| 1. |
- Ganvir, Ashish, 1991-, et al.
(författare)
-
Effect of suspension characteristics on the performance of thermal barrier coatings deposited by suspension plasma spray
- 2020
-
Ingår i: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 47:1, s. 272-283
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the influence of suspension characteristics on microstructure and performance of suspensions plasma sprayed (SPS) thermal barrier coatings (TBCs). Five suspensions were produced using various suspension characteristics, namely, type of solvent and solid load content, and the resultant suspensions were utilized to deposit five different TBCs under identical processing conditions. The produced TBCs were evaluated for their performance i.e. thermal conductivity, thermal cyclic fatigue (TCF) and thermal shock (TS) lifetime. This experimental study revealed that the differences in the microstructure of SPS TBCs produced using varied suspensions resulted in a wide-ranging overall TBC performance. All TBCs exhibited thermal conductivity lower than 1 W/(m. K) except water-ethanol mixed suspension produced TBC. The TS lifetime was also affected to a large extent where 10 wt % solid loaded ethanol and 25 wt % solid loaded water suspensions produced TBCs exhibited the highest and the lowest lifetime, respectively. On the contrary, TCF lifetime was not as significantly affected as thermal conductivity and TS lifetime, and all ethanol suspensions showed marginally better TCF lifetime than water and ethanol-water mixed suspensions deposited TBCs. © 2020
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| 2. |
- Kumar, Nitish, 1995-, et al.
(författare)
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Columnar Thermal Barrier Coatings Produced by Different Thermal Spray Processes
- 2021
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Ingår i: Journal of thermal spray technology (Print). - : Springer. - 1059-9630 .- 1544-1016. ; 30, s. 1437-1452
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Aranke, Omkar, 1994-, et al.
(författare)
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Microstructural Evolution and Sintering of Suspension Plasma-Sprayed Columnar Thermal Barrier Coatings
- 2019
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 28:1-2, s. 198-211
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Tidskriftsartikel (refereegranskat)abstract
- Suspension plasma spray (SPS) is capable of producing coatings with porous columnar structure, and it is also a much cheaper process compared to the conventionally used electron beam physical vapor deposition (EB-PVD). Although TBCs with a columnar microstructure that are fabricated using SPS have typically lower thermal conductivity than EB-PVD, they are used sparingly in the aerospace industry due to their lower fracture toughness and limited lifetime expectancy. Lifetime of TBCs is highly influenced by the topcoat microstructure. The objective of this work was to study the TBCs produced using axial SPS with different process parameters. Influence of the microstructure on lifetime of the coatings was of particular interest, and it was determined by thermal cyclic fatigue testing. The effect of sintering on microstructure of the coatings exposed to high temperatures was also investigated. Porosity measurements were taken using image analysis technique, and thermal conductivity of the coatings was determined by laser flash analysis. The results show that axial SPS is a promising method of producing TBCs having various microstructures with good lifetime. Changes in microstructure of topcoat due to sintering were seen evidently in porous coatings, whereas dense topcoats showed good resistance against sintering.
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| 4. |
- Eriksson, Robert, et al.
(författare)
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Stresses and Cracking During Chromia-Spinel-NiO Cluster Formation in TBC Systems
- 2015
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 24:6, s. 1002-1014
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Tidskriftsartikel (refereegranskat)abstract
- Thermal barrier coatings (TBC) are used in gas turbines to reduce the temperatures in the underlying substrate. There are several mechanisms that may cause the TBC to fail; one of them is cracking in the coating interface due to extensive oxidation. In the present study, the role of so called chromia-spinel-NiO (CSN) clusters in TBC failure was studied. Such clusters have previously been found to be prone to cracking. Finite element modeling was performed on a CSN cluster to find out at which stage of its formation it cracks and what the driving mechanisms of cracking are. The geometry of a cluster was obtained from micrographs and modeled as close as possible. Nanoindentation was performed on the cluster to get the correct Young’s moduli. The volumetric expansion associated with the formation of NiO was also included. It was found that the cracking of the CSN clusters is likely to occur during its last stage of formation as the last Ni-rich core oxidizes. Furthermore, it was shown that the volumetric expansion associated with the oxidation only plays a minor role and that the main reason for cracking is the high coefficient of thermal expansion of NiO. © 2015 ASM International
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| 5. |
- Fefekos, Alexandros G., et al.
(författare)
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Effect of spray angle and substrate material on formation mechanisms and properties of HVAF sprayed coatings
- 2023
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 452
-
Tidskriftsartikel (refereegranskat)abstract
- Thermally sprayed coatings are often used to enhance the surface properties (wear resistance, corrosion resistance, etc.) of engineering components in order to extend their performance and service lifetime. Typically, the industrial components to be coated possess complex geometries and are fabricated using different materials, which can influence the deposited coating’s microstructure and performance. High-velocity air fuel (HVAF) process is a relatively new thermal spray processing technique that has shown tremendous potential to deposit high performance coatings for durable industrial components. However, no detailed studies have been reported on HVAF sprayed coating formation mechanisms so far in relation to the spray angle and substrate properties, and the influence of coating material on the above. The objective of this work was to study the influence of spray angles and substrate materials on splat characteristics, coating microstructure evolution, properties and performance for two distinct coating materials. In this study, one cermet (WC-CoCr) and one metallic (Inconel 625) feedstock were deposited onto three different substrates (aluminium alloy, carbon steel and Hastelloy-X) utilising different spray angles (40°, 60° and 90°). The coating evolution was analysed utilising SEM/EDS, image analysis, and micro-indentation. To determine the tribological performance, coatings were subjected to dry sliding wear test utilising alumina ball as counter surface and specific wear rates were obtained. The results showed that initial splat characteristics were substantially altered on changing the substrate and the spray angle. However, the final coating properties were not affected significantly even though the deposition rate was reduced significantly at lower spray angle, suggesting the versatility of the HVAF process.
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| 6. |
- Ganvir, Ashish, 1991-
(författare)
-
Design of Suspension Plasma Sprayed Thermal Barrier Coatings
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermal barrier coatings (TBCs) are widely used on gas turbine components to provide thermal insulation, which in combination with advanced cooling, can enable the gas turbine to operate at significantly higher temperatures even above the melting temperature of the metallic components. There is a permanent need,mainly due to environmental reasons, to increase the combustion temperature inturbines, hence new TBC solutions are needed. By using a liquid feedstock in thermal spraying, new types of TBCs can be produced. Suspension plasma/flame or solution precursor plasma spraying are examples of techniques that can be utilized for liquid feedstock thermal spraying. This approach of using suspension and solution feedstock, which is an alternative to the conventional solid powder feedstock spraying, is gaining increasing research interest since it has been shown to be capable of producing coatings withsuperior performance. The objective of this research work was to identify relationships between process parameters, coating microstructure, thermal conductivity and lifetime in suspension plasma sprayed TBCs. A further objective was to utilize these relationships to enable tailoring of the TBC microstructure for superior performance compared to state-of-the-art TBC used in industry today, i.e. solid feedstock plasma sprayed TBCs. Different spraying techniques, namely suspension high velocity oxy fuel, solution precursor plasma and suspension plasma spraying (with axial and radial feeding) were explored and compared to solid feedstock plasma spraying. A variety of microstructures, such as highly porous, vertically cracked and columnar, were produced and investigated. It was shown that there are strong relationships between microstructure, thermo-mechanical properties and performance of the coatings. Specifically, axial suspension plasma spraying wasshown as a very promising technique to produce various microstructures as wellas highly durable coatings. Based on the experimental results, a tailored columnar microstructure design for a superior TBC performance is also proposed.
