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Analysis of Thermal Effect on Residual Stresses of Broached Inconel 718
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
Siemens Industrial Turbomachinery, Finspång, Sweden.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
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2014 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Inconel 718 is a nickel based superalloy that is widely used as a turbine disc material in gas turbine industries. This study details the effect of thermal exposure on the residual stresses produced when broaching Inconel 718. The chosen parameters for broaching in this study are similar to those used when manufacturing turbine discs. The broaching operation produced a high level of tensile residual stresses at the broached surface. A layer with tensile residual stresses was formed in the sub-surface region, followed by a layer several times thicker with compressive residual stresses. Thermal exposure was conducted at 550 °C. The depth distributions of residual stresses after thermal exposure are presented and discussed in this paper. Complete relaxation of the surface tensile residual stresses was observed after 30 h thermal exposure, whereas the 3000 h thermal exposure influenced both the surface and sub-surface residual stress states.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2014. Vol. 996, 574-579 p.
Series
Advanced Materials Research, ISSN 1022-6680 ; 996
Keyword [en]
Broaching, Incone 718, Residual Stresses, Thermal Exposure, Recrystallization
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-111057DOI: 10.4028/www.scientific.net/AMR.996.574ISI: 000348282100093OAI: oai:DiVA.org:liu-111057DiVA: diva2:752930
Conference
ECRS9 6-10 July, Troyes, Frankrike
Available from: 2014-10-06 Created: 2014-10-06 Last updated: 2015-02-20Bibliographically approved
In thesis
1. Surface Integrity of Broached Inconel 718 and Influence of Thermal Exposure
Open this publication in new window or tab >>Surface Integrity of Broached Inconel 718 and Influence of Thermal Exposure
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Inconel 718 is a nickel-based superalloy that is extensively used as a disc material in gas turbine engines. The service life of gas turbine discs is normally governed by the modes of material degradation and fatigue failure since they work mostly at high temperatures and are subjected to cyclic mechanical loadings. Fatigue failures often start with the initiation of cracks at the surface and the precise details of the failure process significantly depend on the surface conditions. In turbine disc production, one of the last manufacturing steps is to broach root fixings, commonly of fir-tree design, for blade mounting. It has always been a challenge when machining Inconel 718 due to its high strength retention at elevated temperatures, rapid work hardening, as well as low thermal conductivity. This usually leads to rapid tool wear, and consequently shorter tool life, and at the end to the deterioration of the surface integrity of the machined components.

The aim of this licentiate thesis is to increase our knowledge about the surface integrity, especially microstructure and residual stresses, of broached Inconel 718 and its stability under thermal exposure. This knowledge can later be used for analyzing the initiation and propagation of fatigue cracks in broached Inconel 718, particularly in the case of high temperature fatigue, thereby giving a better understanding of the failure mechanism of gas turbine discs from a fatigue point of view.

A broaching operation has been performed using similar cutting conditions as that used in turbo machinery industries for producing fir-tree root fixings. In addition, service damages were analyzed in a retired dis of Inconel 718. Surface defects, severe plastic deformation and generation of high tensile residual stresses have been found to be the main damages to the surface integrity caused by the broaching operation. The machining induced plastic deformation was found to accelerate the microstructural degradation beneath the broached surface when subjected to thermal exposure. The surface tensile residual stresses can be completely removed after short thermal exposure, the tensile layer in the sub-surface region, however, exhibited a high resistance to stress relief at high temperatures. The damage analysis on the retired disc indicated that presence of the highly deformed layer on the machined surface is negative for preventing the occurrence of fretting fatigue in turbine discs.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 44 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1676
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-111062 (URN)10.3384/lic.diva-111062 (DOI)LIU-TEK-LIC-2014:108 (Local ID)978-91-7519-249-9 (ISBN)LIU-TEK-LIC-2014:108 (Archive number)LIU-TEK-LIC-2014:108 (OAI)
Presentation
2014-10-10, ACAS, A-building, Campus Valla, Linköpings universitet, 10:15 (English)
Opponent
Supervisors
Available from: 2014-10-06 Created: 2014-10-06 Last updated: 2014-10-06Bibliographically approved

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Chen, ZhePeng, RuMoverare, JohanJohansson, Sten

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