bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetic and Non-Genetic Factors on Productive and Reproductive Performance of Indigenous Buffalo
Authors: Paneru Uddhav , Dhungana Keshav Prasad , Kanu Surendra , Sharma Parbati
Published: May 2021

Indigenous buffalo is the black gold of Nepal because of its important contribution to the livelihood of the rural farmers and agricultural economy of the country. A study was done to investigate the performance of indigenous buffalo found in high-hill of the western districts of Nepal. Further, effect of genetic and non-genetic factors on productive and reproductive performance of indigenous buffalo was accessed. This study was done in four districts: Myagdi, Baglung, Parbat and Kaski for 2 consecutive years from 2016 to 2017. A semi-structured and questionnaire survey format was prepared and was filled with verbal answers from 142 farmers on a different aspect of buffalo farming. Further, recording formats were distributed to enumerators for the recording of different information that cannot be collected from the survey. Total of 201 indigenous buffaloes (132 Lime and 69 Parkote) and minimum of 25 buffaloes in each site were measured for determining productive and reproductive performance. Further, 65 collected milk samples were subjected to Animal Nutrition Laboratory of DoAR, Lumle for determination of milk composition. Results of the findings revealed that there was a high variation in productive and reproductive performance of indigenous buffalo. Lactation milk yield of Lime buffalo was observed slightly higher (1180.90 ± 27.94 L) than Parkote buffalo (1170.56 ± 42.29 L) but was non-significant (p>0.05). Lactation yield of indigenous buffalo in Ramja, Parbat (1254.73±38.43 L) was observed significantly higher (P<0.002) than other research locations. Genetic evaluation of indigenous buffaloes and selection of better performers help in increasing productivity and lead to conservation by competitive advantage of indigenous buffaloes. Non-genetic factors play an important role in the productive and reproductive performance of indigenous buffalo and need to account for these effects to select buffalo for its genetic merit.
Economics of Organic vs Inorganic Rice Production: A Case of Chitwan District of Nepal
Authors: Sapkota Bidya Kiran , Subedi Ananta Prakash , Tripathi Kalyani Mishra , Dhakal Shiva Chandra
Published: May 2021

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Rice (Oryza sativa L.) is the major staple food crop of Nepal. A research was conducted in December, 2019 to examine the economic viability of organic rice farming and factors affecting its adoption. Fulbari area of Chitwan district of Nepal was purposively selected for this study on consultation with Agriculture Knowledge Centre, Chitwan and review of past works which showed good practice of organic rice farming. A total of 100 farm households, 50 organic and 50 inorganic were selected using simple random sampling. Primary data were collected through a pre-tested semi-structured interview schedule, while secondary data were collected from related publications. The probit regression analysis showed that the six variables were statistically significant for the decision to adopt organic rice farming, they are: number of schooling years of the household head (p= 0.014), annual household income from agriculture (p= 0.012), membership of any agricultural organization (p= 0.000), subsidy in other inputs in addition to seed and fertilizers (p= 0.000), area of rice cultivated land (p= 0.007) and awareness on climate change (0.086). The benefit cost ratio of organic rice production (2.2) was higher as compared to inorganic (1.9) which showed that the profitability in organic rice production was higher than in inorganic. Furthermore, indexing identified- lengthy certification process (0.85) as the first major hindrance in adoption of organic rice farming followed by lack of proper organic market (0.68), high cost of organic seed and fertilizer (0.56), lack of knowledge and trainings on organic farming (0.48) and lack of government support such as grants and premium price (0.44) as the second, third, fourth and fifth hindrances respectively. The government should promote organic rice farming, prioritizing the small scale and marginal farmers by giving subsidies and premium, facilitating in certification and marketing, and providing knowledge about climate change.
Development and Application of an Interactive Neuropathology iBook as a Complementary Learning Tool for Veterinary Medicine Students
Authors: Arauz Maziel , Fuentealba Carmen , Vanderstichel Raphael , Bolfa Pompei , Sithole Fortune , Laws Antoine , Illanes Oscar
Published: May 2021

Neuropathology is a challenging subject for most medical students. Delivering a gamified learning tool on this topic may motivate students and increase knowledge in the discipline. We report on the development of such a tool in iBook format for the systemic pathology course delivered at Ross University School of Veterinary Medicine. Composed of 10 chapters (cases), this Neuropathology iBook (NP-iB) reviews basic clinical manifestations, neuropathology, and pathogenesis of common non-neoplastic conditions that cause brain disease in domestic animals. The goal of each chapter is to reach a diagnosis by interactively answering specific questions after reviewing relevant medical history, clinical pathology, and autopsy findings. Our hypothesis: the NP-iB improves students’ ability to recognize these diseases, reflected in higher test scores. Using a post-test-only control group design, data were gathered from all students enrolled in the course in two different semesters, fall 2017 and spring 2018 ( n = 300). NP-iB users ( n = 51, 17%) and usage time were identified by answers to multiple-choice questions embedded in the course assessments. Ninety percent of users had a positive perception although no statistically significant differences were found in median test scores between users and non-users. Statistically significant test score differences were found across how much time students used the NP-iB ( p = .005); the lowest test score median values were found for neuropathology questions not related to the NP-iB in students who used it for more than 3 hours. Unexpectedly, a low number of students preferred this digital learning tool, and its use did not improve their learning outcomes.
Pilot Study Evaluating the Use of Typodonts (Dental Models) for Teaching Veterinary Dentistry as Part of the Core Veterinary Curriculum
Authors: Goldschmidt Stephanie L. , Root Kustritz Margaret V.
Published: May 2021

