| 1. |
- Curry, Nicholas, 1984-
(author)
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Design of Thermal Barrier Coating Systems
- 2012
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Licentiate thesis (other academic/artistic)abstract
- Thermal barrier coatings (TBC’s) are used to provide both thermal insulation and oxidation protection to high temperature components within gas turbines. The development of turbines for power generation and aviation has led to designs where the operation conditions exceed the upper limits of most conventional engineering materials. As a result there has been a drive to improve thermal barrier coatings to allow the turbine to operate hotter for longer.The focus of this study has been the development of a new generation of TBC system for industrial implementation. The goal for these new coatings was to achieve lower conductivity and longer lifetime than those coatings used today. The route taken to achieve these goals has been twofold. Firstly an alternative stabiliser has been chosen for the zirconium oxide system in the form of dysprosia. Secondly, Control of the powder morphology and spray parameters has been used to generate coating microstructures with favourable levels of porosity.Samples have been heavily characterised using the laser flash technique for evaluation of thermal properties. Measurements were performed at room temperature and at intervals up to 1200°C. Samples have also been tested in their as produced state and after heat treatments of up to 200 hours.Lifetime evaluation has been performed using the thermo-cyclic fatigue test to expose coating systems to successive cycles of heating and cooling combined with oxidation of the underlying metallic coating.Microstructures have been prepared and analysed using SEM. An image analysis routine has been used to attempt to quantify changes in microstructure features between coating types or coating exposure times and to relate those changes to changes in thermal propertiesResults show that dysprosia as an alternative dopant gives a reduction in thermal conductivity. While small at room temperature and in the as produced state; the influence becomes more pronounced at high temperatures and with thermal exposure time. Overall, the greatest sustained influence on thermal conductivity has been from creating coatings with high levels of porosity.In relation to lifetime, the target of double the thermo-cyclic fatigue life was achieved using a coating with engineered porosity. Introducing a polymer to the spray powder helps to generate large globular pores within the coating together with a large number of delaminations. Such a structure has shown to be highly resistant to TCF testing.
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| 2. |
- Ganvir, Ashish, 1991-, et al.
(author)
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Tailoring columnar microstructure of axial suspension plasma sprayed TBCs for superior thermal shock performance
- 2018
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In: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 144, s. 192-208
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Journal article (peer-reviewed)abstract
- This paper investigates the thermal shock behavior of thermal barrier coatings (TBCs) produced by axial suspension plasma spraying (ASPS). TBCs with different columnar microstructures were subjected to cyclic thermal shock testing in a burner rig. Failure analysis of these TBCs revealed a clear relationship between lifetime and porosity. However, tailoring the microstructure of these TBCs for enhanced durability is challenging due to their inherently wide pore size distribution (ranging from few nanometers up to few tens of micrometers). This study reveals that pores with different length scales play varying roles in influencing TBC durability. Fracture toughness shows a strong correlation with the lifetime of various ASPS TBCs and is found to be the prominent life determining factor. Based on the results, an understanding-based design philosophy for tailoring of the columnar microstructure of ASPS TBCs for enhanced durability under cyclic thermal shock loading is proposed. © 2018 The Authors
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| 3. |
- Kumar, Nitish, 1995-, et al.
(author)
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Columnar Thermal Barrier Coatings Produced by Different Thermal Spray Processes
- 2021
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In: Journal of thermal spray technology (Print). - : Springer. - 1059-9630 .- 1544-1016. ; 30, s. 1437-1452
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Journal article (peer-reviewed)abstract
- Suspension plasma spraying (SPS) and plasma spray-physical vapor deposition (PS-PVD) are the only thermal spray technologies shown to be capable of producing TBCs with columnar microstructures similar to the electron beam-physical vapor deposition (EB-PVD) process but at higher deposition rates and relatively lower costs. The objective of this study was to achieve fundamental understanding of the effect of different columnar microstructures produced by these two thermal spray processes on their insulation and lifetime performance and propose an optimized columnar microstructure. Characterization of TBCs in terms of microstructure, thermal conductivity, thermal cyclic fatigue lifetime and burner rig lifetime was performed. The results were compared with TBCs produced by the standard thermal spray technique, atmospheric plasma spraying (APS). Bondcoats deposited by the emerging high-velocity air fuel (HVAF) spraying were compared to the standard vacuum plasma-sprayed (VPS) bondcoats to investigate the influence of the bondcoat deposition process as well as topcoat-bondcoat interface topography. The results showed that the dense PS-PVD-processed TBC had the highest lifetime, although at an expense of the highest thermal conductivity. The reason for this behavior was attributed to the dense intracolumnar structure, wide intercolumnar gaps and high column density, thus improving the strain tolerance and fracture toughness.
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| 4. |
- Mahade, Satyapal, 1987-, et al.