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| 7. |
- Ganvir, Ashish, 1991-, et al.
(författare)
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Failure analysis of thermally cycled columnar thermal barrier coatings produced by high-velocity-air fuel and axial-suspension-plasma spraying : A design perspective
- 2018
-
Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 44:3, s. 3161-3172
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Tidskriftsartikel (refereegranskat)abstract
- Axial-suspension-plasma spraying (ASPS) is a fairly recent thermal spray technology which enables production of ceramic top coats in TBCs, incorporating simultaneously the properties of both the conventional-plasma sprayed (highly insulating porous structures) and electron-beam-physical-vapor-deposited (strain-tolerant columnar structures) top coats. TBCs are required to insulate the hot components in a gas turbine engine against high temperature and harsh operating conditions. Periodic heating and cooling of turbine engines during operation can create severe thermal cyclic fatigue conditions which can degrade the performance of these coatings eventually leading to the failure. An in-depth experimental investigation was performed to understand the failure behavior of columnar TBCs subjected to thermal cyclic fatigue (TCF) test at 1100 C. The study revealed that the TCF performance was influenced to an extent, by the top coat microstructure, but was primarily affected by the severity of thermally grown oxide (TGO) growth at the bond coat-top coat interface. Mixed failure modes comprising crack propagation through the bond coat-TGO interface, through TGO and within the top coat were identified. Based on the analysis of the experimental results and thorough discussion a novel design of microstructure for the high TCF performance columnar TBC is proposed. © 2017 Elsevier Ltd and Techna Group S.r.l.
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| 8. |
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| 9. |
- Ganvir, Ashish, 1991-, et al.
(författare)
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Thermal conductivity in suspension sprayed thermal barrier coatings : Modelling and experiments
- 2016
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Ingår i: Proceedings of the International Thermal Spray Conference. - : ASM International. ; , s. 368-374
-
Konferensbidrag (refereegranskat)abstract
- Axial Suspension Plasma spraying (ASPS) can generate microstructures with higher porosity and pores in the size range from submicron to nanometre. ASPS Thermal Barrier Coatings (TBCs) have already shown a great potential to produce low thermal conductivity coatings for gas turbine applications. It is important to understand the fundamental relationship between microstructural defects in the coating such as grain boundaries, porosity etc. and thermal conductivity. Object Oriented Finite element analysis (OOF) has been shown to be an effective tool for evaluating thermal conductivity for conventional TBCs as this method is capable of incorporating the inherent microstructure as an input to the model. The objective of this work was to analyse the thermal conductivity of ASPS TBCs using experimental techniques and also to evaluate a procedure where OOF can be used to predict and analyse the thermal conductivity for these coatings. Verification of the model was done using experimental thermal conductivity. Results showed that the varied scaled porosity has a significant influence on the thermal conductivity. Smaller grains, higher overall porosity content and lower columnar density resulted in lower thermal conductivity. It was shown that OOF could be a powerful tool to predict and rank thermal conductivity of ASPS TBCs.
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| 10. |
- Ganvir, Ashish, et al.
(författare)
-
Thermal Conductivity in Suspension Sprayed Thermal Barrier Coatings : Modeling and Experiments
- 2017
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 26:1-2, s. 71-82
-
Tidskriftsartikel (refereegranskat)abstract
- Axial suspension plasma spraying (ASPS) can generate microstructures with higher porosity and pores in the size range from submicron to nanometer. ASPS thermal barrier coatings (TBC) have already shown a great potential to produce low thermal conductivity coatings for gas turbine applications. It is important to understand the fundamental relationships between microstructural defects in ASPS coatings such as crystallite boundaries, porosity etc. and thermal conductivity. Object-oriented finite element (OOF) analysis has been shown as an effective tool for evaluating thermal conductivity of conventional TBCs as this method is capable of incorporating the inherent microstructure in the model. The objective of this work was to analyze the thermal conductivity of ASPS TBCs using experimental techniques and also to evaluate a procedure where OOF can be used to predict and analyze the thermal conductivity for these coatings. Verification of the model was done by comparing modeling results with the experimental thermal conductivity. The results showed that the varied scaled porosity has a significant influence on the thermal conductivity. Smaller crystallites and higher overall porosity content resulted in lower thermal conductivity. It was shown that OOF could be a powerful tool to predict and rank thermal conductivity of ASPS TBCs.
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| 11. |
- Gupta, Mohit Kumar, et al.
(författare)
-
A Diffusion-based Oxide Layer Growth Model using Real Interface Roughness in Thermal Barrier Coatings for Lifetime Assessment
- 2015
-
Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 271:June, s. 181-191
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Tidskriftsartikel (refereegranskat)abstract
- The development of thermo-mechanical stresses during thermal cycling can lead to the formation of detrimental cracks in Atmospheric Plasma Sprayed (APS) Thermal Barrier Coatings systems (TBCs). These stresses are significantly increased by the formation of a Thermally Grown Oxide (TGO) layer that forms through the oxidation of mainly aluminium in the bondcoat layer of the TBC. As shown in previous work done by the authors, the topcoat-bondcoat interface roughness plays a major role in the development of the stress profile in the topcoat and significantly affects the lifetime of TBCs. This roughness profile varies as the TGO layer grows and changes the stress profile in the topcoat leading to crack propagation and thus failure.In this work, a two-dimensional TGO growth model is presented, based on oxygen and aluminium diffusion-reaction equations, using real interface profiles extracted from cross-section micrographs. The model was first validated by comparing the TGO profiles artificially created by the model to thermally cycled specimens with varying interface roughness. Thereafter, stress profiles in the TBC system, before and after the TGO layer growth, were estimated using a finite element modelling model described in previous work done by the authors. Three experimental specimens consisting of the same chemistry but with different topcoat-bondcoat interface roughness were studied by the models and the stress state was compared to the lifetimes measured experimentally. The combination of the two models described in this work was shown to be an effective approach to assess the stress behaviour and lifetime of TBCs in a comparative way.
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| 12. |
- Gupta, Mohit Kumar, et al.
(författare)
-
A modelling approach to design of microstructures in thermal barrier coatings
- 2013
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Ingår i: Journal of Ceramic Science and Technology. - 2190-9385. ; 4:2, s. 85-92
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Tidskriftsartikel (refereegranskat)abstract
- Thermo-mechanical properties of TBCs are strongly influenced by coating defects, such as delaminations and pores, thus making it essential to have a fundamental understanding of microstructure-property relationships in TBCs to produce a desired coating. Object-Oriented Finite element analysis (OOF) has been shown previously as an effective tool for evaluating thermal and mechanical material behaviour, as this method is capable of incorporating the inherent material microstructure as an input to the model. In this work, OOF was used to predict the thermal conductivity and effective Young's modulus of TBC topcoats. A Design of Experiments (DoE) was conducted by varying selected spray parameters for spraying Yttria Stabilized Zirconia (YSZ) topcoat. Microstructure was assessed with SEM and image analysis was used to characterize porosity content. The relationships between microstructural features and properties predicted by modelling are discussed. The microstructural features having the most beneficial effect on properties were sprayed with another spray gun so as to verify the results obtained from modelling. Characterisation of the coatings included microstructure evaluation, thermal conductivity and lifetime measurements. The modelling approach in combination with experiments undertaken in this study was shown to be an effective way in achieving coatings with optimised thermo-mechanical properties.
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| 13. |
- Gupta, Mohit Kumar, et al.
