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Influence of deformation and environmental degradation of Inconel 792
Linköping University, Department of Management and Engineering. Linköping University, Faculty of Science & Engineering.
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Industrial gas turbines are often used as a mechanical drive for pumps and compressors or in power generation as an electric power supply. The gas turbine has for many years been a popular engine due to its flexibility with respect to different types of fuel and due to a design, that enables a high power-to-weight ratio. A simplified description of a gas turbine is that the engine consists of a cold and hot section. The turbo compressor section belongs to cold section and the combustion chamber together with the turbine section belongs to the hot section. In the hot section of a gas turbine, the condition is extremely severe because of an aggressive environment characterized by high temperatures, increased temperature gradients, high pressure and centrifugal forces resulting in large stresses on individual components together with an oxidizing and corroding atmosphere. Materials used in the high temperature section (hot gas path) of a modern gas turbine are different types of superalloys, as single crystal, directionally solidified or polycrystalline alloys, depending on temperature and load conditions. In the first turbine stage, temperature is very high due to exposure to the combustion gas. To handle the problem with creep, single crystal superalloys are often used in this section. In the second row of turbine blades, the temperature of the gas is lower and polycrystalline superalloys are typically used. IN-792 is a cast polycrystalline superalloy with high strength, good resistance to hot corrosion and a cheaper option than single crystals. In the hot section of gas turbine, IN-792 is a suitable material for components such as turbine blades and vans where a complex load condition, high temperature and severe environment prevails. Due to startup and shutdown of the gas turbine engine during service, the components in the hot section are exposed to cyclic load and temperature. This will generate mechanical and thermal fatigue damage in gas turbine components. Steady state temperature gradient arises by the cooling system acting at cold spots during service to introduce tensile stress, which indirectly gives rise to creep damage in the component. This work includes tree studies of deformation and damage mechanisms of superalloy IN-792. The first study is made on test bars exposed to thermomechanical fatigue in laboratory environment, the second and the third study is made on turbine blades used during service. In the second study, the machines are placed off-shore and exposed to marine environment. In the third study the machine is landbased and exposed to an industrial environment. In the second study, the deformation and damage mechanisms are compared between the turbine blades used during service and the test bars exposed to thermomechanical fatigue testing in the first study.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. , 37 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1768
National Category
Energy Engineering Other Materials Engineering Manufacturing, Surface and Joining Technology Other Chemical Engineering Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:liu:diva-133824DOI: 10.3384/lic.diva-133824ISBN: 9789176855997 (print)OAI: oai:DiVA.org:liu-133824DiVA: diva2:1063924
Presentation
2017-03-03, ACAS, Linköping University, Linköping, 13:00 (Swedish)
Opponent
Available from: 2017-01-11 Created: 2017-01-11 Last updated: 2017-02-27Bibliographically approved
List of papers
1. Deformation and damage mechanisms in IN792 during thermomechanical fatigue
Open this publication in new window or tab >>Deformation and damage mechanisms in IN792 during thermomechanical fatigue
2011 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, Vol. 528, no 13-14, 4658-4668 p.Article in journal (Refereed) Published
Abstract [en]

The deformation and damage mechanisms arising during thermomechanical fatigue (TMF) of the polycrystallinesuperalloy IN792 have been investigated. The TMF cycles used in this study are in-phase(IP) and out-of-phase (OP). The minimum temperature used in all TMF-tests is 100 ◦C while the maximumtemperature is 500 or 750 ◦C in the IP TMF-tests and 750, 850 or 950 ◦C in the OP TMF-tests. Themajority of the cracks are transcrystalline, except for the IP TMF-test at 750 ◦C, where some tendencyto intercrystalline crack growth can be seen. In all tests, the cracks were initiated and propagated inlocations where deformation structures such as deformation bands have formed in the material. In thetemperature interval 750–850 ◦C, twins were formed in both IP and OP TMF-tests and this behaviouris observed to be further enhanced close to a crack. Twins are to a significantly lesser extent observedfor tests with a lower (500 ◦C) and a higher (950 ◦C) maximum temperature. Recrystallization at grainboundaries, around particles and within the deformation structures have occurred in the OP TMF-testswith a maximum temperature of 850 and 950 ◦C and this is more apparent for the higher temperature.Void formation is frequently observed in the recrystallized areas even for the case of compressive stressesat high temperature.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Nickel based superalloys, Fatigue, Shear bands, Recrystallization, Twinning
National Category
Engineering and Technology Other Materials Engineering
Identifiers
urn:nbn:se:liu:diva-67259 (URN)10.1016/j.msea.2011.02.063 (DOI)000290004200051 ()
Note
Original Publication: Jan Kanesund, Johan Moverare and Sten Johansson, Deformation and damage mechanisms in IN792 during thermomechanical fatigue, 2011, Materials Science & Engineering: A, (528), 13-14, 4658-4668. http://dx.doi.org/10.1016/j.msea.2011.02.063 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2011-04-06 Created: 2011-04-06 Last updated: 2017-01-11

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