Within the High Velocity Oxygen Fuel Process (HVOF-Process) various fuels can be used to provide the needed thermal and kinetic energy such as ethene, propane, methane or kerosene. Modelling the combustion in a HVOF-System poses a challenge concerning chemical kinetics of the kerosene reaction process. In this work a reduced reaction mechanism and a model describing chemical reactions as well as governing fluid dynamics are presented to simulate kerosene driven HVOF-Process. The kerosene combustion process within a HVOF-System usually takes place above temperatures of 2000 K, where some species dissociate. Therefore, accruing species have to be included in the reaction mechanism. The combustion process is described with a reduced reaction mechanism. The reaction rate is described by a finite rate model in form of Arrhenius. The gas flow is considered as a first phase and the kerosene droplets injected into the combustion chamber become a second phase. Afterwards simulation results are presented and discussed.

Titanium dioxide in anatase phase structure has high antibacterial activity. For this study, titanium dioxide coatings on stainless steel were produced by cold spraying. The bactericidal effect of the coatings was tested with Pseudomonas aeruginosa bacteria at a high concentration of more than 107 CFU (colony-forming units) per milliliter. The bacteria were applied on the surface and exposed to UV light with a peak intensity of 360 nm. A kill rate of 99,99% was already achieved after 5 minutes, while the raw stainless steel reference did not show any significant reduction even after 60 min. The results show that cold-sprayed titanium dioxide coatings can serve as self-disinfecting surfaces.

An experimental set-up has been developed, at the SPCTS Laboratory, to produce fully melted, millimeter-sized, ceramic or metallic drops with impact velocities up to 10 m/s. Such impact velocities allow reaching impact Weber numbers, close to those of the plasma spray process (We = 2300). A fast camera (4000 image/s) combined to a fast pyrometer (4000 Hz), allows following the drop flattening. For studding the flattening at the micrometer scale, a DC plasma torch is used to melt micrometer sized alumina particles (around 45 μm). The experimental set-up is composed of a fast (50 ns) two-color pyrometer and two fast CCD cameras (one orthogonal and other tangential to the substrate). The flattening of millimeter and micrometer sized particles is compared. First are studied impacts of alumina drops (millimeter sized) with impact velocities up to 10 m/s. Then are considered micrometer sized alumina particles (about 45 μm in diameter) sprayed with a DC plasma torch. A correlation has been found between both flattening scales and, in spite of the lower impact velocity at the millimeter scale, ejections are also found at the micrometer scales. This work shows that to compare phenomena at the two different scales it is mandatory to have Weber numbers as close as possible in both cases.

C-BNp/NiCrAl composite coating was deposited by cold spraying using a mechanically alloyed composite powder. To modify coating microstructure, especially the bonding at the interfaces between c-BN particles and NiCrAl alloy matrix, and bonding at the sprayed particle/particle interface, annealing treatment at series of temperatures in Ar atmosphere was carried out. The results show that a zigzag interface layer is formed at the interface between c-BN particle and NiCrAl matrix after annealing at 825°C for 300 min through reaction of c-BN with NiCrAl. It is also observed that the thickness of the interface reaction layer increases with the increasing annealing temperature. Moreover, the interface between spray particles and the plastic deformation ability of the cermet coating can be improved through post-spray annealing. Vickers microhardness test shows that the hardness decreases with increasing annealing temperature due to the reduction of work hardening effect and grain growth of NiCrAl alloy matrix resulting from recovery and recrystallization during annealing treatment.

