| 1. |
- Curry, Nicholas, 1984-, et al.
(författare)
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Evaluation of the Lifetime and Thermal Conductivity of Dysprosia-Stabilized Thermal Barrier Coating Systems
- 2013
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 22:6, s. 864-872
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was the further development of dysprosia stabilised zirconia coatings for gas turbine applications. The target for these coatings was a longer lifetime and higher insulating performance compared to today's industrial stan dard thermal barrier coating. Two morphologies of ceramic top coat were studied; one using a dual layer systems and the second using a polymer to generate porosity. Evaluations were carried out using laser flash technique to measure thermal properties. Lifetime testing was conducted using thermal shock testing and thermo-cyclic fatigue testing. Microstructure was assessed with SEM and Image analysis used to characterise porosity content. The results show that coatings with an engineered microstructure give performance twice that of the present reference coating.
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| 2. |
- Curry, Nicholas, 1984-, et al.
(författare)
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Impact of Impurity Content on the Sintering Resistance and Phase Stability of Dysprosia- and Yttria-Stabilized Zirconia Thermal Barrier Coatings
- 2014
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 23:1-2, s. 160-169
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Tidskriftsartikel (refereegranskat)abstract
- Dysprosia-stabilized zirconia (DySZ) is a promising candidate to replace yttria-stabilized zirconia (YSZ) as a thermal barrier coating due to its lower inherent thermal conductivity. It is also suggested in studies that DySZ may show greater stability to high temperature phase changes compared to YSZ, possibly allowing for coatings with extended lifetimes. Separately, the impurity content of YSZ powders has been proven to influence high-temperature sintering behavior. By lowering the impurity oxides within the spray powder, a coating more resistant to sintering can be produced. This study presents both high purity and standard purity dysprosia and YSZ coatings and their performance after a long heat treatment. Coatings were produced using powder with the same morphology and grain size; only the dopant and impurity content were varied. Samples have been heat treated for exposure times up to 400 h at a temperature of 1150 °C. Samples were measured for thermal conductivity to plot the evolution of coating thermal properties with respect to exposure time. Thermal conductivity has been compared to microstructure analysis and porosity measurement to track structural changes. Phase analysis utilizing x-ray diffraction was used to determine differences in phase degradation of the coatings after heat treatment. © 2013 ASM International.
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| 3. |
- Curry, Nicholas, 1984-, et al.
(författare)
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Next generation thermal barrier coatings for the gas turbine industry
- 2011
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 20:1-2, s. 108-115
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to develop the next generation of production ready air plasma sprayed thermal barrier coating with a low conductivity and long lifetime. A number of coating architectures were produced using commercially available plasma spray guns. Modifications were made to powder chemistry, including high purity powders, dysprosia stabilized zirconia powders, and powders containing porosity formers. Agglomerated & sintered and homogenized oven spheroidized powder morphologies were used to attain beneficial microstructures. Dual layer coatings were produced using the two powders. Laser flash technique was used to evaluate the thermal conductivity of the coating systems from room temperature to 1200 °C. Tests were performed on as-sprayed samples and samples were heat treated for 100 h at 1150 °C. Thermal conductivity results were correlated to the coating microstructure using image analysis of porosity and cracks. The results show the influence of beneficial porosity on reducing the thermal conductivity of the produced coatings. © 2010 ASM International.
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| 4. |
- Gupta, Mohit Kumar, et al.
(författare)
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An Experimental Study of Microstructure : Property Relationships in Thermal Barrier Coatings
- 2013
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 22:5, s. 659-670
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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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| 5. |
- Gupta, Mohit Kumar, et al.
(författare)
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Influence of Topcoat-Bondcoat Interface Roughness on Stresses and Lifetime inThermal Barrier Coatings
- 2014
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 23:1-2, s. 170-181
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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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| 6. |
- Joshi, S. V., et al.
