Detonation spraying is used for applying metal, cermet, polymer and ceramic coatings. The advantages of this technology include good adhesion and density of coatings. Minimal residual stresses in the spray process give the possibility to apply coatings to thin-walled parts and foil. Numerical modeling methods for energy parameters of powder particles give the possibility to predict the interaction of powder particles with the gas flow in and properties of coatings depending on spray parameters. In many cases, existing advantages such as high quality of coatings, little heating of the substrate, efficient and economical use of the powder, make the detonation spray process more attractive in comparison with other spray methods. The new design of D-Gun and software gives the possibility to overcome these limitations and significantly increase the productivity. This result was obtained due to a new design of the valve head, new computer control system, electronics and software that allows the firing rate frequency to be increased, ensure the reliability and extend the maintenance-free lifetime. The paper discusses the results of modeling of acceleration and heating the particles of powders in the new detonation system and also methods of computer simulation of the formation of adhesive contact between powder particles and metal surface.

A new nanoparticle plasma spray process has been developed that uses conventional powder feeders and injectors to produce fine ceramic coatings at high deposition rates. This paper explains how powder feedstocks are prepared and how the resulting coatings compare with coatings by other methods. The feedstock used in the demonstration was produced by adding YSZ nanoparticles to an acrylic liquid resin, which was then solidified, crushed, and screened. SEM images show that the nanoparticles are well dispersed throughout the resin fragments. In the plasma flame, the resin fragments burn down as the nanoparticles are heated and accelerated toward the substrate, producing fine zirconia layers free of microcracks and pores as observed by SEM. The presence of carbon deriving from the resin material is dealt with by post-process heating at different temperatures, the effect of which is assessed by means of thermogravimetry. Vickers hardness of the YSZ phase was measured to estimate the sintered density.

This study investigates the feasibility of using solution precursor plasma sprayed (SPPS) zinc oxide to fabricate NO 2 gas sensors. In the experiments, thin ZnO layers were deposited on Al 2 O 3 substrates that had been printed with interdigitated gold electrodes. FE-SEM images show that the as-sprayed films are highly porous and nanostructured as desired. Diffuse reflectance measurements reveal that significant absorption occurs in the visible light range. In gas sensing tests, the SPPS ZnO films were responsive to concentrations of NO 2 gas down to 0.4 ppm. The performance is attributed to the porous nanostructure and the presence of oxygen vacancies, or mid-bandgap defects, as confirmed by XPS analysis.

In this study, metal oxide films were synthesized from an EDTA·Er·H complex by flame spraying. The erbium oxide (Er 2 O 3 ) layers were deposited on stainless steel using N 2 , air, or O 2 as the carrier gas and a H 2 -O 2 mixture as the combustion gas. Test results indicate that the carrier gas has a significant effect on film thickness and porosity and that O 2 is the ideal carrier gas for producing dense metal oxide films.

This study investigates the spraying characteristics of low-pressure plasma torches with different nozzle sizes. YSZ feedstock powders were sprayed with each torch at different stand-off distances and gas pressures. The plasma jets created were photographed and measured, showing that low-pressure spraying significantly increases plume length and diameter compared to atmospheric conditions. The coatings obtained were examined and microhardness was determined. It was found that the longer nozzle increases the temperature of the plasma jet, and with a longer dwell time, the particles heat more efficiently and evaporate more fully. At a spraying distance of 300 mm, the coatings were mostly composed of equiaxed grains, which were much larger in the coatings produced with the long anode nozzle. At longer spraying distances, more unmelted particles appeared in the coatings, leading to a reduction in hardness.

This study shows that the quality of detonation sprayed coatings can be improved by adding propane or butane to the high-energy acetylene fuel. WC-Co coatings sprayed with binary fuel were found to have very low porosity (< 0.5%), low abrasion wear rates (< 1 mm 3 /1000 rev), high hardness (~1500Hv300g), and good bonding strength (150 MPa). These values were achieved over a range of stand-off distances (150-350 mm) and at a substrate inclination of up to 30°.

The Shock-wave Induced Spray Process (SISP) is a method of applying coatings of various metallic-based materials onto a wide range of different substrates. It utilizes the kinetic and thermal energy induced by a moving shock-wave to accelerate and heat powder particles. A transient axisymmetric model for the process is developed using Fluent. The model is validated with reference to a simplified one-dimensional approximation of the flow field. Values of pressure, axial velocity, Mach number, as well as static and total temperature are carefully examined. It is found that a zone develops in the flow that experiences elevated levels of temperature and velocity simultaneously. This is the main distinction between SISP and traditional CGDS processes. The effects of varying supply pressure and temperature on these flow variables are investigated in detail. Additionally, the effect of changing the driving gas type is investigated using air and helium as examples.

The thin film low pressure plasma spray process (LPPS-TF) has been developed with the aim of efficient depositing uniform and thin coatings with large area coverage by plasma spraying. At high power input (~150 kW) and very low pressure (~100 Pa) the plasma jet properties change considerably and it is even possible to evaporate the powder feedstock material providing advanced microstructures of the deposits. This relatively new technique bridges the gap between conventional plasma spraying and physical vapor deposition. In addition, the resulting microstructures are unique and can hardly be obtained by other processes. In this paper, microstructures made by LPPS-TF are shown and the columnar layer growth by vapor deposition is demonstrated. In addition to the ceramic materials TiO 2 , Al 2 O 3 or MgAl 2 O 4 , the focus of the research was laid on partially yttria-stabilized zirconia. Variations of the microstructures are shown and discussed concerning potential coating applications.

In this paper the characteristics (microstructure, phase compositions) and electrical insulating properties of thermally sprayed alumina coatings produced by suspension-HVOF (S-HVOF) process and conventional HVOF spray method are compared. The electrical resistance (electrical resistivity) and dielectric strength were investigated using DC-electrical resistance measurements, electrochemical impedance spectroscopy (EIS) and dielectric breakdown test. The electrical resistance was determined at room temperature at different relative air humidity (RH) levels, from 6% RH up to 97% RH. Differences in the electrical insulating properties due to the different coating characteristics are discussed. The suspension-sprayed Al 2 O 3 coatings showed better electrical resistance stability at high humidity levels (> 75% RH), which could be explained by a specific microstructure and retention of a higher content of α-Al 2 O 3 . Nonetheless, the values of dielectric breakdown voltage and dielectric strength recorded for suspension sprayed coatings were lower than those of HVOF coatings.