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Functional Performance of Gadolinium Zirconate/Yttria Stabilized Zirconia Multi-Layered Thermal Barrier Coatings
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0003-2475-9284
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Yttria stabilized zirconia (YSZ) is the state of the art ceramic top coat material used for TBC applications. The desire to achieve a higher engine efficiency of agas turbine engine by increasing the turbine inlet temperature has pushed YSZ toits upper limit. Above 1200°C, issues such as poor phase stability, high sinteringrates, and susceptibility to CMAS (calcium magnesium alumino silicates) degradation have been reported for YSZ based TBCs. Among the new materials,gadolinium zirconate (GZ) is an interesting alternative since it has shown attractive properties including resistance to CMAS attack. However, GZ has a poor thermo-chemical compatibility with the thermally grown oxide leading to poor thermal cyclic performance of GZ TBCs and that is why a multi-layered coating design seems feasible.This work presents a new approach of depositing GZ/YSZ multi-layered TBCs by the suspension plasma spray (SPS) process. Single layer YSZ TBCs were also deposited by SPS and used as a reference.The primary aim of the work was to compare the thermal conductivity and thermal cyclic life of the two coating designs. Thermal diffusivity of the YSZ single layer and GZ based multi-layered TBCs was measured using laser flash analysis (LFA). Thermal cyclic life of as sprayed coatings was evaluated at 1100°C, 1200°C and 1300°C respectively. It was shown that GZ based multi-layered TBCs had a lower thermal conductivity and higher thermal cyclic life compared to the single layer YSZ at all test temperatures. The second aim was to investigate the isothermal oxidation behaviour and erosion resistance of the two coating designs. The as sprayed TBCs were subjected toisothermal oxidation test at 1150°C. The GZ based multi-layered TBCs showed a lower weight gain than the single layer YSZ TBC. However, in the erosion test,the GZ based TBCs showed lower erosion resistance compared to the YSZ singlelayer TBC. In this work, it was shown that SPS is a promising production technique and that GZ is a promising material for TBCs.

Place, publisher, year, edition, pages
Trollhättan: University West , 2016. , 70 p.
Series
Licentiate Thesis: University West, 11
Keyword [en]
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: urn:nbn:se:hv:diva-9854ISBN: 978-91-87531-36-1 (Printed)ISBN: 978-91-87531-37-8 (Electronic)OAI: oai:DiVA.org:hv-9854DiVA: diva2:958206
Supervisors
Available from: 2016-09-09 Created: 2016-09-05 Last updated: 2016-09-06Bibliographically approved
List of papers
1. Thermal conductivity and thermal cyclic fatigue of multilayered Gd2Zr2O7/YSZ thermal barrier coatings processed by suspension plasma spray
Open this publication in new window or tab >>Thermal conductivity and thermal cyclic fatigue of multilayered Gd2Zr2O7/YSZ thermal barrier coatings processed by suspension plasma spray
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2015 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 283, 329-336 p.Article in journal (Refereed) Published
Abstract [en]

Rare earth zirconates have lower thermal conductivity, better phase stability, improved sintering resistance and CMAS (calcium magnesium alumino silicates) infiltration resistance than yttria stabilized zirconia (YSZ) at temperatures above 1200 °C. However, their lower fracture toughness and lower coefficient of thermal expansion (CTE) compared to YSZ lead to premature coating failure. In order to overcome these drawbacks at higher temperatures, a multilayered coating approach is attempted in this study and compared with the single layer YSZ. Suspension plasma spray of single layer YSZ, single layer gadolinium zirconate (GZ) and double layer GZ/YSZ was carried out. Additionally, a triple layer coating system, with denser gadolinium zirconate on top of the GZ/YSZ system was sprayed to impart an added functionality of sealing the TBC from CMAS infiltration. Microstructural analysis was done using scanning electron microscopy and optical microscopy. Columnar microstructure with vertical cracks was observed. XRD analysis was used to identify phases formed in the as sprayed TBC samples. Porosity measurements were done using water impregnation method. Thermal diffusivity of single and multi-layered coatings was obtained by laser flash analysis and thermal conductivity of the coating systems was determined. It was found that the thermal conductivity of single layer gadolinium zirconate was lower than YSZ and that the thermal conductivity of multilayered systems were between their respective single layers. The single (YSZ), double (GZ/YSZ) and triple (GZ dense/GZ/YSZ) layer TBCs were subjected to thermal cyclic fatigue (TCF) test at 1100 °C and 1200 °C. It was observed that the single layer YSZ had lowest TCF life whereas the triple layer TBC had highest TCF life irrespective of test temperature.

