bluuebunny/crossref_metadata_2025 huggingface dataset:
Digital Diplomacy and its Prospect for Nepal
Authors: Shrestha Madhavji
Published: September 2022

Change in any dimension ushers in new dawn. The fast-paced advancement of the information, communication, and technological sectors has affected several traditional areas. One area that has been highly impacted is the domain of diplomacy. The digital imprints in diplomacy have shifted the diplomatic activities to a virtual platform. However, there have been difficulties in defining the idea of “digital diplomacy”. This study points out the efforts of the scholars and researchers towards defining the domain of digital diplomacy. Therefore, the primary aim of the article is to explore different facets of digital diplomacy. It explains how the digitization process began in diplomacy and whether digitization has displaced or complemented the traditional forms of diplomacy. The study has highlighted the supremacy of human beings over the new technologies in diplomacy. It deals with the policy goals of digital diplomacy and emphasizes the United Nations’ attempt to enhance the same. Finally, the study has explored digital diplomacy of Nepal and makes policy recommendations for enhancing digital diplomacy in Nepal. The study has used secondary resources, including books, journals, and online media platforms. The information and ideas are put in array for the coherent presentation of the study with the adoption of analytical process.
Web scraping Instagram Pre and During Covid-19: Examining customer engagement on Australian SMEs accounts
Authors: Nguyen Viet Hoang , Sukunesan Suku , Huynh Minh
Published: September 2022

Instagram has gained the attention of hundreds of millions of users and evolved quickly into a critical customer engagement tool for businesses worldwide, more so during Covid-19. Impacts of Covid-19 have fundamentally changed the market, and therefore, this paper explores the relationship between Instagram practices and the engagement of 20 Australian SMEs (Small medium enterprises) pre and during Covid-19. This study aims to answer the following questions: (1) How should user-generated content (UGC) and call to act content (CTA) be included as Instagram posts? (2) How to use #Hashtags and @Tagging in Instagram posts to keep a campaign going? (3) How Instagram can be utilised to mitigate the effect of Covid-19? Findings revealed a statistically significant relationship between the number of UGCs to Instagram engagement, while CTA   content performance recorded a mixed result. However, both UGCs and CTA positively affect the engagement when used to build a virtual community and engage with followers rather than redirecting customers to online selling locations. Also, diversity in @Tagging and #Hashtag uses are found to be effective drivers of engagement. The results imply that addressing the Covid-19 related concerns of followers while showing genuine brand social responsibility can be rewarded by extra engagement.
Desain Perlindungan Hukum Pada Pelayanan Perizinan Berbasis Standar Pelayanan Partisipatif Satu Pintu
Authors: Sirajuddin Sirajuddin
Published: September 2022

The Constitution guarantees the right for services, so that the government  is obliged to provide protection guarantee and legal certainty to each citizen in the government and public services. Ironically, the right for services is often taken away by the egoism of the state elites and the fading professionality among the government apparatus as the providers of services. Therefore, it is interesting to study a proper design of legal protection to the license service recipients based on one-stop    participatory licensing service standard  after the enactment of the Law on Job Creation. This study employed a juridical normative approach. The results showed that the legal protection to the citizens in providing the licenses is still covered by cost uncertainty, service time, and low satisfaction among the citizens to the licensing service. As  a result, it needs a strategy to strengthen the fulfillment of right for services by encouraging changes regulations into  responsive and progressive ones with  transparency  and professionality of service and accompanied by  cultural formation among the service apparatus ending in the legal protection to the licensing service recipients so that one-stop  participatory service standard may be attained
High Strain Rate Deformation Phenomena in Explosive Powder Compaction and Cold Gas Spraying
Authors: Schmidt T. , Gärtner F. , Kreye H.
Published: September 2022

In cold gas spraying, the powder is not molten before impact on the substrate. The bonding of the coating only depends on powder characteristics and impact conditions. To optimize coating microstructure and properties, spray conditions have to be tuned for a particular powder. The optimization procedure usually requires a systematic variation of spray conditions and an analysis of the sprayed coatings which is time consuming and costly. Therefore, alternative test methods which are less expensive and operate with similar load mechanisms on powder particles have to be developed. High strain rate deformation can be easily studied by explosive powder compaction. In this method, the powder is loaded by a shock wave and deformed under high strain rates. The bonding conditions of powder particles should be similar to those obtained in cold spraying. By a special design, shock loading in explosive powder compaction can cover a wide energy range in one single experiment. Therefore, the method appears feasible to determine the energy input required for successful bonding of particles. To evaluate the capability of the method, microstructural features of particle/particle interfaces are investigated and compared to those of cold sprayed coatings. In addition, the results can supply more information concerning the bonding mechanisms in cold gas spraying.
Particle-Substrate Interactions in Cold Gas Dynamic Spraying
Authors: Zhang D. , Shipway P.H. , McCartney D.G.
Published: September 2022

