| 1. |
- Hemphälä, Hillevi, et al.
(författare)
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A method for risk assessment within Visual Ergonomics
- 2015
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Ingår i: Proceedings of the 19th Triennial Congress of the International Ergonomics Association. ; , s. nr 1203-
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Konferensbidrag (refereegranskat)abstract
- IntroductionInsufficient visual ability can lead to increased work load and contribute to eyestrain and musculoskeletal discomfort, since “the eye leads the body” (Anshel, 2005). It has been shown that visually demanding work, such as computer work, is associated with eye discomfort, headaches and muscle pains in mainly the neck and shoulders (Rosenfield, 2011).Although the relation between eyestrain and musculoskeletal discomfort is not fully understood, studies have shown that straining the eyes increases the musculoskeletal activity in neck and shoulders (trapezius), and an association between visually demanding work, eye problems, headache and/or muscle problems have been found (Aarås et al., 2001; IESNA, 2011, Richter et al., 2008; Zetterberg et al., 2013). Problems due to insufficient visual ergonomics not only exist in computer intensive jobs, but in other professions as well. For example, surgeons and other surgical personnel that report eyestrain also report twice as much musculoskeletal discomfort from the upper part of the body (Hemphälä et al., 2011). In an intervention study among postmen, both eyestrain and musculoskeletal discomfort decreased after a visual ergonomic intervention. The intervention included providing customized eyeglasses and optimal lighting conditions (Hemphälä et al., 2012). Apart from health and well-being being affected by a poor visual ergonomic work environment, quality and productivity may also be reduced (Eklund, 2009).The aim of this paper is to present the first version of a practical, easy-to-use, and time-efficient risk assessment method for visual ergonomics. The development of the method including the evaluation will also be described. With such a method, risk factors within the visual environment can hopefully be detected, and interventions implemented in order to reduce the prevalence of symptoms related to poor visual ergonomics among workers.MethodsA first version of the method has been developed, mainly based on existing checklists and instruments (Colon et al. 1999; Børsting et al., 2008, Knave et al., 1985, Sheedy and Shaw-McMinn, 2002; Wilson & Corlett, 2005). During spring 2015, 30 ergonomists will be updated about visual ergonomics and introduced to the risk assessment method. Each ergonomist will thereafter use the method in 10 workplaces, yielding data and practical experiences from 300 risk assessments. These data will then be used to test the validity and reliability of the method, and if necessary to further develop it.ResultsThe first version of the risk assessment method for Visual Ergonomics will be presented at IEA 2015, together with results from the approximately 300 risk assessments made by the ergonomists. So far, the factors included in the method are objective measurements such as illuminance, luminance contrast, uniformity values, expert assessment of the risk for glare, and subjective ratings of the visual ability, eyestrain and musculoskeletal discomfort.DiscussionThe presented method will be compared to other similar methods. The used method for development will be discussed in relation to validity and reliability. Finally the presented risk assessment method will be discussed in relation to usefulness in prevention of discomfort and work related disorders at work places.
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| 2. |
- Ganvir, Ashish, 1991-, et al.
(författare)
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Influence of Microstructure on Thermal Properties of Axial Suspension Plasma-Sprayed YSZ Thermal Barrier Coatings
- 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. 202-212
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Tidskriftsartikel (refereegranskat)abstract
- Suspension plasma spraying is a relatively new thermal spaying technique to produce advanced thermal barrier coatings (TBCs) and enables production of coatings with a variety of structures—highly dense, highly porous, segmented, or columnar. This work investigates suspension plasma-sprayed TBCs produced using axial injection with different process parameters. The influence of coating microstructure on thermal properties was of specific interest. Tests carried out included microstructural analysis, phase analysis, determination of porosity, and pore size distribution, as well as thermal diffusivity/conductivity measurements. Results showed that axial suspension plasma spraying process makes it possible to produce various columnar-type coatings under different processing conditions. Significant influence of microstructural features on thermal properties of the coatings was noted. In particular, the process parameter-dependent microstructural attributes, such as porosity, column density, and crystallite size, were shown to govern the thermal diffusivity and thermal conductivity of the coating.
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| 3. |
- Hemphälä, Hillevi, et al.