(författare)
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Hybrid Plasma-Sprayed Thermal Barrier Coatings Using Powder and Solution Precursor Feedstock
- 2014
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Ingår i: Journal of thermal spray technology (Print). - 1059-9630 .- 1544-1016. ; 23:4, s. 616-624
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Tidskriftsartikel (refereegranskat)abstract
- A novel approach of hybridizing the conventional atmospheric plasma spraying (APS) technique with the solution precursor plasma spray (SPPS) route to achieve thermal barrier coatings (TBCs) with tailored configurations is presented. Such a hybrid process can be conveniently adopted for forming composite, multi-layered and graded coatings employing simultaneous and/or sequential feeding of solution precursor as well as powder feedstock, yielding distinct TBC microstructures that bear promise to further extend coating durability. TBC specimens generated using conventional APS technique, the SPPS method and through APS-SPPS hybrid processing have been comprehensively characterized for microstructure, phase constitution, hardness and thermal cycling life, and the results were compared to demonstrate the advantages that can ensue from hybrid processing.
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| 7. |
- Lohia, A., et al.
(författare)
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Deposition of Nanocomposite Coatings Employing a Hybrid APS + SPPS Technique
- 2014
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Ingår i: Journal of thermal spray technology (Print). - : Springer New York LLC. - 1059-9630 .- 1544-1016. ; 23:7, s. 1054-1064
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Tidskriftsartikel (refereegranskat)abstract
- A novel approach hybridizing the conventional atmospheric plasma spraying and the solution precursor plasma spraying techniques has been explored to develop nanocomposite coatings. The above hybrid processing route involves simultaneous feeding of an appropriate solution precursor and commercially available spray-grade powder feedstock to realize microstructures comprising nanostructured and micron-sized features, which are unique in thermal spraying. The attractive prospects offered by this hybrid technique for deposition of nanocomposite coatings are specifically highlighted in this paper through a case study. Plasma sprayed Mo-alloy coatings are known for their good tribological characteristics and widely used in many applications. Further augmentation in performance of these coatings is expected through incorporation of distributed nanostructured oxide phases in the microstructure. Successful development of such coatings using a spray-grade Mo-alloy powder and a suitable oxide-forming solution precursor has been demonstrated. Splat formation under varied processing conditions has been comprehensively investigated and related to microstructure and tribological behavior of the coatings to assess the efficacy of the above nanocomposite coatings for wear resistant applications. © 2014, ASM International.
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| 8. |
- Lyphout, Christophe, 1981, et al.
(författare)
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Adhesion Strength of HVOF Sprayed IN718 Coating
- 2011
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Ingår i: Journal of Thermal Spray Technology. - 1059-9630 .- 1544-1016.
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Tidskriftsartikel (refereegranskat)abstract
- The adhesion strength of high velocity oxy-fuel thermally sprayed coatings is of prior importance when thick coatings are to be sprayed for aeronautical repair applications. In this study, relationships between process parameters, particle in-flight characteristics, residual stresses and adhesion strength have been explored. Design of Experiments (DoE) was utilized to identify the most important process parameters that influence coating adhesion strength. Residual stress distributions were determined using the Modified Layer Removal Method (MLRM) and adhesion strength was measured using an in-house developed tensile test. Relationships between process parameters, particle in-flight characteristics, coating microstructure and adhesion strength were established. Particle temperature, particle velocity, substrate preparation and deposition temperature were identified as critical parameters to attain high adhesion strength. Controlling these parameters can significantly improve the adhesion strength, thus enabling thick coatings to be sprayed for aeronautical repair applications.
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| 9. |
- Lyphout, Christophe, 1981-, et al.