Aluminium powder of 99.7wt% purity and in the nominal particle size range –75+15µm has been sprayed onto a range of substrates by cold gas dynamic spraying (cold spraying). The substrates examined include metals with a range of hardness, polymers and ceramics. The substrate surfaces had very low roughness before deposition of aluminium in an attempt to separate effects of mechanical bonding from other forms of bonding. The cross-sectional area of a single track of aluminium sprayed onto the substrate was taken as a measure of the ease of initiation of deposition, assuming that once a coating had begun to deposit onto a substrate, its growth would occur at a constant rate regardless of substrate type. It has been shown that initiation of deposition depends critically upon substrate type. For metals where initiation was not easy, then small aluminium particles were seen to be deposited preferentially to large ones (due to their higher impact velocities); these may have acted as an interlayer to promote further building of the coating. A number of phenomena have been observed following spraying onto various substrates, such as substrate melting, substrate and particle deformation and evidence for the formation of a metal-jet (akin to that seen in explosive welding). Such phenomena have been related to the processes occurring during impact of the particles on the substrate. Generally, initiation of aluminium deposition was seen to be poor for non-metallic materials (where no metallic bonding between the particle and substrate was possible) and for very soft metals (in the case of tin, melting of the substrate was observed). Metallic substrates harder than the aluminium particles generally promoted deposition, although deposition onto aluminium alloy was difficult due to the presence of a tenacious oxide layer. Initiation was seen to be rapid on hard metallic substrates, even when deformation of the substrate was not visible.
Plasma-Sprayed Ceramic Coatings for Molten Metal Environments
Authors: Hollis Kendall J. , Peters Marla I. , Bartram Brian D.
Published: September 2022

Coating porosity is an important parameter to optimize for plasma-sprayed ceramics which are intended for service in molten metal environments. Too much porosity and the coatings may be infiltrated by the molten metal causing corrosive attack of the substrate or destruction of the coating upon solidification of the metal. Too little porosity and the coating may fail due to its inability to absorb thermal strains. This study describes the testing and analysis of tungsten rods coated with aluminum oxide, yttria-stabilized zirconia, yttrium oxide, and erbium oxide deposited by atmospheric plasma spraying. The samples were immersed in molten aluminum and analyzed after immersion. One of the ceramic materials used, yttrium oxide, was heat treated at 1000°C and 2000°C and analyzed by X-ray diffractography and mercury intrusion porosimetry. Slight changes in crystal structure and significant changes in porosity were observed after heat treatments.
Erosion Resistance of Arc Spray Composite Coatings at High Temperature on Boiler Tubes of Pulverized Coal Fired Power Station
Authors: Shi-ning Ma , Jun-zhi Hu , Xue-rong Chen , Chang-qing Li , Qian Liu , Hai Jiang
Published: September 2022

Several novel cored wires for producing Fe3Al intermetallic coating, Fe3Al/WC intermetallic coating, FeCrAl/WC intermetallic coating and FeCrNi/WC intermetallic coating by arc spraying were developed. The erosion wastage at high temperature of coatings was researched with different impingement angles and temperatures. The results indicated that impingement angle and temperature greatly affected FeCrAl/WC coating and Fe3Al/WC coating in erosion wastage. At the same time, the FeCrAl/WC coating had little effects on different temperature while impingement angle was 90° and different impingement angle while temperature was 650°C. As compared with water wall tube material (G20 steel) of power station boiler, the erosion resistance at high temperature of Fe3Al coating, Fe3Al/WC coating and FeCrAl/WC coating was higher. The erosion resistance rate of Fe3Al coating was 1.4~2.91 times of that of G20 steel when temperature was 650°C and particle was polygonal silica. At the same time, the erosion resistance rates of Fe3Al/WC coating and FeCrAl/WC coating was 1.4~3.06 and 1.94~2.89 times respectively. The results indicated that erosive condition of high temperature flue gas and fly ash mixture in boiler tube of pulverized coal fired power station could be solved with Fe3Al coating, Fe3Al/WC coating and FeCrAl/WC coating.
Assessing the Feasibility of using Diamond as a Reinforced Phase in Metal Matrix Composite Coatings
Authors: Richardson Andrea.F. , Neville Anne , Wilson John I.B.
Published: September 2022

Metal Matrix Composites (MMCs) are seeing increased use in tribological applications where hardness, toughness and wear resistance are required. Already such qualities have been included within composite coatings by methods such as electrochemical deposition. In this study the feasibility of including diamond as the hard phase in MMC’s using thermal spraying processes has been investigated. In this work the application specifically targeted is that of hard facing for sub sea drill bits, where the coatings experience a harsh environment of high stress abrasion, erosion and corrosion. The coatings were investigated in terms of their microstructure (light microscope, SEM), their elemental composition using EDX and XRD to identify retention of diamond and phases in the coatings, their hardness and abrasion resistance. Preliminary results show that it is possible to produce a hard facing diamond composite coating with good distribution of the diamond phase and little degradation of the diamond during the spraying and that diamond MMCs (DMMC) have potential for improving durability in drill bits. Diamond/metal powder mixture is sprayed onto the surface using an oxyacetylene torch.
The Influence of Matrix Phase Viscosity on the Plasma-Spray Deposition of Silicon-Nitride Composite Coatings
Authors: Bao Y. , Gawne D.T. , Zhang T.
Published: September 2022