Periodontal disease is one the most common disease pathologies in small animal medicine, yet new graduates report they feel unprepared to perform dentistry in general practice. Novel methodologies to close the knowledge gap in veterinary dentistry need to be identified. Typodonts (dental models) are commonly used in human dental schools to teach basic principles prior to practice on clinical patients and have been shown to be an effective teaching tool. The study aimed to determine if independent study and self-guided practice on a veterinary typodont prior to a structured, in-person cadaver laboratory with feedback increases students’ perceived dentistry clinical skills in performing periodontal techniques. We calculated the knowledge gap before and after the cadaver laboratory by comparing the students’ perceived and desired skill levels in performing periodontal charting, ultrasonic cleaning, hand scaling, and root planing. Ninety-six percent of students reported that practice with the dental typodont prior to the cadaver laboratory increased their comfort level in performing periodontal skills. However, practice did not result in a significant decrease in knowledge gap compared with participation in the cadaver laboratory alone. Although students perceived a benefit to practicing with the typodont, self-guided practice was not effective in decreasing the knowledge gap, most likely due to a lack of structured feedback with typodont use. Further investigation into the use of typodonts with direct feedback prior to structured laboratory or, alternatively, as an additional practice tool following a structured laboratory would further define if there is a benefit to typodont practice in veterinary dentistry.
Using Strategies from Physical Training of Athletes to Develop Self-Study Programs for Veterinary Medical Students
Authors: San Miguel Sandra F. , Robertson Mike , McDavid Lindley
Published: May 2021

Veterinary medical students, similar to elite collegiate athletes, are developing strategies for learning new skills and for self-care to take their performance to the next level. As veterinary students learn to successfully navigate an information-dense, high-volume curriculum, many sacrifice wellness, leadership opportunities, extracurricular activities, and social interactions. Strategies from athletes’ physical training were used to design a self-study program for first-year veterinary medical students. Major considerations in program design were the characteristics of the human being, learning goals, and contextual constraints. The study program included a warm-up, study sessions, and a cooldown. The program was offered to first-year veterinary medical students at Purdue University’s College of Veterinary Medicine. Thirty-two students requested study programs and 21 completed surveys at the semester end. Results were analyzed quantitatively and by using an adapted conventional content analysis approach. Responses were organized into three main domains: reason for participation, program utility, and program satisfaction. Students shared that the most helpful aspects of the program were assisting with organization and time management, providing accountability, and reducing overwhelm by enhancing well-being and performance; they reported that these learned skills would support their well-being as future professionals. This article describes the experiences of one group of veterinary students at one college using these programs. The long-term goal is to develop a model program for all veterinary students to manage curricular demands while maintaining well-being.
Thermal Spray Deposition and Evaluation of Low-Z Coatings
Authors: Seals R.D. , Swindeman C.J. , White R.L.
Published: May 2021

Thermally-sprayed low-Z coatings of boron carbide (B4C) on aluminum substrates were investigated as candidate materials for first-wall reactor protective surfaces. Comparisons were made to thermally-sprayed coatings of boron, MgAl204, Al2O3, and composites. Graded bond layers were applied to mitigate coefficient of thermal expansion mismatch. Microstructures, thermal diffusivity before and after thermal shock loading, steel ball impact resistance, CO2 pellet cleaning and erosion tolerance, phase content, stoichiometry by Rutherford backscattering spectroscopy (RBS), and relative tensile strengths were measured.
Development of Reliable Spray and Fuse Coatings for Boiler Protection
Authors: Heath G.R. , Polak R. , Gustafsson S. , Tsujita T.
Published: May 2021

Spray and Fuse coatings are ideally suited to boiler environments. The fusing step gives to optimized coatings a uniform chemistry and microstructure, a metallurgical bonding, no through porosity, a low oxide content and no cracking. The relative simplicity of the traditional processing equipment is suited to on-site and automated application including coating repair. Although enjoying considerable success in traditional boilers, their advance into new applications appears restrained by the issue of substrate property modifications during fusing. This paper studies the modification in substrate boiler tube materials (microstructure and mechanical properties) associated with the coating of advanced NiCrBSi alloys. Charpy impact, tensile strength, yield strength, elongation and thermal expansion coefficient testing between 22°C and 450°C are measured. By optimal coating design to a specific substrate, the effect on mechanical property modifications by fusing could be dramatically reduced to allow new and reliable coatings systems to be demonstrated for advanced applications. The future for Spray and Fuse coatings in boilers is discussed.
The High Temperature Erosion/Corrosion Behavior of Industrial Thermally Sprayed Coatings
Authors: Heath G.R. , Kammer P.A. , Stack M.M.
Published: May 2021

