratio, nodularity, graphite size and modulus of elasticity. These parameters have been correlated and compared with different existing bound and model equations. It has been found that the modulus of elasticity of the graphite phase increases as the aspect ratio and nodularity of the graphite increases, i.e.flake graphite gives a lower modulus of elasticity than spheroidal graphite. The experimental values of the modulus of elasticity show good agreement to bound and model equations, although flake graphite cast irons show higher deviation from the modelled values. An equation for the correlation between the graphite modulus of elasticity and the nodularity is presented. Introducing this linear correlation into an existing model for the determination of the effective modulus of elasticity gives a continuous function, including all grades of cast irons, with a very good agreement with experimental values. The modulus of elasticity of cast irons can be accurately predicted from both bound and especially model equations, using the aspect ratio and nodularity of the contained graphite particles. The fit is improved by using a modulus of elasticity of the graphite phase that is based on the graphite morphology, considering that the modulus of elasticity of the graphite is different in the basal and prismatic planes.

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