Atmospheric plasma spraying (APS) is characterized by complex interactions between input, process and output variables. Process control relies heavily on human expert knowledge and experience. Process diagnostics can provide additional information to the operator and support cognitive processes in task execution. When using non-cascaded torch systems, significant plasma fluctuations occur, affecting the coating quality. High-frequency fluctuations can only be detected by suitable diagnostic systems and interpreted by experienced APS operators. In this study, the state of the plasma jet (area, fluctuation) is investigated depending on total plasma gas flow rate (50 vs. 65 l/min) and the H 2 content of plasma gases (17, 20 and 23 vol. %) using high-speed camera pictures. To evaluate plasma fluctuation effects, particle temperature and velocity as well as resulting coating properties (thickness and porosity) are determined for two ceramic systems. The results show that fluctuations of the plasma jet have a significant effect on the particle state and coating quality. The use of a high-speed camera to evaluate the stability of the plasma jet is an attractive method that, when properly integrated, has the potential to provide the human operator with important information to allow rapid assessment of input parameters or the condition of the plasma torch.

The amorphous Fe-based coating was fabricated on 304 stainless steel matrix by high velocity oxygen fuel (HVOF). The microstructure, friction properties and wear mechanism of the coating were mainly analyzed by scanning electron microscopy, X-ray diffractometer, Vickers microhardness tester, friction and wear tester, three-dimensional optical profilometer. Results show that: most of the coatings were amorphous, and the amorphous content increased first and then decreased with the increase of heat input. When the spraying parameters are kerosene flow rate 21 L/h, oxygen flow rate 56 m 3 /h, powder feeding rate 35 g/min, spraying distance 360 mm, the coating amorphous content is up to 84%, the hardness is over 842 HV 0.2 , the wear resistance advances over 2.9 times than the matrix.

In this work, a novel HVOAF process fueled with ethanol was employed to prepare NiCoCrAlYTa coatings on AISI 304 stainless steel substrate. To be able to add compressed air into the torch, it was designed to add a second-stage combustion chamber. Thereafter, investigations were carried out to determine the influence of different compressed air flow rates on the evolution of the microstructure and properties of the resulting NiCoCrAlYTa coatings. The phase composition, microstructure, porosity, microhardness, bond strength and wear resistance of the as-sprayed coatings have been studied in detail. The results reveal that the compressed air flow rate has a substantial effect on the coating's microstructure. The addition of compressed air also contributes to reduce the degree of oxidation of the coating, which could be attributable to a decrease in the temperature of the flying particles and an increase in their velocity. Although the use of compressed air diminishes the coating's bonding strength, it still has some elevated strength. Furthermore, the injection of compressed air improves the coating's sliding wear resistance dramatically. SEM and EDS were used to investigate the sliding wear mechanism of the coating. Detailed correlation between the compressed air flow rates and the coating properties are elaborated to identify the coatings exhibiting optimum performances.

In this work, a novel liquid fuel HVOF process fueled with ethanol was used to prepare 75wt%Cr 3 C 2 –25wt%NiCr coatings on AISI304 stainless steel substrate. Taguchi method was employed to optimize the spray parameters (ethanol flow rate, oxygen flow rate, powder feed rate and standoff distance) to achieve better erosion resistance at 90° impact angle. The results indicated that ethanol flow rate and oxygen flow rate were identified as the highly contributing parameters on the erosion wear loss. The important sequence of the spray parameter is ethanol flow rate > oxygen flow rate > standoff distance > powder feed rate. The optimal spray parameter (OSP) for minimum erosion wear loss was obtained under ethanol flow rate of 28slph, oxygen flow rate of 420slpm, powder feed rate of 76.7 g/min and standoff distance of 300mm. The phase composition, microstructure, hardness, porosities, and the erosion wear behaviors of the coatings have been studied in detail. Besides, erosion wear testing of the optimized coating was conducted at 30°, 60° and 90° impact angle using air jet erosion testing machine. The SEM images of the erodent samples were taken to analyze the erosion mechanism.

Industrialization of cold spray brings along the questions of cost and time efficiency of various spray procedures. In this work, high rate deposition of tantalum was studied by producing coating specimens where the powder to helium mass flow rate varied from 5% to 14%. Quasi-1D fluid simulations predict a minimal effect of increased powder stream loading on particle impact velocity and temperature over those ranges, but the cost varies substantially. The experimental specimens, examined by using optical micrographs, porosity measurements, and hardness tests, show no discernable differences in the deposited samples. The increased stream loading rate, however, helped reduce the time required for processing the same amount of tantalum by a factor of three using identical helium spray conditions.

The objective of this study is to assess the wear resistance, hardness, and porosity of HVOF-sprayed Cr 3 C 2 -25NiCr coatings applied using different oxygen and C 3 H 8 flow rates. In the experiments, six coating samples were prepared and subjected to various tests. The sample deposited with the highest oxygen flow rate and lowest fuel-oxygen ratio exhibited the lowest porosity and highest microhardness. In general, the higher the surface hardness, the better the erosion and cavitation wear resistance. The most intense wear occurred during the erosion test conducted with an impingement angle of 60°.