Non-oxide ceramics, such as silicon nitride, have a unique combination of high strength, toughness, wear resistance, thermal and chemical stability. However, the use of these materials as thick protective coatings on engineering components has been severely restricted by their decomposition behavior. Silicon nitride, for instance, does not melt but decomposes at ~1900oC and so thermal spraying of pure silicon nitride powder is impracticable. A limited amount of research has been carried out on depositing silicon nitride in various metallic or ceramic matrix materials but none have produced adequate coating microstructures or coating properties. This paper concerns the design of oxide matrix systems for silicon nitride composite coatings. A quantitative model is developed for the viscous flow of two-phase feedstock particles on impact with the substrate and is applied to the deposition of silicon nitride – ceramic matrix coatings. A number of matrix systems are investigated including a series of yttria-alumina and yttria-alumina -silica compositions. The research shows that the oxide matrices successfully protect the silicon nitride from decomposition but that the matrix composition and particle loading have a critical influence on splat flow and coating quality.
A Parametric Study of an HVOF Process for the Deposition of Nanostructured WC-Co Coatings
Authors: Bartuli C. , Valente T. , Cipri F. , Bemporad E. , Tului M.
Published: September 2022

Nanocrystalline WC-Co coatings were deposited by high velocity oxy-fuel from commercial nanostructured composite powders. Processing parameters were optimized for maximal retention of the nanocrystalline size and for minimal decarburation of the ceramic reinforcement. Thermo-chemical and gas-dynamical properties of gas and particles flows within the combustion flame were identified in various operating conditions by CFD simulation. Significant improvements of coatings mechanical properties were evidenced: a decrease of the friction coefficient was measured for the nanostructured coatings, together with an increase of microhardness and fracture toughness.
Protection of Steel Components Against Marine Corrosion by Thermally Sprayed Anodic Coatings
Authors: Schiefler M.F.O. , Gärtner F. , Voyer J. , Kirsten A. , Kreye H. , Buschinelli A.J.A.
Published: September 2022

It is well known that thermally sprayed aluminum and aluminum alloys can be used to protect low-alloyed steel against marine corrosion in offshore applications. The efficiency and service life of this protection can be, however, severely limited by the amount and distribution of defects, which are usually present in coating microstructures. In thermal spraying, microstructures and properties are strongly influenced by the type of spray system used for the production of coatings. To investigate the influence of defects like pores, oxides and cracks on the corrosion performance, coatings were processed by conventional thermal spray techniques, such as Flame Spraying (FS) and Arc Spraying (AS). In addition, the more recently introduced High Velocity Combustion Wire (HVCW) spraying technique was used, which, due to higher particle velocities, results in lower porosity and finer coating microstructures as compared to conventional processes. The influence of spray conditions and related microstructures on the performance in corrosion tests was investigated for protective coatings of Al99.5, AlMg5 and Al - 30 wt. % W2C. The resistance against corrosion was analyzed by different electrochemical methods, such as corrosion potential monitoring, polarization resistance and potentiodynamic anodic polarization measurements. Additionally, the microstructures of the coatings were examined before and after the electrochemical tests. The results from these tests are correlated and attributed to the different microstructures obtained by the various spray techniques and different compositions of the feedstock material.
Tribological Testing of High Velocity Oxy Fuel (HVOF) Sprayed Composite Cermet Coatings Using Ball on Disk Configuration
Authors: Aw P.K. , Tan B.H.
Published: September 2022

Thermal sprayed (HVOF) cermet coatings (WC-17Ni) with and without solid lubricant (PTFE) were deposited on steel disks for sliding wear evaluation using the ball on disk configuration. Alumina (Al2O3) balls were slid against coated disks. The coated disks were ground and lapped to roughness of 0.3µm Ra and 0.05µm Ra respectively. A significant reduction in the average coefficient of friction was observed when solid lubricant was incorporated into the cermet coating. There were reductions in average coefficients of friction from 0.84 to 0.55 for ground disks and from 0.65 to 0.48 for lapped disks. These represented reductions in coefficient of friction of 34.5% and 26% by incorporating solid lubricant into the ground disks and lapped disks respectively. The inclusion of solid lubricant in the coating also resulted in significant reduction in the average specific wear rate for both the ball and disk. Abrasive wear was the predominant wear mechanism observed on the worn samples’ surfaces using optical microscopy. A conceptual wear mechanism with the introduction of solid lubricant into the cermet composite coating was proposed. A hypothesis on the formation of lubricating PTFE films on contacting surfaces during sliding wear was supported with elemental mapping by Scanning Electron Microscopy/Energy Dispersion X-ray (SEM/EDX) analysis of worn ball surfaces after sliding against disk counterfaces deposited with composite cermet coating containing solid lubricant. The EDX mapping showed a homogenous distribution of fluorine element across the surfaces analyzed.
Design of HVOF Sprayed Tungsten Carbide Coatings for Best Sliding Wear and Fatigue Life Characteristics
Authors: Isaac R.V. , Savarimuthu J. , Shadley J.R. , Rybicki E.F. , Emery W.A. , Kalivas W.
Published: September 2022

