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Saarimäki, Jonas
Publications (10 of 12) Show all publications
Saarimäki, J. (2018). Cracks in superalloys. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Cracks in superalloys
2018 (English)Doctoral 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.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. p. 50
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1897
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:liu:diva-144397 (URN)10.3384/diss.diva-144397 (DOI)9789176853856 (ISBN)
Public defence
2018-03-23, ACAS, A-huset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2018-01-18 Created: 2018-01-18 Last updated: 2018-01-18Bibliographically approved
Lundberg, M., Saarimäki, J., Moverare, J. & Peng, R. L. (2017). Effective X-ray Elastic Constant of Cast Iron. Journal of Materials Science, 53(4), 2766-2773
Open this publication in new window or tab >>Effective X-ray Elastic Constant of Cast Iron
2017 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 53, no 4, p. 2766-2773Article in journal (Refereed) Published
Abstract [en]

X-ray diffraction is a non-destructive method used for strain measurements in crystalline materials. Conversion of strain to stress can be achieved using the X-ray elastic constants (XEC), s1 and ½s2. The sin2ψ method was used during in situ loading to determine XEC for flake, vermicular, and spherical graphite iron. A fully pearlitic steel was used as reference. Uniaxial testing was conducted on the cast iron to create a homogeneous strain field, as well as four-point bending in both tension and compression due to the tension/compression asymmetry. The commonly used XEC value ½s2 = 5.81 × 10−6 MPa−1 is theoretically derived from an α-Fe single crystal. When investigating materials that contain ferrite, such as polycrystalline cast iron, this value is not accurate. Determination of an effective XEC for polycrystalline cast iron yields a better correlation between the measured microstrains and the properties observed on a macroscopic scale. The need for an effective XEC is evident, especially when it comes to model validation of, for example, casting simulations. Effective XEC values have been determined for flake, vermicular, and spherical graphite iron. The determined value is lower than the theoretical value.

National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-141980 (URN)10.1007/s10853-017-1657-6 (DOI)000416544500040 ()2-s2.0-85031402118 (Scopus ID)
Note

Funding agencies: Agora Materiae, graduate school, the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]; Volvo Trucks; Vinnova FFI, Scania

Available from: 2017-10-16 Created: 2017-10-16 Last updated: 2018-08-30Bibliographically approved
Saarimäki, J. (2017). Mechanical Properties of Mix Joint TIG Welded Hastelloy X. In: : . Paper presented at EUROMAT17, Thessaloniki 17-21 September 2017,Greece (pp. 1-1).
Open this publication in new window or tab >>Mechanical Properties of Mix Joint TIG Welded Hastelloy X
2017 (English)Conference paper, Oral presentation with published abstract (Refereed)
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-143980 (URN)
Conference
EUROMAT17, Thessaloniki 17-21 September 2017,Greece
Available from: 2018-01-01 Created: 2018-01-01 Last updated: 2018-01-16Bibliographically approved
Lundberg, M., Saarimäki, J., Peng, R. & Moverare, J. (2017). Residual Stresses in Uniaxial Cyclic Loaded Pearlitic Lamellar Graphite Iron. In: Residual Stresses 2016:ICRS-10, Materials Research Proceedings 2 (2016: . Paper presented at International Conference in Residual Stresses ICRS-10, 4-8 July 2016, Sydney, Australia (pp. 67-72).
Open this publication in new window or tab >>Residual Stresses in Uniaxial Cyclic Loaded Pearlitic Lamellar Graphite Iron
2017 (English)In: Residual Stresses 2016:ICRS-10, Materials Research Proceedings 2 (2016, 2017, p. 67-72Conference paper, Published paper (Refereed)
Series
Materials Research Proceeding, ISSN 2474-395X
Keywords
Residual stress, XRD, lamellar graphite iron
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-130893 (URN)10.21741/9781945291173-12 (DOI)000401041500012 ()978-1-9452-9116-6 (ISBN)
Conference
International Conference in Residual Stresses ICRS-10, 4-8 July 2016, Sydney, Australia
Available from: 2016-08-30 Created: 2016-08-30 Last updated: 2018-08-30Bibliographically approved
Storgärds, E., Saarimäki, J., Simonsson, K., Sjöström, S., Månsson, T. & Moverare, J. (2016). Influence of Superimposed Vibrational Load on Dwell Time Crack Growth in a Ni-Based Superalloy. International Journal of Fatigue, 87, 301-310
Open this publication in new window or tab >>Influence of Superimposed Vibrational Load on Dwell Time Crack Growth in a Ni-Based Superalloy
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2016 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 87, p. 301-310Article in journal (Refereed) Published
Abstract [en]