(författare)
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An Experimental Study of Microstructure : Property Relationships in Thermal Barrier Coatings
- 2013
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 22:5, s. 659-670
-
Tidskriftsartikel (refereegranskat)abstract
- The thermal-mechanical properties of thermal barrier coatings are highly influenced by the defects present in coating microstructure. The aim of this study was to meet the future needs of the gas turbine industry by further development of zirconia coatings through the assessment of microstructure-property relationships. A design of experiments was conducted for this purpose with current, spray distance, and powder feed rate as the varied parameters. Microstructure was assessed with SEM and image analysis was used to characterize porosity content. Evaluations were carried out using laser flash technique to measure thermal properties. A bi-layer beam curvature technique in conjunction with controlled thermal cycling was used to assess the mechanical properties, in particular their nonlinear elastic response. Coating lifetime was evaluated by thermo-cyclic fatigue testing. Relationships between microstructure and coating properties are discussed. Dense vertically cracked microstructure and highly porous microstructure with large globular pores were also fabricated. Correlations between parameters obtained from nonlinear measurements and lifetime based on a priori established microstructural analysis were attempted in an effort to develop and identify a simplified strategy to assess coating durability following sustained long-term exposure to high temperature thermal cycling.
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| 14. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
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Bilayer Suspension Plasma-Sprayed Thermal Barrier Coatings with Enhanced Thermal Cyclic Lifetime : Experiments and Modeling
- 2017
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 26:6, s. 1038-1051
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Tidskriftsartikel (refereegranskat)abstract
- Suspension plasma spraying (SPS) has been shown as a promising process to produce porous columnar strain tolerant coatings for thermal barrier coatings (TBCs) in gas turbine engines. However, the highly porous structure is vulnerable to crack propagation, especially near the topcoat-bondcoat interface where high stresses are generated due to thermal cycling. A topcoat layer with high toughness near the topcoat-bondcoat interface could be beneficial to enhance thermal cyclic lifetime of SPS TBCs. In this work, a bilayer coating system consisting of first a dense layer near the topcoat-bondcoat interface followed by a porous columnar layer was fabricated by SPS using Yttria-stabilised zirconia suspension. The objective of this work was to investigate if the bilayer topcoat architecture could enhance the thermal cyclic lifetime of SPS TBCs through experiments and to understand the effect of the column gaps/vertical cracks and the dense layer on the generated stresses in the TBC during thermal cyclic loading through finite element modeling. The experimental results show that the bilayer TBC had significantly higher lifetime than the single-layer TBC. The modeling results show that the dense layer and vertical cracks are beneficial as they reduce the thermally induced stresses which thus increase the lifetime.
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| 15. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
-
Design of high lifetime suspension plasma sprayed thermal barrier coatings
- 2020
-
Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 40:3, s. 768-779
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Tidskriftsartikel (refereegranskat)abstract
- Thermal barrier coatings (TBCs) fabricated by suspension plasma spraying (SPS) have shown improved performance due to their low thermal conductivity and high durability along with relatively low production cost. Improvements in SPS TBCs that could further enhance their lifetime would lead to their widespread industrialisation. The objective of this study was to design a SPS TBC system with optimised topcoat microstructure and topcoat bondcoat interface, combined with appropriate bondcoat microstructure and chemistry, which could exhibit high cyclic lifetime. Bondcoat deposition processes investigated in this study were high velocity air fuel (HVAF) spraying, high velocity oxy fuel spraying, vacuum plasma spraying, and diffusion process. Topcoat microstructure with high column density along with smooth topcoat bondcoat interface and oxidation resistant bondcoat was shown as a favourable design for significant improvements in the lifetime of SPS TBCs. HVAF sprayed bondcoat treated by shot peening and grit blasting was shown to create this favourable design.
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| 16. |
- Gupta, Mohit Kumar, et al.
(författare)
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Design of Low Thermal Conductivity Thermal Barrier Coatings by Finite Element Modelling
- 2011
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Ingår i: Surface Modification Technologies XXIV. ; , s. 353-365
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Konferensbidrag (refereegranskat)abstract
- Fundamental understanding of relationships between coating microstructure and thermal conductivity is important to be able to understand the influence of coating defects, such as delaminations and pores, on heat insulation in thermal barrier coatings (TBC). Object Oriented Finite element analysis (OOF) has recently been shown as an effective tool for evaluating thermo-mechanical material behaviour as this method is capable of incorporating the inherent material microstructure as an input to the model. The objective of this work was to evaluate a procedure where this technique is combined with Tbctool, a plasma-sprayed TBC like morphology generator, thus enabling development of low thermal conductivity coatings by simulation. Input parameters for Tbctool were computed from SEM images of sprayed microstructures using the image analysis software, Aphelion. Microstructures for as-sprayed as well as heat treated samples were evaluated. The thermal conductivities of the artificially generated microstructures were determined using OOF. Verification of the modelling procedure was performed by comparing predicted values by OOF with corresponding measured values using the laser flash technique. The results, although tentative in nature, indicate that the proposed simulation approach can be a powerful tool in the development of new low conductivity coatings.
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| 17. |
- Gupta, Mohit Kumar, 1986-
(författare)
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Design of Microstructures in Thermal Barrier Coatings : A Modelling Approach
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Plasma sprayed Thermal Barrier Coating systems (TBCs) are commonly used for thermal protection of components in modern gas turbine application such as power generation, marine and aero engines. The material that is most commonly used in these applications is Yttria Stabilized Zirconia (YSZ) because of this ceramic’s favourable properties, such as low thermal conductivity, phase stability to high temperature, and good erosion resistance. The coating microstructures in YSZ coatings are highly heterogeneous, consisting of defects such as pores and cracks of different sizes which determine the coating’s final thermal and mechanical properties, and the service lives of the coatings. Determination of quantitative microstructure–property correlations is of great interest as experimental procedures are time consuming and expensive.This objective of this thesis work was to investigate the relationships between coating microstructure and thermal-mechanical properties of TBCs, and to utilise these relationships to design an optimised microstructure to be used for next generation TBCs. Simulation technique was used to achieve this goal. Important microstructural parameters influencing the performance of TBCs were identified and coatings with the identified microstructural parameters were designed, modelled and experimentally verified. TBCs comprising of large globular pores with connected cracks inherited within the coating microstructure were shown to have significantly enhanced performance. Low thermal conductivity, low Young‘s modulus and high lifetime were exhibited by these coatings. The modelling approach described in this work can be used as a powerful tool to design new coatings as well as to achieve optimised microstructures.
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| 18. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
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Design of Next Generation Thermal Barrier Coatings- Experiments and Modelling
- 2013
-
Ingår i: Surface and Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 220, s. 20-26
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Tidskriftsartikel (refereegranskat)abstract
- Thermal barrier coating (TBC) systems have been used in the gas turbine industry since the 1980's. The future needs of both the air and land based turbine industry involve higher operating temperatures with longer lifetime on the component so as to increase power and efficiency of gas turbines. The aim of this study was to meet these future needs by further development of zirconia coatings. The intention was to design a coating system which could be implemented in industry within the next three years. Different morphologies of ceramic topcoat were evaluated; using dual layer systems and polymers to generate porosity. Dysprosia stabilised zirconia was also included in this study as a topcoat material along with the state-of-the-art yttria stabilised zirconia (YSZ). High purity powders were selected in this work. Microstructure was assessed with scanning electron microscope and an in-house developed image analysis routine was used to characterise porosity content. Evaluations were carried out using the laser flash technique to measure thermal conductivity. Lifetime was assessed using thermo-cyclic fatigue testing. Finite element analysis was utilised to evaluate thermal-mechanical material behaviour and to design the morphology of the coating with the help of an artificial coating morphology generator through establishment of relationships between microstructure, thermal conductivity and stiffness. It was shown that the combined empirical and numerical approach is an effective tool for developing high performance coatings. The results show that large globular pores and connected cracks inherited within the coating microstructure result in a coating with best performance. A low thermal conductivity coating with twice the lifetime compared to the industrial standard today was fabricated in this work.
