bluuebunny/crossref_metadata_2025 huggingface dataset:
Swiss Corona Stress Study: survey in high school students, March 2021
Authors: de Quervain Dominique , Coynel David , Aerni Amanda , Amini Ehssan , Bentz Dorothée , Freytag Virginie , Gerhards Christiane , Papassotiropoulos Andreas , Schicktanz Nathalie , Schlitt Thomas , Zimmer Anja , Zuber Priska
Published: May 2021

The last survey of the Swiss Corona Stress Study in November 2020 has shown that the proportion of respondents with moderately severe to severe depressive symptoms was 18%, with the youngest group of 14-24 year olds being the most affected at 29%. Between 8 and 24 March 2021, an additional survey was conducted in the German speaking part of Northwestern Switzerland among 393 high school students with the majority being between 16 and 19 years old. The anonymous survey was completed by 97.5% of the students. The proportion of respondents with moderately severe to severe depressive symptoms was 27%. In this survey, additional questions were asked about school, social life and vaccination. The most significant stressor associated with depressive symptoms was perceived school pressure. 46% of the respondents indicated they were very or extremely stressed because of the pressure of school. Furthermore, the perception that school pressure has increased due to the pandemic (missed material due to closures, quarantine) was strongly correlated with depressive symptoms. Other factors included worries about poorer education or job opportunities and worries about damage to the social network. An additional factor analysis confirmed that stressors related to school build up the factor with the strongest correlation with depressive symptoms (with a large effect size).Other results- 69% of respondents would get vaccinated if the vaccine were available to them.- 41% of respondents would see the change to distance learning as a relief, 46% as a burden and 13% neither.- Only 4% of respondents said they were not at all afraid of infecting their parents/grandparents or another close person belonging to a risk group.- 29% of respondents have at least a moderate to severe fear of suffering from Long-COVID in case of infection.
THE ADVANTAGE AND RELEVANCE OF DISTANCE LEARNING// International Journal of Educational and Scientific Research 4(12), 2021/ Chief Editor K. Kumpulainen /OEAPS OU - Tallinn, Estonia (Open European Academy of Public Sciences). Vienna, Austria 30.04.2021: OEAPS OU., 2021. P. 13-16.
Authors: Imramzieva Sahinat Dzhamaldinovna , Erzhanova Zhanna Borisovna
Published: May 2021

Distance learning is an ideal solution not only for students, but also for employees who want to improve their skills, as well as for those who, for various reasons, cannot travel to university or school. The opportunity to gain knowledge without leaving home makes the learning process comfortable, flexible, for example, because you do not need to spend time getting ready to go to institution or overcoming traffic jams. This article discusses, why the future is distance learning, what challenges can be faced by those who choose this way of learning, and how to overcome them.
The 4th International Conference on Physical Education, Sport and Health (ISMINA) and Workshop: Enhancing Sport, Physical Activity, and Health Promotion for A Better Quality of Life
Authors: Iragraha S. M. Fernanda
Published: May 2021

Survey method through evaluative descriptive approach is used in this study, which aims to determine the existence of woodball athletes coaching at Student Activity Unit (UKM) Unnes so that it can be used as reference for other regions to build up and produce potential athletes for the region, and further for Indonesia. The results of this study indicate that coaching woodball athletes at UKM Unnes going very well, because it is supported by the human resources and facilities and complete woodball sports equipment. The constraints faced include: (1) program/training schedules often conflict with the lectureschedule of students; (2) lack of coaching funds to follow the event and funds to organize events; (3) athletes/students sometimes took too long dispensation (permit college) while following the championship (so that athletes got mind burden for not following the lecture); (4) lackof attention and participation of Universities in Semarang, Central Java, particularly those with sports studies program to jointly develop the woodball sport; and (5) starting early 2017 woodball permanent field area cannot be used in full (athletes began to fret about finding a place to practice).
WAYS OF FORMATION OF STATEMENTS IN A FOREIGN LANGUAGE// International Journal of Educational and Scientific Research 4(12), 2021/ Chief Editor K. Kumpulainen /OEAPS OU - Tallinn, Estonia (Open European Academy of Public Sciences). Vienna, Austria 30.04.2021: OEAPS OU., 2021. P. 21-24.
Authors: Serikbayeva Ulzhamilya Bibatyrovna , Erzhanova Zhanna Borisovna
Published: May 2021

The purpose of the article is to offer a solution to the problem of development of communicative competence of students of non – linguistic faculties. The importance of establishing common goals and objectives by both sides of the educational process is shown. The problems faced by teachers and students in teaching a foreign language due to the lack of understanding of the structure of the studied language by students, their inability to develop an algorithm for the formation of foreign language statements. The importance of developing students ‘ strategic thinking in learning a foreign language is demonstrated. The General methodological principles underlying the tasks and exercises on the formation of the functional structural model of the studied language in the minds of students are formulated. The assessment of the state of foreign language education at the present stage is given. The necessity of changes in the guidelines for teaching students of creative specialties to obtain the expected results is proved. The main scientific result is the authors ‘ proposal on the formation of communicative competence through the development of existential and strategic competencies, as well as the development of an algorithm for the assimilation of knowledge about the structure of the studied language and their application in speech activity.
Fighting Fire with Fire: Optimality of Value Destruction to Mitigate Short-Termism
Authors: Corum Adrian Aycan
Published: May 2021

