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Simulation of oxidation-nitridation-induced microstructural degradation in a cracked Ni-based superalloy at high temperature
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 AB, Finspång, Sweden.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
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2014 (English)In: MATEC Web of Conferences Vol. 14 (2014), EUROSUPERALLOYS 2014 – 2nd European Symposium on Superalloys and their Applications Giens, France, May 12–16, 2014, Les Ulis, France: E D P Sciences , 2014, Vol. 14, no 16004, 16004- p.Conference paper, Published paper (Refereed)
Abstract [en]

In turbine engines, high temperature components made of superalloys may crack in a creep process during service. With the inward flux of the gases, e.g. oxygen and nitrogen, along those cracks, the microstructure of the superalloy substrate nearby the cracks may degrade by internal oxidation and nitridation. The aim of this study is to investigate and simulate the oxidation-nitridation-induced microstructural degradation in superalloys by taking a variant of Ni-based superalloy IN-792 as a sample. After the creep testing of the superalloy in air, the microstructures on the cross section of the superalloy were analysed in a scanning electron microscope, equipped with energy/wavelength dispersive systems. Internal oxidation and nitridation, presenting by Al/Ti oxides and nitrides, were observed under a porous and even cracked Cr-oxide scale which was formed on the superalloy surface or along the creep cracks connecting the superalloy surface. Meanwhile, the reinforcing γ′ precipitates were depleted. Such oxidation-nitridation-induced microstructural degradation was simulated by using an oxidation-diffusion model, focusing the diffusion of the alloying elements in metallic phases of the superalloy.

Place, publisher, year, edition, pages
Les Ulis, France: E D P Sciences , 2014. Vol. 14, no 16004, 16004- p.
Series
MATEC Web of Conferences, ISSN 2261-236X ; Vol. 14
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-111115DOI: 10.1051/matecconf/20141416004ISI: 000351930400058OAI: oai:DiVA.org:liu-111115DiVA: diva2:753472
Conference
MATEC Web of ConferencesVolume 14, 2014, EUROSUPERALLOYS 2014 – 2nd European Symposium on Superalloys and their Applications; Section; Posters: Deformation and Damage Mechanisms II: Fatigue, Oxidation, Crack Propagation, Giens, France, May 12–16, 2014
Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2016-05-26Bibliographically approved
In thesis
1. Oxidation and Corrosion of New MCrAlX Coatings: Modelling and Experiments
Open this publication in new window or tab >>Oxidation and Corrosion of New MCrAlX Coatings: Modelling and Experiments
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

MCrAlY coatings (“M” for Ni and/or Co) are widely used for the protection of superalloy components operated at high temperatures such as in the hot sections of gas turbines. The exposure to high temperature can cause coating degradation due to oxidation or hot corrosion at the coating surface. Microstructures in the coating and the coating life are affected also by the diffusion of alloying elements through the coating-superalloy interface. This PhD project, by applying thermodynamic modelling and experimental tests, investigates the oxidation and hot corrosion behavior of new MCrAlX coatings, in which X, referring to minor elements, is used to highlight the functions of such elements.

In order to understand and predict the coating degradation progress during thermal exposure, an oxidation-diffusion model has been established for MCrAlX coating-superalloy systems, which integrates the oxidation of aluminum at coating surface, diffusion of alloying elements, and the diffusion-blocking effect in the materials. The predicted chemical composition profile and microstructure agreed well with experimental results in a CoNiCrAlYSiTa-Inconel 792 system. The model was further applied in several coating-superalloy systems to study the influence of coating composition, superalloy composition and temperature on the evolution of microstructure in the coating and the coating life. The results have demonstrated the potential of the model in designing new durable MCrAlX coatings. In addition to the applications in coating-superalloy systems, the model was also adapted for studying the microstructural development in a superalloy in which internal oxidation and nitridation occurred in an oxidation process.

The oxidation behavior of some HVOF MCrAlX coatings was studied by thermal exposure at different temperatures (900, 1000, 1100 °C). Different spinels formed above the alumina scale, depending on the oxidation temperature. The minor alloying elements, Ru and Ir, had no direct influence on the oxidation behavior but may affect the phase stability in the coating.

MCrAlX coatings were also tested in 48-hour cycles at 900 °C in different hot corrosion environments containing sulphates and/or SO2. The results showed that the coating performance was dependent on coating quality, concentration of Al and Cr in the coating, and the hot corrosion condition. It was also found that the addition of SO2 in the environment may not necessarily be bad for hot corrosion resistance of some MCrAlY coatings.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 46 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1619
National Category
Materials Engineering Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-111119 (URN)10.3384/diss.diva-111119 (DOI)978-91-7519-247-5 (ISBN)
Public defence
2014-10-30, ACAS, Hus A, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Projects
ELFORSK, AGORA MATERIA, Strategic Faculty Grant AFM
Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2015-09-17Bibliographically approved

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Yuan, KangPeng, RuJohansson, Sten

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