Powder Spray Research Articles

Synthesis of YSZ powders with controlled properties by the CDJP method

In this work, YSZ powders were synthesized by the controlled double-jet precipitation at constant pH values in the range from 3 to 8. It has been shown that weakly bound floccule-like particles with diffuse boundaries, obtained at pH 3, 7 and 8, strongly agglomerate during drying and form large particles of irregular shape. The dense spherical aggregates of zirconium hydroxide are formed only at CDJP at pH 4 and 5 due to the layer-by-layer buildup of primary particles on the surface of the aggregates. These dense aggregates capture less salt, do not undergo additional agglomeration during drying and retain a low size dispersion. YSZ powder obtained at pH 5 has a high bulk density and fluidity, as well as a narrower particle size distribution than conventional thermal spray powders. The use of this powder resulted in the formation of a uniform coating with high adhesion, uniform porosity and reduced roughness.

Plasma protective ceramic coating of the Al2O3–Ni system from cladded powder mixture

To solve the problem of increasing the adhesive-cohesive strength of multifunctional plasma coatings used to protect parts of power and machine building equipment from wear and corrosion, a ceramic coating of the Al2O3–Ni system, obtained from a powder mixture based on corundum clad nickel. The coating was applied by the method of high-energy plasma powder spraying (on the “Thermoplasma” installation) on the intermetallic sublayer of the Ni–Co–Cr–Al–Y system. The aim of this work was to study the microstructure, phase composition, mechanical, tribological and adhesion properties of a plasma ceramic coating formed from a powder material based on aluminum oxide clad with a refractory metal component (nickel). According to the research results, it was found that the initial powder material has a multi-phase composition (Ni + α-Al2O3 + γAl2O3) and a spherical morphology of particles. From it, during high-energy plasma spraying, a coating is formed with a phase composition (Ni + γ-Al2O3 + γ'-Ni3Аl), a layered microstructure with nickel interlayers and a columnar structure of oxide grains. The coating has high values of hardness and adhesive-cohesive strength, low coefficient of friction and is recommended for wear protection of parts of power engineering and mechanical engineering.

Nano-agglomerated powder and thermal shock cycling property of 8YSZ nano-structured thermal barrier coating

Based on the excellent thermodynamic and service performances of nano-structured coatings, 8YSZ nano-agglomerated spraying powder and its nano-structured thermal barrier coating (TBC) were successfully prepared by the integrated application of nanotechnology and atmospheric plasma spraying. The influences of spraying granulation process (solid content of slurry and inlet air temperature) on the spraying powder characteristics and the water quenching-thermal shock cycling behavior at 1050 °C of 8YSZ nano-structured TBC were investigated, respectively. The results showed that the nano-agglomerated powders exhibit apple-like, hollow spheroids with relatively uniform particle size when the spraying granulation process involved a 40% solid content of slurry, a 240 °C inlet air temperature, and a 35 Hz atomizer rotation frequency. The fluidity and apparent density were 57.53 s/50 g and 1.39 g/cm3, respectively. The nano-agglomerated 8YSZ spraying powders met the requirements of plasma-spraying technology. The plasma-sprayed 8YSZ nano-structured coating was composed of a single t-ZrO2 phase, had a layered structure and a certain amount of nanostructures, and presented a special “bimodal microstructure”. The average porosity of the coating was 7.49%. 8YSZ nano-structured TBC failed layer-by-layer after water quenching-thermal shock 264 cycles at 1050 °C. The main reasons for the failure of 8YSZ nano-structured TBC were the large thermal stress and cracks in the substrate caused by the water quench-thermal shock cycle, and the mismatch of thermal expansion between the metal bond coat and the ceramic coat.

WC Decomposition Phenomena in ID-HVOF-Sprayed WC-CoCr Coatings Using Fine Powder Feedstock

Over the last few decades, the high velocity oxygen fuel (HVOF) spraying of WC-CoCr for internal diameter (ID) coating has attracted much interest for hard chrome replacement. Current demands for the ID coating of small cylindrical parts necessitates the use of specialized spray gun equipment and powder feedstocks with small particle size fractions. Due to the limited spray distance inside cylindrical parts with small IDs, the process control, spraying fine WC-CoCr powders, meets new challenges to avoid significant WC decomposition, which increases the risk of mechanical degradation. Within the scope of this study, ID-HVOF spraying using a fine-structured WC-CoCr (−15 + 5 μm) feedstock with a mean WC particle size of 400 nm is examined with respect to the WC decomposition phenomena using X-ray diffraction (XRD). Hence, a statistical design of experiments (DoE) is utilized to systematically analyze various spray parameter settings along with their interaction as part of the WC to W2C conversion.