I study a model of short-termism where a firm's value is affected by the actions of an agent, who can represent the manager or the board, as well as an entrepreneur, venture capital, private equity, or activist shareholder. The agent either has a project with positive NPV and can further increase the NPV by exerting effort, or has a project that destroys value. The agent has a stake in the company and can liquidate it before the NPV of his actions is realized by the market. This ability to exit creates short-term incentives for the agent to not exert effort, as well as opportunities for him to profit even if he is destroying value. I find that replacing a fraction of agents that have positive NPV projects with value-destroying agents can increase average firm value, because it motivates the value-creating agents to work harder and this effect can dominate the added value destruction. Moreover, this result also holds under endogenous entry of agents: Reducing the entry or operating costs for the agents can increase average firm value and gross value destruction simultaneously, even though the fraction of agents with positive NPV projects decreases. Therefore, regulations that aim mitigating short-termism by curbing value destruction can actually yield opposite results and reduce average firm value instead.
Low Vision With A Squint
Authors: Bheemaiah Anil Kumar
Published: May 2021

Low Vision accommodation technologies range from visors which use peripheral vision mapping to sensors, to softwareapplications like vOICe, which when used with wearables or handhelds, convert a field of view from images to soundscapes.Similar accommodation paraphernalia, like smart walking sticks and human assistance based services, like Google Lookout.1In this paper, the author compares these diverse technologies, proving peripheral vision visors are the most efficient anduseful accommodations, and a combination of these technologies is available to an end user. The resulting information ismade available through VUI to a low vision patient..KeywordsLow Vision , visor, peripheral vision, soundscape, vOICe
Abstracting time in memory
Authors: Herbst Sophie K , Mangione Izem , Kononowicz Tadeusz , Shen Yunyun , van Wassenhove Virginie
Published: May 2021

Planning the future relies on the ability to remember how long events last, yet, how durations are stored in memory is unknown. Here, we developed a novel n-item delayed duration reproduction task to assess whether elapsed time is stored as a continuous feature or as a discrete item in memory. In three experiments (N = 58), participants were presented with non-isochronous sequences composed of empty time intervals delimited by brief tones. Time intervals varied in number (n-items) and in duration. Participants had to reproduce as precisely as possible the duration of all time intervals in the sequence following a delay period. We manipulated the number of time intervals (n-item) and the sequence duration to separate their effects on recall precision. In all three experiments, the precision of recall decreased with the number of items in the sequence, showing that durations can be stored as discrete items in working memory. Our analyses emphasize the distinction between reproduction biases that are captured by relative reproduction, and decreased precision which indexes working memory load. Future research is needed to spell out the conditions under which durations are fully abstracted in working memory.
How Does Play Foster Development? A New Executive Function Perspective
Authors: Doebel Sabine , Lillard Angeline
Published: May 2021

Around the world, children play. But why? Does play support learning and development? And if so, how? One enduring idea is that play helps children exercise executive function, strengthening it like a muscle so that it can be applied broadly in the service of self-regulation (Diamond, 2013; White et al., 2017). Yet a growing literature casts doubt on the idea that executive function can be strengthened in this way (Doebel, 2020; Eisenberg et al., 2020; Kassai et al., 2019; Takacs & Kassai, 2019). We propose a previously unconsidered yet crucial way that play likely supports learning and development via executive function—by helping children engage control in the countless ways needed to acquire the knowledge and skills of their culture. Drawing on findings from diverse literatures, we articulate three ideas about how this might work. We suggest that instead of encouraging specific play activities in hopes of strengthening executive function broadly, children should be provided with opportunities to apply their playful natures to learning diverse, culturally valued skills. We end with key questions to guide future research on how play supports learning and development through executive function.
Intermixing of Commercial Pure Breed Chickens with Indigenous (Sakini) Breed of Nepal
Authors: Amatya Gorkhali Neena , Sherpa Chhiring , Kolachhapati Mana Raj , Pokharel Bhoj Raj , Bhattarai Nirajan , Sapkota Saroj
Published: May 2021

The intermixing of pure breeds of commercial chickens with Nepalese indigenous flock of chickens has not been explored yet genetically. The study aims to investigate the status of interbreeding of Nepalese indigenous chickens with exotic breeds. Thirty three samples of indigenous chicken, Sakini, from three different ecological regions, Terai, mid-hill and high hill, were taken for the study. The 522 bp hyper-variable region of D loop mtDNA of each sampled population was PCR amplified and sequenced. The Neighbor joining tree revealed that most of Nepalese Sakini and commercial chickens such as New Hampshire, Rhode Island Red, White Leghorn, White Plymouth Rock and Barred Plymouth Rock lied in same clade. Our study provides first direct evidence that the Sakini was already bred with commercial breeds for the sake of enhancing production performance and also alarms the government to introduce proper strategies and policies to avoid such genetic erosion.
Energy Absorption Capacity of Thermally Sprayed Aluminium Friction Damper
Authors: Ono S. , Nakahira Japan K. , Tsujioka S. , Inoue K.
Published: May 2021