Conventional processes of gas shielded metal arc welding (GMAW) do not offer directly the possibility for cladding heat sensitive materials such as aluminum with iron-based materials due to intermetallic Al/Fe phases form. This paper deals with the first evaluated cladding results of aluminum components with iron-based nanocrystalline solidifying materials by controlled shielded metal arc welding processes to improve wear resistance. In the present work, the design of experiments and data evaluations are systematically applied to get the first results about the dependence between controlled arc welding process parameters and the iron-based coatings of aluminum substrate. In particular, the effect of the chosen parameters such as wire feed speed, welding speed, frequency and further factors on the heat input, welding penetration, micro hardness, rate of welding penetration and width of intermetallic phases in the interface zone are investigated. Optical and scanning electron spectroscopy provide input for further statistical evaluation. The experiments were carried out using various controlled arc technologies which offer different control over the heat input to the substrates. Different power supplies were used.

Liquid metal atomization using de Laval nozzle is an established technique for producing fine (< 100 μm) metal powders for a lot of industrial applications. This process offers a variety of advantages as spherical morphology or low consumption of inert gas for example. Despite its widespread uses, however, the relationships among gas dynamics melt nozzle and de Laval nozzle diameters, processing parameters, and particle size remain defined. As a result, efforts to reduce powder costs by improving particle size control and energy efficiency remain hindered. Then, the optimization of this process is a great challenge. This experimental study examines the atomizing spray behavior depending on the process parameters. Experiments were conducted on copper (at 99.9%). Particle Image Velocimetry technique was implemented in the atomization chamber and measurements were performed to characterize in velocity the atomized droplets. The PIV system was placed in such a way that the atomization zone, comprised between 50 and 110 mm downstream the de Laval nozzle exit, can be monitored by the camera. The evolutions of the particle velocity and particle sizes were finally analyzed versus the working conditions.

The very low pressure plasma Spray (VLPPS) process has been developed with the aim of depositing uniform and thin coatings with large area coverage by plasma spraying. At typical pressures of 100-200 Pa, the characteristics of the plasma jet change compared to conventional low pressure plasma spraying processes (LPPS) operating at 5 – 20 kPa. The combination of plasma spraying at low pressures with enhanced electrical input power has led to the development of the LPPS-TF process (TF = thin film). At appropriate parameters it is possible to evaporate the powder feedstock material providing advanced microstructures of the deposits. This technique offers new possibilities for the manufacturing of thermal barrier coatings (TBCs). Besides the material composition, the microstructure is an important key to reduce thermal conductivity and to increase strain tolerance. In this regard, columnar microstructures deposited from the vapor phase show considerable advantages. Therefore, physical vapor deposition by electron beam evaporation (EB-PVD) is applied to achieve such columnar structured TBCs. However, the deposition rate is low and the line of sight nature of the process involves specific restrictions. In this paper, the deposition of thermal barrier coatings by the LPPS-TF process is shown. It is investigated how the evaporation of the feedstock powder could be improved and to what extend the deposition rates could be increased.

In cold spray and thermal spray applications, one of the primary factors affecting coating deposition is the location where particles are injected into the gas jet. Therefore, a detailed knowledge of the gas flow distribution is required. Non-resonant laser scattering allows to spatially resolve the distribution of drift velocity and mass density within the flow, particularly at locations close to the injector. Based on laser scattering, this paper presents a new diagnostic that locally measures drift velocity, as well as a relative mass density distribution of a gas stream. Its application is mainly focused on cold gas flows, where velocity measurements in a supersonic nozzle, obtained by means of laser scattering, correlate well with theoretical calculations and particle image velocimetry (PIV) experimental results.

Cold gas dynamic spraying (CGDS) can be used to deposit oxygen sensitive materials, such as titanium, without significant chemical degradation of the powder and with minimal heating of the substrate. The process is thus believed to have potential for the deposition of corrosion resistant barrier coatings. However, to be effective a barrier coating must not allow ingress of a corrosive liquid and hence must have minimal interconnected porosity. Thus the aim of the present study was to investigate the effects of processing, including a post-spray annealing treatment, on the deposit meso- and microstructures and corrosion behavior. Commercially pure titanium powder was deposited using pre-heated nitrogen as main and powder carrier gas using a CGT Kinetiks 4000 system to produce coatings on stainless steel. Selected coatings were debonded from the substrate, and the resultant free standing deposits heat treated at 1050° C in vacuum for 60 minutes. Changes in microhardness were measured and correlated with microstructural changes. Optical microscopy, scanning electron microscopy, X-ray diffraction (XRD), helium pycnometry and mercury porosimetry were all employed to examine the microstructural characteristics of coatings and free standing deposits, before and after heat treatment. Their corrosion performance was also investigated using potentiodynamic polarization tests in 3.5 wt% NaCl. The influences of heat treatment and corrosion behavior will be analyzed and discussed in terms of pores structure evolution and microstructural changes.

