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Thermal-­Mechanical Fatigue Behaviour of a New Single Crystal Superalloy: Effects of Si and Re Alloying
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
Department of Materials, University of Oxford, Oxford, United Kingdom.
Department of Materials, University of Oxford, United Kingdom.
Department of Materials, University of Oxford, Oxford, United Kingdom.
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2015 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 95, 456-467 p.Article 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. Vol. 95, 456-467 p.
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-111640DOI: 10.1016/j.actamat.2015.03.060ISI: 000358626200046OAI: oai:DiVA.org:liu-111640DiVA: diva2:758425
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
In thesis
1. On Thermomechanical Fatigue of Single-Crystal Superalloys
Open this publication in new window or tab >>On Thermomechanical Fatigue of Single-Crystal Superalloys
2014 (English)Doctoral 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.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 83 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1626
National Category
Materials Engineering Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-111643 (URN)10.3384/diss.diva-111643 (DOI)978-91-7519-211-6 (ISBN)
Public defence
2014-11-28, ACAS, Hus A, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
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Available from: 2014-10-27 Created: 2014-10-27 Last updated: 2014-10-27Bibliographically approved

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Segersäll, MikaelMoverare, Johan

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