When buildings are subjected to earthquakes, dampers are effective in decreasing their failure by absorbing the input energy. An object of this study is to develop a new type of friction damper, on whose faying surface aluminium is sprayed, and the double friction joint is tightened with a high-strength bolt. When slip occurs on this friction damper, the slip coefficient is high and comparatively stable. Specimens of the friction damper were tested under the dynamic repeated loading condition to investigate the effect of the condition of the faying surface on the dynamic hysteresis characteristics. The parameters of the test are the type of sprayed metal, the sprayed side of the plate(s), thickness of sprayed metal, the finish of the sprayed surface, and initial clamping force (contact pressure). Results indicate that there exists the condition of suitable characteristics of a metal sprayed friction damper.
Applying Traction Coating to Steel Mill Rolls
Authors: Mayor V.C.
Published: May 2021

This paper deals with the problem of feeding hot billets into roll stands for rolling into different shapes and the need to apply a traction coating to the roll surface at the passes so that the rolls grip the hot billet. Steel mills have tried different methods over the years to make the roll surface at the passes rough, from throwing a shovelful of sand as the billet is entering the pass to knurling and embossing a rough pattern on the passes with a pepper chisel. Some mills have tried to use sand blasting on the rolls as the billet is passing through and thus ruining the bearings. The process used for this paper is spraying a 0.006" to 0.008" thick coating on the passes with Bondrite, an 80-20 Nickel Aluminum composite wire manufactured by us. The application of this coating is extremely easy and fast. The only preparation before spraying is to clean the roll surface with a good solvent that does not leave any residue. Bondrite has a very high bondstrength and bonds to the clean smooth surface of the rolls with enough bondstrength to impart a rough traction coating on the passes.
Influence of Ceramic Content and Additives on the Abrasion Resistance of Arc Sprayed Stainless Steel-TiB2 Coatings
Authors: Dallaire S. , Levert H.
Published: May 2021

Arc sprayed coatings are attractive means to protect components from abrasion wear provided they contain enough hard phases. Because of their hardness and toughness 316LTiB2 cermets were selected as the basis for developing wear resistant coatings. Core wires composed of 304 stainless steel sheaths filled with 10 to 65 wt % TiB2, 1 to 15 wt % additives and remaining 316L stainless steel were fabricated and arc sprayed with air. The arc sprayed stainless steel-TiB2 coatings were submitted to the ASTM G65-B abrasion test and the volume loss was measured with an optical profilometer. As expected, the volume loss decreases and the proportion of TiB2 increases. However, large differences in volume loss between coatings that contain about the same volumetric proportion of hard phases cannot be explained by a linear reationship. The inverse rule of mixing was proposed. This inverse rule of mixing was found particularly useful for determining the influence of additives. Tin, added in the core as a fugitive liquid transfer agent, was found to improve the wear resistance of coatings. These advanced arc sprayed stainless steel-TiB2 coatings can be favorably compared with coatings obtained by arc spraying commercially available solid and core wires.
Chromium Carbide Coatings Produced with Various HVOF Spray Systems
Authors: Zimmermann S. , Kreye H.
Published: May 2021

High velocity oxy-fuel (HVOF) experiments were carried out with Diamond Jet (DJ) 2600 and 2700, P-5000, Jet Kote and Top Gun to investigate the influence of the spray system and of the spray parameters on microstructure and properties of Cr3C2-NiCr coatings. The results show that with all applied HVOF systems Cr3C2-NiCr coatings of high density, high bond strength and high wear resistance can be produced. However, microstructure and properties of the coatings mainly depend on the degree of oxidation and carbon loss of the material during the spray process. Due to the relatively low heating of the spray material the decarburization of CrsCa-NiCr was found to be very low using the HVOF systems DJ 2600, DJ 2700 and JP-5000. Additionally favored by the increased particle velocities coatings sprayed with the Diamond Jet systems and the JP- 5000 exceed coatings produced with the traditional HVOF systems with regard to hardness, wear resistance and bond strength.
Studies of the Flame Spraying of Polymers
Authors: Varacalle D.J. , Couch K.W. , Budinger V.S.
Published: May 2021

Experimental studies of the subsonic combustion process have been conducted in order to determine the quality and economics of polyester, epoxy, urethane, and hybrid polyester-epoxy coatings. Thermally sprayed polymer coatings are of interest to several industries for anti-corrosion applications, including the infrastructural, chemical, automotive, and aircraft industries. Classical experiments were conducted, from which a substantial range of thermal processing conditions and their effect on the resultant coating were obtained. The coatings were characterized and evaluated by a number of techniques, including Knoop microhardness tests, optical metallography, image analysis, and bond strength. Characterization of the coatings yielded thickness, bond strength, hardness, and porosity.
Adhesion of Thermal Barrier Coating Systems and Incorporation of an Oxidation Barrier Layer
Authors: Tsui Y.C. , Clyne T.W.
Published: May 2021