There are numerous industrial applications where materials are subjected to simultaneous high temperature oxidation/corrosion and wear (such as erosion). This combination often leads to accelerated degradation. Specific industries include: chemical, waste incineration, power generation and paper/pulp with typical applications including boilers and cyclones. Previous studies have established wrought material compositions and microstructures which can resist these environments. In searching for cost-effective industrial solutions, surface coating via thermal spray becomes attractive. However, the microstructural complexity of such coatings can make the simple extrapolation of bulk material behavior to these coatings dangerous. If these coatings are to be used more widely, a greater understanding of their high temperature erosion/corrosion behavior and the influence of coating process is required. A range of Fe-and Ni-based alloys and thermal spray techniques were studied under various high temperature erosion/corrosion conditions. The critical erosion parameters of impact angle (30° to 90°) and temperature (up to 550°C in air) have been studied in an atmospheric fluidized bed test rig environment, using Al2O3 erodent at a typical impact velocity of 4m/sec and conventional high temperature erosion test equipment. The important microstructural and mechanical features of the coatings and the effect of the thermal spray process are discussed in terms of their high temperature degradation mechanisms.
Ultrasonic Application of Thick Metallic Coatings
Authors: Legoux J.-G. , Jen C.-K.
Published: May 2021

Ultrasonic propagation characteristics in thermal spray materials are affected by the complex microstructures of these coatings. Factors such as oxide stringers, porosity, splat size and morphology can all affect wave propagation. This dependence causes many concerns when one performs nondestructive evaluation of such coatings. However, we find that the unique properties of thermally sprayed coatings can be used for the fabrication of the cladding region of clad solid ultrasonic wave guides (or buffer rods) consisting of a core and a cladding. These wave guides are used as precious quality control devices for on-line monitoring of industrial materials processes. This paper is devoted to the tailoring of the ultrasonic behavior of metallic coatings produced by arcspraying. Experimental results show that by a proper control of the core-cladding system it is possible to minimize ultrasonic spurious signals occurring in a clad wave guide while the tailoring of the splat morphology, intersplat oxidation and porosity enable the appropriate ultrasonic absorption within the coating. The unwanted spurious signals are normally generated at the periphery of the core. Examples of the use of thick (up to 5 mm) stainless steel or bronze coatings as claddings on steel, aluminum or zirconium rods in order to provide good ultrasonic wave guides are given. Compared to a conventional non-clad rod the signal to noise ratio of such clad rods has been improved by more than 40 dB due to the reduction of the spurious signals. The potential applications of these clad buffer rods for thickness measurements and in-situ monitoring of materials at elevated temperatures are demonstrated.
Improved High Temperature Iron Oxide Based Tribological Coatings
Authors: Kleyman A. , Kamo L.
Published: May 2021

The experimental results of developing tribological surface coatings for high temperature application are presented. The primary focus of this work was in the area of high output advanced, low heat rejection (LHR) diesel engines, where high temperature lubrication between the piston ring and the cylinder liner wall surface is essential. The target temperature focused upon in our research is an operating top ring reversal temperature of approximately 1000° F. The technology developed typically involves treating a porous thermal spray coating with chemical binders improving coating strength and integrity and eliminating open porosity to form an almost monolithic appearing coating. The effectiveness of the densification through the coating thickness was studied. It has been shown that densification process improves mechanical properties and dramatically extends coating wear resistance. Good results were obtained using densified plasma spray Iron oxide (hematite) for a cylinder liner coating versus plasma sprayed Tribaloy T 800 for piston ring. Single Cylinder LHR engine test successfully demonstrated the feasibility of this tribological pair for the possible future applications.
Behavior of Some Tungsten Carbide Coatings in Molten Zinc
Authors: Stavros A.J.
Published: May 2021

Two different W-Co-C powders were used in three deposition devices, the Super D-Gun, Jet Kote, and JP-5000 to produce coatings for laboratory immersion tests in molten zinc and %55Al-Zn. Resistance was evaluated as time to failure. Scanning electron microscopy and X-ray diffraction were used to characterize the structures ssid failure mechanism. All coatings were found to fail when the molten metal breached the coating thickness at weak spots and spread out over the underlying interface to lift the coating away from the underlying 316L substrate. These weak spots were "pits" on one Super D-Gun coating (the most resistant coating) and cracks on all the other coatings. No diffusion of zinc through the tungsten carbide coatings was observed.
Cavitation Erosion of HVOF Coatings
Authors: Schwetzke R. , Kreye H.
Published: May 2021

