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| 2. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
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Microstructure and failure analysis of suspension plasma sprayed thermal barrier coatings
- 2020
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 382
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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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| 3. |
- Kovářík, Ondřej, et al.
(författare)
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Damping measurement during resonance fatigue test and its application for crack detection in TBC samples
- 2016
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123 .- 1879-3452. ; 82:Part 2, s. 300-309
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The use of specimen loss factor as fatigue damage indicator of Hastelloy-X substrates with different surface treatments was investigated together with other fatigue damage indicators, namely resonance frequency and crack mouth length. The tested surface treatments included grit-blasting and plasma spraying of NiCoCrAlY bond coat and yttria stabilized zirconia (YSZ) top coat. The loss factors of fatigue test specimens were measured repeatedly during the resonance bending fatigue test using the conventional free decay method. The analysis of the damping spectra, i.e. the model describing the relation of loss factor to maximum macroscopic specimen strain εyy was drafted. The model is based on the combination of defect models developed by Göken and Riehemann [1] and classical dislocation model of Granato and LÌcke [2]. It appears, that the damping spectra can be well approximated as a combination of two defect peaks (C1 and C2) and one dislocation peak (D1). The low strain defect peak (peak C1) is sensitive to the presence of fatigue cracks. The second defect peak (peak C2) can be attributed to the remaining substrate and coating defects such as embedded grit particles, coating porosity, surface roughness and sliding in the sample clamping area. The fatigue damage detection using the C1 peak magnitude was performed and its results were related to the crack length obtained by digital image correlation (DIC) method. In the crack initiation stage I., the C1 peak height shows different behavior than the resonance frequency and therefore provides new information. The underlying processes causing C1 peak changes need to be found yet, however. In the crack growth stage II., both resonance frequency and peak height C1 correlate with the measured fatigue crack size.
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| 4. |
- Kovářík, Ondrej, et al.
(författare)
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Fatigue Crack Growth in Bodies with Thermally Sprayed Coating
- 2016
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 25:1-2, s. 311-320, s. 398-405
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Tidskriftsartikel (refereegranskat)abstract
- Many applications of thermally sprayed coatings call for increased fatigue resistance of coated parts. Despite the intensive research in this area, the influence of coating on fatigue is still not completely understood. In this paper, the localization of crack initiation sites and the dynamics of crack propagation are studied. The resonance bending fatigue test was employed to test flat specimens with both sides coated. Hastelloy-X substrates coated with classical thermal barrier coating consisting of yttria stabilized zirconia and NiCoCrAlY layers. The strain distribution on the coating surface was evaluated by the Digital Image Correlation method through the whole duration of the fatigue test. Localization of crack initiation sites and the mode of crack propagation in the coated specimen are related to the observed resonance frequency. The individual phases of specimen degradation, i.e., the changes of material properties, crack initiation, and crack propagation, were identified. The tested coatings strongly influenced the first two phases, and the influence on the crack propagation was less significant. In general, the presented crack detection method can be used as a sensitive nondestructive testing method well suited for coated parts. © 2015 ASM International
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| 5. |
- Kovářík, Ondrej, et al.
(författare)
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Resonance bending fatigue testing with simultaneous damping measurement and its application on layered coatings
- 2016
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123 .- 1879-3452. ; 82, Part 2, s. 300-309
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The use of specimen loss factor as fatigue damage indicator of Hastelloy-X substrates with different surface treatments was investigated together with other fatigue damage indicators, namely resonance frequency and crack mouth length. The tested surface treatments included grit-blasting and plasma spraying of NiCoCrAlY bond coat and yttria stabilized zirconia (YSZ) top coat. The loss factors of fatigue test specimens were measured repeatedly during the resonance bending fatigue test using the conventional free decay method. The analysis of the damping spectra, i.e. the model describing the relation of loss factor to maximum macroscopic specimen strain εyy was drafted. The model is based on the combination of defect models developed by Göken and Riehemann (2004) and classical dislocation model of Granato and LÌcke (1956). It appears, that the damping spectra can be well approximated as a combination of two defect peaks (C1 and C2) and one dislocation peak (D1). The low strain defect peak (peak C1) is sensitive to the presence of fatigue cracks. The second defect peak (peak C2) can be attributed to the remaining substrate and coating defects such as embedded grit particles, coating porosity, surface roughness and sliding in the sample clamping area. The fatigue damage detection using the C1 peak magnitude was performed and its results were related to the crack length obtained by digital image correlation (DIC) method. In the crack initiation stage I., the C1 peak height shows different behavior than the resonance frequency and therefore provides new information. The underlying processes causing C1 peak changes need to be found yet, however. In the crack growth stage II., both resonance frequency and peak height C1 correlate with the measured fatigue crack size.
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| 6. |
- Mahade, Satyapal, 1987-, et al.