The adhesion of various interfaces in thermal barrier coating systems strongly affects their stability and thermal cycling life. A new spontaneous debonding technique and the four point bend delamination test have been applied to measure the interfacial fracture toughnesses of various interfaces in several thermal barrier coating systems. The spontaneous debonding technique is based on spraying a relatively stiff layer on top of the ZrO2 coating. This raises the strain energy release rate for debonding, the magnitude of which is monitored via modelling of the stress distribution. The critical strain energy release rate for debonding (interfacial fracture energy) was then determined from the stress states before and after debonding. Thermal barrier coatings (TBCs), consisting of a Ni-22wt.%Cr-10wt.%Al-lwt.%Y bond coat and a ZrO2-8%Y2O3 top coat, were deposited on a nickelbased superalloy. Two methods, air (APS) and vacuum (VPS) plasma spraying, were used to produce the bond and the top coats. The corresponding as-sprayed residual stress distributions and the interfacial fracture energies were evaluated. It was found that a VPS bond coat and an APS top coat produced the most mechanically stable structure. A layer of vacuum plasma sprayed AI2O3 was then introduced between the top and the bond coat, designed to act as an oxygen diffusion barrier. The effect on residual stress distributions, and associated crack driving forces for debonding, at different interfaces were determined. The effect of the alumina layer on the oxidation behaviour was also studied. It is shown that the oxidation barrier could significantly enhance the coating life-time.
Manufacture and Characterization of Particle Reinforced Aluminum Coatings
Authors: Wielage B. , Zschunke M. , Henker A. , Steinhäuser S.
Published: May 2021

For reasons of the decrease in weight in the industry light cage design materials like aluminum alloys are frequently used. Because the wear resistance of aluminum alloys and/or aluminum generally is not sufficient, an increased wear resistance can be reached by means of particle reinforced aluminum coatings. The installation of ceramic reinforcing components (for example oxide particles) in the ductile metal matrix brings an essential improvement of the wear resistance particularly with regard to abrasion and short time fatigue wear. The results presented in the paper refer to research works concerning thermally sprayed Al - coatings with Al2O3- and SiC - particles as reinforcement components by vacuum plasma spraying.
Investigations on Thermal Sprayed Carbon-Short-Fiber-Reinforced Aluminum Composites
Authors: Wielage B. , Fleisher K. , Zimmerman G.
Published: May 2021

Composite coatings are increasingly applied for the protection against wear in mechanical constructions. Especially, in the case of abrasion these coatings offer the possibility to protect the base material. The matrix is ductile and the reinforcements cause the higher strength and hardness. A research project presented in this paper dealt with the manufacture of carbon-short-fibre-reinforced aluminum composite coatings by vacuum plasma spraying. The basis of the processing is the agglomeration of aluminum powder and carbon fibres. During the spraying process the aluminum melts, covers the fibres, and so, contributes to the creation of the composite coating and/or the composites. The processing times are so short that the damaging formation of carbides can be suppressed mostly. For the creation of free standing bodies it is necessary to find a qualified core material which allows the removing of the sprayed composites. The investigations on the composites are focused on the metallographical judgement regarding the fibre and void content, the fibre distribution, the characterization of the interface as well as the determination of mechanical properties and the wear resistance.
High Velocity Oxy-Fuel Flame Spraying-Process and Coating Characteristics
Authors: Kreye H. , Schwetzke R. , Zimmermann S.
Published: May 2021

High velocity oxy-fuel (HVOF) spray experiments were carried out using various spray systems. A comparison is made of the systems introduced as a first and second generation (Jet Kote, Diamond Jet, Top Gun, CDS) with the more recently introduced systems of the third generation (JP 5000, DJ 2600, DJ 2700). The comparison is based on particle velocities and experiments to evaluate the heat transfer to the particles. The results show that the systems of the new generation with a converging-diverging nozzle section can produce up to 50% higher particle velocities. The higher kinetic energy allows to reduce the thermal energy and to reduce thermally activated phase transformations of the coating material during the spray process. Carbide coatings produced with one of the new HVOF systems exhibit a higher density, higher bond strength and higher hardness as compared to coatings produced with one of the systems of the first and second HVOF generation. Furthermore, the reduced thermal energy yields less oxidative loss of carbon and opens the possibility to spray coatings with neutral or compressive internal stresses, a prerequisite to produce carbide coatings up to a thickness of several millimeters.
Effect of Grinding Mechanisms on Surface Finish and Hardness of Thermally Sprayed WC-Co
Authors: Ibrahim A. , Sampath S.
Published: May 2021

During grinding of thermally sprayed WC-Co, the grinding ratio G ( ratio of volume of work removed to the volume of wheel consumed) is usually low and the finish produced sometimes is inadequate. Improvement in surface finish accompanies increase in grinding ratio. The objective of this investigation is to study the effect of type of abrasive, table speed, and depth of cut on the surface finish and hardness of WC-Co. Thermally sprayed WC-12 wt % Co and WC-17 wt % Co produced using the high velocity oxygen fuel (HVOF) process, have been ground using silicon carbide and diamond wheels under different operating conditions. The surface profile reveals the significant role played by the above parameters on the surface finish. The grinding ratio, G in case of diamond grinding was found to be larger than silicon carbide grinding however, the quality of the surface finish produced by silicon carbide was better than the diamond. The surface structure of the ground WC-Co was examined by SEM. Surfaces ground using a silicon carbide wheel exhibited extensive plastic flow, while surfaces ground with diamond wheels are highly fractured with localized flow which suggests two different mechanisms of material removal. The surface hardness after grinding, was found to depend on the type of abrasive and table speed. Silicon carbide grinding has shown higher hardness and better surface finish than diamond grinding.
Measured and Simulated Particle Flow Field Parameters in a High Power Plasma Spray
Authors: Swank W.D. , Chang C.H. , Fincke J.R. , Haggard D.C.
Published: May 2021

