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Oxidation and Corrosion of New MCrAlX Coatings: Modelling and Experiments
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
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: urn:nbn:se:liu:diva-111119DOI: 10.3384/diss.diva-111119ISBN: 978-91-7519-247-5 (print)OAI: oai:DiVA.org:liu-111119DiVA: diva2:753496
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
List of papers
1. Modeling of the microstructural evolution and lifetime prediction of MCrAlX coatings on Nickel based superalloys in high temperature oxidation
Open this publication in new window or tab >>Modeling of the microstructural evolution and lifetime prediction of MCrAlX coatings on Nickel based superalloys in high temperature oxidation
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2013 (English)In: Surface and Coatings Technology, Vol. 232, no 15, 204-215 p.Article in journal (Refereed) Published
Abstract [en]

At high temperature, MCrAlX coatings are deposited onto the surface of superalloy to provide oxidation and corrosion protection by forming a thermalgrowing oxide scale. In this project, the oxidation behavior of an HVOF CoNiCrAlYSi coating on IN792 was studied in both isothermal oxidation (900, 1000 and 1100 °C) and thermal cycling (1100-100 °C). The microstructural evolution in the MCrAlX coatings after oxidation was investigated. It was found that Al-rich β phase is gradually consumed due to two effects: surface oxidation and coating-substrate interdiffusion. Some voids and oxides along the coating-substrate interface, or inside the coating, were considered to play a role in blocking the diffusion of alloying elements. Based on the microstructural observation, an oxidation-diffusion model was developed by using Matlab and DICTRA software to predict the lifetime of MCrAlX coatings. Several effects influencing the microstructural evolution were included: surface oxidation, coating-substrate interdiffusion and diffusion blocking. The results showed good agreement between the experimental composition profiles and modeling ones. Furthermore, by choosing suitable diffusion blocking factors, the accuracy of coating life prediction could be improved.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
MCrAlX coating; HVOF; Life prediction; Interdiffusion; Oxidation; Diffusion blocking
National Category
Engineering and Technology Materials Engineering
Identifiers
urn:nbn:se:liu:diva-90013 (URN)10.1016/j.surfcoat.2013.05.008 (DOI)000327691300027 ()
Available from: 2013-03-14 Created: 2013-03-14 Last updated: 2014-10-08Bibliographically approved
2. MCrAIY Coating Design Based on Oxidation-Diffusion Modelling. Part I: Microstructural Evolution
Open this publication in new window or tab >>MCrAIY Coating Design Based on Oxidation-Diffusion Modelling. Part I: Microstructural Evolution
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2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 254, 79-96 p.Article in journal (Refereed) Published
Abstract [en]

To improve the efficiency of modern gas turbines, it is highly desired to develop durable MCrAlY alloys, to be used as protective coatings against oxidation and corrosion for superalloys which are the base materials for some hot components like turbine blades and vanes. In this paper, an oxidation-diffusion model was used to simulate the diffusion of alloying elements and the corresponding microstructural changes in different superalloy-coating systems at high temperature. Two important processes are considered in this model: oxidation of the coating and interdiffusion between the superalloy and the coating. The model showed an accurate predictability of the diffusion and microstructural evolution in real superalloy-coating diffusion couples studied at high-temperature exposure. The model was further applied to investigate the elemental effects of Ni, Co, Cr and Al on the microstructural evolution, considering the development of two important phases in superalloys and coatings, i.e. FCC-γ′ and BCC-β, at different temperatures. The results in this paper deepen the knowledge of the MCrAlY coating design for superalloy-coating systems in high-temperature applications.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
MCrAIY, coating design, superalloy, interdiffusion, oxidation, microstructural evolution
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-109081 (URN)10.1016/j.surfcoat.2014.05.067 (DOI)000340977300011 ()
Available from: 2014-08-06 Created: 2014-08-06 Last updated: 2017-12-05
3. MCrAIY Coating Design Based on Oxidation-Diffusion Modelling. Part II: Lifing Aspects
Open this publication in new window or tab >>MCrAIY Coating Design Based on Oxidation-Diffusion Modelling. Part II: Lifing Aspects
2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 253, 27-37 p.Article in journal (Refereed) Published
Abstract [en]