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| 19. |
- Gupta, Mohit Kumar, 1986-
(författare)
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Design of Thermal Barrier Coatings : A modelling approach
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Atmospheric plasma sprayed (APS) thermal barrier coatings (TBCs) are commonly used for thermal protection of components in modern gas turbine application such as power generation, marine and aero engines. TBC is a duplex material system consisting of an insulating ceramic topcoat layer and an intermetallic bondcoat layer. TBC microstructures are highly heterogeneous, consisting of defects such as pores and cracks of different sizes which determine the coating's final thermal and mechanical properties, and the service lives of the coatings. Failure in APS TBCs is mainly associated with the thermo-mechanical stresses developing due to the thermally grown oxide (TGO) layer growth at the topcoat-bondcoat interface and thermal expansion mismatch during thermal cycling. The interface roughness has been shown to play a major role in the development of these induced stresses and lifetime of TBCs.The objective of this thesis work was two-fold for one purpose: to design an optimised TBC to be used for next generation gas turbines. The first objective was to investigate the relationships between coating microstructure and thermal-mechanical properties of topcoats, and to utilise these relationships to design an optimised morphology of the topcoat microstructure. The second objective was to investigate the relationships between topcoat-bondcoat interface roughness, TGO growth and lifetime of TBCs, and to utilise these relationships to design an optimal interface. Simulation technique was used to achieve these objectives. Important microstructural parameters influencing the performance of topcoats were identified and coatings with the feasible identified microstructural parameters were designed, modelled and experimentally verified. It was shown that large globular pores with connected cracks inherited within the topcoat microstructure significantly enhanced TBC performance. Real topcoat-bondcoat interface topographies were used to calculate the induced stresses and a diffusion based TGO growth model was developed to assess the lifetime. The modelling results were compared with existing theories published in previous works and experiments. It was shown that the modelling approach developed in this work could be used as a powerful tool to design new coatings and interfaces as well as to achieve high performance optimised morphologies.
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| 20. |
- Gupta, Mohit Kumar
(författare)
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Design of Thermal Barrier Coatings : A Modelling Approach
- 2015
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- This book details the relationships between microstructure, interface roughness, and properties of thermal barrier coatings. The author proposes a method for the reduction of the thermal conductivity of the ceramic layer in order to increase the lifetime of thermal barrier coatings. He includes models for the optimization of ceramic layer microstructure and interface roughness.
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| 21. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
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Development of bondcoat layer for long lifetime suspension plasma sprayed thermal barrier coatings
- 2017
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Ingår i: Proceedings of the International Thermal Spray Conference & Exposition (ITSC 2017). - New York : Curran Associates, Inc. - 9781510858220 ; , s. 1158-1163
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Konferensbidrag (refereegranskat)abstract
- Development of thermal barrier coatings (TBCs) manufactured by suspension plasma spraying (SPS) is of high commercial interest as SPS has been shown capable to produce columnar microstructures similar to the conventionally used electron beam – physical vapour deposition (EB-PVD) process. Moreover, SPS is a significantly cheaper process and can also produce more porous coatings than EB-PVD. However, lifetime of SPS coatings needs to be improved further for them to be applicable in commercial applications.The bondcoat microstructure as well as topcoat-bondcoat interface topography affect the TBC lifetime significantly. The objective of this work was to investigate the feasibility of different bondcoat deposition process for SPS TBCs. In this work, a NiCoCrAlY bondcoat deposited by high velocity air fuel (HVAF) was compared to commercial NiCoCrAlY and PtAl bondcoats. All bondcoat variations were prepared with and without grit blasting the bondcoat surface. SPS was used to deposit the topcoats on all samples using the same spray parameters. Lifetime of these samples was examined by thermal cyclic fatigue and thermal shock testing. The effect of bondcoat deposition process and interface topography on lifetime in each case has been discussed. The results show that HVAF could be a suitable process for bondcoat deposition in SPS TBCs.
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| 22. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
-
Development of bondcoats for high lifetime suspension plasma sprayed thermal barrier coatings
- 2019
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 371:SI, s. 366-377
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Tidskriftsartikel (refereegranskat)abstract
- Fabrication of thermal barrier coatings (TBCs) by suspension plasma spraying (SPS) seems to be a promising alternative for the industry as SPS TBCs have the potential to provide lower thermal conductivity and longer lifetime than state-of-the-art allowing higher engine efficiency. Further improvements in lifetime of SPS TBCs and fundamental understanding of failure mechanisms in SPS TBCs are necessary for their widespread commercialisation. In this study, the influence of varying topcoat-bondcoat interface topography and bondcoat microstructure on lifetime was investigated. The objective of this work was to gain fundamental understanding of relationships between topcoat-bondcoat interface topography, bondcoat microstructure, and failure mechanisms in SPS TBCs. Seven sets of samples were produced in this study by keeping same bondcoat chemistry but varying feedstock particle size distributions and bondcoat spray processes. The topcoat chemistry and spray parameters were kept identical in all samples. Three-dimensional surface measurements along with scanning electron microscopy images were used to characterise bondcoat surface topography. The effect of varying interface topography and bondcoat microstructure on thermally grown oxide formation, stresses and lifetime was discussed. The results showed that varying bondcoat powder size distribution and spray process can have a significant effect on lifetime of SPS TBCs. Smoother bondcoats seemed to enhance the lifetime in case of SPS TBCs in case of same bondcoat chemistry and similar bondcoat microstructures. When considering the samples investigated in this study, samples with high velocity air-fuel (HVAF) bondcoats resulted in higher lifetime than other samples indicating that HVAF could be a suitable process for bondcoat deposition in SPS TBCs. © 2018 Elsevier B.V.
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| 23. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
-
Development of plasma sprayed Ni/YSZ anodes for metal supported solidoxide fuel cells
- 2017
-
Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 318, s. 178-189
-
Tidskriftsartikel (refereegranskat)abstract
- Solid oxide fuel cells (SOFCs) offer a promising technique for producing electricity by clean energy conversionthrough an electrochemical reaction of fuel and air. Plasma spraying could be a potential manufacturing routefor commercial SOFCs, as it provides a distinct advantage especially in case of metal supported cells (MSCs) byallowing rapid processing at relatively low processing temperatures preventing thus the degradation of themetallicsubstrate. The objective of this work was to develop nickel/yttria stabilised zirconia (Ni/YSZ) anodes withhigh porosity and homogeneous phase distribution by atmospheric plasma spraying forMSCs. Various feedstockmaterial approaches were explored in this study, both with single injection aswell as separate injection of differentfeedstock materials , and with and without the use of pore formers to create additional porosity. The advantagesand issues with each material route were investigated and discussed. It was shown that agglomerated Ni/YSZ/polyester feedstock material resulted in the best distribution of Ni and YSZ in the anodemicrostructurewithhomogeneous porosity. Subsequently, the Ni/YSZ/polyester material route with different amounts and size distributionsof polyester was chosen to develop anode symmetrical cells using a commercial zirconia sheet as supportfor electrochemical testing. The Ni/YSZ/polyester anode powder with 10 wt.% standard size polyesterexhibited the best electrochemical performance. The results show that plasma spraying of the agglomeratedNi/YSZ/polyester could be a promising route to achieve high performance and rapid production anodes withoutusing the carcinogenic nickel oxide.