In Situ Deposition of Amorphous Al2O3-GAP Ceramic Coating with Excellent Microstructure Stability and Uniformity via Atmospheric Plasma Spraying

A novel Al2O3-GdAlO3 (GAP) amorphous ceramic coating was in situ prepared via atmospheric plasma spraying (APS). The Al2O3/Gd2O3 sprayable powders possessed excellent sphericity and fluidity after heat treatment at 1173 K without solid-phase reaction, which indicated that the Al2O3-GAP coating deposition process was significantly simplified. The Al2O3-GAP amorphous coating showed high glass transition temperature (1155.1 K), initial crystallization temperature (1179.2 K), local activation energy (847.6 kJ/mol) and nucleation resistance (88.3). Compared with almost all amorphous materials, the Al2O3-GAP amorphous coating possessed greater crystallization activation energy, which was conducive to its high-temperature microstructure stability. Furthermore, the hardness and elastic modulus of Al2O3-GAP coating fluctuated with a tiny range when increasing the nanoindentation depth from 500 nm to 2000 nm, which exhibited excellent uniformity of microstructure and mechanical performance of the coating. Therefore, the results showed that the Al2O3-GAP amorphous coating had a better potential for large-scale engineering application under harsh service conditions.

Performance analysis of plasma spray Ni60CuMo coatings on a ZL109 via a back propagation neural network model

Plasma spray coating properties frequently depend -to a great extent- on the spray parameters. However, it is difficult to analyze and obtain a comprehensive model of the entire plasma spray process due to the complex chemical and thermodynamic reactions that take place during the process. In this study, Ni60CuMo coatings were prepared on ZL109 substrates. A Back Propagation (BP) Neural Network model in the artificial neural network was used to predict the change in bonding strength, microhardness, and porosity of the coatings under different spraying distances, spraying powers, and powder feeding rates. The results show that the R-value of the trained network training is 0.8828. Comparison of experimental and predicted results reveals that both show similar trends, which verifies that the BP model can effectively predict the properties of Ni-based coatings.

МНОГОКОМПОНЕНТНОЕ ПОКРЫТИЕ FeCoCrAlTiCuMo, СОЗДАННОЕ АТМОСФЕРНОЙ ПЛАЗМЕННОЙ МЕТАЛЛИЗАЦИИ С КРАТНЫМ ОПЛАВЛЕНИЕМ

The microstructure and phase composition of the coating obtained by plasma spraying of FeCoCrAlTiCuMo powder in an equiatomic ratio of components have been investigated. The results showed the possibility of creating a multicomponent single-phase solid solution by plasma spraying and the expediency of studying it.

Severe Bleeding Gastric Barotrauma Unmasking Collagenous Gastritis

An 83-year-old man with a history of celiac disease, collagenous colitis, and collagenous sprue presented with nausea, vomiting, diarrhea, and weight loss over 3 months, prompting an esophagogastroduodenoscopy. Initial forward view inspection was unremarkable. On retroflexion, diffuse oozing blood was suddenly seen in the fundus (Figure A). Bleeding was treated with hemostatic powder spray. Barotrauma was suspected, despite usual insufflation. Repeat endoscopy 3 days later revealed serpiginous ulceration in the gastric body and fundus (Figure B).

CFD modelling of a powder spraying nozzle used for dry coating

The aim of these studies was to examine the suitability of the Euler–Lagrange approach for modelling the powder spraying process performed with a pneumatic nozzle used for dry coating in spout-fluid bed apparatus. Simulation results were validated using the digital PIV (Particle Image Velocimetry) method and measurement equipment constructed by the authors. The validation process led to the determination of the optimal Ansys Fluent solver settings, which ensure a satisfactory accuracy of the simulation results (the average relative error of all simulation points at the level of 10.5%). The experimental results are most accurately reflected by simulation results obtained with the use of the standard k − ε model that has the discrete random walk (DRW) model activated. The detailed analysis of the operation of the spout-fluid bed apparatus allowed for the examination of the influence of hydrodynamic parameters (the mass flow rate of the gas spraying the powder and plasticizer, as well as spouting gas) on the velocity and concentration of the dispersed phase in the device. The scientific investigation covered the analysis of the velocity profiles and the volume fraction of the coating powder in different zones of the column.