HVOF sprayed tungsten carbide (WC) thermal spray coatings are finding increasing acceptance for replacement of electroplated chromium on aircraft landing gear parts. In order to replace chrome plating by an HVOF WC coating, the latter should exhibit wear and fatigue characteristics at least as good as those of chrome plating. Sliding wear performance and fatigue life of tungsten carbide coated parts depend on morphology and phase composition of the coating which in turn depend on spray parameters such as powder characteristics, powder feed rate, gas flow rates, and spray distance. A Design of Experiments (DOE) approach for a Jet Kote™ HVOF spray system was used to identify optimal spray parameters for WC-Co and WC-Co-Cr coatings based on best sliding wear and best fatigue characteristics. Best sliding wear was defined as minimum block loss in the standard ASTM-G77 wear test in which a rotating WC coated ring is tested against a stationary Al-Ni-Bz block. Best fatigue characteristics were defined as compressive residual stresses in the coating in the range 250 to 450 MPa. Spray parameters found to strongly affect wear were powder feed rate, oxygen flow rate, powder size, and a powder type-powder size interaction. Spray parameters strongly affecting residual stresses include powder type, hydrogen flow rate, and powder feed rate. Some spray parameters were found to be orthogonal with respect to wear behavior and residual stress. This means some parameters can be adjusted to maximize one performance criterion (wear or residual stress) without adversely affecting the other.
New Thermal Spray Coating Technology for Corrosion/Erosion Protection
Authors: Ferree Bill
Published: September 2022

A laminated coating, using the thermal spray and other processes, protects a metal substrate in a highly corrosive and highly erosive environment. The combination of noble metals and ceramics offer highly bonded, pore free coatings for demanding industrial applications. This paper offers case examples to exemplify some success stories.
Plasma Spraying with Low Power Consumption and High Efficiency
Authors: Gao Yang
Published: September 2022

An innovative plasma spraying technology has been developed with low power consumption and high deposition efficiency. The plasma torch was operated at arc currents from 50 to 150A and voltages from 50 to 80V. The powder particles were injected into the arc region from the inside of nozzle entry by the carrier gas that then transferring through the plasma flame. The ceramic coatings of Cr2O3 and ZrO2- Y2O3 were created at power consumption less than 10kW and powder feed rate of 30-50g/min. The deposition efficiency could reach 70%, higher than that of 40kW APS with an external powder feed. In addition, the enthalpy, temperature and velocity of low power plasma jet were also measured by an enthalpy probe.
High-Pressure, Non-Pulsing Powder Feeder for Cold Spray and Thermal Spray Processes
Authors: Roemer Timothy J. , Beatty D.E. , Mayer A.J. , Papyrin A.N. , Blose R.E. , Nichols R.T.
Published: September 2022

The rapid emergence of cold spray technology provides numerous applications that require spraying fine (<10 microns) powders, providing more uniform deposition, improved measurement of deposition efficiency and quick turn around time. The performance of high-pressure commercial powder feeders, currently available, lacks one or more of these desired performance characteristics. Further, researchers are interested in spraying many powders of different materials or particle size distributions where the powder feeder can be quickly and easily cleaned without replacing expensive consumables. The Ktech laboratory powder feeder has been designed to operate under a wide variety of carrier gas pressures (0 – 500 psig). This laboratory feeder delivers a continuous flow of powder, has a variable canister volume and is quick and easy to clean. This unique design facilitates short run research applications or higher volume extended run time dispensing. The feeder is designed to operate in either a locally or remotely through a PC based Ethernet connection. The laboratory powder feeder represents an excellent tool for high-pressure cold spray or low-pressure thermal spray processes requiring the delivery of fine powders.
Preparation of TiO2 Photocatalyst by Thermal Spraying with Liquid Feedstock
Authors: Yang G.-J. , Li C.-J. , Han F. , Mao S.-F.
Published: September 2022

TiO2 is the most promising photocatalyst to decompose industrial pollutants in water and air. Compared with TiO2 powder, the immobilized form is more suitable for application. In the present paper, the nanostructured TiO2 photocatalyst is formed by thermal spraying with liquid feedstock. The microstructure of the nanostructured TiO2 is characterized by infrared spectrum, X-ray diffraction, scanning electron microscope, and transmission electron microscope. The photocatalytic performance is characterized with photodegradation of phenol in aqueous solution. The effects of annealing treatment on the crystalline structure of the TiO2 deposit and the photocatalytic performance are investigated. The results showed that TiO2 photocatalyst deposited by thermal spraying with liquid feedstock presents nanostructure and anatase crystalline structure mainly. The crystalline structure of TiO2 deposit can be controlled by post annealing treatment. The as-sprayed TiO2 coating can decompose phenol in water with the presence of H2O2 and UV light. Phenol can be destroyed easily while the complete mineralization takes a little more time. Annealing treatment can improve the photocatalytic performance of TiO2 coating. The present results revealed that the TiO2 coating in rutile structure presents a better photocatalytic performance compared with as-sprayed TiO2 coating in anatase structure.
Study on Alumina-based Nano Composite Coating Prepared by Plasma Spray
Authors: Suzuki M. , Sodeoka S. , Inoue T.
Published: September 2022