The proposed paper reports a series of experiments to investigate the cavitation erosion mechanism of HVOF coatings. Vibratory cavitation erosion tests according to ASTM G 32 have been carried out with several HVOF coatings including cermets, oxides and metallic alloys. The steady state erosion rate for each coating was determined and the effect of coating composition and microstructure on the erosion rate was investigated. The morphology and microstructure of the various coatings before and after cavitation testing were analyzed by means of light optical and scanning electron microscopy in order to study the erosion mechanism. The results demonstrate that HVOF coatings of NiCrFeBSi, WC-17Co, Cr3C2-25NiCr and Cr2O3 can exhibit a rather high resistance against cavitation erosion and should be considered for application as a protective surface layer against cavitation. Furthermore, it is shown that cavitation testing can provide a useful tool to study and characterize the bond strength between individual splats as well as the brittleness of the individual phases present in the coating.
Titanium Carbide in Wear Resistant Coatings
Authors: Vitiaz P. , Verstak A. , Azarova T. , Talako T. , Lugscheider E.
Published: May 2021

The poblems of metal-titanium carbide coatings processing by air, low pressure and underwater plasma as well as high velocity oxygen fuel spraying are under consideration. Among the different methods of metal-TiC powders production, like mixing of carbides with scale structure metals, agglomeration with binders, a matter of special interest is the high temperature synthesis of TiC in presence of metallic alloy. The characteristic features of these materials include the carbide phases forming, their bonding with the alloy and reactions during spraying, grain size and their distribution, alloy behavior during synthesis and spraying. Finally, the abrasive wear and erosion resistance of Al-Si/TiC, Fe-Cr/TiC and Ni-Cr/TiC coatings is analyzed.
Applying Thermoplastic Powder by Flame Spraying on Various Types of Substrates
Authors: Dominguez R. , Monerie F. , Vardelle A. , Fauchais P.
Published: May 2021

Polymeric coatings are now widely used for their corrosion resistance, low friction coefficient against many materials, decorative properties but also, when doped with ceramic particles, their protection against slipping and their good erosion resistance. Compared to traditional means of deposition, flame spraying in controlled atmosphere extends the scope of their applications either for shapes that can be coated or for site deposition. The materials chosen for spraying were Rislan, Gotalene and Tefzel. In this paper are presented the flame spraying technique which was used and the parameters controlling particles melting as well as, the substrates on which coatings were achieved (metals, woods, concretes, ceramics...) and their preparation. A few applications are then described with for example coatings reinforced by ceramic particles against slipping in wet or greasy area.
Acoustic Emission Studies of Thermal Barrier Coatings during Cyclic Four Point Bend Tests
Authors: Voyer J. , Gitzhofer F. , Boulos M.L. , Dionne J.
Published: May 2021

In this study, Acoustic Emission (AE) signals are used to monitor the degradation of plasma sprayed Thermal Barrier Coatings (TBC) using cyclic four point bend tests. Signal analysis both in time and frequency domains is carried out in order to identify the key parameters which can be used to classify the acoustic emission signals as a function of the damage mechanisms. This classification offers a mean of prediction of the long-term behavior of the thermal barrier coating based on the acoustic emission signal signature at the early stages of bench testing. The samples consist of a Nickel-based alloy blade coated with a duplex TBC made of a 150 μm thick bond coat covered with a 300 μm thick partially-stabilized zirconia coating. Tests were performed on unnotched and perpendicularly notched samples in order to discriminate the AE from perpendicular cracks. Two broadband transducers are used for acquisition of acoustic emission signals. Measuring the time between signal detection by each of the two transducers provides a means of determination of the location of the source of the acoustic signals. A classification of the signals based on their energy and their maximum peak frequency is presented. A comparison is made between the degradation mechanisms of TBC under thermal cycling conditions that were presented elsewhere (1) and the results of four point bend tests presented here.
Plasma Processing of Functionally Graded Materials: Diagnostics and Characterization
Authors: Smith W. , Jewett T.J. , Sampath S. , Berndt C.C. , Herman H. , Fincke J. , Wright R.N.
Published: May 2021

Functionally graded materials (FGMs) offer solutions to such engineering problems involving multi-layer systems with large differences in CTE, i.e. thermal barrier coatings, by allowing for a continuous change in the properties over a defined distance, thus minimizing sharp interface effects. By its nature, plasma spraying is well suited to the fabrication of FGMs. However, in order to achieve optimal performance from the material it is necessary to ensure the FGM is uniform in its compositional variation. The deposition efficiency of the particulate species as well as their trajectories will determine the degree of homogeneity of the FGM. It is therefore important that the inter-relationships between the particle size distributions, injection orientation and feed rates are determined. Towards this end, a series of investigations have been carried out to determine the effects of injection orientation on the particle segregation. Analysis of the particle segregation as a function of particle size distribution was then examined in the formation of FGMs. The results indicate that optimal deposition occurs when the various particle species trajectories converge as they approach the substrate.
Al-SiC Metal Matrix Composite Coatings by Plasma Spraying
Authors: Ghosh K. , Troczynski T. , Chaklader A.C.D.
Published: May 2021