Effect of Spray Distance and Powder Feed Rate on Particle Velocity in Cold Spray Processes

Cold spray technology using micron-sized particles to produce coatings is increasingly used for reparative tasks in various industries. In a cold spray setup, the gun is usually connected to a robotic arm to deposit coatings on components with complex geometries. For these components, the standoff distance used in the cold spray process has to be large enough for easy maneuverability of the gun around a small radial feature. However, a small standoff distance is commonly found in most studies, which is thought to prevent a velocity drop of the particles over a larger distance. Here, a study was carried out by measuring the Inconel 625 particle velocity at different spray distances, ranging from 3 to 40 cm. The highest average velocity of 781 m/s was found at a spray distance of 8 cm. Furthermore, a study with varying powder feed rates was also conducted. An increase in the powder feed rate was found to have a minimal effect on the particle velocity. Inconel 625 coatings deposited at the optimum standoff distance (8 cm) were found to have low porosity and high hardness. The results in this study demonstrate that a larger standoff distance can be applied without a significant drop in velocity for cold spray applications requiring high maneuverability.

Impact of Spray Angle and Powder Velocity Variation in Cold Sprayed IN718 Coatings

Impact of Spray Angle and Powder Velocity Variation in Cold Sprayed IN718 Coatings

Plasma sprayed magnesium aluminate and alumina composite coatings from waste aluminum dross

The absence of structured waste management practices for tons of black aluminum dross (Al-dross) when land-filled affects the ecosystem we live in. Researchers and technologists are now working towards three goals (a) minimization of Al-dross production (b) reducing its toxic effects on the environment and (c) treating the Al-dross to beneficiate useful materials from it in an environmentally friendly manner and to generate useful industrial products. The third aspect has been addressed in this study.Al-dross is an aluminum industry generated waste that mainly contains Al metal (oxidized during processing), Aluminum Nitride (AlN), α-aluminum oxide (α-Al2O3) and magnesium aluminate (MgAl2O4). The oxides are highly suitable for refractory and thermally insulating material applications, but AlN is detrimental for two reasons - (a) thermal conductivity higher than the oxides and (b) carcinogenic gas evolution during processing. Hence AlN must be removed from Al-dross for further processing into refractories. In this work, AlN with minor quantities of halides were removed from Al-dross to extract the major useful refractory oxide constituents in an environmentally friendly manner. The process methodology involved sieving Al-dross to < 600 µm particles, aqueous media treatment to remove the nitrides in the form of NH3 gas, oven drying and calcination at 1000–1150 °C for 2 h (in an electrical muffle furnace in ambient air atmosphere) to obtain a mixture of the composite oxide powder of ∼ 99.0% purity. The calcined compound was mixed with suitable organic binders and sieved to obtain plasma sprayable powder and plasma spray-coated onto bond coated (commercial NiCrAlY) steel substrates. XRD and SEM with EDS facility were used to characterize the powders and coatings. A polished metallographic cross-section was prepared to study the microstructure and interface characteristics. The findings are presented.

Applying different infective structures of Beauveria bassiana to Coffea arabica infested with Hypothenemus hampei (Coleoptera: Curculionidae) under field

Coffee is the most appreciated beverage in worldwide; Brazil is the largest producer and exporter of this commodity. Organochlorine endosulfan was banned from the country in 2013 due to its teratogenic agent-related features. Since then, coffee plantations have experienced increased Hypothenemus hampei infestation rates. The aim of the current study is to assess variations in the rates of Coffea arabica fruits brocaded by H. hampei after the application of entomopathogenic fungal species Beauveria bassiana IBCB66. Experiments were carried out with ‘Catuaí’ and ‘Mundo Novo’ cultivars between 2018 and 2020, during the borer transit period. Three experiments were carried out based on the application of the aforementioned fungal species on the investigated coffee plant species, both by spraying and sprinkling, at 30-day intervals; 10 fruits were collected per face of each useful plant in each repetition. The experiment has followed a randomized blocks design with five treatments, including the control, and five repetitions, each. Beauveria bassiana Ecobass (IBCB66) wettable powder spray, at the concentration of 2 × 1013·ha–1, was used in experiments I and II. On the other hand, the mix used in experiment III was prepared with blastospores at concentration of 5 × 1012·ha–1 blastospores + 0.1% Silwet. The sprinkling process in all three experiments has used dry aerial conidia at concentration of 2 × 1013·ha–1. Collected data were subjected to analysis of variance (ANOVA), which was followed by Fisher’s test at 5% probability level, in the SISVAR software. More than 35,000 fruits were assessed. In addition to variations between experiments, results have evidenced that the rate of brocaded fruits remained high.