In order to obtain nano-structured ceramics composite coating for high temperature application, pre-mixed Al2O3/Y2O3 powders were plasma-sprayed in this study. Plasma spraying of spray-dried Al2O3/Y2O3 powder resulted in the formation of amorphous coating of metastable Al2O3-Y2O3 solid solution. After the heat treatment, α-Al2O3/YAG nano-structured composite coating was successfully obtained via eutectic reaction between Al2O3 and Y2O3. It was possible to control the sizes of Al2O3 and YAG particles widely by heat treatment with proper condition. Hardness of the coatings showed close relationship with their microstructure.
Peculiarities of Structure of Quasicrystalline Al-Cu-Fe System Coatings Produced By Thermal Spraying Methods
Authors: Borisova A. , Borisov Y. , Panko M. , Adeeva L. , Kolomytsev M. , Shakhraj A. , Sladkova V.
Published: September 2022

The effect of methods and conditions of thermal spraying on structure and phase composition of coatings of the Al-Cu-Fe system alloy powders has been investigated. It is shown that the maximum ø-phase content of the coatings can be produced by the method of air-gas plasma spraying. In this case the thermal spray coatings inherit the multi-phase nature of initial powders. Preheating of the substrate prior to spraying allows the ø-phase content of the coatings to be increased.
Influence of Powder Size and Strength on HVOF Spraying – Mapping the Onset of Spitting
Authors: Itsukaichi T. , Osawa S. , Ahmed R.
Published: September 2022

In the case of thermal spraying of cermet powders using HVOF with longer barrel, such as a JP-5000 and a Diamond Jet 2700, spitting and clogging troubles tend to be brought about on the inner wall of the barrel. This phenomenon comes from the existence of fine particles (in spray powders) which tend to fully melt through barrel. This investigation has been carried out to realize the influence of powder particle strength and particle size distribution of agglomerated and sintered Cr3C2-25%NiCr powders during HVOF spraying. It is found that the finer and weaker the powder particles, the higher the deposit efficiency. However, the finer and weaker the powder particles, the easier is the onset of spitting and clogging phenomena. On the contrary, it is found that the coarser and stronger the powder particles, the lower the deposit efficiency with less spitting and clogging phenomena. Finally optimum powder particle strength and particle size distribution of Cr3C2-25%NiCr powders have been found in this study using a JP-5000 system.
Structure and Property of WC-17Co Coatings Sprayed by HVO/AF
Authors: Zha Bailin , Wang Hangong , Su Xunjia
Published: September 2022

The paper analyzed microstructure and property of WC-17Co coatings sprayed by High Velocity Oxygen/Air Fuel Spray under three kinds of spray conditions, which are HVOF, HVO-AF and HVAF. Coatings bond well with the substrate. The average bonding strength exceeds 70Mpa. Coatings are dense and hard, and the average porosity is about 1%. Microhardness of coatings is between HV10000.2 and HV12000.2. Coatings are mainly composed of WC with little W2C and Co3W3C. With the increasing of Nitrogen, decarburization of WC was reduced.
Modeling of the Substrate Temperature Evolution during the APS Thermal Spray Process
Authors: Bolot R. , Li J. , Bonnet R. , Mateus C. , Coddet C.
Published: September 2022

A numerical model is presented for the computation of heat transfers during the APS thermal spray process. This model includes the contributions of both the impinging plasma jet and that of the particle flux on the substrate heating. The contribution of the impinging plasma jet is taken into account using a computational fluid dynamic model describing the impact of the plasma jet on the substrate. For this part of the work, a two-layer extension to the Chen-Kim k-s model was used allowing the description of both the turbulent plasma jet and that of the flow in the viscous sub-layer formed on the substrate surface. The contribution of the sprayed particles is taken into account considering their distribution in the spray jet. Since this is an important parameter that could affect the model accuracy, measurements of the deposit thickness profiles were first performed using the non-destructive acoustic microscopy method and the corresponding particle flux distribution was then deduced. Heat transfers inside the substrate were then computed using a three dimensional in-house code based on a finite volume approach. In the case studied, the results show that the contribution of the sprayed particles forming the coating is much more focalized than that of the plasma flow itself whereas the substrate nature has a strong influence on the thermal flux dissipation (not presented in the following). These elements are expected to provide useful information concerning the coating adhesion mechanisms and the formation of residual stresses during the coating elaboration.
Application of CFD for Wire-Arc Nozzle Geometry Improvement
Authors: Gedzevicius I. , Bolot R. , Liao H. , Coddet C. , Valiulis A.V.
Published: September 2022