In suspension high-velocity oxyfuel (SHVOF) thermal spraying, the suspension is usually injected axially into the combustion chamber. Deposition of oxygen sensitive materials such as graphene can be difficult using this approach as the particles degrade with extended exposure to oxygen at high temperatures. Radial injection outside of the nozzle, however, reduces in-flight particle time thereby accommodating oxygen sensitive nanomaterials. The aim of this study is to investigate how radial injection parameters affect in-flight particle conditions during SHVOF spraying. The models used in this work are shown to accurately predict flame temperature in the combustion chamber for an Al 3 O 2 suspension. Experimental observations of the liquid jet obtained using high-speed imaging are compared to numerically predicted values. The results indicate that in-flight particle characteristics can be improved by more than 30% in SHVOF spraying by optimizing the suspension flow rate and radial injection angle.

Sintering ceramics have been widely used in industries which require electrical and mechanical properties. Thermal sprayed ceramics coatings are also applied for the industries, however the coating which has micron size pores are limited their applications due to inferior electrical and mechanical properties compared with sintering bulk. To expand thermal sprayed ceramics coating applications, dense coatings prepared by suspension plasma spraying are widely studied. Dense Al 2 O 3 coatings are applicable to fabricating equipment for electronics devices, such as ESC. There are no reports regarding electric properties of plasma sprayed dense Al 2 O 3 coating with different spray conditions. In this study to achieve a electric properties of dense Al 2 O 3 coating, spray parameters such as plasma power, gas flow rate and spray distance are investigated. Suspension materials prepared with three microns Al 2 O 3 powder are sprayed by high power suspension plasma spraying system. Spray conditions, plasma power, gas flow rate, and stand-off distance affect the coating density, crystal phase, and mechanical and electrical properties. Mechanism of coating formation by plasma spraying with fine powder suspensions will be discussed based on the findings. Al 2 O 3 coatings obtained by the plasma spraying is applied for application to application utilizing the electrical insulation properties of such electronics devise manufacturing equipment components is proceeding.

ZnO films were deposited by solution precursor plasma spray (SPPS) process with different substrate preheating temperatures and torch powers, which were used to study the effects on crystallizations and microstructures. With increasing substrate preheating temperature from 0 °C to 400 °C, ZnO films were always preferential orientation along (002) plane with much higher crystallinity. And more apparent crystallized particles appeared with higher agglomeration degree forming cauliflower-like microstructure under higher preheating temperature. For adjusting hydrogen flow rate, the moderate hydrogen flow rate was the suitable condition for obtaining oriented growth along (002). Besides, all ZnO films under different hydrogen flow rates with a constant preheating temperature as 400 °C were always combined with crystallized particles. Moreover, the increment of torch power makes microstructure becomes denser with less interspace between neighbouring particles. Moreover, it is found that crystallinity and crystallized particles is more dependent on preheating temperature and torch power plays a more important role on densification by two staggered experiments. Taking applications of metal oxides films via SPPS into consideration, choosing moderate substrate preheating temperature and hydrogen flow rate will obtain crystallized particles, unusual preferentially oriented planes and high specific surface area, which is very favourable for optical, electrical, electrochemical properties.

This study investigates the influence of particle temperature and velocity during reactive plasma spraying and the effect of plasma gases on coating properties. Using hydrogen gas with low flow rate was found to be better for reactive plasma spraying of fine Al 2 O 3 -AlN mixtures. The H 2 gas increased in-flight particle temperature, affecting in-flight vaporization, AlN content, phase transformation, deposition efficiency, and coating thickness. N 2 gas, on the other hand, increased particle velocity, thereby reducing particle residence time in the plasma, which affects melting, nitride conversion, and phase transformation.

This paper describes the development and testing of an emulator representing a single-cathode atmospheric plasma torch. The emulator consists of three subsystems: input, simulator, and output. Arc current intensity, the hydrogen ratio of the forming gas, and its total mass flow rate are taken as input parameters, while in-flight particle temperature and velocity are the designated output. The simulator was developed in a two-stage process. By collecting and analyzing experimental data, a mathematic model expressing plasma torch operation was defined. The model was then tested and compared with experimental data. It is shown to be relatively accurate with an average error of about 2.2% in particle temperature and 1.1% in velocity.

This study investigates the effect of gas composition on the flow characteristics of a three-cathode air plasma torch. A numerical model that couples fluid dynamic, electromagnetic, and thermal relationships is used to simulate temperature and velocity fields at the outlet of the torch. Different gases, including argon, nitrogen, and hydrogen, and gas mixtures are examined in the context of the study. The results show that the use of N 2 or H 2 as a secondary gas improves the output power and efficiency of the torch.