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| 24. |
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| 25. |
- Gupta, Mohit Kumar, et al.
(författare)
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Electrochemical performance of plasma sprayed metal supported planar solid oxide fuel cells
- 2015
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; 68:1, s. 1791-1802
-
Tidskriftsartikel (refereegranskat)abstract
- High production cost is one of the major barriers to widespread commercialization of solid oxide fuel cells (SOFCs). Thermal spray techniques are a low cost alternative for the production of SOFCs. The objective of this work was to evaluate the electrochemical performance of half-cells produced by plasma spraying. The anode was deposited on a porous metallic support by atmospheric plasma spraying (APS) whereas the electrolyte was deposited by plasma spray-thin film (PS-TF) technique which can produce thin and dense coatings at high deposition rates. The cathode was deposited by screen-printing. The electrochemical tests were performed at 650-800°C. Current-voltage characteristics and impedance spectra were measured and analyzed. The impact of electrolyte composition and layer thickness on the gas tightness of the electrolyte and the area specific resistance of the cell is discussed. The results show that the applied thermal spraying techniques are a potential alternative for producing SOFCs. © The Electrochemical Society.
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| 26. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
-
Electrochemical Performance of Plasma Sprayed Metal Supported Planar Solid Oxide Fuel Cells
- 2016
-
Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 163:9, s. F1059-F1065
-
Tidskriftsartikel (refereegranskat)abstract
- High production cost is one of the major barriers to widespread commercialization of solid oxide fuel cells (SOFCs). Thermal spraytechniques are a low cost alternative for the production of SOFCs. The objective of this work was to evaluate the electrochemicalperformance of cells produced by plasma spraying. The anode was deposited on a porous metallic support by atmospheric plasmaspraying (APS) whereas the electrolyte was deposited by plasma spray-thin film (PS-TF) technique, which can produce thin anddense coatings at high deposition rates. The cathode was deposited by screen-printing and in-operando sintering. The electrochemicaltests were performed at 650–800◦C. Current-voltage characteristics and impedance spectra were measured and analyzed. The impactof electrolyte composition and layer thickness on the gas tightness of the electrolyte and the area specific resistance of the cell isdiscussed. The results show that the applied thermal spraying techniques are a potential alternative for producing SOFCs.
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| 27. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
-
Failure Analysis of Multilayered Suspension Plasma-Sprayed Thermal Barrier Coatings for Gas Turbine Applications
- 2018
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 27:3, s. 402-411-
-
Tidskriftsartikel (refereegranskat)abstract
- Improvement in the performance of thermal barrier coatings (TBCs) is one of the key objectives for further development of gas turbine applications. The material most commonly used as TBC topcoat is yttria-stabilized zirconia (YSZ). However, the usage of YSZ is limited by the operating temperature range which in turn restricts the engine efficiency. Materials such as pyrochlores, perovskites, rare earth garnets are suitable candidates which could replace YSZ as they exhibit lower thermal conductivity and higher phase stability at elevated temperatures. The objective of this work was to investigate different multilayered TBCs consisting of advanced topcoat materials fabricated by suspension plasma spraying (SPS). The investigated topcoat materials were YSZ, dysprosia-stabilized zirconia, gadolinium zirconate, and ceria–yttria-stabilized zirconia. All topcoats were deposited by TriplexPro-210TM plasma spray gun and radial injection of suspension. Lifetime of these samples was examined by thermal cyclic fatigue and thermal shock testing. Microstructure analysis of as-sprayed and failed specimens was performed with scanning electron microscope. The failure mechanisms in each case have been discussed in this article. The results show that SPS could be a promising route to produce multilayered TBCs for high-temperature applications.
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| 28. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
-
Improving the lifetime of suspension plasma sprayed thermal barrier coatings
- 2017
-
Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 332, s. 550-559
-
Tidskriftsartikel (refereegranskat)abstract
- Development of thermal barrier coating systems (TBCs) for gas turbine applications allowing higher combustion temperatures is of high interest since it results in higher fuel efficiency and lower emissions. TBCs produced by suspension plasma spraying (SPS) have been shown to exhibit significantly lower thermal conductivity as compared to conventional systems due to their very fine porosity microstructure. However they have not been commercialised yet due to low reliability and life expectancy of the coatings. In addition to the initial topcoat microstructure and its sintering resistance, lifetime of a TBC system is highly dependent on bondcoat chemistry as it influences the growth rate of thermally grown oxide (TGO) layer. To enhance the lifetime of SPS TBCs, fundamental understanding of relationships between topcoat microstructure and its evolution with time, bondcoat chemistry, TGO growth rate, and lifetime is essential. The objective of this work was to study the effect of topcoat microstructure evolution and TGO growth rate on lifetime in SPS TBC systems. Experimental MCrAlY bondcoat powders with different aluminium activities were investigated and compared to a commercial bondcoat powder. High velocity air fuel spraying was used for bondcoat deposition while axial-SPS was used for yttria stabilized zirconia topcoat deposition. Lifetime was examined by thermal cyclic fatigue testing. Isothermal heat treatment was performed to study TGO evolution with time. The changes in microstructure of SPS coatings due to sintering under long term exposure at high temperatures were investigated. Different failure modes in SPS TBCs were also examined. The bondcoat with higher aluminium activity resulted in a significantly higher thermal cyclic lifetime of the corresponding TBC as it could have promoted protective alumina layer growth for a longer period of time. The results indicate that the significant changes in topcoat microstructure due to sintering as observed in this work could have a detrimental effect on TBC lifetime. © 2017 Elsevier B.V.
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| 29. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
-
Influence of Bondcoat Spray Process on Lifetime of Suspension Plasma-Sprayed Thermal Barrier Coatings
- 2018
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 27:1-2, s. 84-97
-
Tidskriftsartikel (refereegranskat)abstract
- Development of thermal barrier coatings (TBCs) manufactured by suspension plasma spraying (SPS) is of high commercial interest as SPS has been shown capable of producing highly porous columnar microstructures similar to the conventionally used electron beam–physical vapor deposition. However, lifetime of SPS coatings needs to be improved further to be used in commercial applications. The bondcoat microstructure as well as topcoat–bondcoat interface topography affects the TBC lifetime significantly. The objective of this work was to investigate the influence of different bondcoat deposition processes for SPS topcoats. In this work, a NiCoCrAlY bondcoat deposited by high velocity air fuel (HVAF) was compared to commercial vacuum plasma-sprayed NiCoCrAlY and PtAl diffusion bondcoats. All bondcoat variations were prepared with and without grit blasting the bondcoat surface. SPS was used to deposit the topcoats on all samples using the same spray parameters. Lifetime of these samples was examined by thermal cyclic fatigue testing. Isothermal heat treatment was performed to study bondcoat oxidation over time. The effect of bondcoat deposition process and interface topography on lifetime in each case has been discussed. The results show that HVAF could be a suitable process for bondcoat deposition in SPS TBCs.