The present study was devoted to the optimization of the nozzle exit geometry of a TAFA 9000 wire-arc spray gun. Computational Fluid Dynamic was first used in order to examine the effect of different nozzle configurations, considering small changes operated on the original design. Finally, one of the modified geometries tested numerically was retained in view of the CFD results and the corresponding new nozzle was machined. In a second step, experiments were performed in order to observe the effect of the new design on in-flight droplet characteristics. For this part, a comparison was made between the original design and the modified one for two different type wires (a steel wire and a stainless steel cored wire). These experiments were performed using the well known DPV 2000 device for different operating conditions. The results indicate that the modified design provides a significant increase in the droplet velocity (about 20% higher for the new design) with unchanged thermal spray parameters, indicating that the gun exit design may have a strong influence on inflight characteristics of the droplets. Moreover, droplets were collected in water and the size distribution was analyzed.
Primary Breakup of Metal in the Wire Arc Spray Process
Authors: Hussary N.A. , Heberlein J.V.R.
Published: September 2022

The significance of metal atomization in the wire arc spray process is directly related to the final coating quality produced. Since the early observations of the melting behavior of the wire tips by Steffens, relatively little has been done to further the understanding of the mechanisms involved. The primary atomization of the molten wire tips show existence of sheets and extrusions on both electrodes which are strongly dependent on the system operating parameters. High-speed imaging has been used in this study, for classification of sheet, membrane and extrusion formations as a function of atomizing gas pressure, voltage and current settings. The breakup of metal structures formed on the electrodes is further classified in a manner consistent with established classifications for the break-up of other liquids, e.g. water or fuel. Quantitative descriptions of metal sheet lengths and breakup times are presented. The improved understanding of the metal breakup mechanisms in the wire arc spray process may provide a basis for (a) modification of existing computational codes for prediction of particle sizes and trajectories, and (b) for modifications to torch designs for providing more uniform particle fluxes.
Oxidation of Ni-Based Alloys Sprayed by a Water-Stabilized Plasma Gun (WSP)
Authors: Voleník K. , Chráska P. , Dubský J. , Had J. , Leitner J. , Schneeweiss O.
Published: September 2022

During air plasma spraying, molten metal particles flying in the plasma jet are oxidized. As a result, a part of the metal melt is converted into oxide melt. After the particle impact and solidification, oxidation continues as a gas – solid reaction. The present paper deals with oxidation of two binary Ni-based alloys. One of them, Ni-20%Cr, is frequently used in thermal spray applications. Another one was a Ni-Fe alloy with an approximate proportion of both components 1:1. The feedstock powders were plasma sprayed by a water-stabilized gun WSP. PAL 160. To analyze the reaction products of the in-flight oxidation stage, the flying particles were trapped and quenched in liquid nitrogen. Oxides resulting from both oxidation stages were studied in the as-sprayed deposits after their cooling down to room temperature. The oxide amounts in the samples were determined indirectly by oxygen level measurement using "extractive fusion" (LECO-method). Structure of the oxides, separated by dissolution of the metallic phase, was investigated by X-ray diffraction. Iron-containing oxides were also characterized by Mössbauer spectroscopy. From the point of view of reaction kinetics, both alloys behaved in a similar way. The particles quenched in liquid nitrogen contained less than 2% of oxygen, whereas in the deposits these values were higher, up to 4.5 %. Two oxide phases were found in all plasma sprayed Ni-Cr samples: a rhombohedral phase similar to (Ni,Cr)2O3 and a tetragonally distorted spinel phase (Ni,Cr)3O4, both of them very rich in chromium. Another oxide, NiO, was present mainly in the deposits. In the oxidation products of Ni-Fe alloy, the dominant phase was similar to nonstoichiometric wüstite FeO. The results of thermodynamic calculations are in sound agreement with the experiments except for the presence of the tetragonal phase, the composition of which is near to Cr3O4, in oxidation products of Ni-Cr alloy.
Dependence of Thermal Sprayed Particle/Substrate Interface Microstructure on Substrate Temperature
Authors: Fukumoto M. , Hamada K. , Shiiba M.
Published: September 2022

Ni, Ni-Al and Ni-Cr powder particles were plasma sprayed onto the mirror polished metallic substrate surface and the effect of substrate temperature on the particle/substrate interface microstructure was investigated. Sprayed particles were fully melted, sphere in a shape and oxidized on their surfaces during spraying in an air atmosphere. The surface oxide layers were detected as Al or Cr rich thin layer, respectively by electron probe micro analysis (EPMA). After spraying of the particles onto the substrate, cross section microstructures at particle/substrate interfaces were investigated. As a result, almost no oxide layer was detected at the particle/substrate interface when the substrate was kept at room temperature. On the other hand, the oxide layer was apparently recognized at the interface when the substrate was kept at a certain elevated temperature, such as at 673K. The difference in the existence of the oxide layer at interface seems to relate the wettability of the substrate by the liquid particles. The transition temperature, Tt, for each powder material was measured. The meaning of elemental addition to the base metal was considered from the changing tendency in Tt value of each powder material. Through the investigation results obtained, dominating factor on the flattening of the thermal sprayed particles onto the flat substrate surface was estimated.
A Numerical Study of the Sources of Variation in In-Flight Particle Characteristics in Atmospheric Plasma Spraying
Authors: Friis M. , Nylén P.
Published: September 2022