(författare)
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A method for assessing risks within visual ergonomics
- 2014
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Ingår i: 11th International Symposium on Human Factors in Organisational Design and Management & 46th Annual Nordic Ergonomics Society Conference. - Santa Monica, CA, USA : The IEA PRESS. - 9788793130135 ; , s. 111-112
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Konferensbidrag (refereegranskat)abstract
- 1. IntroductionInsufficient visual ability can lead to strained work load for employees and can contribute to eyestrain and musculoskeletal discomfort, “the eye leads the body” (Anshel, 2005). An optimal visual environment provides physical conditions for work in the best possible way. Visually demanding work, such as computer work, is associated with eye discomfort, headaches and muscle pains in mainly the neck and shoulders (Rosenfield, 2011). For computer workers in North America studies show that 75-90 % of the workers reported subjective symptoms from the eyes (Anshel, 2005). The causality between eyestrain and musculoskeletal discomfort is not fully understood, but studies have shown that straining the eyes increases the musculoskeletal activity in neck and shoulders (trapezius), and a link between visually demanding work, eye problems, headache and/or muscle problems have been found (Aarås et al., 2001; Richter et al., 2008; Zetterlund et al., 2009; Zetterberg et al., 2013). A study of call-center workers in Sweden showed that 21% of workers have both eyes and neck problems (Wiholm et al., 2007). Ergonomic problems also exist for professions where computer work is not dominant. Surgeons and other surgical personnel, with subjective eye discomfort, reported twice the incidence of musculoskeletal disorders when compared with staff without eye symptoms (Hemphälä et al., 2011). In an intervention study among postmen the eyestrain and musculoskeletal discomfort decreased after visual ergonomic interventions including customized eyeglasses and optimal lighting conditions (Hemphälä et al., 2012). Apart from health and well-being being affected by a poor visual ergonomic work environment, the quality and productivity are also involved (Eklund, 2009).Lighting is an important factor; both the lighting quantity (strength) and quality (e.g. light distribution, direction, glare and contrast). Too low illumination makes it difficult to see clearly and may thus lower performance, high illuminance can cause glare and lead to increased eye fatigue and decreased productivity (IESNA, 2011).2. MethodsThere are several factors to consider when developing a method for visual ergonomics risk assessment of subjective symptoms and discomfort of the eyes (Colon et al. 1999; Børsting et al., 2008, Knave et al., 1985). There are also checklists used in eye exams or medical appointments (Sheedy and Shaw-McMinn, 2002; Wilson & Corlett, 2005). These will be used as basis in the presents the project intended to develop a risk assessment instrument for visual ergonomics.3. ResultsA preliminary version of a risk analysis method for Visual Ergonomics has been developed and will be presented, with a focus on discussing with the audience which factors should primarily be included. The factors included so far in the method are the objective measurements such as illuminance, luminance contrast, uniformity values, expert assessment of the risk for glare; indirect measurements such as subjective ratings of the visual ability, eyestrain and musculoskeletal discomfort. The goal is to develop a practical time efficient method that is easy to use. With such a tool, actions needed to reduce the visual load among the workers, the companies and the society’s negative consequences induced by work-related eyestrain and musculoskeletal discomfort can hopefully be identified.
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| 4. |
- Joshi, Shrikant V., 1960-, et al.
(författare)
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Advanced Coatings by Thermal Spray Processes
- 2019
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Ingår i: Technologies. - : MDPI. - 2227-7080. ; 7:4, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- Coatings are pivotal in combating problems of premature component degradation in aggressive industrial environments and constitute a strategic area for continued development. Thermal spray (TS) coatings offer distinct advantages by combining versatility, cost-effectiveness, and the ability to coat complex geometries without constraints of other in-chamber processes. Consequently, TS techniques like high-velocity oxy-fuel (HVOF) and atmospheric plasma spray (APS) are industrially well-accepted. However, they have reached limits of their capabilities while expectations from coatings progressively increase in pursuit of enhanced efficiency and productivity. Two emerging TS variants, namely high-velocity air-fuel (HVAF) and liquid feedstock thermal spraying, offer attractive pathways to realize high-performance surfaces superior to those hitherto achievable. Supersonic HVAF spraying provides highly adherent coatings with negligible porosity and its low processing temperature also ensures insignificant thermal ‘damage’ (oxidation, decarburization, etc.) to the starting material. On the other hand, liquid feedstock derived TS coatings, deposited using suspensions of fine particles (100 nm–5 µm) or solution precursors, permits the production of coatings with novel microstructures and diverse application-specific architectures. The possibility of hybrid processing, combining liquid and powder feedstock, provides further opportunities to fine tune the properties of functional surfaces. These new approaches are discussed along with some illustrative examples.
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| 5. |
- Joshi, Shrikant V., 1960-, et al.
(författare)
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New Generation Ceramic Coatings for High-Temperature Applications by Liquid Feedstock Plasma Spraying : Defense, Security, Aerospace and Energy Applications
- 2020
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Ingår i: Handbook of Advanced Ceramics and Composites. - Cham : Springer. - 9783319732558 ; , s. 1-42
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Plasma spraying with liquid feedstock offers an exciting opportunity to obtain coatings with characteristics that are vastly different from those produced using conventional spray-grade powders. The two extensively investigated variants of this technique are suspension plasma spraying (SPS), which utilizes a suspension of fine powders in an appropriate medium, and solution precursor plasma spraying (SPPS), which involves use of a suitable solution precursor that can form the desired particles in situ. The advent of axial injection plasma spray systems in recent times has also eliminated concerns regarding low deposition rates/efficiencies associated with liquid feedstock. The 10–100 μm size particles that constitute conventional spray powders lead to individual splats that are more than an order of magnitude larger compared to those resulting from the fine (approximately 100 nm–2 μm in size) particles already present in suspensions in SPS or formed in situ in SPPS. The distinct characteristics of the resulting coatings are directly attributable to the above very dissimilar splats (“building blocks” for coatings) responsible for their formation. This chapter discusses the salient features associated with SPS and SPPS processing, highlights their versatility for depositing a vast range of ceramic coatings with diverse functional attributes, and discusses their utility, particularly for high-temperature applications through some illustrative examples. A further extension of liquid feedstock plasma processing to enable use of hybrid powder-liquid combinations for plasma spraying is also discussed. This presents a novel approach to explore new material combinations, create various function-dependent coating architectures with multi-scale features, and enable convenient realization of layered, composite, and graded coatings as demonstrated through specific examples.
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| 6. |
- Kumara, Chamara, et al.
(författare)
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Microstructure modelling of laser metal powder directed energy deposition of alloy 718
- 2019
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 25, s. 357-364
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Tidskriftsartikel (refereegranskat)abstract
- A multi-component and multi-phase-field modelling approach, combined with transformation kinetics modelling, was used to model microstructure evolution during laser metal powder directed energy deposition of Alloy 718 and subsequent heat treatments. Experimental temperature measurements were utilised to predict microstructural evolution during successive addition of layers. Segregation of alloying elements as well as formation of Laves and δ phase was specifically modelled. The predicted elemental concentrations were then used in transformation kinetics to estimate changes in Continuous Cooling Transformation (CCT) and Time Temperature Transformation (TTT) diagrams for Alloy 718. Modelling results showed good agreement with experimentally observed phase evolution within the microstructure. The results indicate that the approach can be a valuable tool, both for improving process understanding and for process development including subsequent heat treatment.
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| 7. |
- Markocsan, Nicolaie, 1967-, et al.
(författare)
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Liquid Feedstock Plasma Spraying : An Emerging Process for Advanced Thermal Barrier Coatings
- 2017
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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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| 8. |
- Bahbou, M. Fouzi, 1973-, et al.
(författare)
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A parameter study of the Protal® Process to optimise the adhesion of Ni5Al Coatings
- 2004
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Ingår i: Thermal Spray 2004 : Advances in technology and applications. - 9780871708090 ; , s. 898-902
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Konferensbidrag (refereegranskat)abstract
- The Protal process combines surface preparation using a laser and thermal spraying in one production step. The laser preparation is based on a photomechanical reaction induced by the interaction between a laser of high instantaneous power and a polluted surface. The mechanism of bonding and the coating-substrate interface are then changed in comparison with grit blasting resulting in a significantly reduced substrate roughness. This study is aimed at finding the optimal Protal process parameters for the coating adhesion of a Ni5%Al sprayed on Ti6Al4V and IN718 alloys. The parameters investigated are laser beam intensity, the time delay between the laser impact and the spray impact, powder feed rate, substrate roughness and temperature. A test plan including these parameters is analysed by means of a fractional factorial design of experiment method. The adhesions of the coatings are measured using the ASTM C633 standard test. Data are analysed by a multiple linear regression model using a least squares fit. In addition, the coating/substrate interface is examined by optical and electron scanning microscopy (SEM) techniques as well as by Auger electron spectroscopy. Substrate roughness, substrate temperature and laser intensity are all shown to have a negative correlation with adhesion strength within the investigated range. Areas of diffusion are noticed at the coating/substrate interface.
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| 9. |
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| 10. |
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| 11. |
- Bahbou, M. Fouzi, 1973-, et al.
(författare)
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On-Line measurement of plasma-sprayed ni-particles during impact on a ti-surface : influence of surface oxidation
- 2007
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 16:6, s. 506-511
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to analyze the impact of plasma-sprayed Ni5%Al particles on polished and grit-blasted Ti6Al4V samples under oxidized and nonoxidized conditions. For this purpose, measurements of thermal radiation and velocity of individual plasma-sprayed particles were carried out. From the thermal radiation at impact, splat diameter during flattening and temperature evolution during cooling were evaluated. Characteristic parameters related to the quality of contact between the splat and the substrate were retrieved. The flattening speed was introduced to characterize wetting, while the cooling rate was used to characterize solidification. The idea was to get a signature of particle impact for a given surface roughness and oxidation state by identifying parameters which strongly affect the splat behavior. Sieved Ni5%Al powder in a narrow range (+65 −75 μm) was sprayed on four sets of titanium alloy surfaces, consisting of polished and grit-blasted samples, one set had a nonoxidized surface and the other one was oxidized in an oven at 600 °C for two hours. Resulting splats after impact were characterized by scanning electron microscopy, the splats on oxidized surface showed pores in their core and detached fingers at the periphery. The cooling rate and flattening degree significantly increased on the oxidized smooth surface compared to the nonoxidized one. This trend was not found in grit-blasted surfaces, which implies that impact phenomena are different on grit-blasted surfaces than on smooth surfaces thus further work is needed.
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| 12. |
- Bahbou, M. Fouzi, 1973-, et al.
(författare)
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Relationship between surface topgraphy parameters and adhesion strength for plasma spraying
- 2005
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Ingår i: ITSC 2005. - : The Material Information Society. ; , s. 1027-1031
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Konferensbidrag (refereegranskat)abstract
- To achieve sufficient adhesion strength within thermal spraying, the surface to be coated has to be modified. Grit blasting is the most common way to generate a clean and roughened surface. The bonding mechanism between the grit-blasted substrate and the coating is assumed to be due to mechanical anchoring, why an optimal surface roughness is essential. The surface roughness is usually evaluated using Ra which cannot fully characterize the complex nature of the chaotic substrate topography. This study was performed in order to evaluate if Ra can be replaced by other surface characteristic parameters such us R.q, Rpk, Rpv, Rk…with higher correlation to adhesion strength. Average roughness was measured by a perthometer and with white light interferometry to get 3D images of the surface topography. Disc shaped substrate samples of Ti6Al4V (AMS 4928) were grit blasted with aluminium oxide grit and plasma sprayed with a Ni5%Al coating. Adhesion strength was determined according to the ASTM C633 standard. The correlation between a number of different surface-parameters and adhesion strength were evaluated and compared with Ra.
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| 13. |
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| 14. |
- Balachandramurthi, Arun Ramanathan
(författare)
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Fatigue Properties of Additively Manufactured Alloy 718
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive Manufacturing (AM), commonly known as 3D Printing, is a disruptive modern manufacturing process, in which parts are manufactured in a layer-wise fashion. Among the metal AM processes, Powder Bed Fusion (PBF) technology has opened up a design space that was not formerly accessible with conventional manufacturing processes. It is, now, possible to manufacture complex geometries, such as topology-optimized structures, lattice structures and intricate internal channels, with relative ease. PBF is comprised of Electron Beam Melting (EBM) and Selective Laser Melting (SLM) processes.Though AM processes offer several advantages, the suitability of these processes to replace conventional manufacturing processes must be studied in detail; for instance, the capability to produce components of consistent quality. Therefore, understanding the relationship between the AM process together with the post treatment used and the resulting microstructure and its influence on the mechanical properties is crucial, to enable manufacturing of high-performance components. In this regard, for AM built Alloy 718, only a limited amount of work has been performed compared to conventional processes such as casting and forging. The aim of this work, therefore, is to understand how the fatigue properties of EBM and SLM built Alloy 718, subjected to different thermal post-treatments, is affected by the microstructure. In addition, the effect of as-built surface roughness is also studied.Defects can have a detrimental effect on fatigue life. Numerous factors such as the defect type, size, shape, location, distribution and nature determine the effect of defects on properties. Hot Isostatic Pressing (HIP) improves fatigue life as it leads to closure of most defects. Presence of oxides in the defects, however, hinders complete closure by HIP. Machining the as-built surface improves fatiguelife; however, for EBM manufactured material, the extent of improvement is dependent on the amount of material removed. The as-built surface roughness, which has numerous crack initiation sites, leads to lower scatter in fatigue life. In both SLM and EBM manufactured material, fatigue crack propagation is transgranular. Crack propagation is affected by grain size and texture of the material.
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| 15. |
- Balachandramurthi, Arun Ramanathan, 1989-
(författare)
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Towards understanding the fatigue behaviour of Alloy 718 manufactured by Powder Bed Fusion processes
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive Manufacturing (AM) is a disruptive modern manufacturing process in which parts are manufactured in a layer-wise fashion. Among the metal AM processes, Powder Bed Fusion (PBF) technology — comprised of Electron Beam Powder Bed Fusion (EB-PBF) and Laser Beam Powder Bed Fusion (LB-PBF) —has opened up a design space that was formerly unavailable with conventionalmanufacturing processes. PBF processes offer several advantages; however, thesuitability of these processes to replace the conventional processes must be investigatedin detail. Therefore, understanding the AM process – post-processing –microstructure – property relationships is crucial for the manufacturing of high performance components. In this regard, only limited work has been done towards understanding the fatigue behaviour of PBF Alloy 718. The aim of this work, therefore, is to understand how the fatigue behaviour of PBF Alloy 718 is affected by its microstructure. Besides, the influence of the rough as-built surface is also investigated. In general, the <100> fibre texture along the build direction that resulted from PBF processing of Alloy 718 led to anisotropy in Young's modulus. Consequently,the fatigue performance under controlled amplitudes of strain was anisotropic such that the low-modulus direction had longer fatigue life and vice versa. This texture-induced elasticity-dependent anisotropic strain-life behaviour couldbe normalized by the pseudo-elastic stress vs fatigue life approach.Inclusions and defects had a detrimental effect on fatigue performance. Numerousfactors, such as their geometry, volume fraction, and distribution, determinedthe effect on fatigue behaviour. Hot Isostatic Pressing (HIP) eliminated most defect sand led to an improvement in fatigue performance. However, HIP did not alter the inclusions, which acted as crack initiation sites and reduced fatigue life. The rough as-built surface, which had numerous notch-like crack initiation sites, deteriorated fatigue performance; however, it lowered the scatter in fatigue life. Machining off the as-built surface improved fatigue life but increased the scatter.
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| 16. |
- Bolelli, G., et al.
(författare)
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Sliding and abrasive wear behaviour of HVOF- and HVAF-sprayed Cr3C2-NiCr hardmetal coatings
- 2016
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 358-359, s. 32-50
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides a comprehensive characterisation of HVOF- and HVAF-sprayed Cr3C2–25 wt.% NiCr hardmetal coatings. One commercial powder composition with two different particle size distributions was processed using five HVOF and HVAF thermal spray systems.All coatings contain less Cr3C2 than the feedstock powder, possibly due to the rebound of some Cr3C2-rich particles during high-velocity impact onto the substrate.Dry sand-rubber wheel abrasive wear testing causes both grooving and pull-out of splat fragments. Mass losses depend on inter- and intra-lamellar cohesion, being higher (≥70 mg after a wear distance of 5904 m) for the coatings deposited with the coarser feedstock powder or with one type of HVAF torch.Sliding wear at room temperature against alumina involves shallower abrasive grooving, small-scale delamination and carbide pull-outs, and it is controlled by intra-lamellar cohesion. The coatings obtained from the fine feedstock powder exhibit the lowest wear rates (≈5x10−6 mm3/(Nm)). At 400 °C, abrasive grooving dominates the sliding wear behaviour; wear rates increase by one order of magnitude but friction coefficients decrease from ≈0.7 to ≈0.5. The thermal expansion coefficient of the coatings (11.08x10−6 °C−1 in the 30–400 °C range) is sufficiently close to that of the steel substrate (14.23x10−6 °C−1) to avoid macro-cracking
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| 17. |
- Bolelli, G., et al.
(författare)
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Tribology of HVOF- and HVAF-sprayed WC-10Co4Cr hardmetal coatings : A comparative assessment
- 2015
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Ingår i: Surface and Coatings Technology. - : Elsevier. - 0257-8972. ; 265, s. 125-144
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Tidskriftsartikel (refereegranskat)abstract
- his paper provides a comprehensive assessment of the sliding and abrasive wear behaviour of WC–10Co4Cr hardmetal coatings, representative of the existing state-of-the-art. A commercial feedstock powder with two different particle size distributions was sprayed onto carbon steel substrates using two HVOF and two HVAF spray processes.Mild wear rates of < 10-7 mm3/(Nm) and friction coefficients of ≈ 0.5 were obtained for all samples in ball-on-disk sliding wear tests at room temperature against Al2O3 counterparts. WC–10Co4Cr coatings definitely outperform a reference electrolytic hard chromium coating under these test conditions. Their wear mechanisms include extrusion and removal of the binder matrix, with the formation of a wavy surface morphology, and brittle cracking. The balance of such phenomena is closely related to intra-lamellar features, and rather independent of those properties (e.g. indentation fracture toughness, elastic modulus) which mainly reflect large-scale inter-lamellar cohesion, as quantitatively confirmed by a principal component analysis. Intra-lamellar dissolution of WC into the matrix indeed increases the incidence of brittle cracking, resulting in slightly higher wear rates. At 400 °C, some of the hardmetal coatings fail because of the superposition between tensile residual stresses and thermal expansion mismatch stresses (due to the difference between the thermal expansion coefficients of the steel substrate and of the hardmetal coating). Those which do not fail, on account of lower residual stresses, exhibit higher wear rates than at room temperature, due to oxidation of the WC grains.The resistance of the coatings against abrasive wear, assessed by dry sand–rubber wheel testing, is related to inter-lamellar cohesion, as proven by a principal component analysis of the collected dataset. Therefore, coatings deposited from coarse feedstock powders suffer higher wear loss than those obtained from fine powders, as brittle inter-lamellar detachment is caused by their weaker interparticle cohesion, witnessed by their systematically lower fracture toughness as well.
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| 18. |
- Chen, Y., et al.
(författare)
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Characterization and understanding of residual stresses in a NiCoCrAlY bond coat for thermal barrier coating application
- 2015
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 94, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- The residual stresses in a NiCoCrAlY bond coat deposited on a Ni-base superalloy substrate after oxidation at 1150 °C were studied by X-ray diffraction using the sin2Ψ technique. The stresses were found to be tensile; they first increased and then decreased with oxidation time. High temperature stress measurement indicated that the stress developed and built up upon cooling, predominantly within the temperature range from 1150 °C to 600 °C. Microstructural examination suggested that, due to the limited penetration depth into the bond coat, the X-ray only probed the stress in a thin surface layer consisting of the single γ-phase formed through Al depletion during oxidation. Quantitative high temperature X-ray diffraction analysis revealed that, above 600 °C, the volume fraction of the β-phase in the bond coat increased with decreasing temperature. The mechanisms of stress generation in the bond coat were examined and are discussed based on the experiments designed to isolate the contribution of possible stress generation factors. It was found that the measured bond coat stresses were mainly induced by the volume change of the bond coat associated with the precipitation of the β-phase upon cooling.
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| 19. |
- Chen, Ying, et al.
(författare)
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Measurements of elastic modulus and fracture toughness of an air plasma sprayed thermal barrier coating using micro-cantilever bending
- 2019
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 374, s. 12-20
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Tidskriftsartikel (refereegranskat)abstract
- The elastic modulus and fracture toughness of an air plasma sprayed thermal barrier coating (APS TBC) were measured using the micro-cantilever bending technique. The micro-cantilevers were machined by a focused ion beam with their central arms either parallel or normal to the bond coat/topcoat interface. Such orientations allowed direct measurements of both the in-plane and out-of-plane elastic moduli as well as mode I fracture toughness by bending. The calculated elastic modulus along the in-plane and out-of-plane direction is 144 GPa and 110 GPa, respectively, suggesting that the APS TBC is elastically anisotropic at microscale. The derived mode I fracture toughness along the plane parallel to the interface is 0.40 MPam. This relatively low toughness reflects the weak fracture resistance of the highly-flawed APS for short cracks at microscale. The measurements in this study can be incorporated into micromechanical life time prediction models of the APS TBCs. © 2019 Elsevier B.V.
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| 20. |
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| 21. |
- Clement, C., et al.
(författare)
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Corrosion behavior of HVAF- and HVOF-sprayed high-chromium Fe-based coatings
- 2015
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Konferensbidrag (refereegranskat)abstract
- Fe-based coatings with three particular elemental compositions and two different powder particle size were prepared by high-velocity air fuel (HVAF) and high-velocity oxy fuel (HVOF) techniques. The corrosion behavior of which were comparatively studied in 3.5 wt.% NaCl solution. The results indicated that the coatings produced by HVAF process exhibited denser structure with lower porosity. Polarization and electrochemical impedance spectroscopy (EIS) tests indicated that the HVAF coatings provided better corrosion resistance than the HVOF coatings. The presence of defects was significant in HVOF coatings. The investigation illustrated that the corrosion paths initiated and grow through defects of the coating. Furthermore, adding Cr strongly improved the corrosion resistance of the coatings. The results confirmed that the cheap HVAF process could be a potential alternative to HVOF to fabricate Fe-based coatings for industrial applications.
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| 22. |
- Curry, Nicholas, 1984-
(författare)
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Design of Thermal Barrier Coating Systems
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermal barrier coatings (TBC’s) are used to provide both thermal insulation and oxidation protection to high temperature components within gas turbines. The development of turbines for power generation and aviation has led to designs where the operation conditions exceed the upper limits of most conventional engineering materials. As a result there has been a drive to improve thermal barrier coatings to allow the turbine to operate hotter for longer.The focus of this study has been the development of a new generation of TBC system for industrial implementation. The goal for these new coatings was to achieve lower conductivity and longer lifetime than those coatings used today. The route taken to achieve these goals has been twofold. Firstly an alternative stabiliser has been chosen for the zirconium oxide system in the form of dysprosia. Secondly, Control of the powder morphology and spray parameters has been used to generate coating microstructures with favourable levels of porosity.Samples have been heavily characterised using the laser flash technique for evaluation of thermal properties. Measurements were performed at room temperature and at intervals up to 1200°C. Samples have also been tested in their as produced state and after heat treatments of up to 200 hours.Lifetime evaluation has been performed using the thermo-cyclic fatigue test to expose coating systems to successive cycles of heating and cooling combined with oxidation of the underlying metallic coating.Microstructures have been prepared and analysed using SEM. An image analysis routine has been used to attempt to quantify changes in microstructure features between coating types or coating exposure times and to relate those changes to changes in thermal propertiesResults show that dysprosia as an alternative dopant gives a reduction in thermal conductivity. While small at room temperature and in the as produced state; the influence becomes more pronounced at high temperatures and with thermal exposure time. Overall, the greatest sustained influence on thermal conductivity has been from creating coatings with high levels of porosity.In relation to lifetime, the target of double the thermo-cyclic fatigue life was achieved using a coating with engineered porosity. Introducing a polymer to the spray powder helps to generate large globular pores within the coating together with a large number of delaminations. Such a structure has shown to be highly resistant to TCF testing.
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| 23. |
- Curry, Nicholas, 1984-
(författare)
-
Design of Thermal Barrier Coatings
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermal barrier coatings (TBC’s) are used to provide both thermal insulation and oxidation protection to high temperature components within gas turbines. The development of turbines for power generation and aviation has led to designs where the operation conditions exceed the upper limits of most conventional engineering materials. As a result there has been a drive to improve thermal barrier coatings to allow the turbine to operate at higher temperatures for longer.The focus of this thesis has been to design thermal barrier coatings with lower conductivity and longer lifetime than those coatings used in industry today. The work has been divided between the development of new generation air plasma spray (APS) TBC coatings for industrial gas turbines and the development of suspension plasma spray (SPS) TBC systems.The route taken to achieve these goals with APS TBC’s has been twofold. Firstly an alternative stabiliser has been chosen for the zirconium oxide system in the form of dysprosia. Secondly, control of the powder morphology and spray parameters has been used to generate coating microstructures with favourable levels of porosity.In terms of development of SPS TBC systems, these coatings are relatively new with many of the critical coating parameters not yet known. The focus of the work has therefore been to characterise their lifetime and thermal properties when produced in a complete TBC system.Results demonstrate that dysprosia as an alternative stabiliser gives a reduction in thermal conductivity. While small at room temperature and in the as produced state; the influence becomes more pronounced at high temperatures and with longer thermal exposure time. The trade-off for this lowered thermal conductivity may be in the loss of high temperature stability. Overall, the greatest sustained influence on thermal conductivity has been from creating coatings with high levelsof porosity.In relation to lifetime, double the thermo-cyclic fatigue (TCF) life relative to the industrial standard was achieved using a coating with engineered porosity. Introducing a polymer to the spray powder helps to generate large globular pores within the coating together with a large number of delaminations. Such a structure was shown to be highly resistant to TCF testing.SPS TBC’s were shown to have much greater performance relative to their APS counterparts in thermal shock life, TCF life and thermal conductivity. Columnar SPS coatings are a prospective alternative for strain tolerant coatings in gas turbine engines.
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| 24. |
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| 25. |
- Ericsson, Mikael, 1975-, et al.
(författare)
-
A look at the optimization of robot welding speed based on process modelling
- 2007
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Ingår i: Welding Journal. - 0043-2296. ; 86:8, s. 238-244
-
Tidskriftsartikel (refereegranskat)abstract
- Simulation tools to search for optimal process parameters are of great interest to reduce the number of experiments and thereby reduce cost and production time. In this paper, robot simulation has been used in combination with finite element simulations to optimize robot speed in order to minimize distortion while keeping complete joint penetration. In an earlier work performed by the authors, a finite element model was developed to predict heat transfer and residual stresses of parts with complex shapes. An interface between a robot simulation model and a finite element analysis model was also constructed. In this paper, an iterative method for robot speed optimization has been developed using MATLAB. The algorithm is designed to maintain complete joint penetration while maximizing productivity by utilizing the fastest weld speed. The method makes it possible to optimize the heat input to the component and thereby minimize component deformation for parts with complex shapes. The system was evaluated on stainless steel plates with varying thicknesses. Robot weld paths were defined off line and automatically downloaded to the finite element software where the optimization was performed. Simulations and experimental validations are presented.
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| 26. |
- Ericsson, Mikael, 1975-, et al.
(författare)
-
Off-line programming of robots for metal deposition
- 2005
-
Ingår i: Trends in welding research. - 0871708426 ; , s. 629-634
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Metal Deposition (MD) is a rapid prototyping technique to build parts by depositing metal in a required fashion. When a complex-shaped part is to be built, a simulation tool is needed to define robot trajectories. Three different simulation-based methods for robot trajectory generation are introduced and compared in this study. The methods are; reversed milling, adapted rapid prototyping and application programming in a computer aided robotics software. All methods were shown capable of creating robot paths for complex shapes, with the CAR software approach being the most flexible. Using this method, the geometry to be built is automatically sliced into layers and a robot path is automatically generated. The method was tentatively evaluated and appears to provide a powerful technique in the design and optimisation of robot paths for MD. Experiments showed that it is possible to manufacture fully dense parts using an Nd-Yag laser.
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| 27. |
- Ericsson, Mikael, 1975-, et al.
(författare)
-
Three-dimensional simulation of robot path and heat transfer of a TIG-welded part with complex geometry
- 2002
-
Ingår i: 11th International Conferences on Computer Technology in Welding. - : Society of Manufacturing Engineers, North American Manufacturing Research Institution. ; , s. 309-316
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The application of commercial software (OLP) packages for robot simulation, and programming, use interactive computer graphics, provide powerful tools for creating welding paths off-line. By the use of such software, problems of robot reach, accessibility, collision and timing can be eliminated during the planning stage. This paper describes how such software can be integrated with a numerical model that predicts temperature-time histories in the solid material. The objective of this integration is to develop a tool for the engineer where robot trajectories and process parameters can be optimized on parts with complex geometry. Such a tool would decrease the number of weld trials, increase productivity and reduce costs. Assumptions and principles behind the modeling techniques are presented together with experimental evaluation of the correlation between modeled and measured temperatures.
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| 28. |
- Ericsson, Mikael, 1975-, et al.
(författare)
-
Three Dimensional Simulation of Robot path, Heat Transfer and Residual Stresses of a TIG-welded Part with Complex Geometry
- 2002
-
Ingår i: Trends in Welding Research: Proceedings of the 6th International Conference. ; , s. 973-978
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper a system is presented that combines a robot off-line programming software with a finite element model that predicts temperature-time histories and residual stress distributions. The objective is to develop a tool for the engineer where robot trajectories and welding process parameters can be optimized on parts with complex geometry. The system was evaluated on a stainless steel gas turbine component. Robot weld paths were defined off-line and automatically downloaded to the finite element program, where transient temperatures and residual stresses were predicted. Temperature dependent properties and phase change, were included in the analysis. Assumptions and principles behind the modeling techniques are presented together with predicted temperature histories, residual stresses, and fixture forces.
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| 29. |
- Ericsson, Mikael, 1975-, et al.
(författare)
-
Three dimensional simulation of robot path, heat transfer and residual stresses of a welded part with complex geometry
- 2005
-
Ingår i: International jourrnal for the joining of materials. - 0905-6866. ; 17:2, s. 42-51
-
Tidskriftsartikel (refereegranskat)abstract
- In this article a simulation system is presented that combines computer aided robotics software used to define the welding operation, with a finite element model that predicts temperature-time histories and residual stress distributions for welding applications. The objective is to develop a tool for engineering processes in which robot trajectories and welding process parameters can be optimized off-line on parts with complex geometries. The system was evaluated on a stainless steel gas turbine component. Temperature dependent properties and phase change were included in the analysis. The turbine component was welded using an in-house TIG welding cell. The assumptions and principles that underpin the modeling techniques are presented together with predicted temperature histories, residual stresses, and fixture forces. Predicted residual stresses were compared with neutron diffraction measurements.
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| 30. |
- Eriksson, Robert, et al.
(författare)
-
Stresses and Cracking During Chromia-Spinel-NiO Cluster Formation in TBC Systems
- 2015
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 24:6, s. 1002-1014
-
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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| 31. |
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| 32. |
- Fasth, Angelica, et al.
(författare)
-
A comparative study of mechanical properties between HVOF-sprayed Maxphase materials
- 2009
-
Ingår i: Proceedings of the 22nd International Conference on Surface Modification Techniques. - 9780981706511 ; , s. 149-156
-
Konferensbidrag (refereegranskat)abstract
- Mn+1AXn –phases (MAX-phase materials) are ternary compounds consisting of an early transition metal (M), such as Ti or V, a p-element from group III-V (A) and C and/or N (X). The phases have a layered structure in which the A element form planes separated by MX slabs. This nanolaminated atomic arrangement gives rise to a unique set of properties. These properties in combination with a good match in thermal expansion between substrate and coating make MAX-phase materials challenging materials to extend the lifetime of thermal barrier coatings. Evaluation of properties of HVOF sprayed MAX-phase materials and to compare these properties with commercially used bond coat materials such as MCrAlY coatings is thus of great interest which was the aim of this study.The non-linear load displacement relationships and Young’s modulus for HVOF-sprayed Ti2AlC coatings and APSsprayed NiCoCrAlY coatings onto Hastalloy X substrates were determined using data from both Berkovich andspherical microindentation. Results between Berkovich and spherical microindentation measurements are comparedand discussed.
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| 33. |
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| 34. |
- Ganvir, Ashish, 1991-, et al.
(författare)
-
Characterization of Microstructure and Thermal Properties of YSZ Coatings Obtained by Axial Suspension Plasma Spraying (ASPS)
- 2015
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 24:7, s. 1195-1204
-
Tidskriftsartikel (refereegranskat)abstract
- The paper aims at demonstrating various microstructures which can be obtained using the suspension spraying technique and their respective significance in enhancing the thermal insulation property of a thermal barrier coating. Three different types of coating microstructures are discussed which were produced by the Axial Suspension Plasma Spraying. Detailed characterization of coatings was then performed. Optical and scanning electron microscopy were utilized for microstructure evaluations; x-ray diffraction for phase analysis; water impregnation, image analysis, and mercury intrusion porosimetry for porosity analysis, and laser flash analysis for thermal diffusivity measurements were used. The results showed that Axial Suspension Plasma Spraying can generate vertically cracked, porous, and feathery columnar-type microstructures. Pore size distribution was found in micron, submicron, and nanometer range. Higher overall porosity, the lower density of vertical cracks or inter-column spacing, and higher inter-pass porosity favored thermal insulation property of the coating. Significant increase in thermal diffusivity and conductivity was found at higher temperature, which is believed to be due to the pore rearrangement (sintering and pore coarsening). Thermal conductivity values for these coatings were also compared with electron beam physical vapor deposition (EBPVD) thermal barrier coatings from the literature and found to be much lower. © 2015 ASM International
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| 35. |
- Ganvir, Ashish, 1991-, et al.
(författare)
-
Comparative study of suspension plasma sprayed and suspension high velocity oxy-fuel sprayed YSZ thermal barrier coatings
- 2015
-
Ingår i: Surface and Coatings Technology. - : Elsevier. - 0257-8972. ; 268, s. 70-76
-
Tidskriftsartikel (refereegranskat)abstract
- Suspension Thermal Spraying is a relatively new thermal spaying technique to produce advanced thermal barrier coatings. This technique enables the production of much different performance thermal barrier coatings than conventional thermal spraying which uses solid powder as a feedstock material. In this work a comparative study is performed on four different types of thermal barrier coatings sprayed with two different thermal spay processes, suspension high velocity oxy-fuel spraying (SHVOF) and suspension plasma spraying (SPS) using two different water-based suspensions. Tests carried out include microstructural analysis with SEM, porosity analysis using weight difference by water infiltration, thermal conductivity measurements using laser flash analysis and lifetime assessment using thermo-cyclic fatigue tests. The results showed that SPS coatings were much porous and hence showed lower thermal conductivity than SHVOF coatings produced with the same suspension. From the thermo-cycling tests it was observed that the SPS coatings showed a higher lifetime than the SHVOF ones.
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| 36. |
- Ganvir, Ashish, 1991-
(författare)
-
Design of Suspension Plasma Sprayed Thermal Barrier Coatings
- 2018
-
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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| 37. |
- Ganvir, Ashish, 1991-, et al.
(författare)
-
Influence of Microstructure on Thermal Properties of Columnar Axial Suspension Plasma Sprayed Thermal Barrier Coatings
- 2015
-
Ingår i: Proceedings of the International Thermal Spray Conference. - : ASM International. - 9781510811546 ; , s. 498-505
-
Konferensbidrag (refereegranskat)abstract
- Suspension Plasma Spraying is a relatively new thermal spraying technique to produce advanced thermal barrier coatings. This technique enables the production of a variety of structures from highly dense, highly porous, segmented or columnar coatings. In this work a comparative study is performed on six different suspension plasma sprayed thermal barrier coatings which were produced using axial injection and different process parameters. The influence of coating morphology and porosity on thermal properties was of specific interest. Tests carried out include microstructural analysis with SEM, phase analysis using XRD, porosity calculation using Archimedes experimental setup, pore distribution analysis using mercury infiltration technique and thermal diffusivity/conductivity measurements using laser flash analysis. The results showed that columnar and cauliflower type coatings were produced by axial suspension plasma spraying process. Better performance coatings were produced with relatively higher overall energy input given during spraying. Coatings with higher energy input, lower thickness and wider range of submicron and nanometer sized pores distribution showed lower thermal diffusivity and hence lower thermal conductivity. Also, in-situ heat treatment did not show dramatic increase in thermal properties.
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| 38. |
- Ganvir, Ashish, 1991-, et al.
(författare)
-
Thermal conductivity in suspension sprayed thermal barrier coatings : Modelling and experiments
- 2016
-
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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| 39. |
- 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
-
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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| 40. |
- Gupta, Mohit Kumar, et al.
(författare)
-
A modelling approach to design of microstructures in thermal barrier coatings
- 2013
-
Ingår i: Journal of Ceramic Science and Technology. - 2190-9385. ; 4:2, s. 85-92
-
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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| 41. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
-
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
-
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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| 42. |
- Gupta, Mohit Kumar, et al.
(författare)
-
Design of Low Thermal Conductivity Thermal Barrier Coatings by Finite Element Modelling
- 2011
-
Ingår i: Surface Modification Technologies XXIV. ; , s. 353-365
-
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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| 43. |
- Gupta, Mohit Kumar, 1986-, et al.
(författare)
-
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
-
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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| 44. |
- 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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| 45. |
- 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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| 46. |
- Gupta, Mohit Kumar, et al.
(författare)
-
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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| 47. |
- Hansbo, Anita, 1960-, et al.
(författare)
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Models for the simulation of spray deposition and robot motion optimization in thermal spraying of rotating objects
- 1999
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Ingår i: Surface & Coatings Technology. - 0257-8972 .- 1879-3347. ; 122:2-3, s. 191-201
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we consider methods to simulate deposit build-up in thermal spraying and to optimize the robot motion so as to obtain the desired layer thickness. We derive a simplified mathematical model for spray deposition on a rotating large object with a smooth, rotationally symmetric, curved surface, yet allowing varying spray distance and direction. Further, we discuss how to obtain and incorporate an empirically determined deposit rate model. In particular, the simplified spray deposition model is chosen to make possible a reasonably cheap method to approximate a deposit rate from the results of layer thickness measurements. We also propose an iterative method to obtain good initial values for robot feed optimization. Numerical examples are presented. © 1999 Elsevier Science S.A.
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| 48. |
- Jiang, Janna, 1978-, et al.
(författare)
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Microindentation and Inverse Analysis to Characterize Elastic-Plastic Properties for Thermal Sprayed Ti2AlC and NiCoCrAlY
- 2009
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Ingår i: Journal of thermal spray technology (Print). - : Springer. - 1059-9630 .- 1544-1016. ; 18:2, s. 194-200
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Tidskriftsartikel (refereegranskat)abstract
- Elastic-plastic material properties for HVOF sprayed Ti2AlC (sprayed with Maxthal 211 powder) and plasma sprayed NiCoCrAlY coatings were investigated using modeling and experimental Berkovich microindentation. Optical microstructure evaluations were also performed. The theories of Hertz, Oliver and Pharr were combined with finite element analysis for extracting the material properties. Empirically based material models for both thermal sprayed Ti2AlC and NiCoCrAlY coatings are proposed.
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| 49. |
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| 50. |
- Jiang, Janna, 1978-, et al.
(författare)
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Numerical modelling of the compression behaviour of single-crystalline MAX-phase materials
- 2010
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Ingår i: Advanced materials research. - : Trans Tech Publications. - 1022-6680. ; 89-91, s. 262-267
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Tidskriftsartikel (refereegranskat)abstract
- In this article a numerical model to describe the mechanical behaviour of nanophased singlecrystalline Ti3SiC2 is proposed. The approach is a two dimensional finite element periodic unit cell consisting of an elastic matrix interlayered with shear deformable slip planes which obey the Hill's yield criterion. The periodic unit cell is used to predict compression material behaviour of Ti3SiC2 crystals with arbitrary slip plane orientations. Stress strain relationships are derived for Ti 3SiC2, and the effect of slip plane volume fraction as well as orientation of the slip planes are investigated. The two main deformation mechanisms of the material namely; ordinary slip and so called kinking are considered in the study.
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