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Hot corrosion behavior of HVOF-sprayed CoNiCrAlYSi coatings in a sulphate environment
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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2015 (English)In: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 122, no Part A, 47-53 p.Article in journal (Refereed) Published
Abstract [en]

HVOF-sprayed CoNiCrAlYSi coatings were tested at 900 °C in a hot corrosion environment containing sodium–potassium sulphates. The HVOF spraying caused the typical splat-on-splat structure. The results after the hot corrosion testing showed that the corrosion preferentially occurred at the coating surface and the splat boundaries. The oxidation along the splat boundaries can isolate the splat from the underlying coating matrix. In those isolated splats or coating parts, internal oxidation and nitridation of Al took place, following that the Al-depleted coating fragments were then oxidized to spinels. For those coatings which had a worse splat boundary quality (i.e. with higher porosity and intersplat oxides) or had a worse coating surface quality (i.e. with more small coating fragments therefore more interfaces), heavier corrosion attack was observed on those coatings due to the corrosion of the splats or the coating fragments. The results indicated that the as-sprayed coating quality including porosity and surface morphology was important for the hot-corrosion resistance of the coatings.

Place, publisher, year, edition, pages
Elsevier, 2015. Vol. 122, no Part A, 47-53 p.
Keyword [en]
Hot corrosion; Sulphate; MCrAlY; HVOF
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-111117DOI: 10.1016/j.vacuum.2015.09.015ISI: 000364732100008OAI: oai:DiVA.org:liu-111117DiVA: diva2:753478
Note

On the day of the defence date the status of this article was Manuscript and the article title was Hot corrosion behavior of MCrAlY coatings containing Ru and Ir.

Funding agencies: Siemens Industrial Turbomachinery AB (Finspang, Sweden); Swedish Energy Agency through KME consortium - ELFORSK; research school of Agora Materials and Strategic Faculty Grant AFM in Linkoping University

Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2017-12-05Bibliographically 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, KangLin Peng, RuJohansson, Sten

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