The resulting thermal and mechanical properties of atmospheric plasma sprayed coatings, are strongly dependent on the particle in-flight characteristics, which in turn depend on the spray gun variables. In industrial production the spray gun variables are set to constant values and closed loop controlled. However, calibrations of the variable levels are regularly performed and variations within specified tolerance limits allowed, which cause variations in the particle in-flight characteristics. The objective of this work was to investigate how these calibration variations affect the particle in-flight characteristics and the final coating properties. The investigation was performed using three-dimensional computational fluid dynamics simulations. The process model correspond to the SM-F-100 Connex gun, spraying ZrO2 for thermal barrier coating applications. Particle in-flight characteristics were calculated using a stochastic discrete particle model. Validation of the model was performed using the optical DPV2000 system, and fair agreement was found. Voltage, arc current, primary, secondary and carrier gas flow rates were systematically varied one factor at a time and their separate effects on the particle in-flight characteristics evaluated. The most important variables influencing the particle characteristics were current and voltage. Final simulations considering extreme cases enabled determination of the particle characteristics limiting conditions due to tolerance variations. Coating microstructure evaluations of two of these extreme cases revealed that the total porosity could vary up to 4% due to tolerance variations.
Particle Temperature and Velocity Characterization in Spray Tooling Process by Thermal Imaging Technique
Authors: Mohanty P.S. , Allor R. , Lechowicz P. , Parker R. , Craig J.
Published: September 2022

A two-color imaging pyrometer system is employed to examine twin wire arc spray gun used in Spray Tooling Process. Key aspects analyzed in this study include particle temperature, particle velocity, and particle distribution. The influence of process parameters such as gas flow rate, type of gas (N2, and air), voltage and current, as well as, spray cap design has been studied. Influence of a super atomizer called the arc jet has also been investigated. The measurements were taken at 80 mm, 160 mm and 200 mm from the gun tip. Finally, the influence of the material on the spray characteristics has been examined. The material list includes 0.8% carbon steel, 0.8% Carbon steel with B, stainless steel, Molybdenum, Ni, Ni-Al and Copper. The type of gas used for atomization significantly influences the particle temperature and velocity. Lowest temperature is observed with nitrogen gas and the highest temperature with the arc jet. Arc jet also produced particles with significantly higher velocity. The flow rate did influence the particle velocity where as temperature wasn’t affected noticeably. The wire material has considerable impact on the particle temperature and velocity. Lower melting point alloys showed higher temperature whereas the velocity has complex dependence on the density and viscosity of the material. Cap type affects the temperature and velocity of the particle. As cap opening increases the temperature and velocity decrease.
Particle Properties Tailor Coating Microstructure, Porosity and Phase Composition
Authors: Döring J.-E. , Vaßen R. , Stöver D. , Castro R.G.
Published: September 2022

During plasma spraying in-flight particle characteristics are influenced by the many operating parameters associated with the deposition process. The distinctive temperature and velocity signals given by particles as they exit the plasma torch can be used to develop processing maps for defining the optimal operating envelope. Knowing the temperature and velocity history of the particles, the evolution of the microstructure, the amount of porosity and the phase composition can potentially be predicted. In this paper, the relationship of system parameters (stand-off distance, torch power, plasma gas composition and process gas flow) was correlated to in-flight particle characteristics of yttria stabilized zirconia and compared to the resulting coating features such as thickness, microstructure, porosity and phase composition. The appearance of the coating (i.e., color) was also compared after the deposition process. Yttria stabilized zirconia was deposited on grit blasted samples using an F4 (Sulzer Metco) plasma torch. Before depositing each sample on the substrate, the particle properties were measured at the desired stand off distance perpendicular to the particle jet covering an area of 18x18 mm2 using the Tecnar DPV2000 inflight particle analyzer. The coatings were cross-sectioned for microstructure analysis, thickness measurements and deposition efficiency. Free standing films were used for mercury intrusion porosimetry. Grey levels of the coatings were obtained by optical microscopy and subsequent digital image recording. X-ray-diffraction analysis was also used to obtain the phase composition. Results showed that different particle temperature and velocity conditions lead to specific porosity and varying colors of the deposit. The color of the deposit was correlated directly to the amount of monoclinic phase in the as-deposit material.
Residual Stress Analysis in Thermally Sprayed Layer Composites, Using the Microhole Milling and Drilling Method
Authors: Escribano M. , Gadow R. , Buchmann M.
Published: September 2022