The use of aluminum in the automobile engines and other critical parts require a superior surface property of the same. This has led to the development of plasma sprayable surface coatings in the automotive components. To impart the maximum bonding strength, along with hardness to the coatings, an aluminum based composite (Al-SiC) was chosen to be the most suitable. The presence of a hard second phase within a soft matrix improves the wear resistance of the material. The metal matrix composite powders were made by mechanical alloying of 6061 aluminum alloy (particle size 40-60 μm) along with fine SiC particles (≈ 8μm). Content of SiC was varied from 20-75vol% the balance being aluminum alloy. An organic material was used as Process Control Agent to optimize distribution of ceramic within metal matrix. The coatings obtained by plasma spraying the powders were characterized for their microstructure, adherence, wear and other physical properties.
Self-Lubricating Composite Plasma Sprayed Coatings
Authors: Niebuhr D. , Scholl M. , Clayton P.
Published: May 2021

Composite self-lubricating coatings were developed using high-energy plasma spraying (HEPS). These coatings would be potentially used in high contact pressure rolling/sliding systems. The coatings are based on a steel coating deposited by high energy plasma spraying using wire feedstock. Solid lubricants such as graphite and soft metal were investigated. Twin roller rolling/sliding tests were performed at 5% and 35% creep and contact loads of 700 N to 1700 N on a 5 mm contact face. Reduced friction, compared to a steel coating-steel or 1080 wrought steel couple was observed under these rolling-sliding contact conditions.
Properties of a Thermal Barrier Coating Fabricated by R.F. Plasma Spraying
Authors: Crabos F. , Monge-Cadet P. , Lucchese P. , Blein F. , Rigal E.
Published: May 2021

A P.S.Z. coating elaborated by r.f. plasma spraying was studied and compared to industrial arc plasma-sprayed P.S.Z. coatings to evaluate the quality of the corresponding thermal barrier coating system for gas turbine applications. One commercial ZrO2 - 8% Y2O3 powder was sprayed with two industrial d.c. torches (7MB and F4) and one r.f. plasma torch (Tekna PL50). Physical properties such as density, porosity and thermal diffusivity were measured on the three types of P.S.Z. coating. The microstructure and quantitative phase analysis were respectively investigated by S.E.M. and X-Ray diffraction. The burner rig tests on the T.B.C. systems showed that the thermal shocks resistance on the r.f. coating was at least the same as the others. Induction plasma spraying gave a high deposit efficiency (around 80%) and a P.S.Z. coating with very interesting thermal properties. All these facts demonstrate that r.f plasma spraying can be a competitive process to produce high quality thermal barrier coatings.
Phase Formation during In-Flight Treatment of MoSi2 Powders in an R.F. Induction Plasma
Authors: Fan X. , Ishigaki T.
Published: May 2021

The in-flight modification of MoSi2 powders has been carried out by using an Ar-H2 induction plasma. Reactor pressure, powder feed rate and plate power level were taken as the experimental parameters to alter the thermal history of the injected powder particles. Metastable hexagonal structure of P-MoSi2 is the major phase observed in the induction plasma treated molybdenum disilicide powders, the stable phase of tetragonal structure of α-MoSi2 usually retains approximately 30 wt.%. Following the change in experimental condition and the deviation from stoichiometry in raw materials, low silicides, Mo5Si3 and Mo3Si, and free Si were observed. The formation of these phases are explained in terms of metastable eutectic reaction during rapid solidification processing. The relationship between the quantities of all these phases and the experimental conditions has been discussed.
The Characteristics of Diamond Film Deposited by Magnet-Enhanced Plasma Jet CVD
Authors: Zhou K. , Dair M. , Wang D. , Han P. , Feng B.
Published: May 2021

A diameter of 30 mm polycrystalline diamond film has been deposited by magnet-enhanced DC plasma jet CVD. The diamond film was characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and surface profilograph. Results reveal that under the same depositing parameters, magnetic field can increase purity of diamond film, improve thickness uniformity of diamond film, but no influence on crystal perfection and size of microcrystal of diamond film. A discussion on magnetic effect is presented.
Effect on Reverse Transferred Arc Treating on Bonding Strength in Low Pressure Plasma Spraying
Authors: Honda K. , Chida I. , Fuse T. , Murakami T. , Kobayashi K.F.
Published: May 2021

Both bonding strength of coating to substrate in low pressure plasma spraying and the effect of reverse transferred arc treating before spraying are studied in this paper. It is difficult to obtain the bonding strength precisely in low pressure plasma spraying by standard testing methods, such as, ASTM Standard C633-79 and JIS H8666-80. Therefore, for the bonding strength test rather than using a conventional adhesive, we believe a vacuum brazing process using Ag-Cu-In-Ti active filler metal at 1023 K should be used. We have also confirmed the practicality of this step. By the above test method, it has been proven that the bonding strength of low pressure plasma sprayed coating is over 100 MPa. Also, that reverse transferred arc treating after blasting enhances the bonding strength of low pressure plasma sprayed coating. It is also believed that the projections formed on the substrate surface by reverse transferred arc treating are buried into the coating and perform the pile effect.
Iron-Based Deposits Produced by High-Throughput Water Stabilized Plasma
Authors: Dobler K. , Branco J.R.T. , Sampath S. , Berndt C.C. , Herman H. , Chráska P.J.
Published: May 2021