The aim of this work is to obtain a better understanding of high-velocity suspension flame spraying though detailed modeling and analysis. A numerical model was developed and is used to analyze the effects of process parameters including droplet size, injection velocity, secondary droplet breakup, solution evaporation and combustion, mass flow rate, flame temperature, and the location of the injection point. The results show that initial injection parameters play an important role in controlling the process and should be specified to minimize cooling effects and promote droplet evaporation inside the combustion chamber. It was also found that the ideal location for the injection point is inside the chamber, which in practice, can be achieved by slightly modifying gun geometry.

This study investigates the potential of external powder injection for producing functionally graded coatings by twin wire arc spraying. In spray trials, the position of the injection port was altered along the spray axis and perpendicular to the arc and different powders and carrier gases were used. Real-time images were captured by a high-speed camera during spraying to detect correlations between gas flow rates, hard particle wetting, and atomization of the molten pool. The optimal location for injection was found to be dependent on the size and density of the powder and the flow rate of the carrier gas. In the case of embedding B 4 C in a Fe-based matrix, a strong metallurgical bond was formed, confirming that powder injection is a viable approach for controlling the composition of twin wire arc sprayed coatings.

Low-temperature oxygen fuel (LTOF) spraying is a modification of the high-velocity oxyfuel (HVOF) process. By injecting room temperature gas into the mixing chamber, process temperature is reduced, allowing temperature-sensitive materials to be successfully deposited. In the LTOF process, the gas mixture is accelerated to supersonic speeds through a Laval nozzle. The purpose of this work is to establish a 2D mathematical model to simulate gas dynamics and particle behavior during LTOF spraying. The model is used to predict the temperature and velocity of flow fields and the heating and trajectory of in-flight particles for different gas mixes, mass flow rates, particle sizes, and injection conditions.

The aim of this study is to better understand the bonding mechanism of coatings produced by vacuum kinetic spraying. Fe-based amorphous alloy was selected as the feedstock material because it exhibits brittleness, similar to ceramics, as well as plasticity, in contrast. Prior to spraying, the powder was ball milled to a sufficiently small size to form an aerosol state. The powder was then deposited on glass substrates using different gas flow rates to control the kinetic energy of sprayed particles. Powder size and coating thickness were measured, the phases in the powder and coatings were analyzed, and the microstructure of the coatings was examined. The results show that the plasticity of feedstock materials and the size of the powder have a major effect on deposition behavior during vacuum kinetic spraying.

This paper demonstrates the use of commercial simulation software to evaluate a new heater design for cold gas spraying. The gas heater consists of a heating unit and a self-cooling housing. The heating unit is a coiled tube encased in an insulating enclosure. The housing is a double-walled shell through which gas continually circulates, carrying heat away from the outer surface of the insulating enclosure. Simulation results indicate that there is no heat loss in the design as verified by experimental testing.

Submicro-sized anatase TiO 2 powder was used to prepare light scattering layers by vacuum cold spraying at room temperature. The microstructure of the TiO 2 coatings was characterized to be correlated with optical property and adhesion/cohesion of the coatings. Results show that the light-reflecting ability of the coatings decreased with the increase of accelerating gas flow rate from 3.5 to 7.5 L/min and increased with the increase of coating thickness from 2 to 10 µm. Both the cohesion and adhesion of the coatings increased with the increase of the accelerating gas flow rate, due to the improvement of the particle-particle contact and the particle-substrate contact by the high velocity impact resulting from the increased powder particle velocity.

Coatings, a few-millimeter thick, are widely used to protect new mechanical parts against abrasion and erosion or rebuild worn parts. The plasma transferred arc process is a commonly used process to deposit such coatings. It makes it possible to bring about a metal bath inside which melted powders are introduced to form an alloyed coating between the feedstock material and substrate material with metallurgical adhesion. The main parameters of the process are the arc current intensity, plasma and shrouding gas flow rates, distance between the cathode tip and piece, velocity of plasma torch displacement; they all have a notable effect on the produced coating. This study investigates the plasma behavior and properties of the clad by using a design of experiments. The properties of the coating are the dilution level, porosity, and efficiency of material deposition, heat flux transferred to a water-cooled calorimeter, and the hardness in the clad and the substrate to estimate the thermally affected area.

Electrical double-layer capacitors (EDLCs) owe their large capacitance to high specific surface area carbon-based electrode materials adhered to a current collector via an adhesive. However, recent studies attribute greater electrical energy storage capacity to transition metal oxides/nitrides: a new generation of electrode materials for use in super-capacitors with mixed double-layer and pseudo-capacitive properties. Solution Precursor Plasma Spray (SPPS) deposition is a technique that allows coatings to be fabricated with fine grain sizes, high porosity levels, and high surface area; characteristics ideal for application as transition metal oxide super-capacitor electrodes. A liquid injection apparatus was designed to inject the liquid into the DC-arc plasma and to investigate the effects of various operating parameters such as spray distance, solution concentration and solution flow rate on the chemistry and surface topography of the deposits. Understanding and controlling the evolution of the precursor solution in the DC-arc plasma jet is crucial in producing coatings of the desired structures. DTA/TGA, SEM, XRD, and electrochemical analyses performed to characterize the coatings will be discussed, and the potential of the deposits for use in super-capacitors will be assessed.