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| 30. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
-
Influence of bondcoat surface characteristics on lifetime in suspension plasma sprayed thermal barrier coatings
- 2017
-
Ingår i: Proceedings of the International Thermal Spray Conference & Exposition (ITSC 2017). - New York : Curran Associates, Inc. - 9781510858220 ; , s. 883-887
-
Konferensbidrag (refereegranskat)abstract
- Development of TBCs allowing higher combustion temperatures in gas turbines is of high commercial interest since it results in higher fuel efficiency and lower emissions. It is well known that TBCs produced by suspension plasma spraying (SPS) have lower thermal conductivity as compared to conventional systems due to their very fine porous microstructure. Moreover, columnar structured SPS TBCs are significantly cheaper to produce as compared to the conventionally used electron beam - physical vapour deposition (EB-PVD). However, SPS TBCs have not yet been commercialised due to low reliability and life expectancy of the coatings. Lifetime of a TBC system is significantly dependent on topcoat-bondcoat interface topography. The objective of this work was to study the effect of topcoat-bondcoat interface in SPS TBCs by changing bondcoat spray parameters and bondcoat surface heat treatment High velocity air fuel (HVAF) spraying was used for bondcoat deposition while axial-SPS was used for topcoat deposition. Same topcoat spray parameters were used for all samples. Lifetime was examined by thermal cyclic fatigue and thermal shock testing. The influence of surface roughness on lifetime has been discussed. The results show that HVAF could be a suitable process for bondcoat deposition to achieve long lifetime SPS TBCs.
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| 31. |
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| 32. |
|
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| 33. |
- Gupta, Mohit Kumar, et al.
(författare)
-
Influence of topcoat-bondcoat interface roughness on stresses and lifetime in Thermal Barrier Coatings
- 2013
-
Ingår i: Proceedings of the International Thermal Spray Conference. - : ASM International. - 9781632666819 ; , s. 596-601
-
Konferensbidrag (refereegranskat)abstract
- Failure in Atmospheric Plasma Sprayed (APS) Thermal Barrier Coatings (TBCs) is associated with the thermomechanical stresses developing due to the Thermally Grown Oxide (TGO) layer growth and thermal expansion mismatch during thermal cycling. The interface roughness has been shown to play a major role in the development of these induced stresses and lifetime of TBCs. Modeling has been shown as an effective tool to understand the effect of interface roughness on induced stresses. In previous work done by the research group, it was observed that APS bondcoats performed better than the bondcoats sprayed with High Velocity OxyFuel (HVOF) process which is contrary to the present literature data. The objective of this work was to understand this observed difference in life-time with the help of finite element modeling by using real surface topographies. Different TGO layer thicknesses were evaluated. The modeling results were also compared with existing theories established on simplified sinusoidal profiles published in earlier works. It was shown that modeling can be used as an effective tool to understand the stress behavior in TBCs with different roughness profiles.
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| 34. |
- Gupta, Mohit Kumar, et al.
(författare)
-
Influence of Topcoat-Bondcoat Interface Roughness on Stresses and Lifetime inThermal Barrier Coatings
- 2014
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 23:1-2, s. 170-181
-
Tidskriftsartikel (refereegranskat)abstract
- Failure in Atmospheric Plasma Sprayed (APS) Thermal Barrier Coatings (TBCs) is associated with the thermo-mechanical stresses developing due to the Thermally Grown Oxide (TGO) layer growth and thermal expansion mismatch during thermal cycling. The interface roughness has been shown to play a major role in the development of these induced stresses and lifetime of TBCs. Modeling has been shown as an effective tool to understand the effect of interface roughness on induced stresses. In previous work done by our research group, it was observed that APS bondcoats performed better than the bondcoats sprayed with High Velocity Oxy-Fuel (HVOF) process which is contrary to the present literature data. The objective of this work was to understand this observed difference in lifetime with the help of finite element modeling by using real surface topographies. Different TGO layer thicknesses were evaluated. The modeling results were also compared with existing theories established on simplified sinusoidal profiles published in earlier works. It was shown that modeling can be used as an effective tool to understand the stress behavior in TBCs with different roughness profiles.
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| 35. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
-
Microstructure and failure analysis of suspension plasma sprayed thermal barrier coatings
- 2020
-
Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 382
-
Tidskriftsartikel (refereegranskat)abstract
- Improvements in performance of thermal barrier coatings (TBCs) used in gas turbine engines are highly desired as they can result in higher engine efficiency leading to reduction of harmful emissions. Suspension plasma spraying (SPS) has been shown to produce high performance porous columnar TBCs that can provide low thermal conductivity and high durability. Apart from the topcoat microstructure and chemistry, the lifetime of TBCs is also dependent on bondcoat microstructure and chemistry, and topcoat-bondcoat interface roughness. In case of SPS TBCs, the interface roughness can significantly affect the columnar topcoat microstructure, thus making the bondcoat selection even more crucial. In this work, six different sets of samples were produced by fabricating bondcoats with conventional atmospheric plasma spraying (APS), high velocity air fuel (HVAF) spraying, or hybrid water/argon stabilised plasma (WSP-H) gun, and SPS topcoats using axial SPS (ASPS) or WSP-H spray guns. The objective of this study was to investigate the influence of varying the topcoat microstructure, bondcoat microstructure and topcoat-bondcoat interface roughness on oxide growth behaviour and thermal cyclic fatigue (TCF) lifetime of SPS TBCs. Samples after failure were investigated to understand the failure mechanism in each case. The results showed that changing the bondcoat spray process and spray gun resulted in significant variation in bondcoat surface roughness. A porous columnar structure was created by the ASPS process, while a feathery columnar structure was created by the WSP-H spray gun in this study. Samples with WSP-H bondcoat resulted in highest cyclic lifetime in this study, despite showing severe oxidation of the bondcoat as compared to APS and HVAF bondcoats. This result could be attributed to the very high bondcoat surface roughness in these samples that could have resulted in improved mechanical anchoring of the topcoat. The HVAF bondcoats showed the best oxidation resistance in this study. © 2019 Elsevier B.V.
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| 36. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
-
Multilayered suspension plasma sprayed thermal barrier coatings for high temperature gas turbine applications
- 2017
-
Ingår i: Proceedings of the International Thermal Spray Conference & Exposition (ITSC 2017). - New York : Curran Associates, Inc. - 9781510858220 ; , s. 382-387
-
Konferensbidrag (refereegranskat)abstract
- Improvement in the performance of thermal barrier coating systems (TBCs) is one of the key objectives for further development of gas turbine applications. The material most commonly used as TBC topcoat is yttria stabilised zirconia (YSZ). However, the usage of YSZ is limited by the operating temperature range which in turn restricts the engine efficiency. Materials such as pyrochlores, perovskites, rare earth garnets, etc. are suitable candidates which could replace YSZ as they exhibit lower thermal conductivity and higher phase stability at elevated temperatures.The objective of this work was to investigate different multi-layered TBCs consisting of advanced topcoat materials fabricated by Suspension Plasma Spraying (SPS). The investigated topcoat materials were YSZ, dysprosia stabilised zirconia, gadolinium zirconiate, cerium doped YSZ and yttria fully stabilised zirconia. All topcoats were deposited with TriplexPro-210 plasma spray gun and radial injection of suspension. Lifetime of these samples was examined by thermal cyclic fatigue and thermal shock testing. Microstructure analysis of as-sprayed and failed specimens was performed with scanning electron microscope. The failure mechanisms in each case have been discussed in this article. The results show that SPS could be a promising route to produce multilayered TBCs for high temperature applications.
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| 37. |
|
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| 38. |
- Gupta, Mohit Kumar, et al.
