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  • 1.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Segersäll, Mikael
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Using the Student Diversity as a Strength in a Material Selection Course2014Conference paper (Other (popular science, discussion, etc.))
  • 2.
    Leidermark, Daniel
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Segersäll, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Evaluation of Fatigue Crack Initiation in a Notched Single-crystal Superalloy Component2011In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 10, p. 619-624Article in journal (Refereed)
    Abstract [en]

    The fatigue crack initiation in a notched single-crystal nickel-base superalloy component at 500 °C was investigated and analysed. A critical plane approach in combination with a critical distance method has been adopted, in which the total shear strain ranges on the discrete slip planes are evaluated. Furthermore, a Coffin-Manson type of expression is used to predict the number of cycles to fatigue crack initiation. The experimental test specimens were studied by microscopy to determine on which crystallographic plane the fatigue initiation occurred. A good correlation between the experimental results and the simulated results were found.

  • 3.
    Leidermark, Daniel
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Segersäll, Mikael
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Modelling of Thermomechanical Fatigue Stress Relaxation in a Single-Crystal Nickel-Base Superalloy2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 90, p. 61-70Article in journal (Refereed)
    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.

  • 4.
    Leidermark, Daniel
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Segersäll, Mikael
    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.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Modelling of TMF Crack Initiation in Smooth Single-Crystal Superalloy Specimens2014Conference paper (Refereed)
    Abstract [en]

    In this paper the TMF crack initiation behaviour of the single-crystal nickel-base superalloyMD2 is investigated and modelled. TMF tests were performed in both IP and OP for varying mechanicalstrain ranges in the [001] crystallographic direction until TMF crack initiation was obtained. Acrystal plasticity-creep model was used in conjunction with a critical-plane approach, to evaluate thenumber of cycles to TMF crack initiation. The critical-plane model was evaluated and calibrated ata stable TMF cycle, where the effect of the stress relaxation had attenuated. This calibrated criticalplanemodel is able to describe the TMF crack initiation, taking tension/compression asymmetry aswell as stress relaxation anisotropy into account, with good correlation to the real fatigue behaviour.

  • 5.
    Moverare, Johan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Segersäll, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Sato, Atsushi
    Dept of Metallurgy and Materials, University in Birmingham, UK.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Reed, Roger
    Dept of Metallurgy and Materials, University of Birmingham, UK.
    Thermomechanical Fatigue of Single-Crystal Superalloys: Influence of Composition and Microstructure2012In: Superalloys 2012: 12th International Symposium on Superalloys, The Minerals, Metals, and Materials Society, 2012, p. 369-377Conference paper (Refereed)
    Abstract [en]

    The thermomechanical fatigue (TMF) behaviour of a new high Cr-containing single crystal superalloy, known as STAL-15, is investigated. This is a candidate alloy for future industrial gas turbine (IGT) applications. TMF involves complex interactions between high and low temperature deformation mechanism, and this study highlights important factors controlling their interrelationship. Emphasis is placed particularly on the microslructural aspects which control deformation. It is demonstrated that the TMF performance of the new alloy is comparable to that of a second generation alloy such as CMSX-4, despite the absence of Re alloying. An addition of 0.25wt% Si significantly improves the resistance to TMF further; this is attributed to a greater resistance to recrystallization and cracking along the deformation bands that develops across the cross section of the specimen during testing. The TMF resistance increases with increasing primary γ′ size, but the degree of solutioning of the γ′ phase caused by the solution heat treatment seems to have no significant effect.

  • 6.
    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
  • 7.
    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
  • 8.
    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)
  • 9.
    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.

  • 10.
    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.

  • 11.
    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.

  • 12.
    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.

  • 13.
    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.

  • 14.
    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)
  • 15.
    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.

  • 16.
    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.

1 - 16 of 16
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