(author)
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Effect of spray parameters on the microstructure and porosity content of gadolinium zirconate TBCs deposited by suspension plasma spray
- 2017
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In: Proceedings of the International Thermal Spray Conference & Exposition (ITSC 2017). - New York : Curran Associates, Inc. - 9781510858220 ; , s. 31-35
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Conference paper (peer-reviewed)abstract
- Gadolinium zirconate (GZ) is considered as a promising top coat candidate for high temperature(>1200°C) thermal barrier coating (TBC) applications. Suspension plasma spray (SPS) technique has shown the capability to generate a wide range of microstructures which includes the more desirable columnar microstructure. In this study, GZ single layer TBCs were deposited by axial SPS process. The variable parameters include the standoff distance, solid load content of the suspension and input power. The cross section and top surface of the as sprayed TBCs were analyzed by SEM. The phase content in the as sprayed TBCs was analyzed by XRD. The porosity content of the as sprayed TBCs was measured using image analysis. In the SEM analysis, it was observed that a lower solid load content in the suspension favoured the formation of a columnar microstructure. Additionally, at lower solid load content, increase in standoff distance resulted in columnar microstructure with high porosity content in the TBC. However，with higher solid content suspension and alteration of input power, only adense vertical cracked microstructure can be obtained.
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| 5. |
- Mahade, Satyapal, 1987-, et al.
(author)
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Erosion Behavior of Gadolinium Zirconate/YSZ Multi-Layered Thermal Barrier Coatings Deposited by Suspension Plasma Spray
- 2016
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In: Proceedings of the International Thermal Spray Conference. ; , s. 343-347
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Conference paper (peer-reviewed)abstract
- 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.
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| 6. |
- Mahade, Satyapal, 1987-, et al.
(author)
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Functional performance of Gd2Zr2O7/YSZ multi-layered thermal barrier coatings deposited by suspension plasma spray
- 2017
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In: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 318, s. 208-216
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Journal article (peer-reviewed)abstract
- 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.
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| 7. |
- Mahade, Satyapal, 1987-, et al.
(author)
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Tailored microstructures of gadolinium zirconate/YSZ multi-layered thermal barrier coatings produced by suspension plasma spray : Durability and erosion testing
- 2019
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In: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 264, s. 283-294
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Journal article (peer-reviewed)abstract
- This work employed an axial suspension plasma spray (SPS) process to deposit two different gadolinium zirconate (GZ) based triple layered thermal barrier coatings (TBCs). The first was a 'layered' TBC (GZ dense/GZ/YSZ) where the base layer was YSZ, intermediate layer was a relatively porous GZ and the top layer was a relatively dense GZ. The second triple layered TBC was a 'composite' TBC (GZ dense/GZ + YSZ/YSZ) comprising of an YSZ base layer, a GZ + YSZ intermediate layer and a dense GZ top layer. The as sprayed TBCs (layered and composite) were characterized using SEM/EDS and XRD. Two different methods (water intrusion and image analysis) were used to measure the porosity content of the as sprayed TBCs. Fracture toughness measurements were made on the intermediate layers (GZ + YSZ layer of the composite TBC and porous GZ layer of the layered TBC respectively) using micro indentation tests. The GZ + YSZ layer in the composite TBC was shown to have a slightly higher fracture toughness than the relatively porous GZ layer in the layered TBC. Erosion performance of the as sprayed TBCs was evaluated at room temperature where the composite TBC showed higher erosion resistance than the layered TBC. However, in the burner rig test conducted at 1400 °C, the layered TBC showed higher thermal cyclic lifetime than the composite TBC. Failure analysis of the thermally cycled and eroded TBCs was performed using SEM and XRD. © 2018 Elsevier B.V.
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| 8. |
- Vardelle, Armelle, et al.
(author)
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Erratum to The 2016 Thermal Spray Roadmap
- 2017
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In: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 26:5, s. 985-986
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Journal article (peer-reviewed)
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| 9. |
- Vardelle, Armelle, et al.
(author)
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The 2016 Thermal Spray Roadmap
- 2016
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In: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 25:8, s. 1376-1440
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Journal article (peer-reviewed)abstract
- Considerable progress has been made over the last decades in thermal spray technologies, practices and applications. However, like other technologies, they have to continuously evolve to meet new problems and market requirements. This article aims to identify the current challenges limiting the evolution of these technologies and to propose research directions and priorities to meet these challenges. It was prepared on the basis of a collection of short articles written by experts in thermal spray who were asked to present a snapshot of the current state of their specific field, give their views on current challenges faced by the field and provide some guidance as to the R&D required to meet these challenges. The article is divided in three sections that deal with the emerging thermal spray processes, coating properties and function, and biomedical, electronic, aerospace and energy generation applications. © 2016, ASM International.
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| 10. |
- Vassen, Robert, et al.
(author)
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Editorial
- 2009
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In: Journal of Thermal Spray Technology. - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 18:2, s. 131-
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Journal article (other academic/artistic)
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| 11. |
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