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Influence of Precracked Diffusion Coating of Pt-Modified Aluminide on HCF Fracture Mechanism of IN 792 Nickel-Based Superalloy
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.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
2012 (English)In: Applied Mechanics and Materials, ISSN 1660-9336, E-ISSN 1662-7482, Vol. 148-149, 24-29 p.Article in journal (Refereed) Published
Abstract [en]

High-cycle-fatigue (HCF) fracture mechanism of nickel-based superalloy IN 792 coated with Pt-modified aluminide outward-diffusion coating is studied with focus on the influence of coating cracks. It is found that cracking of the diffusion coating prior to HCF tests has little influence on the fatigue limit of specimens with thin coating (50 μm) but lowers the fatigue limit of specimens with thick coating (70 μm). By fractographic analysis, three types of fractural modes are established according to their crack initiations: internal, external and mixed. While external fractural mode is related to the propagation of existing cracks in the coating, internal facture initiates often at Ti-Ta-W-rich carbides and/or topological-close-packed (TCP) phases and grainboundaries in the superalloy. Increasing the thickness of diffusion coating or the amplitude stress promotes the fractural mode transition from internal/mixed to external. The influence of precracking of coatings on the HCF fracture mechanism can be qualitatively explained by its influence on the stress intensity factor.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2012. Vol. 148-149, 24-29 p.
Keyword [en]
Diffusion coating, Nickel-based superalloy, HCF, Fracture mechanism
National Category
Engineering and Technology Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-72633DOI: 10.4028/www.scientific.net/AMM.148-149.24OAI: oai:DiVA.org:liu-72633DiVA: diva2:460911
Conference
ICMEME2011, International Conference on Mechanical Engineeering in Dalian, China, October 18-20, 2011
Available from: 2011-12-01 Created: 2011-12-01 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Thermal and Mechanical Behaviors of High Temperature Coatings
Open this publication in new window or tab >>Thermal and Mechanical Behaviors of High Temperature Coatings
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

With superior oxidation and corrosion resistance, metallic coatings (i.e. diffusion coatings and MCrAlX coatings) are widely used to protect hot components made of superalloys in turbine engines. Two issues are critically important for the coating at high temperatures: thermal property related to oxidation/corrosion behavior and microstructure stability, and mechanical properties (e.g. creep and fatigue). The aim of this project is to develop better understanding of the thermal and mechanical behaviors of metallic coatings on superalloys and to improve the accuracy of prediction of their lifetime by thermodynamic modeling. The present work includes an investigation on the oxidation behavior of MCrAlX coating with a new lifetimeprediction model and a study on the influence of diffusion coatings on creep and fatigue behaviors of the superalloy IN792.

Experiments on isothermal and thermal cycling oxidation were designed to investigate the oxidation behavior of a HVOF CoNiCrAlYSi coating on superalloy IN792. It is found that the oxidation behaviors of the coating are related to its thermodynamic property. A diffusion model has been established using the homogenization models in the DICTRA software and taking into consideration of the influence of surface oxidation, coating-substrate interdiffusion and diffusion blocking effect caused by internal voids and oxides. The simulation results show an improved accuracy of lifetime prediction by introducing the diffusion blocking effect.

Microstructural evolution during creep process at high temperatures was studied in different diffusion coatings (NiAl and PtAl). It is found that the inward diffusion of aluminum controls the thickening rate of the diffusion coatings. The developed coatings displayed two types of mechanical behavior - being easily plasticized or cracked - dependent on temperature and type of coating, and therefore could be considered as non-load carrying material during creep test. The influence of cracking of PtAl coating on the high-cycle fatigue (HCF) behavior of the IN792 was also investigated. The results show that precracking of the coating prior to the fatigue test has little influence on the fatigue limit of specimens with thin coating (50 μm) but lowers the fatigue limit of specimens with thick coating (70 μm). The through-coating crack has enough mobility to penetrate into the substrate and causes fatigue failure only when the driving force for crack propagation is increased above a critical value due to a higher applied stress or a larger crack length (thicker coating).

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 44 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1569
National Category
Engineering and Technology Materials Engineering
Identifiers
urn:nbn:se:liu:diva-89500 (URN)LIU-TEK-LIC-2013:3 (Local ID)978-91-7519-708-1 (ISBN)LIU-TEK-LIC-2013:3 (Archive number)LIU-TEK-LIC-2013:3 (OAI)
Presentation
2013-02-21, A 39, A-huset, Campus Valla, Linköpings universitet, Linköping, 10:00 (English)
Opponent
Supervisors
Note

Som minor changes has been done in the electronic version compared to the printed version such as acknowledgement among others.

Available from: 2013-03-14 Created: 2013-02-26 Last updated: 2013-03-15Bibliographically approved

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Yuan, KangPeng, RuJohansson, Sten

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