(författare)
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Influence of processing conditions on the microstructure and sliding wear of a promising Fe-based coating deposited by HVAF
- 2021
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 409, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- Thermal spray is a versatile and cost-effective process to deposit wear and corrosion resistant coatings. In this work, a relatively new ‘Fe-based’ chemistry comprising boride and carbides, is explored as a ‘greener’ alternative to the relatively expensive and carcinogenic Co-based coatings to mitigate wear. The emergent thermal spray process of high-velocity air-fuel (HVAF) spraying was chosen to deposit the Fe-based coatings, with the high-velocity oxy-fuel (HVOF) also being employed solely for the purpose of preliminary comparison. Detailed characterization of the HVOF and HVAF sprayed Fe-based coatings was carried out. Microstructure, porosity, hardness and phase analysis results demonstrate the influence of processing conditions, where specific spray conditions yielded minimal undeformed particulates content, high hardness, low porosity and feedstock phase retention. Differences in microstructural features of the as-deposited coatings in relation to their processing conditions are discussed in detail. The coatings were subjected to ball-on-disc tribometry tests at different load conditions and their friction and wear performance were evaluated. The coefficient of friction results of investigated coatings concurred with their respective microstructural features. Post-mortem of the worn coating surface, the mating alumina ball surface and wear debris was performed using SEM/EDS analysis to understand the associated wear mechanisms and material transfer. This work provides new insights on identifying appropriate HVAF processing conditions to achieve acceptable microstructural features and phases in Fe-based coatings for improved wear performance.
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| 7. |
- Mahade, Satyapal, 1987-, et al.
(författare)
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Sliding wear behavior of a sustainable Fe-based coating and its damage mechanisms
- 2022
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 500-501
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Tidskriftsartikel (refereegranskat)abstract
- The current industry demand is to identify suitable alternatives to the risk-of-supply prone and/or toxic, WC-Co and electrolytic hard chrome coatings without comprising the desired wear performance. Therefore, compositions based on abundantly available elements (e.g. ‘Fe’) that possess adequate wear resistance are desirable from health, sustainability and economic standpoints. In this work, crystalline Fe-based (Rockit-401) coatings were processed using two different thermal spray routes, i.e. HVOF and HVAF spraying. The influence of deposition route and processing conditions on the microstructure, porosity content, hardness and phase composition was examined. The as-deposited coatings were subjected to mild (5 N) and harsh (15 N) dry sliding wear test conditions by employing alumina ball as the counter surface material, and their wear performance was examined. Mild sliding wear test conditions (5 N) resulted in anomalous wear behavior, where the abrupt drop in CoF at several instances during the test was observed in all the investigated coatings. On the other hand, under harsh wear test conditions (15 N), such an abrupt dip in CoF was not observed. Detailed wear mechanisms of the coatings were revealed under different test conditions (5 N and 15 N). This work sheds light on processing, wear behavior and wear mechanisms of a sustainable and high-performance coating that fulfills non-toxic and sustainability goals in tandem for tribological applications. © 2022 The Authors
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| 8. |
- Musalek, Radek, et al.
(författare)
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Evaluation of failure micromechanisms of advanced thermal spray coatings by in-situ experiment
- 2014
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Ingår i: Key Engineering Materials. - 1013-9826 .- 1662-9795. ; 606, s. 187-190
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Tidskriftsartikel (refereegranskat)abstract
- Identification of failure mechanisms of thermal spray coatings by means of traditional fractography of failed parts is often troublesome. The reason for this is a highly inhomogeneous character of the coating microstructure and harsh in-service conditions which may obscure evidentiary fractographic marks. In this study, failure evolution of advanced thermal barrier coating (TBC) prepared by plasma spraying was studied in-situ at high magnification in a scanning electron microscope under well-defined laboratory conditions of three-point bending (3PB). © (2014) Trans Tech Publications, Switzerland.
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| 9. |
- Musalek, Radek, et al.
(författare)
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Fatigue Performance of TBC on Structural Steel Exposed to Cyclic Bending
- 2014
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Ingår i: Proceedings of the International Thermal Spray Conference. - : ASM International. ; , s. 880-885
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Konferensbidrag (refereegranskat)abstract
- For applications with variable loading, fatigue performance of coated parts is of utmost importance. In this study, fatigue performance of conventional structural steel coated with thermal barrier coating (TBC) was evaluated in cyclic bending mode by "SF-Test" device. Testing was carried out for as-received and grit-blasted substrates, as well as for samples with Ni-based bond-coat and bond-coat with YSZ-based top-coat. Comparison of results obtained for different loading amplitudes supplemented by fractographic analysis enabled identification of dominating failure mechanisms and evaluation of fatigue resistance alteration due to the deposited coatings.
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| 10. |
- Musalek, Radek, et al.
(författare)
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Fatigue performance of TBCs on hastelioy X substrate during cyclic bending
- 2015
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Ingår i: Thermal Spray 2015. - : ASM International. - 9781510811546 ; , s. 406-412
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Konferensbidrag (refereegranskat)abstract
- Our previous experiments with low-cost steel substrates confirmed that individual steps of conventional thermal barrier coating (TBC) deposition may influence fatigue properties of the coated samples differently. In this study, testing was carried out for TBC samples deposited on industrially more relevant Hastelioy X substrates. Samples were tested after each step of TBC deposition process: As-received (non- coated), grit-blasted, bond-coated (NiCoCrAlY) and bond- coated + top-coated (yttria-stabilized zirconia - YSZ). Conventional atmospheric plasma spraying (APS) with gas stabilized plasma torch was used for deposition of both bond coat and top coat. In addition, for one half of the samples, bond coat was prepared by consecutive combination of HVAF (High Velocity Air Fuel) and APS processes. Samples were tested both in as-sprayed condition and after 100 hours annealing at 980 °C, which simulated in-service conditions. Obtained results showed that different fatigue performance may be expected for various stages of the TBC deposition as well as due to the variation of the deposition process and sample temperature history. © Copyright (2015) by ASM International All rights reserved.
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