High power supersonic plasma guns operating in excess of 200 kW can produce molten particles with 3 to 4 times the impact velocity of conventional plasma sprays. With this increased range of particle velocity it is important to understand the relationship between the torch input parameters and the sprayed particle velocity, temperature, pattern and size. Stainless steel particle velocity, temperature, size and relative number are measured for a high power plasma spray system operating at 110 kW. At the same torch operating conditions the plasma and particle flow fields are simulated with a newly developed computational model. It was found that the injection geometry plays an important role in the particle entrainment, heating and acceleration. In spite of the complexity of the system, i.e. supersonic plasma velocity with a high swirl component, the simulation produced reasonalble particle trajectories resulting in good agreement between the calculated and measured particle velocity, temperature and size distributions.
Vaporization of Metal Powders in Plasma Sprays
Authors: Li K.-I. , Vardelle M. , Vardelle A. , Fauchais P. , Trassy C.
Published: May 2021

In plasma spraying, deposition efficiency depends, to a great extent, on powder losses at the injection point, vaporization phenomena and particle rebound at impact. This paper discusses an attempt to determine the mass balance in metal spraying by studying the injection and vaporization of a metal powder in a plasma jet and correlating the results to the mass deposition efficiency of the process. The study of particle vaporization consisted of measuring the metal atoms concentration by absorption spectroscopy while injection was examined by a 2-D imaging technique.
Mathematical Model for Process Thermal Spraying Coating Formation
Authors: Ilyuchenko A. , Vityaz P. , Okovity V. , Abrashin V. , Gromyko G. , Veremeinko T. , Zajac G.
Published: May 2021

This paper presents a mathematical model of the plasma-spray coating formation process that allows one to estimate bond strength energy, a parameter related to coating quality. Bond strength energy is defined on the basis of particle-substrate or system balance. Unknown quantities in the energy equation are obtained from nonstationary Navier-Stokes equations for velocity field and pressure and from thermoelasticity equations for temperature and stress. Complexities associated with particle spreading and nonlinear hydrodynamics have made it necessary to develop a stable numerical technique.
On-Line Diagnostics of Traditional Flame Spraying as a Tool to Increase Reproducibility
Authors: Wigren J. , Hansson M.-O. , Gougeon P. , Moreau C.
Published: May 2021

Although very frequently used, traditional (low velocity) flame spraying is a much forgotten process. No major research has been performed during the last decade. This paper focuses on the problem of reproducibility of a typical flame gun used with modern automated process equipment. An on-line diagnostic process control tool measuring the temperature, velocity, size and position of the powder in the flame was applied during spraying of abradable coatings of NiCrAl/Bentonite, coatings which are commonly applied to fan and compressor housings of gas turbines. An automated closed loop flame spray unit with mass flowmeters for the oxygen and acetylene gases was used. Influence of different process parameters on the sprayed particles, such as nozzle design, gas flows, and powder feed rate is discussed. Coating properties, such as erosivity, porosity, microstructure and tensile strength, are evaluated. It is demonstrated that even fairly small process changes influence the flame sprayed particles as well as the properties of the resultant coating.
Parametric Study of Suspension Plasma Sprayed Hydroxyapatite
Authors: Boyer E. , Gitzhofer F. , Boulos M.
Published: May 2021

Thermal plasma spraying is a suitable technique for hydroxyapatite [HA, Ca10(P04)6(OH)2] coating preparation. Suspension Plasma Spraying (SPS) is a newly developed process based on a suspension of fine (<10 μm) or even ultrafine (<100 μm) powders, axially fed into the RF plasma through an atomization probe. The atomization of the suspension results in microdroplets (20 μm in size). They are flash dried, melted and finally impacted onto the substrate to solidify and build the coating. The aqueous suspension of HA is chemically synthesized. Our experiments included variations of the plasma gas composition (Ar/O2, Ar/H2), the plasma deposition reactor pressure. Characterizations techniques (e.g. X-ray diffraction, scanning electron microscope and transmission electron microscope) were applied to resultant SPS HA coatings which possessed good crystallinity and about 3% weight α-TCP and lime. The texture examination has shown that preferential crystal orientation followed the (001) Miller's plane family. SPS by RF induction plasma has proved to be a reliable process for the production of thick (200 μm) HA coatings with high deposition rate (>150 μm/min).
Experimental/Analytical Investigations of Air Plasma Spray Tungsten Carbide-Cobalt Coatings at Kelly Air Force Base
Authors: Varacalle D.J. , Acosta E. , Figert J. , Syma M. , Worthington J. , Carrillo D.
Published: May 2021