Iron-based thermal spray deposits have been used for reclamation of machine components and wear resistance. Current thermal spray processes can be used to spray deposits a few millimeters thick at rates of 3 to 10 kg/hr. With a throughput over 100 kg/hr for metals, the Water Stabilized Plasma torch enables cost-effective processing of very thick (>1 cm) deposits at very high rates. However, limited information exists in the literature on the ability of this technology for deposition of oxygen sensitive metals. In this investigation, iron-based coatings were produced with the water stabilized plasma system. The deposits sprayed in air and with an inerting shroud were evaluated using x-ray diffraction, light microscopy, oxygen analysis and microhardness in an effort to understand the processing effects on microstructure and properties.
Particle Size Effects on Chemistry and Structure of Al-Cu-Fe Quasicrystalline Plasma Sprayed Coatings
Authors: Sordelet D. , Besser M.
Published: May 2021

A brief study was performed to examine the influence of starting powder composition, starting powder particle size and spraying environment on the chemistry, phase assemblage and porosity of Al-Cu-Fe plasma sprayed coatings involving a quasicrystaliine phase. It was found that a loss of Al during spraying results from the extremely low thermal conductivity of the quasicrystaliine phase in the starting powders. This loss changes the bulk composition of the deposited coating and partially controls the phases that develop. Smaller starting powder particles tended to lose more Al and, therefore, form less of the quasicrystaliine phase. Larger starting powder particles did not lose Al to the same degree, and produced coatings with more of the quasicrystaliine phase. However, these powders produced coatings also had a higher amount of porosity.
Effects of Pressure Deposition on Plasma Jet and Coatings Microstructure
Authors: Valente T. , Bertamini L. , Tului M.
Published: May 2021

Pressure inside the spray chamber plays a key role during coatings manufacturing by thermal spraying and coating properties can be strongly affected by the selected pressure value. Spraying at low pressure results in a longer plasma jet length, higher particle velocity, lower coating porosity and higher purity and phase stability. For what concerns plasma-particle interactions, a reduction of pressure value drastically decreases heat transfer towards particles, therefore high power plasma equipment must be used to achieve a suitable melting degree of sprayed powders. Effects of low pressure values are well known, but few investigation have been carried out on effects of pressure for values higher than 1,000 mbar. In this paper a preliminary evaluation of pressure effects on plasma jet modifications, particle velocity and coatings microstructure is presented. By using the very innovative CAPS (Controlled Atmosphere Plasma Spraying) system, Ni-20%Al powders were sprayed at different pressure values, up to 3,600 mbar. The length and width of the visible part of the plasma jet was measured and controlled. Average particle velocity was also evaluated as a function of pressure. Coatings, manufactured on stainless steel substrates, were characterized by means of scanning electron microscopy and energy dispersive spectroscopy, x-ray diffraction and Vickers microhardness measurements. Results indicate that the higher the spraying pressure the lower the plasma jet length and particle velocity; but also a lower selective evaporation of aluminum and higher microhardness values were observed.
Ceramic Impregnation of Plasma Sprayed Thermal Barrier Coatings
Authors: Kathikeyan J. , Berndt C.C. , Ristorucci A. , Herman H.
Published: May 2021

Reducing the pore size and pore volume can lead to improved mechanical properties and enhanced corrosion resistance of plasma sprayed thermal barrier coatings. In this work, plasma sprayed 8 wt.% yttria stabilized zirconia coatings were removed from the substrate and machined to obtain 25x5x1 mm test specimens. These specimens were vacuum impregnated with alumina sol, calcined at 873 K for an hour and then heat treated at 1273 K for an hour to produce ceramic impregnated specimens. As-sprayed and impregnated specimens were investigated using optical microscopy, XRD, SEM, mercury intrusion porosimetry and electron microprobe analysis. This technique can impregnate the entire thickness of the specimens. Pores in the as-sprayed specimens were impregnated with α alumina grains, resulting in microstructural variations and reduction of the size and volume of the specimen pores.
Computational Fluid Dynamics Analysis of a Wire-Feed, High-Velocity Oxygen-Fuel (HVOF) Thermal Spray Torch
Authors: Lopez A.R. , Hassan B. , Oberkampf W.L. , Neiser R.A. , Roemer T.J.
Published: May 2021

The fluid and particle dynamics of a High-Velocity Oxygen-Fuel Thermal Spray torch are analyzed using computational and experimental techniques. Three-dimensional Computational Fluid Dynamics (CFD) results are presented for a curved aircap used for coating interior surfaces such as engine cylinder bores. The device analyzed is similar to the Metco Diamond Jet Rotating Wire (DJRW) torch. The feed gases are injected through an axisymmetric nozzle into the curved aircap. Premixed propylene and oxygen are introduced from an annulus in the nozzle, while cooling air is injected between the nozzle and the interior wall of the aircap. The combustion process is modeled using a single-step finite- rate chemistry model with a total of 9 gas species which includes dissociation of combustion products. A continually-fed steel wire passes through the center of the nozzle and melting occurs at a conical tip near the exit of the aircap. Wire melting is simulated computationally by injecting liquid steel particles into the flow field near the tip of the wire. Experimental particle velocity measurements during wire feed were also taken using a Laser Two-Focus (L2F) velocimeter system. Flow fields inside and outside the aircap are presented and particle velocity predictions are compared with experimental measurements outside of the aircap.
On the Modeling Approach of DC Arc Plasma Flows by Implementation of the CFD Phoenics Code
Authors: Eichert P. , Coddet C. , Imbed M.
Published: May 2021

