liu.seSearch for publications in DiVA
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Crack initiation and propagation in air plasma sprayed thermal barrier coatings, testing and mathematical modelling of low cycle fatigue behaviour
Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
2004 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, Vol. 379, no 1-2, 45-57 p.Article in journal (Refereed) Published
Abstract [en]

In the present paper failure mechanisms in air plasma sprayed thermal barrier coatings for land-based gas turbines have been studied. This has been done by finite element simulations and fractographic investigations of low cycle fatigue (LCF) tested material, here chosen as an 350 μm thick partially stabilised zirconia top coat (TC) together with a 150 μm thick Ni-Co-Cr-Al-Y bond coat (BC) on a nickel base substrate (Haynes 230). Both LCF testing, modelling results and fractographic investigations point in the same direction. An increased thickness of the thermally grown oxide (TGO) does decrease the LCF life of a coated structural alloy. Several points of crack initiation were found, in the TGO at the TC/BC interface, at the oxide network within the BC and at oxide inclusions between BC and substrate. During LCF tests the initiated cracks will grow radially into the substrate material. The behaviour is explained by increased TC/BC delamination stresses and changed oxidation behaviour with increased oxidation times.

Place, publisher, year, edition, pages
2004. Vol. 379, no 1-2, 45-57 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-22790DOI: 10.1016/j.msea.2003.12.063Local ID: 2123OAI: oai:DiVA.org:liu-22790DiVA: diva2:243103
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-11-28
In thesis
1. Delamination in APS applied thermal barrier coatings: life modelling
Open this publication in new window or tab >>Delamination in APS applied thermal barrier coatings: life modelling
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Thermal barrier coatings, TBCs, are used in gas turbines as a thermal shield resulting in lower temperature in coated components. The decrease of temperature allows higher gas temperatures in the turbine, which increase the efficiency. The bimaterial construction with an outer ceramic layer applied onto a metallic material give rice to problems during thermal cycling. Thermal induced stresses will gradually break down the coating. The ceramic layer will delaminate from the substrate, resulting in spallation, and the component will break down due to overheating.

The delamination process is investigated in this thesis by finite element simulations. The growth of an internal alumina layer in the top/bond coat interface is investigated by 3D finite element simulations which show that the local stress state change in such way that the alumina growth help nucleation and growth of small delamination cracks. Finite element simulations, in which t he energy release rate and stress intensity factors are calculated, investigate the growth of small delamination cracks in or close to the top/bond coat interface. Experiments show that these cracks grow parallel to or in the sinusoidal top/bond coat interface and the results of the simulations show that the mode mixity changes as the delamination cracks grow.

A new delamination life model is proposed which is based on results of the fracture mechanical simulations and experimental observations. The model predicts the growth of small cracks in the TBC before they form a large delamination crack. The model is based on a modified Paris law where a mode mixity dependence on the crack growth rate is included, meaning lower crack growth rate in mode 2 load compared with mode 1. Parameters of the model are obtained by optimisation of the model against experimental data, describing the delamination damage evolution in the TBC. The data are obtained from interrupted thermal cycling tests and the prediction of the model corresponds well with these data.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2004. 20 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 902
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-24067 (URN)3627 (Local ID)91-85295-55-8 (ISBN)3627 (Archive number)3627 (OAI)
Public defence
2004-10-27, Sal C3, Fysikhuset, Linköpings Universitet, Linköping, 10:15 (Swedish)
Opponent
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-01-23
2. Failure of thermal barrier coatings under thermal and mechanical fatigue loading: microstructural observations and modelling aspects
Open this publication in new window or tab >>Failure of thermal barrier coatings under thermal and mechanical fatigue loading: microstructural observations and modelling aspects
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Industrial and air-borne gas turbine hot components suffer from creep, oxidation, corrosion and microstructural degradation if not shielded from the hot and aggressive combustion gases. Two major strategies commercially available are adopted; film cooling by pressurised air and application of protective coatings. Protective coatings form a slow-growing oxide that protects from oxidation and corrosion. By application of a thermal insulator, a thermal barrier coating, the material will be protected from high temperature through good insulation properties of the coating system.

If thermal barrier coatings are to be used in situations where capabilities and possibilities for inspections are limited, better knowledge of the fatigue properties of the coatings is also needed. Therefore development of a reliable fatigue life model is needed. The present work aims at serving as a basis from which a general physically founded thermal barrier coating life model can be formulated. The effects of exposure to high temperatures and mechanical loads on thermal barrier coatings under service like conditions have been investigated in the present thesis. Emphasis is put on the coupling between materials science and solid mechanics approaches in order to establish a better knowledge concerning degradation mechanisms and fatigue life issues than what is common if only one discipline is explored.