Air plasma sprayed tungsten carbide-cobalt coatings are being used at Kelly Air Force Base for a fretting application for convergent seals in aircraft engines. Experimental and analytical studies were conducted to investigate the plasma spraying of two powders for this application. Statistical processing schemes were accomplished in conjunction with analytical modeling of the air plasma spray (APS) process. Classical and statistically designed experiments (SDE) chosen to be conducted were determined by analytical modeling. The coatings were characterized for composition, hardness, porosity, surface roughness, deposition efficiency, and microstructure. Attributes of the coatings are correlated with the changes in operating parameters. Wear screening of the coatings from the experiments was conducted using an abrasion tester based on ASTM Standard Test B611-85.
An Experimental Study of Twin-Wire Electric Arc Sprayed Zinc and Aluminum Coatings
Authors: Varacalle D.J. , Hagrman D.L. , Fincke J.R. , Swank W.D. , Zanchuck V. , Sampson E.
Published: May 2021

An experimental study of twin-wire electric arc spraying of zinc and aluminum coatings demonstrates the suitability of the process for anticorrosion applications. Experiments were conducted using Box-type full-factorial designs. Operating parameters were varied around the following process parameters: nozzle diameter, nozzle geometry, and system pressure. A systematic design of experiments displayed the range of processing conditions and their effect on the resultant coatings. The coatings were characterized with hardness and deposition efficiency tests, and optical metallography. Coating properties are quantified with respect to roughness, hardness, porosity, thickness, bond strength, and microstructure. The features of the coatings are correlated with the process changes. Selected analytical calculations and process diagnostics of the meltpool dynamics are presented.
Mechanical Properties of Water Stabilized Plasma Spray-Formed Alumina-13wt% Titania
Authors: Leigh S.H. , Berndt C.C. , Sampath S. , Herman H.
Published: May 2021

Mechanical properties of water stabilized plasma spray-formed Al2O3-13wt%TiO2 have been investigated by using indentation techniques and a four-point bend test. Young's modulus was determined by four point bend, nano- and Knoop indentation tests. Modulus of rupture was measured by the four-point bend test. The anisotropic behavior as well as the reduced Young's modulus and strength of thermal spray deposits are extensively investigated and can be related to the unique microstructure; i.e., the spheroidal shape of pores, cracks and splats as well as inter-lamellar boundaries. The heat treatment substantially enhanced the mechanical properties and the microstructure becomes more homogeneous and isotropic; that is, the deposits lose their unique nature and become more similar to bulk materials.
Residual Stress Calculation by Finite Element Methods
Authors: Gruhn H. , Fischer W. , Funke C. , Malléner W. , Stöver D.
Published: May 2021

For simulating residual stresses in plasma sprayed multilayer systems a finite element and an analytic model are compared with measured results. The measured stresses which depend on substrate temperature of the plasma spray process are produced exactly by the finite element model. Mesh deformation and simulated stress distribution of the sample are studied.
Analysis of the Stress State in Thermal Barrier Coatings during a Thermal Cycle
Authors: Jönsson G. , Persson C.
Published: May 2021

Thermal barriers made up by a ceramic top coating and a metallic bond coating are subjected to thermal cycles in service. The thermal stresses vary during the cycles and the residual stresses change as a result of plastic flow and creep. The stress state in thermal barrier coatings during a thermal cycle has been examined with a finite element method using temperature dependent material data. The calculated results were verified by measurements of the residual stresses with the layer removal technique before and after cycling of specimens heated in furnace with air environment. According to the simulation of a thermal cycle to 700 ° C, using a finite element method, the bond coat is approximately stress free after 1 hour dwell time. Thus, the residual stresses after a thermal cycle is a result of thermal expansion mismatch and temperature drop.
Characterization of Thermally Sprayed Coatings Using Manual vs. Automated Microhardness Testing
Authors: Blann G.A. , Hoffmann M.
Published: May 2021

Thermally sprayed coatings are applied to various substrates for the purpose of providing a wear-resistant, corrosion-resistant, or heat barrier surface. The materials used to coat a substrate will vary in hardness with respect to each other and with respect to the substrate. Denser coatings produce more reliable hardness data than less dense coatings due to the absence of pores and other inconsistencies in the coating. Variations in coatings will cause preparation problems such as pullout, edge rounding, or coating-to-substrate relief which effects the reliability of hardness determinations. The repeatability of hardness data is directly related to the density of the coating. This paper deals with the effect of coating characteristics (density) on the reliability of manual and automated hardness measurements.
A Potential NDT Method for Rapid Quality Control of Thermal Sprayed Coatings
Authors: Lugscheider E. , Remer P. , Herbst C. , Barbezat G.
Published: May 2021