Place, publisher, year, edition, pages
Lausanne: Elsevier Sequoia, 2015
Keyword
Gadolinium zirconate; Multilayered thermal barrier coating; Suspension plasma spray; Thermal conductivity; Thermal cyclic fatigue; Thermal diffusivity; Yttria stabilized zirconia
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-8779 (URN)10.1016/j.surfcoat.2015.11.009 (DOI)2-s2.0-84949467152 (ScopusID)
External cooperation:
Available from: 2015-12-09 Created: 2015-12-09 Last updated: 2016-09-15Bibliographically approved
2. Isothermal Oxidation Behavior of Gd2Zr2O7/YSZ Multilayered Thermal Barrier Coatings
Open this publication in new window or tab >>Isothermal Oxidation Behavior of Gd2Zr2O7/YSZ Multilayered Thermal Barrier Coatings
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2016 (English)In: International Journal of Applied Ceramic Technology, ISSN 1744-7402, Vol. 13, no 3, 443-450 p.Article in journal (Refereed) Published
Abstract [en]

Efficiency of a gas turbine can be increased by increasing the operating temperature. Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used in gas turbine applications. However, above 1200°C, YSZ undergoes significant sintering and CMAS (calcium magnesium alumino silicate) infiltration. New ceramic materials of rare earth zirconate composition such as gadolinium zirconate (GZ) are promising candidates for thermal barrier coating applications (TBC) above 1200°C. Suspension plasma spray of single-layer YSZ, double-layer GZ/YSZ, and a triple-layer TBC comprising denser GZ on top of GZ/YSZ TBC was attempted. The overall coating thickness in all three TBCs was kept the same. Isothermal oxidation performance of the three TBCs along with bare substrate and bond-coated substrate was investigated for time intervals of 10 h, 50 h, and 100 h at 1150°C in air environment. Weight gain/loss analysis was carried out by sensitive weighing balance. Microstructural analysis was carried out using scanning electron microscopy (SEM). As-sprayed single-layer YSZ and double-layer GZ/YSZ showed columnar microstructure, whereas the denser layer in the triple-layer TBC was not columnar. Phase analysis of the top surface of as-sprayed TBCs was carried out using XRD. Porosity measurements were made by water intrusion method. In the weight gain analysis and SEM analysis, multilayered TBCs showed lower weight gain and lower TGO thickness compared to single-layer YSZ.

Keyword
Gadolinium zirconate, multilayered thermal barrier coatings, isothermal oxidation, suspension plasma spray, yttria-stabilized zirconia
National Category
Manufacturing, Surface and Joining Technology Ceramics
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-9275 (URN)10.1111/ijac.12527 (DOI)
Available from: 2016-04-06 Created: 2016-04-01 Last updated: 2016-09-06Bibliographically approved
3. Functional performance of Gd2Zr2O7/YSZ multi-layered thermal barrier coatings deposited by suspension plasma spray
Open this publication in new window or tab >>Functional performance of Gd2Zr2O7/YSZ multi-layered thermal barrier coatings deposited by suspension plasma spray
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(English)In: Surface and Coatings TechnologyArticle in journal (Refereed) Submitted
Abstract [en]