(författare)
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Structure-property Relationships in Thermal Barrier Coatings by Finite Element Modelling
- 2012
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Ingår i: Surface Modification Technologies XXV : proceedings of the Twenty Fifth International Conference on Surface Modification Technologies. - [Chennai] : Valardocs. - 9788191057140 ; , s. 175-184
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Konferensbidrag (refereegranskat)abstract
- The thermal and mechanical properties of Thermal Barrier Coating systems (TBCs) are strongly influenced by coating defects, such as delaminations and pores, thus making it essential to have a fundamental understanding of microstructure-property relationships in TBCs, to produce a desired coating. Object-Oriented Finite element analysis (OOF) has been shown previously as an effective tool for evaluating thermal and mechanical material behaviour, as this method is capable of incorporating the inherent material microstructure as an input to the model. In this work, OOF was used to predict the thermal conductivity and effective Young’s modulus of TBC topcoats. A Design of Experiments (DoE) was conducted by varying selected spray parameters for spraying Yttria Partially Stabilized Zirconia (YPSZ) topcoat. Characterisation of the coatings included microstructure, porosity and crack content and thermal conductivity measurements. The relationships between microstructural features, thermal conductivity and Young’s modulus are discussed.
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| 39. |
- Jonnalagadda, Krishna Praveen, 1988-, et al.
(författare)
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Hot gas corrosion and its influence on the thermal cycling performance of suspension plasma spray TBCs
- 2019
-
Ingår i: Proceedings of ASME Turbo Expo 2019. - New York, NY : American Society of Mechanical Engineers. - 9780791858677
-
Konferensbidrag (refereegranskat)abstract
- Thermal barrier coatings (TBCs) manufactured with suspension plasma spray (SPS) are promising candidates for use in gas turbines due to their high strain tolerance during thermal cyclic fatigue (TCF). However, corrosion often occurs alongside thermal fatigue and coating durability under these conditions is highly desirable. The current study focuses on understanding the corrosion behavior and its influence on the thermal cyclic fatigue life of SPS TBCs. Corrosion tests were conducted at 780 OC using a mixed-gas (1SO2-0.1CO-20CO2-N2(bal.) in vol. %) for 168h. They were later thermally cycled between 100-1100 ⁰C with a 1h hold time at 1100 ⁰C. Corrosion test results indicated that the damage predominantly started from the edges and a milder damage was observed at the center. Nickel sulfide was observed on top of the top coat and also in the columnar gaps of the top coat. Chromium oxides were observed inside the top coat columnar gaps but close to the bond coat/top coat interface. They were believed to reduce the strain tolerance of SPS TBCs to an extent and also amplify the thermal mismatch stresses during TCF tests. This, together with a fast growth of alumina during the TCF, resulted in a significant drop in the TCF life compared to the standard TCF tests.
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| 40. |
- Kuhn, Joel, et al.
(författare)
-
The Effect of Fuel Electrode Roughness on the Properties of Plasma Sprayed Solid Oxide Cells
- 2018
-
Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 165:9, s. F693-F701
-
Tidskriftsartikel (refereegranskat)abstract
- Solid oxide cell electrolytes fabricated by atmospheric plasma spraying are frequently found to have considerable gas leak rates.Electrode surface roughness is known to have an influence on electrolyte leak rates. A jet of high velocity air, produced with an airknife, was aimed at the plasma plume during fuel electrode deposition to reduce the surface roughness prior to electrolyte deposition.The resulting fuel electrode masses, electrode compositions, and electrode surface roughnesses were measured for varying air knifeinlet pressures. Surface asperity populations and maximum heights were significantly reduced using air knife pressures of >6 barat the expense of deposition efficiency. The nickel volume fraction in the fuel electrode increased slightly with increasing air knifepressure. Open circuit voltages were larger on the smoother fuel electrodes that were produced at higher air knife pressures, but nosignificant effect of air knife pressure on cell power density could be discerned.© 2018 The Electrochemical Society
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| 41. |
- Kuhn, Joel, et al.
(författare)
-
The effect of fuel electrode roughness on the properties of plasma sprayed solid oxide cells
- 2017
-
Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; 78:1, s. 1477-1487
-
Tidskriftsartikel (refereegranskat)abstract
- Solid oxide cell electrolytes fabricated by atmospheric plasma spraying are frequently found to have nonzero gas leak rates. Electrode surface roughness is known to have an influence on electrolyte leak rates. A jet of high velocity air, produced with an air knife, was aimed at the plasma plume during fuel electrode deposition to reduce the surface roughness prior to electrolyte deposition. The resulting fuel electrode masses, electrode compositions, and electrode surface roughnesses were measured for varying air knife inlet pressures. Surface asperity populations and maximum heights were significantly reduced using air knife pressures of > 6 bar at the expense of deposition efficiency. The distribution of surface gradients was also improved with the use of the air knife, but some regions with steep gradients still remained in surfaces prepared with an air knife pressure of 8 bar. © The Electrochemical Society.
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| 42. |
- Kumara, Chamara, et al.
(författare)
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Effect of columnar cracks and dense layer in suspension plasma sprayed thermal barrier coatings on the coating stresses under thermal shock loadings : A modelling approach
- 2016
-
Ingår i: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings. - Lund : Swedish Production Academy. ; , s. 1-8
-
Konferensbidrag (refereegranskat)abstract
- Suspension Plasma Spraying (SPS) has been shown as a promising process to produce porous columnar strain tolerant coatings for thermal barrier coating applications in gas turbine engines. However, the highly porous structure is vulnerable to crack propagation, especially near the top coat-bond coat interface, where high stresses are generated due to thermal shock conditions that occur during engine operation. These stresses directly influence the coating lifetime. A topcoat layer with high toughness near the top coat-bond coat interface could thus be beneficial to withstand the stresses. In this work, a bilayer coating system was fabricated by SPS using yttria stabilised zirconia. The bilayer coating consisted of a dense topcoat layer near the top coat-bond coat interface which could provide the necessary toughness followed by a porous columnar structured layer which contains columnar cracks which could provide the necessary strain tolerance. The objective of this work is to study the effect of the columnar/vertical crack features on the generated stresses in the thermal barrier coating during thermal cyclic loading. A finite element modelling approach has been used for this purpose. The results show that the bilayer coating structure reduces the thermally induced stresses and could thus increase the lifetime.
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| 43. |
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| 44. |
- Markocsan, Nicolaie, 1967-, et al.
(författare)
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Liquid Feedstock Plasma Spraying : An Emerging Process for Advanced Thermal Barrier Coatings
- 2017
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 26:6, s. 1104-1114
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Tidskriftsartikel (refereegranskat)abstract
- Liquid feedstock plasma spraying (LFPS) involves deposition of ultrafine droplets of suspensions or solution precursors (typically ranging from nano- to submicron size) and permits production of coatings with unique microstructures that are promising for advanced thermal barrier coating (TBC) applications. This paper reviews the recent progress arising from efforts devoted to development of high-performance TBCs using the LFPS approach. Advancements in both suspension plasma spraying and solution precursor plasma spraying, which constitute the two main variants of LFPS, are presented. Results illustrating the different types of the microstructures that can be realized in LFPS through appropriate process parameter control, model-assisted assessment of influence of coating defects on thermo-mechanical properties and the complex interplay between pore coarsening, sintering and crystallite growth in governing thermal conductivity are summarized. The enhancement in functional performances/lifetime possible in LFPS TBCs with multilayered architectures and by incorporating new pyrochlore chemistries such as gadolinium zirconate, besides the conventional single 8 wt.% yttria-stabilized zirconia insulating ceramic layer, is specifically highlighted.
