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Microstructure Influence on Functional Properties of GZ/YSZ & 48YSZ/YSZ TBC Systems
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
2019 (English)Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesisAlternative title
Mikrostrukturpåverkan på de funktionella egenskaperna hos GZ / YSZ och 48YSZ / YSZ TBC system (Swedish)
Abstract [en]

Protection of the metallic components from high working temperature is of the most interest in the gas turbine applications. Thermal Barrier Coatings (TBCs) have been promising since they reduce the temperature reaching underlying metallic substrate up to a considerable amount. Production of these TBCs with different microstructural features and without inducing any heavy cost is of particular interest. With Suspension Plasma Spray (SPS) technique it is possible to use sub-micrometric or nano sized feedstock to fabricate porous-columnar microstructures. SPS has higher deposition rates and is more economical than the conventional Electron Beam Physical Vapour Deposition (EB-PVD) technique, which is nowadays used in industry.

Survival of the TBCs in the harsh environment of the gas turbines mostly depends on the topcoat (TC) microstructure. The main objective of this work was to analyse the multilayer TBCs produced using axial SPS by altering the process parameters. Three suspensions with 25% solid load in ethanol, namely 8 wt.% Yttria Stabilized Zirconia (YSZ), 48 wt.% Yttria Stabilized Zirconia (48YSZ) and Gadolinium Zirconate (GZ) were used to spray the TCs. NiCoCrAlY bond coat was sprayed on Hastelloy-X substrate using High Velocity Air Fuel (HVAF) process. Scanning Electron Microscopy (SEM) was employed to analyse the SPS produced TBCs. Coatings showed columns originating from underlying YSZ layer and growing in GZ or 48YSZ layer. The lifetime of the TBCs was decided using number of cycles survived in Thermal Cyclic Fatigue (TCF) testing and Burner Rig Testing (BRT). Fracture toughness of the coating was calculated using indentation method. Image Analysis was used to determine the porosity content in the coatings and a Laser Flash Analysis (LFA) was carried out to determine the thermal conductivity.

Results obtained show that the microstructure of two TCs plays a crucial role for achieving TBCs with longer lifetime. Densest underlying TC do not confer (all time) the highest lifetime highlighting the important role played by the strain tolerance of the two topcoats.

Place, publisher, year, edition, pages
2019. , p. 34
Keywords [en]
Thermal cyclic fatigue, multilayer thermal barrier coatings, gadolinium zirconate, yttria stabilized zirconia, suspension plasma spray
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:hv:diva-14494Local ID: EXM902OAI: oai:DiVA.org:hv-14494DiVA, id: diva2:1356350
Subject / course
Mechanical engineering
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Available from: 2019-10-04 Created: 2019-10-01 Last updated: 2019-10-04Bibliographically approved

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