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.

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.

In Warm Spraying (WS), the temperature of the combustion flame is reduced and controlled by injecting nitrogen gas into the combustion flame before the injection of spray powders. Thus, temperatures of spray particles are kept under their melting points with moderately heated and thermally softened states. As compared to HVOF-spraying, the oxidation of particles can be significantly suppressed due to lower deposition temperatures, whereas, as compared to cold spraying, the degree of particle deformation upon impact can be enhanced by attaining higher particle temperatures. In the present study, Ti, Cu, and Al coatings were fabricated by WS under various nitrogen flow rates. The mechanical properties of the coatings were evaluated by tubular coating tensile (TCT) and micro flat tensile (MFT) tests. For the lower impact temperature regime, the coatings became denser and the ultimate strengths of Ti or Cu coatings increased reaching a maximum by decreasing the nitrogen flow rates. A further decrease of nitrogen flow rates and reaching the upper temperature regime reduced the coating strength. These results clearly demonstrate how particle temperatures affect the microstructures and mechanical properties of WS coatings and that optimum spray conditions have to be balanced between softening and oxidation by adjusting particle temperatures.

The MCrAlY type coatings provide oxidation protection and good adhesion between the ceramic topcoat and the substrate. The high velocity oxy fuel (HVOF) process is currently being introduced to make the bond coats instead of conventional low pressure plasma spraying due to lower cost. In this research, the METJET-III HVOF liquid fuel system was used to produce MCrAlY coatings and the Tecnar DPV2000 was used to investigate in-flight particle temperature, velocity and diameter. To examine the coating-build, the wipe test was used to reveal the particle deformation on the substrate with different spraying parameters and correlated impact behaviour with particle properties. It was found that increasing of total fuel plus oxygen flow rate, percent stoichiometry and stand-off distances did not dramatically change the particle temperature. Increasing of percent stoichiometry and stand off distance led to reduction in particle velocity while increasing of the total fuel plus oxygen flow rate led to increase in the particle velocity. The average particle velocity below 640 m/s seems to make less splat formation than the average particle velocity above 750 m/s. Compiling results of the coating microstructure, the splat formation and the in-flight particle measurements revealed the effect of spraying parameters on the coating characteristics.

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.

The use of a liquid feedstock carrier in suspension plasma spray (SPS) permits injection of fine powders, providing the possibility of producing sprayed coatings that are both thin and dense and have fine microstructures. These characteristics make SPS an attractive process for depositing highly efficient electrodes and electrolytes for solid oxide fuel cell (SOFC) applications. In the present study, NiO-yttria stabilized zirconia (YSZ) anode and YSZ electrolyte half cells were successfully deposited on porous Hastelloy X substrates by SPS. The NiO-YSZ anode deposition process was optimized by design of experiment. The YSZ electrolyte spray process was examined by changing one parameter at a time. The results from the design-of-experiment trials indicate that the porosity of the as-deposited coatings increased with an increase of suspension feed rate while it decreased with an increase of total plasma gas flow rate and standoff distance. The deposition efficiency increased with an increase of total plasma gas flow rate, suspension feed rate and standoff distance. The microstructure examination by SEM shows that the NiO and YSZ phases were homogeneously distributed and that the YSZ phase had a lamellar structure. It was observed that the density of the YSZ electrolyte layer increased as input power of the plasma torch increased.

HVOF has the potential to produce Hydroxyapatite HA (Bio-ceramic) coatings based on its experience with other sprayed ceramic materials. This technique should offer mechanical and biological results comparable to other thermal spraying processes such as plasma spray currently FDA approved for HA deposition. Deposition of HA via HVOF is a new venture especially using the Sulzer Metco Diamond Jet (DJ) process, hence the aim of this paper. In this research, a Design of Experiment (DOE) model as developed to optimize the HVOF process for the deposition of HA. Five parameters (factors) were researched over two levels namely: oxygen flow rate, propylene flow rate, air flow rate, spray distance and powder flow rate. Coating crystallinity and purity were measured as the responses to the factors used. The research showed that: propylene, air flow rate, spray distance and powder feed rate had the largest effect on the responses and the study aimed to find the desired optimised settings. This research found crystallinity and purity values of 93.8% and 99.8% respectively for a set of HVOF parameters which were improved findings compared to the crystallinity and purity of 87.6 % and 99.4 % respectively found using the FDA approved Plasma thermal spray process. Hence a new technique for HA deposition now exists using the DJ HVOF facility. Future research aims to evaluate the biological response to these coatings through in vitro tests.

TiN coatings and some particle of TiN were prepared by reactive plasma spraying, in which titanium powder react with nitrogen under different flow rate, at the same time keeping all other parameters invariableness. The microstructure of the TiN coatings and particles were analyzed by means of SEM and the rate of TiN coating was tested by XRD. The results show that the microstructure and transformation rate of TiN coatings are greatly affected by nitrogen flow rate. The microstructure and transformation rate of TiN coatings were the best when the nitrogen flow rate was 1500 L/h.

The influence of spray parameters on particle with the improved plasma gun was studied by using SpryWatch-2i System. The results show that the particle velocity increases and exceeds the velocity of sound when using a new designed nozzle (C2 nozzle) during the plasma spraying. Under a certain condition, the particle velocity varies as the spray distance rise firstly, decline then, as the primary gas pressure increases, the particle velocity increases, the particle temperature drops firstly then increase, the velocity increase a little. But as the steadily increase of the flow rate, the influence on the particle temperature drops, the influence of arc voltage on particle velocity and temperature is slightly. Arc current influent little on particle temperature, but the particle velocity increase in a range.

Impact of liquid injection on atmospheric plasma has been measured by an enthalpy probe and visualized by shadowgraphy. Liquid was injected by two nozzles. A solid stream nozzle with 0.3 mm diameter and an atomizing nozzle with a spray angle of 30°. For constant liquid flow rate and varied plasma current an optimal injection parameter has been obtained. Influence of different flow rates on plasma characteristics has been examined. Full profiles along each axis show differences for different injection techniques in enthalpy, temperature, velocity and composition.