This paper is devoted to the presentation of a modeling approach of DC arc plasma flows by implementation of the CFD PHOENICS code. The equations of mass, momentum and energy, of elliptic type, are discretized using a finite/control volumes method. The closure of the equations set is obtained with the standard k-ε turbulence model. Finally, the algebraic equations set is solved by means of the SIMPLE algorithm. 3D calculations are performed from the point of the cold gas injection into the torch to the plasma ejection into the surrounding atmosphere, taking into account some currently used spray parameters (i.e., plasma gas flow rate, power, etc.). Results are discussed and compared with experimental values taken from the literature.
Voltage and Current Fluctuations in Wire Arc Spraying as Indications for Coating Properties
Authors: Watanabe T. , Wang X. , Heberlein J. , Pfender E. , Herwig W.
Published: May 2021

Electric arc spraying with dual wires is an economical coating process finding diverse applications. Turbulence and velocity of an atomizing gas exert strong effects on the droplet formation and therefore on the coating properties. Turbulence intensity of an atomizing gas flow can be estimated by analysis of the waveforms of arc voltage fluctuations, and the velocity can be estimated by the frequency and the amplitude of these waveforms. Higher gas velocities result in higher frequencies and smaller amplitudes of the voltage fluctuations, and in smaller molten droplets leading to coatings with lower porosity but higher oxidation levels. Lower turbulence levels at the electrode tips result in more periodic waveforms with less high frequency content, and in lower oxidation of the coatings. Nozzle configurations such as a converging-diverging nozzle provide higher gas velocities with less turbulence leading to coatings with lower oxidation and lower porosity.
Coating Thickness Prediction and Robot Trajectory Generation of Thermal Sprayed Coatings
Authors: Nylén P. , Fransson I. , Wretland A. , Mårtensson N.
Published: May 2021

Off-line programming (OLP) techniques can be used to reduce programming time and to be able to better control process parameters, such as spray distance and nozzle orientation. This paper presents a simulation method to predict coating thickness build-up on complex geometries. Discretization in time and space is done by using a finite difference model. The model starts with an empirical deposit rate function, which calculates the thickness on a flat surface normal to the spray cone. This model is integrated into a commercial robot simulation program (IGRIP) where discretization of a free form surface into planar polygons is carried out. The thickness is then calculated by stepping the process in increments of time. A robot trajectory is calculated, maintaining spraying distance and normal orientation to the surface. This trajectory is optimized numerically giving a collision free path and a uniform coating thickness. Devices are then programmed, the programs are translated and finally downloaded to the robot controller.
A Complete Predictor Methodology for the Plasma Spray Process
Authors: Varacalle D.J. , Barnett K.
Published: May 2021

To enhance usage of the plasma spray process, a better physical understanding of the process is required, which entails a synergistic mix of analytical and empirical studies. Better understanding can lead to development of optimal thermal spray coatings for future applications. This study presents an analytical method that can be used for these purposes. Experimental and analytical studies were conducted to investigate gas, particle, and coating dynamics and the resulting coating properties in the plasma spray process for the Tribaloy 800 powder system. Historical full-factorial statistically designed experiments were the basis for the analytical-experimental comparisons. The thermal plasma produced by a commercial plasma spray torch was then numerically modeled from the electrodes to the standoff distance in the free plume for sixteen experiments. This information was then used as boundary conditions to solve the plasma/particle interaction problem for the experiments. The predicted temperature and velocity of the droplets at the spray distance were then used as initial conditions to a coating dynamics code. Multiple polynomial regression analysis was then used to establish the sequential relationship between the process parameters (i.e., power, total flow, hydrogen flow), the coating properties (porosity, oxides), and the coating mechanical performance properties (tensile strength, microhardness, superficial hardness). The equations derived from the regression analysis were used to construct a predictor code for the process. The code predicts the process and coating attributes reasonably well. The predicted coating properties exhibit excellent correlation with the actual properties obtained from the experimental studies in the range of the parameter settings.
The Effect of Spray Distance and Chemistry on Pore and Crack Development in Plasma Sprayed Ceramic Deposits
Authors: Ilavsky J. , Long G.G. , Allen A.J. , Herman H. , Berndt C.C.
Published: May 2021