Sustained loads have for some Ni-based superalloys been shown to give rise to increased crack growth rate at elevated temperature. Such loads generate a history dependent fatigue problem due to weakening and cracking of grain boundaries during dwell times, later broken apart during subsequent load cycles. So far most studies have focused on the interaction of load cycles, overloads, and temperature. However, vibrations of different kinds are to some extent always present in engine components, and an investigation of how such loads affect the dwell time cracking, and how to incorporate them in a modelling context, is therefore of importance. In this paper a study of the most frequently used gas turbine material, Inconel 718, has been carried out. Mechanical crack propagation testing has been conducted at 550 °C for surface cracks with and without the interaction of superimposed vibrational loads. Subsequent investigation of the fracture behaviour was performed by scanning electron microscopy and the modelling work has been conducted by incorporating the vibration load description within a history dependent crack growth law. The obtained results show reasonable accuracy with respect to the mechanical test results.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Dwell time, vibrational load, crack growth modelling, Inconel 718, high temperature
National Category
Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-126921 (URN)10.1016/j.ijfatigue.2016.02.018 (DOI)000374615900032 ()
Note

Funding agencies:  Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through the Swedish research programme TURBO POWER

Available from: 2016-04-07 Created: 2016-04-07 Last updated: 2017-11-30
Storgärds, E., Saarimäki, J., Simonsson, K., Sjöström, S., Gustafsson, D., Månsson, T. & Moverare, J. (2016). Scatter in Dwell Time Cracking for a Ni-Based Superalloy in Combination With Overloads. Journal of engineering for gas turbines and power, 138(1), 012502-012502
Open this publication in new window or tab >>Scatter in Dwell Time Cracking for a Ni-Based Superalloy in Combination With Overloads
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2016 (English)In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, no 1, p. 012502-012502Article in journal (Refereed) Published
Abstract [en]

In this paper, scatter in crack growth for dwell time loadings in combination with overloads has been investigated. Multiple tests were performed for surface cracks at 550 °C in the commonly used high temperature material Inconel 718. The test specimens originate from two different batches which also provide for a discussion of how material properties affect the dwell time damage and overload impact. In combination with these tests, an investigation of the microstructure was also carried out, which shows how it influences the growth rate. The results from this study show that, in order to take overloads into consideration when analyzing spectrum loadings containing dwell times, one needs a substantial amount of material data available as the scatter seen from one batch to the other are of significant proportions.

Place, publisher, year, edition, pages
ASME Press, 2016
National Category
Mechanical Engineering Materials Engineering Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-121007 (URN)10.1115/1.4031157 (DOI)000371127900013 ()
Note

Funding agencies: Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through Swedish research programme TURBO POWER

Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2017-12-04Bibliographically approved
Saarimäki, J., Moverare, J. & Hörnqvist Colliander, M. (2016). Time- and Cycle-Dependent Crack Propagation in Haynes 282. Journal of Materials Science and Engineering: A, 658, 463-471
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
Saarimäki, J. (2015). Effect of Dwell-times on Crack Propagation in Superalloys. (Licentiate dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Effect of Dwell-times on Crack Propagation in Superalloys
2015 (English)Licentiate 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.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. p. 49
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1739
National Category
Materials Engineering Energy Engineering Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:liu:diva-123306 (URN)10.3384/lic.diva-123306 (DOI)978-91-7685-871-4 (ISBN)
Presentation
2016-01-22, ACAS, A-huset, Campus Valla, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Funder
Swedish Energy Agency
Available from: 2015-12-10 Created: 2015-12-10 Last updated: 2016-12-09Bibliographically approved
Storgärds, E., Saarimäki, J., Simonsson, K., Sjöström, S., Månsson, T. & Moverare, J. (2015). Impact of high cycle fatigue on dwell time crack growth in a Ni-based superalloy.
Open this publication in new window or tab >>Impact of high cycle fatigue on dwell time crack growth in a Ni-based superalloy
Show others...
2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Sustained load have been shown to give rise to increased crack growth rate at elevated temperature. Such loads generate a history dependent fatigue problem due to weakening and cracking of grain boundaries during dwell times, later broken apart during subsequent load cycles. So far most studies have focused on sustained load and the interaction of load cycles, overloads, and temperature, but few studies have been carried out for vibrations and how these affect the dwell time crack growth. Vibrations of different kinds are frequently seen in engine components, and present in combination with sustained loads a more realistic loading situation than the latter itself. An investigation of how a vibrational load affects the dwell time cracking and how to incorporate it in a modelling context is therefore of importance. In this paper a study of the most frequently used gas turbine material, Inconel 718, has been carried out. Mechanical testing has been conducted at 550◦C for surface cracks with and without the interaction of engine vibrations on sustained load, here represented by a superimposed high cycle fatigue (HCF) load. Subsequent investigation of the fracture behaviour was performed by Scanning Electron Microscope (SEM) and the modelling work has been conducted by incorporating the HCF load description within a history dependent crack growth law. The obtained results show reasonable accuracy with respect to the mechanical tests.

Keywords
Hold time effects, Dwell times, Sustained load, Crack growth modelling, Inconel 718, High temperature
National Category
Mechanical Engineering Materials Engineering Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-121009 (URN)
Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2015-09-02Bibliographically approved
Storgärds, E., Saarimäki, J., Simonsson, K., Sjöström, S., Gustafsson, D., Mansson, T. & Moverare, J. (2015). SCATTER IN DWELL TIME CRACKING FOR A NI-BASED SUPERALLOY IN COMBINATION WITH OVERLOADS. In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2015, VOL 7A: . Paper presented at ASME Turbo Expo: Turbine Technical Conference and Exposition. ASME Press (V07AT28A004)
Open this publication in new window or tab >>SCATTER IN DWELL TIME CRACKING FOR A NI-BASED SUPERALLOY IN COMBINATION WITH OVERLOADS
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2015 (English)In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2015, VOL 7A, ASME Press, 2015, no V07AT28A004Conference paper, Published paper (Refereed)
Abstract [en]

In this paper scatter in crack growth for dwell time loadings combination with overloads has been investigated. Multiple Jsts were performed for surface cracks at 5500C in the commonly sed high temperature material Inconel 718. The test specimens -iginate from two different batches which also provides for a disission of how material properties affect the dwell time damage rnd overload impact. In combination with these tests an investiation of the microstructure was also carried out, which shows 9w it influences the growth rate. The results from this study show tat, in order to take overloads into consideration when analysing,ectrum loadings containing dwell times, one needs a substantial mount of material data available as the scatter seen from one atch to the other is of significant proportions.

Place, publisher, year, edition, pages
ASME Press, 2015
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:liu:diva-129516 (URN)10.1115/GT2015-42709 (DOI)000375810700014 ()978-0-7918-5676-5 (ISBN)
Conference
ASME Turbo Expo: Turbine Technical Conference and Exposition
Available from: 2016-06-20 Created: 2016-06-20 Last updated: 2016-06-20
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