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Erosion Performance of Gadolinium Zirconate-Based Thermal Barrier Coatings Processed by Suspension Plasma Spray
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0003-2475-9284
Treibacher Industrie AGAlthofenAustria.ORCID iD: 0000-0003-0209-1332
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0003-1181-0415
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0002-9578-4076
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2017 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 26, no 1-2, p. 108-115Article in journal (Refereed) Published
Abstract [en]

7-8 wt.% Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used by the gas turbines industry due to its excellent thermal and thermo-mechanical properties up to 1200 °C. The need for improvement in gas turbine efficiency has led to an increase in the turbine inlet gas temperature. However, above 1200 °C, YSZ has issues such as poor sintering resistance, poor phase stability and susceptibility to calcium magnesium alumino silicates (CMAS) degradation. Gadolinium zirconate (GZ) is considered as one of the promising top coat candidates for TBC applications at high temperatures (>1200 °C) due to its low thermal conductivity, good sintering resistance and CMAS attack resistance. Single-layer 8YSZ, double-layer GZ/YSZ and triple-layer GZdense/GZ/YSZ TBCs were deposited by suspension plasma spray (SPS) process. Microstructural analysis was carried out by scanning electron microscopy (SEM). A columnar microstructure was observed in the single-, double- and triple-layer TBCs. Phase analysis of the as-sprayed TBCs was carried out using XRD (x-ray diffraction) where a tetragonal prime phase of zirconia in the single-layer YSZ TBC and a cubic defect fluorite phase of GZ in the double and triple-layer TBCs was observed. Porosity measurements of the as-sprayed TBCs were made by water intrusion method and image analysis method. The as-sprayed GZ-based multi-layered TBCs were subjected to erosion test at room temperature, and their erosion resistance was compared with single-layer 8YSZ. It was shown that the erosion resistance of 8YSZ single-layer TBC was higher than GZ-based multi-layered TBCs. Among the multi-layered TBCs, triple-layer TBC was slightly better than double layer in terms of erosion resistance. The eroded TBCs were cold-mounted and analyzed by SEM.

Place, publisher, year, edition, pages
2017. Vol. 26, no 1-2, p. 108-115
Keywords [en]
columnar microstructureerosion, test gadolinium, zirconatemulti-layered thermal barrier, coating, suspension plasma spray, yttria-stabilized zirconia
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-10498DOI: 10.1007/s11666-016-0479-4ISI: 000392060300011Scopus ID: 2-s2.0-85001975445OAI: oai:DiVA.org:hv-10498DiVA, id: diva2:1062916
Note

This article is an invited paper selected from presentations at the 2016 International Thermal Spray Conference, held May 10-12, 2016, in Shanghai, P. R. China, and has been expanded from the original presentation.

Available from: 2017-01-09 Created: 2017-01-09 Last updated: 2018-06-18Bibliographically approved
In thesis
1. Functional Performance of Gadolinium Zirconate/Yttria Stabilized Zirconia Multi-Layered Thermal Barrier Coatings
Open this publication in new window or tab >>Functional Performance of Gadolinium Zirconate/Yttria Stabilized Zirconia Multi-Layered Thermal Barrier Coatings
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Yttria stabilized zirconia (YSZ) is the state-of-the-art ceramic top coat material used for thermal barrier coating (TBC) applications. Demand for higher efficiency in gas turbine engines has led to a continuous increase in the gas in let temperature. However, this increase in temperature has pushed YSZ to its upper limit. Above1200 °C, issues such as poor phase stability, high sintering rate, and susceptibility to CMAS (Calcium Magnesium Alumino Silicates) degradation limit the durability of YSZ based TBCs. Among the new top coat materials suggested for high temperature TBC applications, gadolinium zirconate (GZ) is an interesting alternative to YSZ since it has shown attractive properties which include a better resistance to CMAS attack. However, GZ has poor thermo-chemical compatibility with the thermally grown oxide (alumina), leading to poor thermalcyclic fatigue performance of single layered GZ TBCs. Therefore, a multi-layered GZ/YSZ based TBC design seems promising. This work presents a new approach of depositing multi-layered (double and triple layered) GZ/YSZ TBCs using the recently developed suspension plasma spray(SPS) process. SPS was employed in this work because of its capability to mimic the electron beam physical vapour deposition (EB-PVD) process in terms of producing columnar microstructured TBCs. Single layer YSZ TBCs were also deposited by SPS process and used as a reference for comparing the functional performance of multi-layered GZ based TBCs. The primary aim of this work was to improve the durability of GZ based multilayered TBCs at high temperatures. Durability tests were performed in the temperature range 1100 °C - 1400 °C under different thermal cyclic test conditions (with and without thermal gradient). The results indicate that multilayered GZ based TBCs improve durability compared to the single layer YSZTBCs at all the test temperatures. Failure analysis of the multi-layered GZ/YSZTBCs revealed spallation within the GZ layer close to GZ/YSZ interface and the reason was believed to be the inferior fracture toughness of GZ. In order to improve the fracture toughness in the region of failure, a composite approach comprising multi-layered GZ+YSZ based TBC was considered. It was shown that the composite GZ+YSZ based TBCs did not improve the thermal cyclic lifetime, although improvement in fracture toughness was observed. As a further extension of this work, the influence of YSZ layer thickness on the durability of GZ/YSZTBCs was investigated. It was shown that an increase in YSZ layer thickness in the GZ/YSZ TBC led to poor durability. Additionally, the other important performance criteria for TBCs, i.e. thermal conductivity, was measured experimentally and compared with the single layer YSZ TBC. It was shown that the GZ based TBCs had lower thermal conductivity than YSZ. The second aim was to investigate and compare the erosion performance of multi-layered GZ based TBCs and single layered YSZ TBCs. In the erosion testconducted at room temperature, the GZ based TBCs showed lower erosion resistance compared to the single layer YSZ TBC. The main reason for this difference was attributed to the inferior fracture toughness of GZ. In case of the composite multi-layered GZ+YSZ based TBC, an improvement in erosion resistance was observed compared to the multi-layered GZ based TBC. Based on the results obtained, this work has demonstrated that SPS is a promising processing technique to produce columnar microstructured TBCs irrespective of the composition (GZ, YSZ, GZ+YSZ). It was also shown that GZ/YSZ multilayered TBCs are promising for high temperature TBC applications due to theirl ow thermal conductivity and high thermal cyclic fatigue lifetime. However, low erosion resistance for certain applications might be an issue for the GZ basedTBCs.

Place, publisher, year, edition, pages
Trollhättan: University West, 2018. p. 82
Series
PhD Thesis: University West ; 18
Keywords
Composite; Erosion; Gadolinium Zirconate; Suspension Plasma Spray; Thermal Barrier Coatings; Thermal Cyclic Test; Thermal Conductivity; Yttria Stabilized Zirconia.
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-12301 (URN)978-91-87531-86-6 (ISBN)978-91-87531-85-9 (ISBN)
Public defence
2018-06-05, F104, Trollhättan, 10:15 (English)
Opponent
Supervisors
Available from: 2018-05-16 Created: 2018-05-15 Last updated: 2018-05-16Bibliographically approved

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Mahade, SatyapalCurry, NicholasBjörklund, StefanMarkocsan, NicolaieNylén, Per

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