Optimization of a High-pressure Water-Powder Mixing Prototype for Offshore Platforms

A new device is designed to promote the mixing of high-pressure water jets and powders in typical industrial applications. The water and powder mixing devices traditionally used on offshore platforms are detrimentally affected by the geometrical configuration of the water nozzle and the powder spraying pipe, which are parallel, resulting in small intersecting volumes of liquid and powder. By allowing the related jets to intersect, in the present work the optimal horizontal distance, vertical distance and intersection angle are determined through a parametric investigation. It is also shown that such values change if the number of water layers is increased from one to two. In such a case, the water and powder intersection volume can be greatly increased because the trajectory of the dry powder particles becomes more chaotic.

COMBINED TECHNOLOGY FOR RESTORATION AND HARDENING OF BUSHINGS OF GEAR HYDRO MOTORS USING GAS-DYNAMIC SPRAYING

Over the past 10-15 years, the use of aluminum alloy parts in the structures of hydraulic systems of agricultural machinery has increased significantly. A large proportion of such parts account for sliding bearings (bushings), the working surfaces of which are subjected to significant wear during operation. Micro-arc oxidation is a modern method of hardening aluminum alloy parts, but it does not allow to restore parts with wear greater than 0.15 millimeters. For the restoration of parts made of aluminum alloys with significant wear, the method of supersonic gas dynamic spraying is promising. (Research purpose) The research purpose is analyzing the technical condition of worn bushings REXROTH of gear hydraulic motors and develop a combined technology for restoring their working surfaces by gas-dynamic spraying with subsequent hardening by micro-arc oxidation. (Materials and methods) Sixty bushings were chosen for the study. A digital micrometer MCC-25-0.001 GOST 6507 was used to measure wear. Powders A-80-13 and A-20-11 by Obninsk Powder Spraying Center were used. A silicate-alkaline electrolyte KOH-Na2SiO3 was used for microarc oxidation. (Results and discussion) Based on the information on wear, authors have developed a combined recovery technology with hardening of the end surfaces of gear motor bushings, which includes: cleaning of bushings; fault detection; pre-machining; supersonic gas dynamic spraying of worn surfaces; hardening by micro-arc oxidation; finishing mechanical treatment of the coating and final control. (Conclusions) The developed combined technology of bushings will allow to increase their wear resistance up to 2.2-2.3 times and significantly increase the service life of hydraulic motors. The technology is universal, and the possibility of restoring the bushings of foreign hydraulic motors using the proposed technology is especially relevant due to the need for large-scale import substitution.

Recent Research Advances in Plasma Spraying of Bulk-Like Dense Metal Coatings with Metallurgically Bonded Lamellae.

Although thermal spray metallic coatings have been widely used for materials protection from wear, corrosion and oxidation, its porous feature limits the full utilization of materials potential. Moreover, the oxidation inherent to thermal spraying in the ambient atmosphere is detrimental to interlamellar bonding formation, which further degrades the performance of thermal spray metal coatings. How to tape out the full potential of spray materials in the form of the coating is a still great challenge to thermal spray coating technology. Facing such challenge, recent efforts have been made to deposit dense metallic coatings with sufficiently bonded lamellae by oxide-free molten droplets through atmospheric plasma spraying. In this paper, the strategies for depositing bulk-like metal coatings will be reviewed. The formation of the bulk-like coating through post-spray treatments is briefly reviewed including post-spray heat treatment and laser remelting following the brief introduction to the features of thermal spray metallic coatings. The effect of the substrate preheating temperature on the splat formation and subsequently the adhesion formation was examined to reveal the dominant limitation of resultant oxide scale. Then, the role of the deposition temperature on the formation of bulk-like metal deposits with neglecting the effect of oxidation during spraying by vacuum plasma spraying practices is shortly presented. The recent progress on the new strategies to develop spread-fusing bonding mechanism and in-situ in-flight deoxidizing mechanism through developing ultra-hot metallic droplets will be introduced. The thermodynamics and kinetics requirements for the in-situ in-flight deoxidizing through deoxidizer elements adding to alloy spray powders for achieving oxide-free molten droplets in the ambient atmosphere are examined. The conditions to develop the spread-fusing mechanism during the spreading of impacting molten metal droplet for metallurgical bonding are presented. It is obvious from this review paper that the realization of two mechanisms depends on both the spray materials design and heating control of in-flight particles. Through the generation of ultra-hot droplets by plasma spraying to achieve oxide-free molten droplets, strategically it will be possible to deposit bulk-like dense metallic coating through spread-fusing of splat surfaces with limited post-spray oxidation. Such strategies will tape out the full potential of coating materials and open up the new application fields for plasma spraying.