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| 45. |
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| 46. |
- Musalek, Radek, et al.
(författare)
-
Microstructures and properties of thermal barrier coatings deposited by hybrid water-stabilized plasma torch
- 2019
-
Ingår i: Proceedings of the International Thermal Spray Conference. - : ASM International. - 9781510888005 ; , s. 738-745
-
Konferensbidrag (refereegranskat)abstract
- Hybrid Water-Stabilized Plasma (WSP-H) torch provides high-enthalpy plasma which may be utilized for high-throughput and yet economical spraying of coatings from powders, suspensions, and solutions. It was previously demonstrated that microstructures and functional properties of the WSP-H coatings may be tailored to a wide extent for various new applications, namely those requiring high coating thickness and/or coating of large components. In this study, applicability of WSP-H technology for spraying of novel thermal barrier coatings (TBCs) is demonstrated. WSP-H technology was used for spraying of yttria-stabilized zirconia (YSZ) top-coats from powder, suspension and solution. Yttria content in the top-coat feedstock was 7-8 wt.%. NiCrAlY bond-coat was also sprayed by WSP-H and Hastelloy-X alloy was used as substrate material. Microstructure, phase composition, and endurance of the deposited coatings in thermal cycling fatigue (TCF) test were evaluated. Each thermal cycle consisted of rapid heating to 1100 °C, followed by one hour dwell and rapid cooling. All coatings showed excellent stability and TCF resistance withstanding more than 700 cycles surpassing in TCF test some of the currently commercially used TBCs. Lifetime of TBC with columnar top-coat deposited from suspension exceeded even more than 900 cycles. © 2019 ASM International. All rights reserved.
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| 47. |
- Musalek, Radek, et al.
(författare)
-
Microstructures and Thermal Cycling Properties of Thermal Barrier Coatings Deposited by Hybrid Water-Stabilized Plasma Torch
- 2020
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 29:3, s. 444-461
-
Tidskriftsartikel (refereegranskat)abstract
- Hybrid water-stabilized plasma (WSP-H) torches provide high-enthalpy plasma which may be utilized for high-throughput and yet economical spraying of coatings from powders, suspensions, and solutions. It was previously demonstrated that microstructures and functional properties of the WSP-H coatings may be tailored to a wide extent for new applications, namely those requiring high coating thickness and/or coating of large components. In this study, applicability potential of WSP-H technology for spraying of novel thermal barrier coatings (TBCs) is demonstrated. WSP-H technology was used for spraying of yttria-stabilized zirconia (YSZ) top-coats from powder, suspension, and solution. Yttria content in the top-coat feedstock was 7-8 wt.%. In addition, gadolinium zirconate (Gd2Zr2O7-GZO) was sprayed from suspension for comparison. NiCrAlY bond-coat was also deposited by WSP-H, and Hastelloy-X alloy was used as substrate material. Microstructure, phase composition, and endurance of the deposited coatings in thermal cycling fatigue (TCF) test and during high-temperature short-term annealing were evaluated. All coatings showed excellent high-temperature stability and TCF resistance withstanding more than 650 cycles, surpassing some of the currently commercially used TBCs. Lifetime of the TBC with columnar top-coat deposited from YSZ suspension exceeded even more than 900 cycles.
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| 48. |
- Ossiansson, Mattias, et al.
(författare)
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Assessment of CrFeCoNi and AlCrFeCoNi High-Entropy Alloys as Bond Coats for Thermal Barrier Coatings
- 2022
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Nature. - 1059-9630 .- 1544-1016. ; 31, s. 1404-1422
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Tidskriftsartikel (refereegranskat)abstract
- High-entropy alloys (HEAs) represent a relatively new group of multicomponent alloys that have shown great potential for applications requiring tribological and oxidation resistant properties. Consequently, thermally sprayed coatings of different HEA chemistries have received increasing research attention. In this paper, atomized equimolar CrFeCoNi and AlCrFeCoNi feedstocks were used for high velocity air-fuel spraying (HVAF) to produce overlay coatings using two different nozzle configurations. The microstructure, phase constitution and hardness of the coatings were analyzed along with the primary aim of testing the coatings for their oxidation behavior. The performance of the two HEA chemistries was compared with two commercial MCrAlY coatings that are well-established bond coat materials for thermal barrier coatings (TBCs). An investigation was conducted to test the coatings’ performance as bond coats by applying suspension plasma sprayed yttria-stabilized zirconia top coats and evaluating the thermal cycling behavior of the TBCs. The AlCrFeCoNi-coating was found to demonstrate a lower oxidation rate than the CrFeCoNi-coating. However, the AlCrFeCoNi-coating was found to form more rapid oxide scales compared with the commercial bond coat material that also contained reactive elements. © 2022, The Author(s).
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| 49. |
- Tano, Ingrid, 1968-, et al.
(författare)
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Relationships between Coating Microstructure and Thermal Conductivity in Thermal Barrier Coatings – A modelling Approach
- 2010
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Ingår i: International Thermal Spray Conference and Exposition, ITCS Singapore 2010. - Düsseldorft : DVS Media. - 9783871555909 ; , s. 66-72
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Konferensbidrag (refereegranskat)abstract
- Fundamental understanding of relationships between coating microstructure and thermal conductivity is important to be able to understand the influence of coating defects, such as delaminations and pores, on heat insulation in thermal barrier coatings. Object-Oriented Finite element analysis (OOF) has recently been shown as an effective tool for evaluating thermo-mechanical material behaviour, because of this method's capability to incorporate the inherent material microstructure as an input to the model. In this work, this method was combined with multi-variate statistical modelling. The statistical model was used for screening and tentative relationship building and the finite element model was thereafter used for verification of the statistical modelling results. Characterisation of the coatings included microstructure, porosity and crack content and thermal conductivity measurements. A range of coating architectures was investigated including High purity Yttria stabilised Zirconia, Dysprosia stabilised Zirconia and Dysprosia stabilised Zirconia with porosity former. Evaluation of the thermal conductivity was conducted using the Laser Flash Technique. The microstructures were examined both on as-sprayed samples as well as on heat treated samples. The feasibility of the combined two modelling approaches, including their capability to establish relationships between coating microstructure and thermal conductivity, is discussed.
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| 50. |
- Torkashvand, Kaveh, 1990-, et al.
(författare)
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Advances in Thermally Sprayed WC-Based Wear-Resistant Coatings : Co-free Binders, Processing Routes and Tribological Behavior
- 2022
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 31:3, s. 342-377
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Tidskriftsartikel (refereegranskat)abstract
- A growing understanding of wear behavior of various thermally sprayed ceramic–metallic matrix coatings has occurred over recent years. This has resulted from the continuous evolution in spraying methods as well as material feedstock, and the corresponding new aspects of the field that have been thoroughly explored. This paper aims to review recent developments in thermally sprayed tungsten carbide-based coatings, with specific emphasis on evaluating alternative binders, processing routes and tribological behavior of the coatings. A comprehensive evaluation of various compositions as binders for WC-based coatings, considering environmental concerns and market requirements has been carried out. The properties and performance of various potential alternatives for cobalt as a conventional binder for these coatings have been assessed. Moreover, different thermal spray methods have been reviewed, particularly highlighting the role of processing parameters, phase change and feedstock characteristics in the high-velocity oxy-fuel (HVOF) and high-velocity air fuel (HVAF) techniques. A comparison is made between HVAF and HVOF coatings in terms of their performance under different wear environments. Finally, various scenarios of material removal in HVAF and HVOF coatings, under various wear conditions, have also been reviewed.
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