An overview on potential non-destructive testing (NDT) methods for the inspection of thermally sprayed coatings in production lines is given. The suitability of several NDT techniques has been investigated with view on their sensitivity for the detection of defect sizes possibly being critical for Thermal Spray coatings. Eventually, a method is presented that shows qualification for detection of subsurface flaws in coatings such as delaminations and cracks and offers flaw distinction by image analysis procedures. A storage and archiving of test results is possible thus completing full quality control and meeting possible warranty claims. The major advantage of the NDT process is its very high detection speed which guarantees high productivity even for high volume production systems. Thus a full-area detection of large coated components becomes possible. The process is not restricted to plain components, but is usable for the detection of internally coated cylinders as well.
Modeling of the Laser Engraving at Plasma Sprayed AI2O3, TiO2 and AI2TiO5 Coatings for Anilox Rolls
Authors: Groc M. , Pawlowski L. , Smurov I.
Published: May 2021

Paper presents a study of modeling and numerical simulation of laser engraving process. The 1-D simulation concerned CO2 c.w. pulsed laser engraving of plasma sprayed alumina, titania and aluminum titanate coatings. These coatings will possibly replace the Cr2O3 ones used currently in manufacturing of anilox rolls. The model was refined in comparison to the previous one (1) by taking into account the speed of the roll at the engraving. The actual thermophysical coefficients of plasma sprayed alumina, titania and aluminum titanate were input to the computations. The model enabled calculation of the engraving's depth in function of the principal laser treatment parameters viz. pulse length and laser power density. Finally, the overflow effect at the laser treatment of new ceramics was discussed and compared to that occurring at Cr2O3 engraving.
Erosion Resistance of Arc Sprayed Coatings to Iron Ore at 25°C and 330°C
Authors: Dallaire S. , Levert H.
Published: May 2021

Iron ore pellets are sintered and reduced in continuous large industrial oil-fired furnaces. From the furnace, large volumes of hot gas are sucked by powerful fans. Being exposed to gas-borne iron particles and temperatures ranging between 125°C and 328°C fan components are rapidly deteriorated. Extensive part repair or replacement are required for maintaining a profitable operation. The arc spraying technique has been suggested for repair provided it could produce erosion resistant coatings. Commercial wires were arc sprayed using various spray parameters to produce thick coatings. Arc-sprayed coatings and reference specimens were erosion tested at 25°C and 330°C and impact angles of 25° and 90° in a laboratory gas-blast erosion rig. This device was designed to impact materials with coarse (32 -300 μm) iron ore particles at a speed of 100 m/s. The volume loss was accurately measured with a laser profilometer. Few arc sprayed coatings exhibited erosion resistance comparable with structural steel at low impact angles. Erosion of arc sprayed coatings and reference specimens dramatically increases at 330°C for both 25° and 90° impact angles. Erosion-enhanced oxidation was found responsible for the increase in wastage above room temperature. Though arc spraying can be appropriate for on-site repair, the development of erosion resistant coatings is required for intermediate temperatures.
Abrasive Wear Characteristics of Ni-base Self-fluxing Alloy Spraywelding Overlays
Authors: Ding Z. , Knight R. , Smith R.W.
Published: May 2021

The results of low stress, pin-on-disc and high stress grinding abrasive wear tests on coatings produced by plasma and oxy-acetylene flame spraywelding are presented. FNil5A and FNiWC35 Ni-based self-fluxing alloys were selected as typical spraywelding materials for abrasive wear resistance. The abrasive wear resistance mechanisms of welded overlays produced by various materials and processes were also characterized by hardness tests, microstructural and compositional analyses, and through analysis of the effect of different kinds of abrasive on the wear resistant of Ni-base self-fluxing spraywelding overlays. Results showed that FNiWC35 overlays exhibited improved resistance under low stress abrasion, but the relative wear resistances of FNiWC35 and FNil5A still depended primarily on the type and hardness of the abrasive medium used. For the same material, the abrasive wear resistance of oxyacetylene flame sprayed overlays was higher than that produced by plasma spraywelding. The wear resistance of the plasma spraywelding overlays depended not only on the material, but also strongly on the spraywelding process parameters.
Corrosion Resistance of Thermal Sprayed Titanium Coating with Resin Seal in Chloride Solution
Authors: Ishikawa K. , Suzuki T. , Kitamura Y. , Tobe S.
Published: May 2021

Corrosion behavior of a flame sprayed titanium coating sealed by some resins was investigated in 3.5% NaCl solution by an electrochemical polarization measurement and an immersion test. The composition and structure of the sprayed film was also analyzed by SEM and EPMA. Although an as-sprayed titanium had no resistance to the corrosion because of its porosity, the sprayed titanium sealed with epoxy or silicon resin showed an excellent resistivity against the chloride corrosion. In spite that almost half amount of the titanium changed to oxide, nitride and carbide through the gas flame spraying, the conversion of the metal to the compounds had little effect to decrease the corrosion resistivity. The sprayed and sealed titanium coating obtained by a conventional onsite thermal spraying is expected as an economical material for chloride containing environments.
Production of Recycled Polyethylene Terephthalate Coatings by HVOF and Plasma Spray
Authors: Lima R.S. , Takimi A.S. , Lima M.D. , Bergmann C.P.
Published: May 2021