Coatings from MCrAlY-type alloys are commonly used for oxidation and corrosion protection in gas turbines. As coated components are exposed to high temperature, the coating provides oxidation protection by the formation of an alumina scale, thus depleting the coating of Al which, eventually, will cause the coating to fail. The present study deals with MCrAlY alloy design from a lifing perspective. A previously developed coupled oxidation-diffusion model was used to study the influence of coating composition, substrate composition and oxidation temperature on the expected life of MCrAlY coatings. Eight model coatings, covering the wide range of MCrAlY compositions used industrially, and two model substrates, corresponding to a blade material and a combustor material, were evaluated by the oxidation-diffusion model. Three life criteria were tried: 1) beta-phase-depletion, 2) critical Al content at the coating surface, and 3) a critical TGO thickness. It was shown that the critical TGO thickness was the most conservative life criterion for high-Al coatings on high-Al substrates. For low-Cr and low-Co coatings, the beta-depletion criterion was usually the most conservative. For cases where beta-stability was high (such as at low temperatures and for coatings high in Cr, Co and Al) the critical-Al criterion was often the most conservative.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
MCrAIY, coating, life prediction, alloy design, al depletion, oxidation
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-109082 (URN)10.1016/j.surfcoat.2014.05.010 (DOI)000339150200004 ()
Available from: 2014-08-06 Created: 2014-08-06 Last updated: 2017-12-05Bibliographically approved
4. Simulation of oxidation-nitridation-induced microstructural degradation in a cracked Ni-based superalloy at high temperature
Open this publication in new window or tab >>Simulation of oxidation-nitridation-induced microstructural degradation in a cracked Ni-based superalloy at high temperature
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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
Series
MATEC Web of Conferences, ISSN 2261-236X ; Vol. 14
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-111115 (URN)10.1051/matecconf/20141416004 (DOI)000351930400058 ()
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
5. Some aspects of elemental behaviour in HVOF MCrAlY coatings in high-temperature oxidation
Open this publication in new window or tab >>Some aspects of elemental behaviour in HVOF MCrAlY coatings in high-temperature oxidation
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2015 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 261, 86-101 p.Article in journal (Refereed) Published
Abstract [en]

MCrAlY coatings are widely used to protect superalloys against oxidation and corrosion at high temperature in gas turbine engines. To design a durable MCrAlY coating, the elemental behaviour in coating-superalloy couples needs to be better understood. After oxidation tests in temperature range between 900 °C to 1100 °C, the microstructural development in the samples were analysed. The investigation was mainly focused on the microstructures at the coating surface or in areas near the coating-superalloy interface. Some interdiffusion simulations were also done to model the diffusion behaviour of alloying elements in different coatingsuperalloy couples. The results showed that both oxidation at the coatings’ surfaces and the elements’ diffusion inside of the materials were temperature- and chemical-composition dependent. The behaviour of some minor elements like Y, Hf, Ru and Ir in the oxidation processes was particularly studied by tracking their position and composition in the materials.

Keyword
MCrAlY; oxidation; interdiffusion; elemental behaviour
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-111116 (URN)10.1016/j.surfcoat.2014.11.053 (DOI)000348255500012 ()
Note

On the day of the defence date the status of this article was Manuscript.

Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2017-12-05Bibliographically approved
6. Hot corrosion behavior of HVOF-sprayed CoNiCrAlYSi coatings in a sulphate environment
Open this publication in new window or tab >>Hot corrosion behavior of HVOF-sprayed CoNiCrAlYSi coatings in a sulphate environment
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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
Keyword
Hot corrosion; Sulphate; MCrAlY; HVOF
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-111117 (URN)10.1016/j.vacuum.2015.09.015 (DOI)000364732100008 ()
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
7. Hot corrosion of MCrAlY coatings in sulphate and SO2 environment at 900 °C: is SO2 necessarily bad?
Open this publication in new window or tab >>Hot corrosion of MCrAlY coatings in sulphate and SO2 environment at 900 °C: is SO2 necessarily bad?
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2015 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 261, 41-53 p.Article in journal (Refereed) Published
Abstract [en]

MCrAlY coatings can be corroded due to the basic fluxing (Type-I corrosion) of suppose-to-be protective alumina scale in a molten sulphate environment. In this study, two MCrAlY coatings, coating A (10 wt.% Al, 20 wt.% Cr) and coating B (7 wt.% Al, 28 wt.% Cr), were tested in a sodium-potassium sulphate environment with and without SO2 (500 ppm) in air with 100-900 °C thermal cycling up to about 500 hours. The aim was to test the effect of SO2 at the typical Type-I-corrosion temperature – 900 °C. The results showed that the corrosion behavior of the MCrAlY coatings depended not only on the coating composition but also on the corrosion environment. It was found that in coating A alumina scale was more resistant in the sulphate plus SO2 condition than that in the sulphate only condition. Such phenomenon indicated a beneficial effect of SO2. On Coating B, however, a mixed oxide layer, consisting of alumina and other oxides and sulphides, after a certain cycles in the sulphate environments with and without SO2 gas. In this coating, the addition of SO2 in the sulphate environment changed the corrosion mode from the basic fluxing of alumina to the sulfidation of Cr.

Place, publisher, year, edition, pages
Elsevier, 2015
Keyword
Hot corrosion; Basic fluxing; MCrAlY; SO2; Alumina
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-111118 (URN)10.1016/j.surfcoat.2014.11.065 (DOI)000348255500007 ()
Note

On the day of the defence date the status of the article was Manuscript.

Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2017-12-05Bibliographically approved

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