Investigations of material exposed to isothermal oxidation and thermal cyclic fatigue were performed on plasma-sprayed systems with NiCoCrAIY or NiCrAIY bond coats and yttria partially stabilised zirconia top coats. It has been shown that the thermally grown oxide that will form upon high temperature exposure influences the failure behaviour. If the oxide is composed mainly of alumina, the fatigue properties are good since the adhesion between the ceramic top coat and the metallic bond coat is good. This is also shown in a comparison between different plasma sprayed thermal barrier coating systems. If the oxide formed is based on alurnina and spinel is avoided the fatigue properties benefit from a relatively flat interface where out-of plane stresses are low in comparison to a rough interface between top- and bond coat. These findings indicate that the bonding in air-plasma sprayed systems is dependent on so called chemical bonding if the thermally grown oxide is not voluminous with high growth stresses.

It is possible to establish a fatigue life model for thermal barrier coatings. This has been shown with a model based on a modified Paris law formulation. The formulation needs to be modified with regards to mode rnixity of growth. Results achieved in the present project show that it is possible to extract crack growth data for interfacial crack growth. However a combination of mechanical testing and finite element modelling is needed since the load situation in critical areas cannot be measured. Crack growth results are presented and crack growth data are compared to predictions with good agreement.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2004. 73 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 898
Keyword
thermal barrier coating, TBC, delamination, crack initiation, crack propagation, crack growth, oxidation, alumina, spinel, MCrAIY, diffusion, fatigue, modelling, modeling, degradation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-22793 (URN)2126 (Local ID)91-852-9540-X (ISBN)2126 (Archive number)2126 (OAI)
Public defence
2004-10-29, Sal C3, Hus C, Linköpings Universitet, Linköping, 10:15 (Swedish)
Opponent
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-01-31
3. Aspects of fatigue life in thermal barrier coatings
Open this publication in new window or tab >>Aspects of fatigue life in thermal barrier coatings
2001 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Thermal barrier coatings (TBC) are applied on hot components in airborne and land-based gas turbines when higher turbine inlet temperature, meaning better thermal efficiency, is desired. The TBC is mainly applied to protect underlying material from high temperatures, but also serves as a protection from the aggressive corrosive environment.

Plasma sprayed coatings are often duplex TBC's with an outer ceramic top coat (TC) made from partially stabilised zirconia - ZrO2 + 6-8% Y2O3. Below the top coat there is a metallic bond coat (BC). The BC is normally a MCrAlX coating (M=Ni, Co, Fe ... and X=Y, Hf, Si ... ). In gas turbine components exposed to elevated temperatures nickel-based superalloys are commonly adopted as load carrying components. In the investigations performed here a commercial wrought Ni-base alloy Haynes 230 has been used as substrate for the TBC. As BC a NiCoCrAlY serves as a reference material and in all cases 7% yttria PS zirconia has been used. Phase development and failure mechanisms in APS TBC during service-like conditions have been evaluated in the present study. This is done by combinations of thermal cycling and low cycle fatigue tests. The aim is to achieve better knowledge regarding how, when and why thermal ban'ier coatings fail. As a fmal outcome of the project a model capable of predicting fatigue life of a given component will help engineers and designers of land based gas turbines for power generation to better optimise TBC's.

In the investigations it is seen that TBC life is strongly influenced by oxidation of the BC and interdiffusion between BC and the substrate. The bond coat is known to oxidise with time at high temperature. The initial oxide found during testing is alumina. With increased time at high temperature Al is depleted from the bond coat due to interdiffusion and oxidation. Oxides others than alumina start to form when the Al content is reduced below a critical limit. It is here believed that spinel appears when the Al content is lowered below 2w/o in the bond coat. Here it was shown that a faster growing oxide, rich in Ni, Cr and Co forms at the interface. Al depletion is also linked to BC phases. Initially the bond coat is a γ/ß-material possibly with very fine dispersed γ'. Simultaneously with Al-depletion the ß-phase is found to disappear. This occurs simultaneously with the formation of spinel. However, oxidation is not only a disadvantage. Low cycle fatigue tests reveal that oxide streaks within the bond coat will slow down crack growth due to crack deflection and crack branching. Therefore benefit of or damage from oxide growth on crack initiation and propagation is dependent on crack mode, spalling of the ceramic TC or growth of "classic" cracks perpendicular to the surface.

From the observations conclusions are drawn regarding fatigue behaviour ofTBC systems. The basic idea is that all cracks leading to failure initiate in the thermally grown oxide (TGO). Following the initiation, they can, however, grow to form either delamination cracks leading to top coat spallation or cracks transverse to the surface leading to component failure.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2001. 50 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 898
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-30049 (URN)15509 (Local ID)91-7373-085-8 (ISBN)15509 (Archive number)15509 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-11-28

Open Access in DiVA

No full text

Other links

Publisher's full text

Authority records BETA

Jinnestrand, MagnusBrodin, Håkan

Search in DiVA

By author/editor
Jinnestrand, MagnusBrodin, Håkan
By organisation
Solid MechanicsThe Institute of TechnologyEngineering Materials
In the same journal
Materials Science & Engineering: A
Engineering and Technology

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 240 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf