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Auswahl der wissenschaftlichen Literatur zum Thema „Cold kinetic deposition“
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Zeitschriftenartikel zum Thema "Cold kinetic deposition"
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Yu, Hai Jiao, Yu Ya Wang, Jun Xue und Zun Wang. „An Advanced Metal Deposition Technique-Kinetic Metallization“. Materials Science Forum 817 (April 2015): 510–15. http://dx.doi.org/10.4028/www.scientific.net/msf.817.510.
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Kinetic metallization (KM) is a sonic cold spray metal deposition technique, which offers promise as a way to produce coatings with a wild range of thickness. It is a solid-state process, from which the obtained coating is oxide free, high compactness (the porosity ratio may less than 0.1%), and has a strong bonding with the matrix. KM now is extensively applied in many fields, such as part/structure dimensional repair, solar battery manufacture, corrosion resistance and protection, wear resistance, oxidation resistance, and polymer spray. The present work presented the elements and advantages of KM, related it with high velocity oxy-fuel (HVOF) and common cold spray (CS), and reviewed the progress of KM over the two decades. Finally, the further development of the KM was discussed.
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Koivuluoto, Heli, Andrea Milanti, Giovanni Bolelli, Jyrki Latokartano, Francesco Marra, Giovanni Pulci, Jorma Vihinen, Luca Lusvarghi und Petri Vuoristo. „Structures and Properties of Laser-Assisted Cold-Sprayed Aluminum Coatings“. Materials Science Forum 879 (November 2016): 984–89. http://dx.doi.org/10.4028/www.scientific.net/msf.879.984.
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In the cold spray process, solid particles impact on a surface with high kinetic energy, deform plastically and form a coating. This enables the formation of pure and dense coating structures. Even more, coating performance and deposition efficiency can be improved by assisting the process with a laser. Laser-assisted cold spraying (LACS) has shown its potential to improve coating properties compared with traditional cold spraying. In this study, coating quality improvement was obtained by using a co-axial laser spray (COLA) process which offers a new, cost-effective laser-assisted cold spray technique, for high-quality deposition and repair. In the COLA process, the sprayed surface is laser heated while particles hit the surface. This assists the better bonding between particles and substrate and leads to the formation of tight coating structures. This study focuses on the evaluation of the microstructural characteristics and mechanical properties (e.g., hardness and bond strength) of LACS metallic coatings.
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Lee, Jae Chul, Doo Man Chun, Sung Hoon Ahn und Caroline S. Lee. „Material Properties of Thick Aluminum Coating Made by Cold Gas Dynamic Spray Deposition“. Key Engineering Materials 345-346 (August 2007): 1097–100. http://dx.doi.org/10.4028/www.scientific.net/kem.345-346.1097.
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Cold gas dynamic spray is a relatively new coating process by which coatings can be produced without significant heating during the process. Cold gas dynamic spray is conducted by powder sprayed using supersonic gas jet, and generally called the kinetic spray or cold spray. Its low process temperature can minimize the thermal stress and also reduce the deformation of the substrate. In this study, thick or macro scale deposition was studied while most researches on cold-spray have focused on micro scale coating. Measured material properties of macro scale deposition layer showed that elastic modulus and hardness were lower and electrical resistivity was higher than those of reference substrate material. The main causes of changed material properties were investigated by FE-SEM (Field Emission Scanning Electron Microscope) and EDS (Energy Dispersive X-ray Spectrometer) data. In this result, porous micro structure generated by imperfect plastic deformation might cause decrease in elastic modulus and hardness of the deposition layer by cold spray, and oxidized Al particles increased the electrical resistivity.
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W. J., W. J. „Effects of Metal Particles on Cold Spray Deposition onto Ti-6Al-4V Alloy via Abaqus/Explicit“. Journal of Engineering Sciences 7, Nr. 2 (2020): E19—E25. http://dx.doi.org/10.21272/jes.2020.7(2).e4.
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Titanium alloy is the main structural material of the aerospace system component. About 75 % of titanium and titanium alloys in the world are used in the aerospace industry. Hence, it is of great significance to study the surface deposition characteristics by cold spraying technology, taking Ti-6Al-4V alloy as an example, smoothed particle hydrodynamics (SPH) method in Abaqus/Explicit was used to spray aluminum, Ti-6Al-4V, copper, tungsten alloy (W alloy) and titanium particles onto Ti-6Al-4V substrate. The simulation results show that the deposition effect is good over 600 m/s, and higher energy is obtained for Ti-6Al-4V particles with the same properties as the matrix. For aluminum, Ti-6Al-4V, copper, W alloy, and titanium particles with different properties, under the same initial speed condition, the greater the density of the material, the deeper the foundation pit. W Alloy has the largest initial kinetic energy, the deepest foundation pit, and better surface bonding performance. The aluminum particle has the smallest initial kinetic energy, the shallowest foundation pit. However, the deposition effect of multiple aluminum particles has not improved. The collision process’s kinetic energy is transformed into internal energy, frictional dissipation, and viscous dissipation. Besides, the internal energy is mainly plastic dissipation and strain energy. Therefore, it is recommended to use Ti-6Al-4V, copper, nickel, W alloy, and titanium particles for different occasions, such as Ti-6Al-4V substrate surface restorative and protective coatings. Pure aluminum particles are not recommended.
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Oyinbo, Sunday Temitope, und Tien-Chien Jen. „Feasibility of numerical simulation methods on the Cold Gas Dynamic Spray (CGDS) Deposition process for ductile materials“. Manufacturing Review 7 (2020): 24. http://dx.doi.org/10.1051/mfreview/2020023.
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The techniques of cold gas dynamic spray (CGDS) coating involve the deposition of solid, high speed micron to nano particles onto a substrate. In contrast to a thermal spray, CGDS does not melt particles to retain their physico-chemical properties. There have been many advantages in developing microscopic analysis of deformation mechanisms with numerical simulation methods. Therefore, this study focuses on four cardinal numerical methods of analysis which are: Lagrangian, Smoothed Particles Hydrodynamics (SPH), Arbitrary Lagrangian-Eulerian (ALE), and Coupled Eulerian-Lagrangian (CEL) to examine the Cold Gas Dynamic Spray (CGDS) deposition system by simulating and analyzing the contact/impact problem at deformation zone using ductile materials. The details of these four numerical approaches are explained with some aspects of analysis procedure, model description, material model, boundary conditions, contact algorithm and mesh refinement. It can be observed that the material of the particle greatly influences the deposition and the deformation than the material of the substrate. Concerning the particle, a higher-density material such as Cu has a higher initial kinetic energy, which leads to a larger contact area, a longer contact time and, therefore, better bonding between the particle and the substrate. All the numerical methods studied, however, can be used to analyze the contact/impact problem at deformation zone during cold gas dynamic spray process.
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Tului, Mario, Cecilia Bartuli, Alessia Bezzon, Angelo Luigi Marino, Francesco Marra, Susanna Matera und Giovanni Pulci. „Amorphous Steel Coatings Deposited by Cold-Gas Spraying“. Metals 9, Nr. 6 (12.06.2019): 678. http://dx.doi.org/10.3390/met9060678.
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Cold-gas spray (CGS) deposition of amorphous steel coatings starting from a commercial feedstock powder containing boron, tungsten, and silicon was investigated. Microstructural characterization, carried out by X-ray diffraction (XRD), transmission electron microscopy, and backscattered electron diffraction (EBSD) analysis, confirmed the amorphous nature of deposited coatings. The amorphization phenomenon is related to high-strain/strain-rate deformation with shear instability caused by very high particle kinetic energy, with a mechanism that resembles the severe plastic deformation process. The CGS coatings were heat-treated at temperatures ranging from 650 to 850 °C to induce partial recrystallization. The effect of nanocrystal nucleation and growth on the hardness of the coatings was investigated, and the hardness of heat-treated samples was found to increase with respect to as-sprayed coatings, outperforming conventional high-velocity oxy-fuel (HVOF) deposits. Hardness was found to decrease after prolonged (<90 min) or higher temperature (>750 °C) exposures.
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Spencer, Kevin, Daniel Fabijanic und Ming Xing Zhang. „Cold Spray of Al-MMC Coatings on Magnesium Alloys for Improved Corrosion and Wear Resistance“. Materials Science Forum 618-619 (April 2009): 377–80. http://dx.doi.org/10.4028/www.scientific.net/msf.618-619.377.
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Cold spray coatings are considered promising for surface protection of Mg alloys from wear and corrosion since the process temperature is low enough to avoid oxidation of the Mg or any adverse affects on artificial ageing heat treatments. A special version of cold spray known as Kinetic Metallization has been used to produce pure Al and Al alloy metal matrix composite (MMC) coatings on AZ91 Mg alloy substrates in the present work. This surface treatment produces dense coatings with high adhesive and cohesive strength, which have substantially higher hardness and wear resistance than the AZ91 substrate material. The influence of coating composition and subsequent heat treatment on wear and corrosion performance have been investigated, using pin-on-disc wear tests, salt spray testing and electrochemical polarisation techniques. The heat treatment of the cold spray coatings is compatible with the solutionising and T6 ageing heat treatment of AZ91Mg. The results show that cold spray deposition of MMC coatings is a simple and effective technique for improving the surface properties of Mg alloys, both in the as-cast and in the heat treated condition
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Koivuluoto, Heli, Jussi Larjo, Danilo Marini, Giovanni Pulci und Francesco Marra. „Cold-Sprayed Al6061 Coatings: Online Spray Monitoring and Influence of Process Parameters on Coating Properties“. Coatings 10, Nr. 4 (03.04.2020): 348. http://dx.doi.org/10.3390/coatings10040348.
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Process optimization and quality control are important issues in cold spraying and coating development. Because the cold spray processing is based on high kinetic energy by high particle velocities, online spray monitoring of particle inflight properties can be used as an assisting process tool. Particle velocities, their positions in the spray jet, and particle size measurements give valuable information about spraying conditions. This, in turn, improves reproducibility and reliability of coating production. This study focuses on cold spraying of Al6061 material and the connections between particle inflight properties and coating characteristics such as structures and mechanical properties. Furthermore, novel 2D velocity scan maps done with the HW CS2 online spray monitoring system are presented as an advantageous powder and spray condition controlling tool. Cold spray processing conditions were similar using different process parameters, confirmed with the online spray monitoring prior to coating production. Higher particle velocities led to higher particle deformation and thus, higher coating quality, denser structures, and improved adhesions. Also, deposition efficiency increased significantly by using higher particle velocities.
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Bala, Niraj, Harpreet Singh und S. Prakash. „An Overview of Cold Spray Technique“. Materials Science Forum 561-565 (Oktober 2007): 2419–22. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.2419.
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The Cold spray or cold gas dynamic spraying is the new progressive step in the direction of development of high kinetic energy coating processes. The cold spray is a method for coating substrates under atmospheric conditions. In this process micron sized solid particles are accelerated and transported to substrates by means of supersonic free jets. Upon impacting the substrates, particles stick to the surface and form coatings which possess very low porosity. The paper outlines the principles involved in cold spray method and the equipment used for the technique. The cold spray method is related to classical thermal spray methods but it has some interesting additional features, which has been discussed in the paper. A fundamental feature of cold spray method i.e. concept of critical velocity along with the plausible mechanism theory responsible for the deposition of coating has been discussed briefly. Successful applications of cold spray process and its environment friendly aspect has been elaborated. It is reported that well founded cold spray technology will be able to compete for a good market share of VPS/PVD coatings in various fields like power, electronic/electrical, biotechnology, turbines and other industries. The cold spray process is still primarily in the research and development stage and only now becoming commercially available, and has been accepted as a new and novel thermal spray technique mainly in developed countries. The technology has great potential for future research especially with reference to its application to real industrial solution.
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Krumdieck, S. „Kinetic model of low pressure film deposition from single precursor vapor in a well-mixed, cold-wall reactor“. Acta Materialia 49, Nr. 4 (Februar 2001): 583–88. http://dx.doi.org/10.1016/s1359-6454(00)00356-6.
Der volle Inhalt der QuelleDissertationen zum Thema "Cold kinetic deposition"
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Šteiniger, Jakub. „Hodnocení využití technologie studené kinetické depozice na materiálech používaných v elektrotechnice“. Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-442436.
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The master´s thesis deals with a process called cold kinetic deposition technology. Using this technology, a copper layer was formed on a sample with an aluminium base by high-pressure cold spraying at a pressure of 25 bar. In the experimental part, the influence of corrosion degradation in the salt chamber was assessed at the time cycles of 100 h, 200 h and 300h, where changes in internal and surface resistances before and after corrosion were measured. Subsequently, the analysis of corrosion products was performed, where the extent of corrosion attack was determined using an electron microscope. These methods led to a final evaluation of the boundary limits of the applied coating layer by cold kinetic deposition, after the effect of corrosion. Finally, a theoretical application of this technology was suggested. It was discovered that the sample placed and left in the corrosion chamber for the longest time was the most affected by corrosion. Finally, a theoretical application of cold kinetic deposition was proposed.
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Sámel, Maroš. „Využití technologie studené kinetické depozice na materiálech používaných v elektrotechnice“. Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-442477.
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The purpose of this diploma thesis is to get a better understanding of cold kinetic deposition (cold spray), principles of functioning of this method followed by an evaluation of advantages and disadvantages of cold spray and its comparison to conventional thermal methods and a simple summary of the practical use of cold spray with respect to different materials. Next there is a summary of the properties and uses of frequently applied metals in electrical engineering, aluminium and copper, description of metal corrosion and an understanding of the diagnostic method of acoustic emission. In the practical part, a sample with copper cold spray coating on aluminium substrate was created. Following, this sample was split for corrosion tests, where the split samples were exposed to a corrosive environment for different times of exposure. The extent of corrosion degradation of the samples was evaluated by acoustic emission and metallographic analysis for corrosion-loaded samples for 100, 200 and 300 hours. In the end, an illustrative design of the application of the cold spray technology was created.
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Wu, Bo-Yu, und 吳柏諭. „Kinetics study and material analysis of metalorganic chemical vapor deposition copper films-Precursor: (hfac)CuI(COD)“. Thesis, 2006. http://ndltd.ncl.edu.tw/handle/ygbv29.
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碩士國立臺灣科技大學
化學工程系
94
Growth kinetics and material analysis of copper films with metalorganic chemical vapor deposition (MOCVD) reaction system using hexafluoroacetonate-Cu(I)-1,5-cyclooctadiene (hfac)CuI(COD) as the precursor was studied. In this study, the kinetic data of MOCVD Cu thin films as a function of deposition temperature and partial pressure of precursor were investigated. In addition, the effect of different deposition temperatures on the surface morphology、crystal structure、microstructure and film electricity was discussed. It was found that the growth rate of copper between 120~190℃was written surface reaction limited regime with the value of activation energy as 18.32KJ/mol. Above 190℃, growth rate was in the mass transfer limited regime with an activation energy of 0.652KJ/mol. Through the analysis on the growth kinetics, the kinetic model of chemical vapor deposition as follows: -ra=k2Pa^2/(1+K1Pa)^2 where k2=6.96x106(nm*min-1*torr-2)，K1=324.54(torr-1) When the deposition temperature was 190℃, the best copper film electricity was obtained. The electricity of copper film, deposited at 190℃ was better than that of the copper films of deposited at 140℃, because the former could grow the flatter and denser copper films, and stronger preferred orientation of Cu(111). As a result, this lowered electron scattering of grain boundary. The electricity of copper films deposited at 230℃ is worse than that of copper films deposited at 190℃, because the former had large voids in the films due to huge copper grains. Consequently, this caused higher surface electron scattering.
Buchteile zum Thema "Cold kinetic deposition"
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Bailyn, Charles D. „Outflows and Jets“. In What Does a Black Hole Look Like? Princeton University Press, 2014. http://dx.doi.org/10.23943/princeton/9780691148823.003.0003.
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This chapter looks at the presence of outflows or jets, a somewhat unexpected feature of accretion flows. There is strong observational evidence that some fraction of the infalling material reverses course near the accreting object and is shot out perpendicularly to the accretion disk. In some cases, narrow collimated beams of emission are observed emerging from the central-most regions of galaxies and continuing across the whole of the galaxy, depositing their energy hundreds of kiloparsecs away from their origin. These phenomena are sometimes described as jets “emerging” from a black hole. This parlance is misleading—the jets do not, and indeed could not, emerge from inside the event horizon. Rather, some mechanism redirects the energy generated by the accretion process into a fraction of the infalling material and provides enough bulk kinetic energy for the material to escape the accretion process before the material enters the event horizon.
Konferenzberichte zum Thema "Cold kinetic deposition"
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Celeste, Geoffrey, Vincent Guipont und Djamel Missoum-Benziane. „Investigation of Agglomerated and Porous Ceramic Powders Suitable for Cold Spray“. In ITSC2021, herausgegeben von F. Azarmi, X. Chen, J. Cizek, C. Cojocaru, B. Jodoin, H. Koivuluoto, Y. C. Lau et al. ASM International, 2021. http://dx.doi.org/10.31399/asm.cp.itsc2021p0139.
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Abstract Cold gas spraying is a solid-state deposition process developed for metallic powders as feedstock materials. For ceramic materials; such low temperature-high velocity kinetic process is still questionable but could have interesting advantages. In the CERASOL project (ANR-19-CE08-0009); the nature and the architecture of porous ceramic powders involving agglomerated sub-micrometric grains are investigated. To that purpose; three oxide ceramics powders (alumina; zirconia and yttria) have been prepared for cold spray. These powders were analyzed in order to assess their architecture (composition; particle size; porosity; density; crystallite sizes…). Preliminary cold spray experiments were carried out implementing velocities measurements for various stand-off distances and spraying of coupons with line experiments. The characteristics of the deposited layers have been examined by SEM and XRD in order to discuss the role of the powder architecture on the impact behavior of the nanostructured agglomerated particles. The role of the gas stream that affects the kinetic and the trajectory of the particles are also discussed.
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Gao, Hong, Liangju Zhao, Danling Zeng und Lijuan Gao. „Molecular Dynamics Simulation of Au Cluster Depositing on Au Surface in Cold Gas Spray“. In 2007 First International Conference on Integration and Commercialization of Micro and Nanosystems. ASMEDC, 2007. http://dx.doi.org/10.1115/mnc2007-21609.
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Cold gas spray is a relatively new coating technique by which coatings can be formed without significant heating of the sprayed powder. In contrast to the conventional thermal spray processes, such as flame, arc, and plasma spraying, in cold spraying there is no melting of particles prior to impact on the substrate. In cold spray, particles are accelerated to a very high velocity by a flowing gas with supersonic speed and the temperature of spray particles is much lower than its melting point. However, being accomplished in so short an interval, the impact and deposition processes are difficult to be observed by experimental ways. Using molecular dynamics simulation, the deposition of nano-scale Au clusters on Au (001) surface was studied. The many-body potential is used to simulate the interatomic force between the atoms. By taking “snapshot”, the impact, deposition process and the final appearances of the cluster and the substrate were observed directly. It is found that both the substrate and the cluster deform and lose the crystalline structure. But after reconstruction and relaxation, both of them recover the crystalline structure. By calculating the temperatures of the substrate and the local area influenced by impinging, it is found that the melt phenomenon occurs during impact and deposition, whereas the temperature of the rest region of the substrate is still below the melt point. In addition, the influence factors on deposition, such as incident velocity and the size of the cluster, are discussed in the paper. Simulation results show that the higher incident velocity or the larger size of the cluster could result in stronger interaction between the substrate and the cluster owing to the higher kinetic energy of the cluster.
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Ren, Baihua, und Jun Song. „Peridynamic Simulation of Particles Impact and Interfacial Bonding in Cold Spray Process“. In ITSC2021, herausgegeben von F. Azarmi, X. Chen, J. Cizek, C. Cojocaru, B. Jodoin, H. Koivuluoto, Y. C. Lau et al. ASM International, 2021. http://dx.doi.org/10.31399/asm.cp.itsc2021p0396.
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Abstract Recently, cold spray (CS) technology has attracted extensive interest as an alternative to thermal spray methods to build a coating, which uses high kinetic energy solid particles to impact and adhere to the substrate. To date, numerous numerical studies have been carried out to investigate the deposition processes and associated mechanisms during multiple particle impact in CS. However, in the commonly used numerical techniques, the individual powder particles are often treated separately from one another, thus fail to properly consider the adhesion mechanisms during deposition. In this study, we propose a new numerical approach on base of peridynamics (PD), which incorporates interfacial interactions as a part of constitutive model to capture deformation, bonding and rebound of impacting particles in one unified framework. Two models are proposed to characterize the adhesive contacts: a) a long-range Lenard-Johns type potential that reproduce the mode I fracture energy by suitable calibrations, and b) a force - stretch relation of interface directly derived from the bulk materials mode I fracture simulations. The particle deformation behavior modeled by the peridynamic method compares well with the benchmark finite element method results, which indicates the applicability of the peridynamic model for CS simulation. Furthermore, it is shown that the adhesive contact models can accurately describe interfacial bonding between the powder particles and substrate.
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Yu, Minjae, Hiroki Saito, Chrystelle Bernard, Yuji Ichikawa und Kazuhiro Ogawa. „Influence of the Low-Pressure Cold Spray Operation Parameters on Coating Properties in Metallization of Ceramic Substrates Using Copper and Aluminum Composite Powder“. In ITSC2021, herausgegeben von F. Azarmi, X. Chen, J. Cizek, C. Cojocaru, B. Jodoin, H. Koivuluoto, Y. C. Lau et al. ASM International, 2021. http://dx.doi.org/10.31399/asm.cp.itsc2021p0147.
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Abstract The low-pressure cold spray (LPCS) technique could be an attractive method for copper metallization of ceramic substrates to power module applications due to its one-step quick and lowtemperature process. However; manufacturing pure copper coating on a ceramic substrate by LPCS is still challenging due to its low deposition efficiency and poor adhesion strength. Our previous study successfully demonstrated the possibility of obtaining a zirconia substrate's metallization by using a feedstock powder mixture of copper and aluminum. However; the copper content in the coating was not high enough for power module applications. Therefore; in this study; we aim to improve the copper content in the coating layer composed of the composite powder deposited by LPCS on alumina and zirconia substrates. The influence of the gas pressure and standoff distance on the copper content and coating thickness are evaluated. The coating build-up with a high copper content and thickness is highly dependent on the kinetic energy of particles; enhanced by high gas pressure and short stand-off distance.
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Dai, S., J. P. Delplanque, E. J. Lavernia und R. H. Rangel. „Modeling of Reactive Spray Atomization and Deposition“. In ITSC 1998, herausgegeben von Christian Coddet. ASM International, 1998. http://dx.doi.org/10.31399/asm.cp.itsc1998p0341.
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Abstract Recent experimental investigations of reactive spray deposition of aluminum alloys have indicated that oxides could not be detected for atomization gas oxygen contents lower than 10%. In order to elucidate this behavior, an analysis of the oxidation kinetics during reactive spray deposition based on the Mott-Cabrera theory of oxidation is proposed herein. A linear growth law is obtained that indicates that the oxide growth rate decreases with decreasing temperature or oxygen pressure. Furthermore, the oxide growth rate is found to decrease faster at low oxygen pressure with decreasing temperature as well as at low temperature with decreasing oxygen pressure. Calculations of the width of oxide stringers as a function of oxygen content and superheat temperature based on this analysis are in good agreement with the experimental observations.
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Weiss, H. J., V. T. Turitto und H. R. Baumgartner. „FACTORS INFLUENCING FIBRIN DEPOSITION ON SUBENDOTHELIUM“. In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1642950.
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During the past several years, we have initiated studies to determine the role of plasma factors and platelets, and the properties of the blood vessel, which influence the activation of the coagulation mechanism on the subendothelium. Studies were performed by exposing everted segments of de-endothelialized rabbit aorta, mounted in a perfusion chamber, to non-anticoagulated human blood for 5 to 10 minutes under a range of flow conditions, and measuring fibrin and platelet deposition on the subendothelium, and fibrinopepstide A (FPA) levels in post-chamber blood. In normal subjects, platelet deposition increased progressively with increasing shear rates (50-2600 sec-1 ), whereas fibrin deposition and FPA levels decreased sharply at shear rates greater than 650 sec-1 . To examine the role of plasma coagulation factors, we utilized a shear rate of 650 sec-1 to study patients with severe deficiencies of factors XII, XI, IX or VIII. In contrast to the partial thromboplastin time (PTT), which was most strikingly abnormal in patients with factor XII or XI deficiency, fibrin deposition and FPA levels were greater in patients deficient in factor XII or XI than in those with factor VIII or IX deficiency. In addition, we observed smaller platelet thrombi in hemophilia (but not afibrinogenemia), suggesting that thrombin influenced the formation of platelet thrombi under these shear conditions. The findings suggested that tissue factor-Vila activation of factor IX could be important in mediating fibrin deposition on subendothelium and might explain why patients with factor XII deficiency (and some with factor XI deficiency) do not bleed. Initial studies to demonstrate tissue factor activity in subendothelium were inconclusive. More recently, utilizing shorter (1.5, 2 and 3 min) perfusion periods, we have observed decreased fibrin deposition and FPA levels in patients with factor VII deficiency and we have obtained further support for the presence of tissue factor in subendothelium in experiments utilizing a monoclonal antibody to tissue factor. Our studies suggest that activation of factor IX by tissue factor-Vila could account for the results obtained in patients with plasma coagulation defects. Direct experimental verification of this hypothesis will require more extensive studies on the kinetics governing the activation of coagulatjon factors on the subendothelium. In subsequent studies, we examined the role of platelets in mediating fibrin deposition. At a shear rate of 650 sec-1 we found (utilizing patients with thrombocytopenia) that platelets were required for fibrin deposition ; little or no fibrin was deposited on the subendothelium when platelet adhesion was less than 4%, corresponding to blood platelet counts less than 5000/ul. Studies performed in patients with functional platelet disorders provided additional information on the specific platelet properties that contribute to fibrin deposition at this shear rate. Decreased fibrin deposition was observed in a patient with Scott Syndrome, a disorder characterized by an impaired capacity of the platelets to catalyze the conversion of factor X to factor Xa (in the presence of factor IXa and VIII) and prothrombin to thrombin (in the presence of factor Va), the latter defect owing to a decreased factor Xa-binding capacity of the platelets. In contrast to the findings in Scott Syndrome, both fibrin deposition and FPA values were completely normal (and possibly increased) in patients with glycoprotein Ilb/IIIa deficiency. In patients with glycoprotein lb deficiency, the major defect was an impaired association of fibrin with platelets, but not subendothelium. The findings in patients with functional platelet disorders indicate that a monolayer of platelets (including those deficient in glycoprotein Ilb/IIIa) is completely active in promoting fibrin deposition on subendothelium. In addition, they suggest that an agent capable of inducing a platelet defect similar to that observed in Scott Syndrome might prevent platelet-fibrin thrombi at shear rates (200-800 sec-1 ) comparable to those in the coronary circulation. Studies performed at a variety of shear rates in both normal subject^ and patients with platelet disorders suggested that, under the conditions used, platelets were essential for fibrin formation at intermediate (650 sec-1 ), but not low (50 sec-1 ) shear rates. Since platelets have been shown to bind activated coagulation proteins (such as factor Xa, Va, and IXa) to their surface, the presence of adherent platelets on the subendothelium could, with increasing shear rates, serve to maintain activated coagulation proteins in the .boundary layer at a concentration that would otherwise be reduced through convective diffusion in their absence. Thus, at low shear rates (50 sec-1 ), the concentration of activated coagulation factors in the boundary layer might be sufficient to support fibrin deposition despite the absence of platelets, whereas at very high shear rates (2,600 sec-1 and above), even the presence of platelets is insufficient to maintain the required concentration. The shear-dependent defect of fibrin formation that we observed in Scott Syndrome is consistent with such a theory. The results of our various studies demonstrate the complex role of blood flow, plasma coagulation factors, specific platelet properties, and the procoagulant properties (tissue factor) of the vessel in mediating subendothelium-induced coagulation and suggest further experiments for studying the mechanisms involved.
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Papa, Stefano, Giuseppe di Gironimo, Federica Casoria und Gioacchino Micciché. „Virtual Prototyping and Simulation of Robotic Devices and Maintenance Procedures for Remote Handling Activities in the Access Cell of DONES“. In 2018 26th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/icone26-82390.
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The paper describes the activities of conceptual design of tools and procedures and the virtual simulation of the Remote Handling (RH) tasks provided in the maintenance of the systems present in the Access Cell (AC) of DONES (DEMO Oriented Neutron Source) facility. In particular, the RH maintenance of the Target Assembly (TA) is critical because of its position in the most severe region of neutron irradiation, the Test Cell (TC), where the material specimen are tested to understand the degradation of the materials properties throughout the reactor operational life. The main RH maintenance activity includes the replacement of the entire TA and the cleaning of the surfaces of connection in the TC. The cleaning operation is fundamental because it allows the removal of any lithium solid deposition from the surfaces: any further deposition on the surfaces could compromise the sealing of the TA. The RH is based on the idea of a reconfigurable modular chain of devices connected to the Access Cell Mast Crane (ACMC) located in the AC. To increase the modularity and to reduce the costs of the Remote Handling System (RHS), a telescopic boom is used equipped with a Gripper Change System (GCS) that allows the use of different end effectors. To perform the tasks, a Parallel Kinematic Manipulator (PKM) and a Robotic Arm (RA) are proposed, allowing the tools to move with more degree of freedom in the AC space. The modeling of the devices and the 3D kinematic simulations maintenance operations tasks were simulated and tested in virtual reality environment, aimed at developing and validating the implemented maintenance procedures, in collaboration with the IDEAinVR Laboratory of CREATE/University of Naples Federico II, and the research center at ENEA Brasimone, Italy.
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Rotavera, Brandon, Nolan Polley, Eric L. Petersen, Kara Scheu, Mark Crofton und Gilles Bourque. „Ignition and Combustion of Heavy Hydrocarbons Using an Aerosol Shock-Tube Approach“. In ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-22844.
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Results from a heterogeneous shock-tube approach recently demonstrated at Texas A&M University, wherein a hydrocarbon fuel is introduced in liquid phase with gaseous oxidizer, are presented. The shock tube has been designed for controlled measurement of ignition delay times, sooting phenomena, radical species concentrations, time-dependent species profiles, and nanoparticle-aided combustion using heavy hydrocarbons which are difficult to study using the traditional shock tube approach. Aerosol is generated in a high-vacuum manifold positioned 4-m from the endwall where optical and pressure-based diagnostics are stationed. The approach reduces the propensity for fuel-film deposition near the endwall avoiding optical and/or kinetic disturbances that could result. The aerosol enters the shock tube initially as a two-phase flow of liquid fuel and gaseous oxidizer/inert gas. Liquid droplets partially evaporate while resident in the shock tube, prior to shock wave generation, and are then completely vaporized behind the incident shock wave. Behind the reflected shock wave, then, resides a pure gas-phase fuel and oxidizer mixture. The primary benefit of the aerosol shock tube approach is the ability to inject fuels of low vapor pressure at high or low concentrations. The classic shock-tube approach introduces gas-phase constituents only, and has difficulty accommodating low vapor-pressure liquids, except when component partial pressures are much lower than what is usually required. In the present work, n-heptane aerosol (C7H16, Pvap, 20 °C ∼ 35 torr), was generated with O2/Ar carrier gas and dispersed in the shock tube in a uniform manner. Stoichiometric ignition delay times with temperature varied from 1240 K to 1600 K and pressure maintained near 2.0 atm are compared to gas-phase data at similar conditions and a chemical kinetic model for heptane combustion. Excellent agreement was found between the two-phase aerosol approach and the classical method involving vapor-phase n-heptane and pre-mixed gases. The measured activation energy for the stoichiometric mixture at 2.0 atm (EA = 42.3 kcal /mol), obtained with the two-phase technique, compares well with the literature value.
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Suman, Alessio, Nicola Casari, Elettra Fabbri, Michele Pinelli, Luca di Mare und Francesco Montomoli. „Gas Turbine Fouling Tests: Review, Critical Analysis and Particle Impact Behavior Map“. In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-76934.
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Fouling affects gas turbine operation and airborne or fuel contaminants, under certain conditions, become very likely to adhere to surfaces if impact takes place. Particle sticking implies the change in shape in terms of roughness of the impinged surface. The consequences of these deposits could be dramatic: these effects can shut an aircraft engine down or derate a land-based power unit. This occurrence may happen due to the reduction of the compressor flow rate and the turbine capacity, caused by a variation in the HPT nozzle throat area (geometric blockage due to the thickness of the deposited layer and the aerodynamic blockage due to the increased roughness, and in turn boundary layer). Several methods to quantify particle sticking have been proposed in literature so far, and the experimental data used for their validation vary in a wide range of materials and conditions. The experimental analyses have been supported by (and have given inspiration to) increasingly realistic mathematical models. Experimental tests have been carried out on (i) a full scale gas turbine unit, (ii) wind tunnel testing or hot gas facilities using stationary cascades, able to reproduce the same conditions of gas turbine nozzle operation and finally, (iii) wind tunnel testing or hot gas facilities using a coupon as the target. In this review, the whole variety of experimental tests performed is gathered and classified according to composition, size, temperature and particle impact velocity. Using particle viscosity and sticking prediction models, over seventy (70) tests are compared with each other and with the model previsions providing a useful starting point for a comprehensive critical analysis. Due to the variety of test conditions, the related results are difficult to be pieced together due to differences in particle material and properties. The historical data of particle deposition obtained over thirty (30) years are classified using particle kinetic energy and the ratio between particle temperature and its softening temperature. Qualitative thresholds for the distinction between particle deposition, surface erosion and particle break-up, based on particle properties and impact conditions, are identified. The outcome of this paper can be used for further development of sticking models or as a starting point for new insight into the problem.
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Austin, Morgan, Thao Tran-Le, Robert Kunz, Timothy Simpson und Rui Ni. „Experimental and Computational Studies of Particle Scavenge Flow in Direct Laser Metal Sintering“. In ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-4965.
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Abstract Powder Bed Fusion (PBF) cross-flow systems are designed to flow gas across the build plane and entrain metallic powder particles that are ejected during the build, due to the thermal and attendant released kinetic energy of the laser melt process. It is important that these particles be removed from the build chamber so that they do not redeposit on the build surface, as this uncontrolled particle deposition can degrade the part quality. Optimal design of these sub-systems involves tailoring a cross-flow jet such that most of the ejected particles are entrained and removed from the build chamber, while the top layer of particles that are freshly spread on the build plate are not entrained. Accordingly, a combined experimental and CFD study has been executed with the goal of developing engineering design guidance for these cross-flow systems. The closed loop small footprint wind tunnel incorporates a 0.305 m × 0.305 m × 0.915 m test section, a variable height build plate upon which powder can be spread, a variable geometry inlet nozzle, and variable flow rate so that a variety of cross-flow configurations can be tested. Helium bubble particle tracking velocimetry (PTV) was used to characterize the single-phase flow at a number of these operating conditions / configurations. In addition, high speed videography was used to study particle liftoff and entrainment at these same conditions. Using these measurements and attendant CFD models, critical particle liftoff Shield numbers were obtained using CFD predictions of friction velocity. Specifically, close agreement between CFD and measurements were obtained, so that predicted Shields numbers, Sh, could be correlated with particle Reynolds number, Reτ. In this paper we present details of the experimental facility and test program, experimental results including uncertainty/error analysis for the PTV measurements, as well as the videography results for an aluminum alloy powder. The results of the CFD modeling are compared to the single phase measurements. Since very good agreement is observed, predicted wall-shear stress values are used to estimate Sh vs. Reτ at flow rates where incipient particle lift-off is observed experimentally.