(författare)
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Adhesion strength of HVOF sprayed IN718 coatings
- 2012
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 21:1, s. 86-95
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Tidskriftsartikel (refereegranskat)abstract
- The adhesion strength of high-velocity oxyfuel thermally sprayed coatings is of prime importance when thick coatings are to be sprayed in repair applications. In this study, relationships between process parameters, particle in-flight characteristics, residual stresses, and adhesion strength were explored. The most important process parameters that influence HVOF sprayed IN718 coating adhesion strength on IN718 substrate material were identified. Residual stress distributions were determined using the modified layer removal method, and adhesion strength was measured using an in-house-developed tensile test. Relationships between process parameters, particle in-flight characteristics, coating microstructure, and adhesion strength were established. Particle temperature, particle velocity, substrate preparation, and deposition temperature were identified as critical parameters to attain high adhesion strength. Controlling these parameters can significantly improve the adhesion strength, thus enabling thick coatings to be sprayed for repair applications. © 2011 ASM International.
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| 10. |
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| 11. |
- Lyphout, Christophe, 1981-, et al.
(författare)
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Internal Diameter HVAF Spraying for Wear and Corrosion Applications
- 2014
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 24:1-2, s. 235-243
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Tidskriftsartikel (refereegranskat)abstract
- Electrolytic hard chrome (EHC) methods are still widely utilized in the printing, automotive and off-shore industries. Alternative methods to EHC have been widely developed in the past decade by conventional HVOF processes and more recently HVAF systems, which are processing at higher kinetic energy and more particularly at lower temperature, significantly increasing wear and corrosion resistance properties. A dedicated internal diameter HVAF system is here presented, and coatings characteristics are compared to the one obtained by standard HVAF coatings. Specially R&D designed fixtures with inside bore of 200 mm have been manufactured for this purpose, with a possibility to spray samples at increasing depth up to 400 mm while simulating closed bottom bore spraying. WC-based and Cr3C2-based powder feedstock materials have been deposited onto high-strength steel substrates. Respective coating microstructures, thermally induced stresses and corrosion resistance are discussed for further optimization of coating performances. The fact that the ID-HVAF system is utilized both for spraying and gritblasting procedures is also given a particular interest.
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| 12. |
- Lyphout, Christophe, 1981-, et al.
(författare)
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Mechanical Property of HVOF Inconel 718 Coating for Aeronautic Repair
- 2014
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 23:3, s. 380-388
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Tidskriftsartikel (refereegranskat)abstract
- The module of elasticity is one of the most important mechanical properties defining the strength of a material which is a prerequisite to design a component from its early stage of conception to its field of application. When a material is to be thermally sprayed, mechanical properties of the deposited layers differ from the bulk material, mainly due to the anisotropy of the highly textured coating microstructure. The mechanical response of the deposited layers significantly influences the overall performance of the coated component. It is, therefore, of importance to evaluate the effective module of elasticity of the coating. Conventional experimental methods such as microindentation, nanoindentation and four-point bending tests have been investigated and their results vary significantly, mainly due to inhomogeneous characteristics of the coating microstructure. Synchrotron radiation coupled with a tensile test rig has been proposed as an alternative method to determine the coating anisotropic elastic behavior dependence on crystallographic orientations. The investigation was performed on Inconel 718 (IN718) HVOF coatings sprayed on IN718 substrates. Combining these experimental techniques yield a deeper understanding of the nature of the HVOF coating Young’s modulus and thus a tool for Design Practice for repair applications. © 2013 ASM International.
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| 13. |
- Lyphout, Christophe, 1981-, et al.
(författare)
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Relationships between process parameters, microstructure, and adhesion strength of HVOF sprayed IN718 coatings
- 2011
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Ingår i: Journal of thermal spray technology (Print). - 1059-9630 .- 1544-1016. ; 20:1-2, s. 76-82
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Tidskriftsartikel (refereegranskat)abstract
- Fundamental understanding of relationships between process parameters, particle in-flight characteristics, and adhesion strength of HVOF sprayed coatings is important to achieve the high coating adhesion that is needed in aeronautic repair applications. In this study, statistical Design of Experiments (DoE) was used to identify the most important process parameters that influence adhesion strength of IN718 coatings sprayed on IN718 substrates. Special attention was given to the parameters combustion ratio, total gas mass flow, stand-off distance and external cooling, since these parameters were assumed to have a significant influence on particle temperature and velocity. Relationships between these parameters and coating microstructure were evaluated to fundamentally understand the relationships between process parameters and adhesion strength. © 2010 ASM International.