The polyethylene terephtalate (PET) is a polymer with a high melting (265°C) and glass transition (67°C) temperatures, insensitive to moisture and common solvents. Also it has an wide range of mechanical properties attainable by variations of molecular weight, orientation and crystallinity. Due to these characteristics allied with the glass-like transparency, light weight and unbreakable character, PET is used to form high performance bottles for carbonated soft drinks, wines, beers and food packing. The world annual consumption of PET for these purposes is increasing, with impressive prospects for the future. This characteristic leads to other situation. The consumption of energy and natural resources together with the environmental problems caused by disposable plastics, make the engineering and materials scientists try to find for different ways to recycled plastics. The characteristics of PET mentioned above seen to be very proper to use as a material for coating.
DC Plasma Polymer Composite Coatings for Abrasion Resistant Protective Surfaces
Authors: Tufa K.Y. , Gitzhofer F.
Published: May 2021

A new concept of high energy recovery of dc plasma torch has been developed and applied to the deposition of polymer composites. The heat transferred to low cost fillers, such as alumina or silica injected into the high temperature zone of the plasma, is recovered in the applied polymer coating, which is injected downstream in a much cooler zone of the plasma. The result is a polymer/ceramic composite spraying process having the following benefits: Shrinkage phenomena due to polymer recrystallisation is eliminated, providing a good coating adhesion, a high spray material throughput rate is achieved and die risk of coating polymer combustion is greatly reduced. The polymer composite form decreases the overall costs of coatings and the type of filler employed influences the properties of the composite. Abrasion resistant composites have been produced with alumina and silica fillers (50 wt.%). Medium density polyethylene (MDPE), sprayed with 50 wt.% reinforcement, have shown abrasion resistance as high as UHMWPE. Polymer degradation, abrasion mechanisms and microstructures of these composite coatings are explained.
Influence of a Filler Composition and Conditions of Flame Spraying on a Structure and Mechanical Properties of Composite Polymer Coatings
Authors: Borisov Yu. , Korzhik V. , Sviridova I. , Skorokhod A.
Published: May 2021

In thermal spraying of metal-polymer coatings, the processes of polymers oxidation and destruction can have special features, as the temperature of heating of the filler particles can significantly exceed the temperature of destruction of the polymer binder. Hence, the need to study the features of the process of formation of thermal sprayed coatings from filled polymers and their physico-chemical, mechanical and service properties. This paper describes the influence of a filler composition and conditions of flame spraying on a structure and mechanical properties of composite polymer coatings. It is observed that addition of 5-10 vol. % of Fe-Ni-B alloy powder to low-pressure polyethylene polymer matrices, improves the wear resistance of thermal sprayed coatings 1.2-1.3 times under the conditions of gas-abrasive wear, compared to purely polymer coating, owing to the combination of the higher hardness of the coating with the high damping properties of the polymer matrix.
The Effects of Silica Content and Thermal Cycles on Young’s Modulus and Residual Stresses in Yttria Stabilized Zirconia Thermal Barrier Coatings
Authors: McGrann R.T.R. , Rybicki E.F. , Shadley J.R. , Sanchez R.E. , Brindley W.J.
Published: May 2021

The Young's modulus of the ceramic top coat of a plasma sprayed thermal barrier coating (TBC) has been reported to vary by as much as a factor of three with changes in processing parameters and by as much as a factor of four due to prolonged thermal exposure. Since the residual stress is expected to vary directly with the modulus of the ceramic layer, it follows that a change in modulus will change the residual stresses in the ceramic layer. The objective of this study was to evaluate the modulus of plasma sprayed coatings as a function of thermal cycle exposure and silica content of the ceramic. The study employed the Cantilever Beam Bending Method to examine Young's modulus for an yttria stabilized zirconia TBC applied by plasma spraying, for zero and ten thermal cycles and for silica contents of 0.1% and 1.0%. Results are discussed in terms of mechanisms that may affect modulus and the effect of modulus variations on residual stresses.
Thermal Spraying of Nanostructured Coatings by Hypersonic Plasma Particle Deposition
Authors: Heberlein J. , Rao N.P. , Neuman A. , Blum J. , Tymiak N. , McMurry P.H. , Girshick S.L.
Published: May 2021

A novel plasma spray process for producing nanostructured coatings, hypersonic plasma particle deposition (HPPD), has been experimentally investigated. In HPPD, vapor phase precursors are injected into a plasma stream generated by a DC arc. The plasma is quenched by supersonic expansion through a nozzle into a vacuum (~ 2 torr) deposition chamber. Ultrafine particles nucleated in the nozzle are accelerated in the hypersonic free jet downstream of the nozzle and inertially deposited onto a substrate. The short transit times between the nozzle and the substrate (< 50 μs) prevent inflight agglomeration, while the high particle deposition velocities result in the formation of a consolidated coating. We have investigated the production of silicon and silicon carbide coatings using SiCl4 and CH4 precursors. Silicon deposits analyzed by transmission electron microscopy were found to have nanostructured regions with grain sizes varying from 5-20 nm. Corresponding particle size distributions measured before deposition using an extractive aerosol probe peaked around 15 nm, suggesting negligible grain growth occurred in the samples studied. Silicon carbide particle size distributions measured at various deposition chamber pressures verify that the low residence time characteristic of the HPPD process minimizes in-flight agglomeration.