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Failure mechanisms in APS and SPS thermal barrier coatings during cyclic oxidation and hot corrosion
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
2017 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Thermal Barrier Coatings (TBCs) are advanced material systems that are being used in the hot sections of gas turbines such as combustor, turbine blades, and vanes. The top ceramic coating in TBCs provides insulation against the hot gases and the intermediate metallic bond coat provides oxidation and corrosion resistance to the underlying turbine components.

Durability of thermal barrier coatings is very important for the overall performance of the gas turbine. TBCs can fail in several different ways and there is a combination of more than one failure mechanism in most situations. One of the most widely used TBC is atmospheric plasma sprayed (APS) yttria stabilized zirconia (YSZ). Both the deposition technique and the TBC material have certain limitations. The main aim of this research is to study new TBC materials and/or new deposition techniques and compare with the conventional YSZ and understand their failure mechanisms during cyclic oxidation and hot corrosion.

Thermal cyclic oxidation of a newly developed high purity nano YSZ thermal barrier coating has been studied. Cross sectional analysis of exposed as well as completely failed samples showed a mixed-type failure caused by crack propagation parallel to the bond coat/top coat interface. The majority of the damage occurred towards the end of the coating life. A finite element model has been developed to study the probability of crack growth along different paths that leads to the final failure.

Hot corrosion mechanism in suspension plasma sprayed two-layer gadolinium zirconate/YSZ, three-layer dense gadolinium zirconate/gadolinium zirconate/YSZ, and a single-layer YSZ has been studied in the presence of sodium sulfate and vanadium pentoxide. The test results showed that gadolinium zirconate coatings were more susceptible to corrosion compared to YSZ coatings despite gadolinium zirconate coatings having lower reactivity with the corrosive salts.

Thermal cycling behavior of a high chromium bond coat has been studied. Cross-sectional analysis showed formation of sandwich type microstructure with chromium rich oxide and alumina as the top and the bottom layers.

Inter-diffusion of minor elements between different MCrAlY coatings – substrate systems has been studied using, diffusion simulation software, DICTRA. The simulation results showed that the diffusion of minor elements in the coatings is dependent on the rate of β phase depletion in the beginning. After the depletion of β phase there was no clear dependence of the coating composition on the diffusion of minor elements.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2017. , s. 45
Serie
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1770
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik Korrosionsteknik Materialkemi Metallurgi och metalliska material
Identifikatorer
URN: urn:nbn:se:liu:diva-134379DOI: 10.3384/lic.diva-134379ISBN: 9789176855942 (tryckt)OAI: oai:DiVA.org:liu-134379DiVA, id: diva2:1072644
Presentation
2017-03-10, A37, A-huset, Campus Valla, Linköping, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2017-02-08 Skapad: 2017-02-08 Senast uppdaterad: 2019-10-12Bibliografiskt granskad
Delarbeten
1. Hot Corrosion Mechanism in Multi-Layer Suspension Plasma Sprayed Gd2Zr2O7 /YSZ Thermal Barrier Coatings in the Presence of V2O5 + Na2SO4
Öppna denna publikation i ny flik eller fönster >>Hot Corrosion Mechanism in Multi-Layer Suspension Plasma Sprayed Gd2Zr2O7 /YSZ Thermal Barrier Coatings in the Presence of V2O5 + Na2SO4
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2017 (Engelska)Ingår i: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 26, nr 1, s. 140-149Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

This study investigates the corrosion resistance of two-layer Gd2Zr2O7/YSZ, three-layer dense Gd2Zr2O7/ Gd2Zr2O7/YSZ, and a reference single-layer YSZ coating with a similar overall top coat thickness of 300-320 µm. All the coatings were manufactured by suspension plasma spraying resulting in a columnar structure except for the dense layer. Corrosion tests were conducted at 900 °C for 8 h using V2O5 and Na2SO4 as corrosive salts at a concentration of approximately 4 mg/cm2. SEM investigations after the corrosion tests show that Gd2Zr2O7-based coatings exhibited lower reactivity with the corrosive salts and the formation of gadolinium vanadate (GdVO4), accompanied by the phase transformation of zirconia was observed. It is believed that the GdVO4 formation between the columns reduced the strain tolerance of the coating and also due to the fact that Gd2Zr2O7 has a lower fracture toughness value made it more susceptible to corrosion-induced damage. Furthermore, the presence of a relatively dense layer of Gd2Zr2O7 on the top did not improve in reducing the corrosion-induced damage. For the reference YSZ coating, the observed corrosion-induced damage was lower probably due to combination of more limited salt penetration, the SPS microstructure and superior fracture toughness of YSZ.

Ort, förlag, år, upplaga, sidor
New York: Springer, 2017
Nyckelord
gadolinium zirconatehot corrosionmulti-layer thermal barrier coatingssuspension plasma sprayingvanadium pentoxide + sodium sulfate
Nationell ämneskategori
Korrosionsteknik Bearbetnings-, yt- och fogningsteknik Materialkemi
Identifikatorer
urn:nbn:se:liu:diva-134375 (URN)10.1007/s11666-016-0486-5 (DOI)000392060300014 ()
Anmärkning

Funding agencies: Vinnova in Sweden

Tillgänglig från: 2017-02-08 Skapad: 2017-02-08 Senast uppdaterad: 2019-02-26Bibliografiskt granskad
2. Thermal fatigue failure of thermal barrier coatings with a high-Cr MCrAIY bond coat
Öppna denna publikation i ny flik eller fönster >>Thermal fatigue failure of thermal barrier coatings with a high-Cr MCrAIY bond coat
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2016 (Engelska)Ingår i: Proceedings of the International Thermal Spray Conference (ITSC), 2016, Vol. 324, s. 273-278Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Thermal barrier coatings (TBCs) were air-plasma sprayed onto Hastelloy X substrates. The TBCs consisted of a high-Cr MCrAlY (M for Ni and Co) bond coat and a yttria-stabilized zirconia (YSZ) top coat. The TBC samples were thermally cycled between 100 ºC and 1100 ºC with 1 hour dwell time at 1100 ºC. The thermal fatigue failure of the TBCs was investigated via microstructure analyses. The final fatigue failure of the TBCs was caused by the formation of interface-parallel cracks in the YSZ top coat. The formation of the cracks was found to be strongly related to the oxidation behaviour of the MCrAlY bond coat. The development of the oxide layers was therefore studied in detail. A thermokinetic model was also used to deepen the understanding on the elemental diffusion behavior in the materials.

Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik Metallurgi och metalliska material Materialkemi Kompositmaterial och -teknik
Identifikatorer
urn:nbn:se:liu:diva-134377 (URN)
Konferens
International Thermal Spray Conference (ITSC), May 10-12, 2016, China
Tillgänglig från: 2017-02-08 Skapad: 2017-02-08 Senast uppdaterad: 2017-02-16Bibliografiskt granskad

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