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Crystal plasticity and crack initiation in a single-crystal nickel-base superalloy: Modelling, evaluation and appliations
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this dissertation the work done in the projects KME-410/502 will be presented.The overall objective in these projects is to evaluate and develop tools for designingagainst fatigue in single-crystal nickel-base superalloys in gas turbines. Experimentshave been done on single-crystal nickel-base superalloy specimens in order toinvestigate the mechanical and fatigue behaviour of the material. The constitutivebehaviour has been modelled and veried by FE-simulations of the experiments.Furthermore, the microstructural degradation during long-time ageing has been investigatedwith respect to the material's yield limit. The eect has been includedin the constitutive model by lowering the resulting yield limit. Moreover, the fatiguecrack initiation of a component has been analysed and modelled by using acritical plane approach in combination with a critical distance method. Finally, asan application, the derived single-crystal model was applied to all the individualgrains in a coarse grained specimen to predict the dispersion in fatigue crack initiationlife depending on random grain distributions.

This thesis is divided into three parts. In the rst part the theoretical framework,based upon continuum mechanics, crystal plasticity, the critical plane approachand the critical distance method, is derived. This framework is then used in thesecond part, which consists of six included papers. Finally, in the third part, detailsof the used numerical procedures are presented.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2011. , 59 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1410
Keyword [en]
Single-crystal superalloy, Crystal plasticity, Fatigue crack initiation, Critical plane model, Theory of critical distance, Rafting, Tension/compression asymmetry
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:liu:diva-72093ISBN: 978-91-7393-022-2 (print)OAI: oai:DiVA.org:liu-72093DiVA: diva2:457045
Public defence
2011-12-16, C3, Hus C, Campus Valla, Linköpings universitet, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2011-11-16 Created: 2011-11-16 Last updated: 2011-12-05Bibliographically approved
List of papers
1. Room temperature yield behaviour of a single-crystal nickel-base superalloy with tension/compression asymmetry
Open this publication in new window or tab >>Room temperature yield behaviour of a single-crystal nickel-base superalloy with tension/compression asymmetry
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2009 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 47, no 2, 366-372 p.Article in journal (Refereed) Published
Abstract [en]

The constitutive behaviour at room temperature of a single-crystal nickel-base superalloy is presented in a new model. This model is based on crystal plasticity and takes Schmid- as well as non-Schmid stresses, elastic anisotropy and tension/compression asymmetry into account. By comparison with uniaxial tensile and compressive tests, the model is shown to reproduce the real behaviour well, including the tension/compression asymmetry. The model also shows that typically encountered deviations in orientations ofcastings have a non-negligible influence on stiffness and yield limit, which must be taken into account for industrial applications.

Keyword
Tension/compression asymmetry, Single-crystal superalloy, Crystal plasticity, Yield surface
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-50547 (URN)10.1016/j.commatsci.2009.08.012 (DOI)
Available from: 2009-10-12 Created: 2009-10-12 Last updated: 2017-12-12
2. Tension/Compression asymmetry of a single-crystal superalloy in virgin and degraded condition
Open this publication in new window or tab >>Tension/Compression asymmetry of a single-crystal superalloy in virgin and degraded condition
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2010 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 58, no 15, 4986-4997 p.Article in journal (Refereed) Published
Abstract [en]

The mechanical behaviour at room temperature of a single-crystal superalloy exposed to long term ageing at elevated temperature has been investigated, a topic important for the material’s resistance to thermal-mechanical fatigue. Specimens with several different crystallographic orientations were plastically deformed in either tension or compression before and after the long term furnace exposure. While the thermally activated degradation of the microstructure causes a reduction in yield limit of up to 25% for specimens initially deformed in the |001 and |011| directions, none or only moderate reduction was seen for specimens initially deformed along the |111| direction. This can be explained by the strong correlation between yield limit reduction and the amount of γ coarsening. By introducing an isotropic degradation function in a newly developed crystal plasticity model, the constitutive behaviour of both virgin and degraded materials has been described with good agreement with the experimental results.

Place, publisher, year, edition, pages
Elsevier, 2010
Keyword
Deformation mechanisms, Rafting/Coarsening, Tension/compression asymmetry, Single-crystal superalloy
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-56590 (URN)10.1016/j.actamat.2010.05.032 (DOI)000280570500008 ()
Available from: 2010-05-25 Created: 2010-05-25 Last updated: 2017-12-12
3. Fatigue crack initiation in a notched single-crystal superalloy component
Open this publication in new window or tab >>Fatigue crack initiation in a notched single-crystal superalloy component
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2010 (English)In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 2, no 1, 1067-1075 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, the fatigue crack initiation in notched single-crystal test specimens of material MD2 is investigated and analysed. A critical plane approach is adopted, in which the total strain ranges on the discrete slip planes are evaluated. Furthermore, a Coffin-Manson type of expression is used to describe the number of cycles to fatigue crack initiation. This relation is determined from a set of smooth test specimens loaded uniaxially in the [001], [011] and directions at 500 °C with Rε=−1. The numerical procedure is then applied to a series of experiments, in which notched single-crystal test specimens were exposed to uniaxial cyclic loading in the [001] direction at 500 °C with Rε=0.

Place, publisher, year, edition, pages
Elsevier, 2010
Keyword
Fatigue initiation; Low cycle fatigue; Critical plane approach; Single-crystal superalloy
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-56588 (URN)10.1016/j.proeng.2010.03.115 (DOI)
Available from: 2010-05-25 Created: 2010-05-25 Last updated: 2017-12-12Bibliographically approved
4. A combined critical plane and critical distance approach for predicting fatigue crack initiation in notched single-crystal superalloy components
Open this publication in new window or tab >>A combined critical plane and critical distance approach for predicting fatigue crack initiation in notched single-crystal superalloy components
2011 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 33, no 10, 1351-1359 p.Article in journal (Refereed) Published
Abstract [en]

The fatigue crack initiation in notched single-crystal components of material MD2 is 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 crystallographic slip planes are evaluated. To determine the critical distance two approaches were evaluated, a mean value approach and a cycle dependent approach. Furthermore, a Coffin-Manson type of expression (derived from the results of a set of 12 smooth specimens) is used to predict the number of cycles to fatigue crack initiation. The numerical procedure is applied to a series of experiments, in which notched single-crystal components were exposed to uniaxial cyclic loading in the nominal [001] crystal direction at 500 degrees C with R(epsilon) = 0. A good correlation between the experimental results and the simulated results was found.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Single-crystal superalloy; Fatigue crack initiation; Critical plane approach; Notch correction; Critical distance theory
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-69763 (URN)10.1016/j.ijfatigue.2011.05.009 (DOI)000292795100002 ()
Available from: 2011-08-10 Created: 2011-08-08 Last updated: 2017-12-08Bibliographically approved
5. Evaluation of Fatigue Crack Initiation in a Notched Single-crystal Superalloy Component
Open this publication in new window or tab >>Evaluation of Fatigue Crack Initiation in a Notched Single-crystal Superalloy Component
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2011 (English)In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 10, 619-624 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
single-crystal superalloy, fatigue crack initiation, critical plane approach, notch correction, critical distance theory
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-70548 (URN)10.1016/j.proeng.2011.04.103 (DOI)
Available from: 2011-09-12 Created: 2011-09-12 Last updated: 2017-12-08
6. The effect of random grain distributions on fatigue crack initiation in a notched coarse grained superalloy specimen
Open this publication in new window or tab >>The effect of random grain distributions on fatigue crack initiation in a notched coarse grained superalloy specimen
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2012 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 51, no 1, 273-280 p.Article in journal (Refereed) Published
Abstract [en]

Coarse grained superalloys are of large interest in high temperature applications, and can be found in e.g.gas turbine components, where great care must be given with respect to high temperature fatigue. Due tothe large grain size, the material behaviour at e.g. sharp notches cannot be considered homogeneous. As aconsequence, the fatigue behaviour is likely to expose a large variation. In order to numerically investigatethis variation, a Monte Carlo analysis has been carried out by 100 FE-simulations of notched specimens,where placements and orientations of the grains were randomised. Furthermore, each grain wasmodelled as a unique single-crystal, displaying both anisotropic elastic and plastic behaviour and tension/compression asymmetry. The effect of randomness was investigated by the obtained dispersion infatigue crack initiation life. It was concluded that the fatigue life behaviour of coarse grained nickel-basesuperalloys may show a considerable variation, which cannot be captured by one single deterministicanalysis based on data for a homogenised material. Furthermore, the dispersion is of such a magnitudethat it needs to be taken into account in industrial applications where highly stressed coarse grainedmaterials are used.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Coarse grained superalloy, Fatigue crack initiation, Critical plane approach, Crystal plasticity, Monte Carlo analysis
National Category
Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-72092 (URN)10.1016/j.commatsci.2011.07.054 (DOI)000296214300034 ()
Note
Funding agencies|Swedish Research Council| 60628701 |Siemens Industrial Turbomachinery AB in Sweden||Swedish Energy Agency via the Research Consortium of Materials Technology for Thermal Energy Processes| KME-502 |National Supercomputer Centre in Linkoping, Sweden||Available from: 2011-11-16 Created: 2011-11-16 Last updated: 2017-12-08Bibliographically approved

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