7-8 wt% yttria stabilized zirconia (YSZ) is the standard ceramic top coat material used in gasturbines to insulate the underlying metallic substrate. However, at higher temperatures(>1200 °C), phase stability and sintering becomes an issue for YSZ. At these temperatures,YSZ is also susceptible to CMAS (calcium magnesium alumino silicates) infiltration. New ceramic materials such as pyrochlores have thus been proposed due to their excellent properties such as lower thermal conductivity and better CMAS attack resistance compared to YSZ. However, pyrochlores have inferior thermo mechanical properties compared to YSZ.Therefore, double-layered TBCs with YSZ as the intermediate layer and pyrochlore as the top ceramic layer have been proposed. In this study, double layer TBC comprising gadoliniumzirconate (GZ)/YSZ and triple layer TBC (GZdense/GZ/YSZ) comprising relatively denser GZtop layer on GZ/YSZ were deposited by suspension plasma spray. Also, single layer 8YSZ TBC was suspension plasma sprayed to compare its functional performance with the multilayered TBCs. Cross sections and top surface morphology of as sprayed TBCs were analyzed by scanning electron microscopy (SEM). XRD analysis was done to identify phases formed in the top surface of as sprayed TBCs. Porosity measurements were made using water intrusionand image analysis methods. Thermal diffusivity of the as sprayed TBCs was measured using laser flash analysis and thermal conductivity of the TBCs was calculated. The multi-layered GZ/YSZ TBCs were shown to have lower thermal conductivity than the single layer YSZ. Theas sprayed TBCs were also subjected to thermal cyclic testing at 1300 ºC. The double and triple layer TBCs had a longer thermal cyclic life compared to YSZ. The failed samples were cold mounted and analyzed by SEM.

Keyword
Columnar microstructure, Gadolinium zirconate, Multi-layered thermal barrier coating, Suspension plasma spray, Thermal conductivity, Thermal cyclic test, Yttria stabilized zirconia
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-9855 (URN)
External cooperation:
Note

Ingår i licuppsats

Available from: 2016-09-05 Created: 2016-09-05 Last updated: 2016-09-06Bibliographically approved
4. Erosion Behavior of Gadolinium Zirconate/YSZ Multi-Layered Thermal Barrier Coatings Deposited by Suspension Plasma Spray
Open this publication in new window or tab >>Erosion Behavior of Gadolinium Zirconate/YSZ Multi-Layered Thermal Barrier Coatings Deposited by Suspension Plasma Spray
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2016 (English)In: Proceedings of the International Thermal Spray Conference, 2016, 343-347 p.Conference paper (Refereed)
Abstract [en]

Yttria stabilized zirconia (8YSZ) is the standard ceramic material for thermal barrier coating (TBC)applications. However, above 1200º C, it has limitations such as poor sintering resistance & susceptibility to CMAS(Calcium Magnesium Alumino Silicates) degradation. Gadolinium zirconate (GZ) is considered as one of the promising top coat candidates for TBC applications at high temperature (>1200 ºC) due to its lower thermal conductivity, good sintering resistance and CMAS infiltration resistance. Single layer 8YSZ, double layer GZ/YSZand triple layer GZdense/GZ/YSZ TBCs were deposited by suspension plasma spray (SPS). Microstructuralanalysis was carried out by SEM (scanning electron microscopy). Phase analysis of as sprayed TBCs was carriedout using XRD (X ray diffraction). The as sprayed multi-layered TBCs were subjected to erosion test at room temperature and their erosion resistance was compared with single layer 8YSZ. It was observed that the erosion resistance of 8YSZ TBC was higher than GZ/YSZ multi-layered TBCs at room temperature. Among the multilayered TBCs, triple layer TBC was slightly better than double layer in terms of erosion resistance.

Keyword
Thermal barrier coating
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-9856 (URN)
External cooperation:
Conference
International Thermal Spray Conference, May 10-12, 2016, Shanghai, DVS Media
Available from: 2016-09-05 Created: 2016-09-05 Last updated: 2016-09-06Bibliographically approved

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Mahade, Satyapal
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