Mechanical and tribological properties of layer composites like hardness, bonding strength, friction and wear coefficients as well as operation performance, component reliability and finally the system lifetime are mainly influenced by residual stresses after the thermal spraying and machining process. The residual stress situation in thermally spray coated composites is superimposed by different stress mechanisms occurring during the manufacturing process based on heat and mass transfer during the coating deposition. Using the microhole milling and drilling method, residual stress fields can be measured in a quasi non destructive way over the drilling depth with appropriate resolution. In several drilling and micromilling operations a circular, cylindrically shaped microhole is brought step by step into the component surface. The residual stresses are locally relieved due to material removal, deform the surface around the drilled microhole and are measured by high resolution measurement tools, e.g. strain gauges (DMS), for every drilling step in form of relaxed surface strains. Using calibration curves and material data (E, μ) the measured surface strains are converted into nominal strains at the bottom of the drilled hole for every drilling step. Out of the differentiated strains, in-plane stress fields can be incrementally determined by Hooke's law. This study describes residual stress measurement features, the FEM-calculation and idealization of calibration curves as well as results of exemplary stress measurements.
Photocatalytic Properties of TiO2 Coatings as a Function of Coating and Substrate Characteristics
Authors: Toma F.L. , Berger-Keller N. , Bertrand G. , Klein D. , Coddet C.
Published: September 2022

Titanium dioxide (TiO2) is an attractive material for numerous technological applications such as photocatalytic applications. The photocatalysts allow the environmental purification of air and water by the decomposition of toxic organic compounds and removal of harmful gases. This work was focused on the production and evaluation of the environmental properties of titanium dioxide coatings obtained by the plasma spray technique. To carry out the step of validation of the TiO2 coatings for their environmental functionalities, a control test of the photocatalytic effectiveness was performed with respect to nitrogen oxides. A custom-designed test chamber has been developed. The photocatalytic properties of different coatings were studied as a function of various parameters (porosity, anatase/rutile ratio, nature of the substrate).
Investigation of Heat Treatment on the Microstructure of Twin Wire Arc Sprayed Copper Alloys
Authors: Wielage B. , Steinhäuser S. , Reisel G. , Wank A. , Brandt O.
Published: September 2022

During the last decades, the application of copper alloys has become very prominent in engineering. Judging from the properties of bulk materials or galvanic copper coatings, a thermal sprayed coating shows significant disadvantages. The reason for this effect is the build up of a thermal sprayed coating by individual droplets. The main aim of this work is to improve the properties of the twin wire arc sprayed copper alloys, thereby expanding the application of these kind of coatings to the areas where galvanic copper plating technique are mainly used. A copper-cobalt-beryllium alloy has been investigated and the possibility of its application in the twin wire arc process evaluated. The arc sprayed coatings were classified based on the properties of bulk material. The improvement of properties like hardness is based on an investigation of several spraying parameters of the arc spray process. To achieve a maximum value of thermal or electrical conductivity, minimum porosity of the coatings was the aim. Furthermore, a post heat treatment of the sprayed coatings, with the aim of reducing residual tensile stresses within the coating and to improve the wear resistance by means of hardening effects, was carried out. The investigations involved metallographic examination of the coatings using optical microscopy and scanning electron microscopy. Phase composition and residual stresses were detected by X-ray diffraction analysis. Microhardness was measured in the as sprayed as well as in the heat treated state.
Characterization of Modified Thick Thermal Barrier Coatings
Authors: Ahmaniemi S. , Tuominen J. , Vippola M. , Vuoristo P. , Mäntylä T. , Cernuschi F. , Gualco C. , Bonadei A. , Di Maggio R.
Published: September 2022

In gas turbines and diesel engines there is a demand for Thick Thermal Barrier Coatings (TTBCs), because of the increased process combustion temperatures. Unfortunately the increased thickness of plasma sprayed TBCs normally leads to a reduced coating lifetime. So for that reason the coating structures have to be modified. When modifying the structure of TTBCs, the focus is normally set on elastic modulus reduction of the thick coating, in order to improve the coating strain tolerance. On the other hand, coating structural modification procedures, such as sealing treatments, can be performed when increased hot corrosion resistance or better mechanical properties are needed. In this paper we introduced several modified zirconia based TTBC structures and their specific microstructural properties. Coating surface sealing procedures such as phosphate sealing, laser-glazing and sol-gel impregnation were studied as potential methods in increasing the hot corrosion and erosion resistance of TTBCs. Some microstructural modifications were also made by introducing segmentation cracks into the coating structures by laserglazing and by using special spraying parameters. These last two methods were studied in order to increase the strain tolerance of TTBCs. The coating microstructures were characterized by optical microscopy, SEM, TEM, EDS analysis and X-ray diffraction. The effect of sealing procedures was studied on basic thermal and mechanical properties of the coatings. In the paper it was also presented some correlations between the coating properties and microstructures, and discussed about the advantages and drawbacks of each modification procedure.