Cold Gas Spraying of Solution-Hardened 316L Grade Stainless Steel Powder

Austenitic steels are characterized by their outstanding corrosion resistance. They are therefore suitable for a wide range of surface protection requirements. The application potential of these stainless steels is often limited by their poor wear resistance. In the field of wrought alloys, interstitial surface hardening has become established for simultaneously acting surface stresses. This approach also offers great potential for improvement in the field of coating technology. The hardening of powder feedstock materials promises an advantage in the treatment of large components and also as a repair technology. In this work, the surface hardening of AISI 316L powder and its processing by thermal spraying is presented. A partial formation of the metastable expanded austenitic phase was observed for the powder particles by low-temperature gas nitrocarburizing. The successful deposition was demonstrated by cold gas spraying. The amount of expanded austenitic phase within the coating structure strongly depends on the processing conditions. Microstructure, corrosion and wear behavior were studied. Process diagnostic methods were used to validate the results.

Change in spray behavior of pharmaceutical particles by creating bypass hole in dry powder inhaler

This study presents the effects of adding bypass holes in a dry powder inhaler on aerosol particle characteristics. A commercially available inhaler device was modified with bypass holes, and the resulting drug powder spray characteristics were investigated in terms of how the direction, size, and position of the bypass holes in the inhaler passage affect the spray output to find the optimal design. All three factors influenced the aerosol behavior, and in particular, it is most significantly affected by the direction of bypass hole faces. Adding bypass holes to the inhaler passage was found to decrease the mean penetration length of the drug particles by 12%; however, at the same time, the spray angle is increased by 35%, which leads to a significant decrease in forward particle momentum.

Newly designed mouthpiece to improve spray characteristics of pharmaceutical particles in dry powder inhaler

This study presents the effects of mouthpiece designs in carrier-based dry powder inhalation on aerosol particle characteristics. Simulation models are developed to investigate drug powder spray characteristics from mouthpieces of four different-shaped flow channels. The simulation results agree well with the results of two experiments, one involving particle image velocimetry and the other the Anderson cascade impactor. A mouthpiece with a spiral channel and mixing chamber is discovered to be effective for low axial-flow velocities in the forward direction and yielded a more uniform dispersion of particles in the radial direction as the drug particles are ejected through the mouthpiece. This results in more effective delivery of the drug particles to the peripheral target regions of the respiratory system.

Structure and electrical properties of yttrium oxide sprayed by plasma torches from powders and suspensions

Yttrium oxide was sprayed by a plasma torch using a coarse thermal spray powder, which must be in size range of tens of micrometers to ensure good penetration into the plasma stream. Thick coatings on steel substrates were produced with two sprays systems facilitating gas stabilized plasma (GSP) and hybrid water-argon stabilized plasma (WSP–H) techniques. Additionally, an ultra-fine yttrium oxide powder was sprayed from a suspension. Hybrid water-argon stabilized plasma system was used for this purpose. Markedly thinner compact coatings were produced this way. All three sorts of plasma sprayed deposits were studied by the same methods. Dielectric properties were studied in a broad range of frequencies and temperatures. The microstructure aspects as well as crystallite size were analyzed and discussed in relation to electrical properties. All coatings exhibited stable dielectric parameters versus changing frequency and temperature, comparable with literature values for various samples. Concerning sintered bulks, and especially their thermal stability of capacitance, the plasma sprayed coatings were slightly worse. However due to shape and size variability of the plasma spraying are yttria coatings prospective for technical applications.