The porous microstructure of plasma-sprayed deposits prepared from gray-alumina feedstock and from two different yttria-stabilized zirconia (YSZ) feedstocks were studied as a function of spray distance. For each material, the behavior of the two major void systems—intralamellar cracks and interlamellar pores—was investigated. The results offer the first proof that the quantity and the character of the porosity in these materials can be controlled independently by selecting the appropriate processing protocols.
Microstructure and Properties of Thermally Sprayed TiC-Ni and (Ti,Mo) C-NiCo Coatings
Authors: Vuoristo P. , Stenberg T. , Mäntylä T. , Berger L.-M. , Nebelung M.
Published: May 2021

Hardmetal-like coatings on the base of titanium carbide as a hard phase and nickel as a metal binder were prepared from agglomerated and sintered powders by plasma spray, detonation gun spray and high-velocity oxygen-fuel spray processes. The powders used in the spray experiments were plain TiC-Ni type and alloyed (Ti,Mo)C-NiCo type powders with different binder content. The coatings were characterized by optical and scanning electron microscopy, microhardness measurements, XRD analysis and in an abrasion wear test. The results showed that the sprayability of these novel hardmetal-like powders is good in all spray processes studied and the coatings deposited were found to have dense microstructures and good properties. The XRD analysis showed that the coatings have a phase structure similar to that found in the spray powder. The amount of retained carbides in the coatings was high. Some regions in which the carbides had dissolved with the metallic binder phase during spraying were also found, especially in plasma sprayed coatings. In such microstructural regions submicron size reprecipitated carbides were detected. These were clearly detectable in detonation gun sprayed coatings. HVOF sprayed coatings were found to contain a very high content of retained carbide phase. In this process the heat effect to the material seemed to be the lowest. The wear tests clearly showed the importance of alloying the hard phase and the binder phase in order to improve the wear resistance of the coatings. All studied spray processes produced coatings with nearly similar coating wear properties.
The Structure and Thermal Properties of Plasma Sprayed Beryllium for the International Thermonuclear Experimental Reactor (ITER)
Authors: Castro R.G. , Bartlett A.H. , Elliot K.E. , Hollis K.J.
Published: May 2021

Plasma spraying is under investigation as a method for in-situ repair of damaged beryllium and tungsten plasma facing surfaces for the International Thermonuclear Experimental Reactor (ITER), the next generation magnetic fusion energy device, and is also being considered as a potential fabrication method for beryllium and tungsten plasma-facing components for the first wall of ITER. Investigators at the Los Alamos National Laboratory's Beryllium Atomization and Thermal Spray Facility have concentrated on investigating the structure property relationship between the as-deposited microstructures of plasma sprayed beryllium coatings and the resulting thermal properties of the coatings. In this study, the effect of the initial substrate temperature on the resulting thermal diffusivity of the beryllium coatings and the thermal diffusivity at the coating/beryllium substrate interface (i.e. interface thermal resistance) was investigated. Results have shown that initial beryllium substrate temperatures greater than 600°C can improve the thermal diffusivity of the beryllium coatings and minimize any thermal resistance at the interface between the beryllium coating and beryllium substrate.
Stereological Characterization of the Apparent Void Content of Thermal Spray Deposits
Authors: Montavon G. , Coddet C.
Published: May 2021

Properties and characteristics of a material depend mainly upon its morphological structure. In the case of plasma sprayed deposits, the properties (i.e., mechanical, thermal, electrical, etc.) are especially related to the deposit void content. Voids are coming from pores, cracks and delaminations. Implementing image analysis and stereological protocols, the apparent void content (AVC) of a vacuum plasma sprayed deposit was studied, in terms of the pore size distribution and spatial distribution. Results were compared with data obtained implementing water immersion porosimetry. This study showed on the one hand that the pore size distribution is described by a bimodale function, and, on the other hand, that pores are spatially distributed evenly within the deposit (isotropic distribution). In such a condition, the stereological protocol can be implemented on a single random plane section of the deposit.
A Comprehensive Approach for Advancing Plasma Spray Processing Technology
Authors: Sampath K. , Onesto E.J.
Published: May 2021

A comprehensive approach is presented for facilitating the implementation of advanced plasma spray processing technology in the manufacture, repair, and refurbishment of industrial components. This approach employs an integrated methodology for combining several advanced computer-based methods, including: 1) an interactive multimedia-based education and training tool to effectively store and retrieve plasma spray processing information in a variety of formats; 2) an expert system to select plasma spray feedstock material for a specific coating function; 3) a one-dimensional plasma spray process model that allows simulation of plasma spray processing conditions for identifying operational envelopes for a selected feedstock material; 4) an interface fracture model for identifying appropriate acceptance criteria for reduced cracking along the coating/substrate interface; and 5) a set of computer-based nondestructive test methods for performing quality assurance and control. This comprehensive approach and the integrated methodology provide an advanced engineering tool for the selection, optimization and implementation of specific advances in plasma spray processing technologies. A major outcome is the reduced need for expensive and time-consuming trial-and-error methods in evaluating the application of plasma spray coatings for the manufacture, repair, and refurbishment of specific industrial components. This comprehensive approach and integrated methodology can be extended to include other thermal spray processing technologies as well.