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| 14. |
- Lyphout, Christophe, 1981-, et al.
(författare)
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Screening Design of Supersonic Air Fuel Processing for Hard Metal Coatings
- 2014
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 23:8, s. 1323-1332
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Tidskriftsartikel (refereegranskat)abstract
- Replacement of electrolytic hard chromium method by thermal spray technology has shown a growing interest in the past decades, mainly pioneered by depositing WC-based material by conventional HVOF processes. Lower thermal energy and higher kinetic energy of sprayed particles achieved by newly developed Supersonic Air Fuel system, so-called HVAF-M3, significantly reduces decarburization, and increases wear and corrosion resistance properties, making HVAF-sprayed coatings attractive both economically and environmentally. In the present work, full factorial designs of experiments have been extensively utilized to establish relationships between hardware configurations, process and engineering variables, and coatings properties. The relevance of those process factors is emphasized and their significance is discussed in the optimization of coatings for improved abrasion wear and corrosion performances. © 2014 ASM International.
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| 15. |
- Musalek, Radek, et al.
(författare)
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Fatigue Testing of TBC on Structural Steel by Cyclic Bending
- 2014
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 24:1-2, s. 168-174
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Tidskriftsartikel (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 at each stage of the TBC preparation process, i. e., for as-received and grit-blasted substrates, as well as for samples with Ni-based bond-coat and complete TBC: 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 demonstrated applicability of the high-frequency resonant bending test for evaluation of fatigue resistance alteration at each stage of the TBC deposition process.
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| 16. |
- Nylén, Per, 1960-, et al.
(författare)
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Relationships between Process Parameters, Microstructure and Adhesion Strength of HVOF Sprayed IN718 Coating
- 2010
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Ingår i: Proceedings of the 2010 International Thermal Spray Conference. - : Springer Science and Business Media LLC. - 9783871555909 ; , s. 1-7
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Konferensbidrag (refereegranskat)abstract
- Fundamental understanding of relationships between process parameters, particle in-flight characteristics, and adhesion strength of HVOF sprayed coatings is important to achieve the high coating adhesion that is needed in aeronautic repair applications. In this study, statistical Design of Experiments (DoE) was used to identify the most important process parameters that influence adhesion strength of IN718 coatings sprayed on IN718 substrates. Special attention was given to the parameters combustion ratio, total gas mass flow, stand-off distance and external cooling, since these parameters were assumed to have a significant influence on particle temperature and velocity. Relationships between these parameters and coating microstructure were evaluated to fundamentally understand the relationships between process parameters and adhesion strength.
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| 17. |
- Holmberg, Ulf, et al.
(författare)
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Assessing the profitability of intraday opening range breakout strategies
- 2013
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Ingår i: Finance Research Letters. - : Elsevier. - 1544-6123 .- 1544-6131. ; 10:1, s. 27-33
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Tidskriftsartikel (refereegranskat)abstract
- Is it possible to beat the market by mechanical trading rules based on historical and publicly known information? Such rules have long been used by investors and in this paper, we test the success rate of trades and profitability of the Open Range Breakout (ORB) strategy. An investor that trades on the ORB strategy seeks to identify large intraday price movements and trades only when the price moves beyond some predetermined threshold. We present an ORB strategy based on normally distributed returns to identify such days and find that our ORB trading strategy result in significantly higher returns than zero as well as an increased success rate in relation to a fair game. The characteristics of such an approach over conventional statistical tests is that it involves the joint distribution of low, high, open and close over a given time horizon.
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| 18. |
- Lönnbark, Carl, 1981-, et al.
(författare)
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Value at risk for large portfolios
- 2011
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Ingår i: Finance Research Letters. - : Elsevier. - 1544-6123 .- 1544-6131. ; 8:2, s. 59-68
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Tidskriftsartikel (refereegranskat)abstract
- We argue that the practise used in the valuation of the portfolio is important for the calculation of the Value at Risk. In particular, when liquidating a large portfolio the seller may not face horizontal demand curves. We propose a partially new approach for incorporating this fact in the Value at Risk and in an empirical illustration we compare it to a competing approach. We find substantial differences.
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| 19. |
- Giannetti, Mariassunta
(författare)
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Liquidity constraints and occupational choice
- 2011
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Ingår i: Finance Research Letters. - : Elsevier. - 1544-6123. ; 8:1, s. 37-44
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Tidskriftsartikel (refereegranskat)abstract
- I show that liquidity constraints are related to individuals’ occupational choice. A proxy for the prospect of becoming liquidity constrained affects negatively the probability of being self-employed as opposed to being employed in the private or the public sectors. Furthermore, individuals with higher probability of facing liquidity constraints are more likely to be employed in the public sector, which offers the highest level of job and income security, instead of being employed in the private sector.
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| 20. |
- Hjalmarsson, Erik, 1975
(författare)
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Some curious power properties of long-horizon tests
- 2012
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Ingår i: Finance Research Letters. - : Elsevier BV. - 1544-6123. ; 9:2, s. 81-91
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Tidskriftsartikel (refereegranskat)abstract
- Based on simulations and asymptotic results, I highlight three distinct properties of long-horizon predictive tests. (i) The asymptotic power of long-horizon tests increases only with the sample size relative to the forecasting horizon. Keeping this ratio fixed as the sample size increases does not lead to any power gains asymptotically. (ii) Although the power of long-horizon tests increases with the magnitude of the slope coefficient for alternatives close to the null hypothesis, there are no gains in power as the slope coefficient grows large. That is, the power curve is asymptotically horizontal when viewed as a function of the slope coefficient. (iii) For endogenous regressors—i.e., when the innovations to the regressand are contemporaneously correlated with the innovations to the regressor—traditional tests based on the standard long-run OLS estimator result in power curves that are sometimes decreasing in the magnitude of the slope coefficient.
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| 21. |
- Näppä, Ulla, et al.
(författare)
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Avoiding harmful palliative chemotherapy treatment in the end of life : development of a brief patient-completed questionnaire for routine assessment of performance status
- 2012
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Ingår i: The journal of supportive oncology. - : Elsevier. - 1544-6794. ; 10:6, s. 230-237
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Earlier studies have shown that up to 43% of patients with incurable cancer are treated with palliative chemotherapy in the last month of their lives. Although pretreatment blood tests are acceptable, the patient's general condition may not permit further palliative chemotherapy treatment (PCT). Presently, there is no patient self-assessment tool available to monitor performance status during PCT.OBJECTIVES: To describe the development process of the Performance Status in Palliative Chemotherapy (PSPC) questionnaire, and the testing of its psychometric properties.METHODS: The questionnaire was developed by the authors based on the Eastern Cooperative Oncology Group Performance Status Rating (ECOG PSR) scale as well as their clinical experience with PCT. Adult patients who were diagnosed with epithelial cancers (n = 118) were enrolled to test the PSPC questionnaire for reliability, sensitivity for change, and validity.RESULTS: After stepwise modifications of the PSPC questionnaire, psychometric tests revealed acceptable values for reliability (via a test-retest method), sensitivity for change (via a comparison of patients with progressive disease over time), and validity (via a comparison of the PSPC vs the Edmonton Symptom Assessment System [ESAS]).LIMITATIONS: At this stage of questionnaire development, we are unable to conclude whether the PSPC is superior to the conventional ECOG PSR in the evaluation of performance status and the prediction of chemotherapy response.CONCLUSION: Psychometric tests suggest that the PSPC questionnaire may be a useful patient-completed tool in the late stages of cancer disease to routinely monitor performance status in palliative chemotherapy treatments so as to minimize the risk of inflicting more harm than good.
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