Thermal spraying technology still suffers from a lack of reproducibility due to uncontrollable factors during the process. Current methods of process control by means of observing process parameters like gas- and powder flow are insufficient to guarantee a constant quality of coatings, while a direct analysis of the deposited layer is time- consuming and can only be conducted after the process. Furthermore, recently developed mathematical models which correlate process parameters to coating properties are not applicable for all materials. As the particles’ behavior during the process affects the coating properties, a direct process control by the observation of the particles seems expedient. This method is applicable on running processes and thus avoids defective production. In this study, HVOF spraying experiments were conducted. The in-flight particles’ behavior was investigated using an optical diagnostic system, while coating properties were analysed by metallographical methods.

While the improvement in mechanical properties of nanocomposites makes them attractive materials for structural applications, their processing still present significant challenges. In this paper, cold spray was used to consolidate Al 2 O 3 /Al nanocomposite powders obtained from mechanical milling. The microstructure and nanohardness of the feedstock powders as well as of the resulting coatings were analysed. The results show that the large increase in hardness of the Al powder after mechanical milling is preserved after cold spraying. Good quality coating with low porosity is obtained from milled Al. However, the addition of Al 2 O 3 to the Al powder during milling decreases the powder nanohardness. This lower hardness is attributed to non-optimised milling parameters for proper Al 2 O 3 embedding and dispersion in Al and results in a lower coating hardness compared with the milled Al coating. The coating produced from the milled Al 2 O 3 /Al mixture also shows lower particle cohesion and higher amount of porosity. The overall results are promising and it is believed that an optimization of Al milling with Al 2 O 3 will allow production of sound coatings with improved hardness.

The gas-cooled fast reactor is a 4th generation nuclear reactor currently under development. Its design concept requires protective coatings able to operate at 850°C and protect the underlying structure in case of extreme cases, where the functional temperature can increase up to 1250°C and there is depressurization from 70 bars to atmospheric pressure. The parts to be covered are made in 1-mm thick materials resistant to heat and erosion with high mechanical properties at high temperatures, such as the Haynes 230 nickel-based alloy. In this study, the potential of the suspension plasma spraying technique for forming the first layers of a ceramic coating on smooth 1-mm thick Haynes substrate was explored. In order to meet these specifications, the coating material selected was partially stabilized zirconia of standard composition (8 mol.% Y 2 O 3 -ZrO 2 ).

Thermal spray coating processes have been employed in the current study to deposit well-adhered, dense skins on the surfaces of open-cell nickel foams. Using foam with 10 and 40 PPI (pores per inch) pore sizes, square channels were made with a height of 20mm and having a length of 250mm. In a unique process that prevents the deposited skin from penetrating the foam substrate via a paste comprised of a thermoset resin and powder particles, a dense stainless steel skin with an average thickness of 400 μm is applied to the exterior of the foam sample. The result is a channel that consists of a Ni foam core and a stainless steel skin wall that can be used as a compact heat-exchanger by directing the coolant flow through the foam. To study the feasibility of the metallic foam heat-exchangers, hydraulic and heat-transfer characteristics were investigated experimentally. The local wall and fluid temperature distribution and the pressure drop along the length of the heat exchanger were measured for heat-flux of 1540.35 – 9627.38 W/m 2 . Experiments were conducted using air as the coolant and varying flow velocity from 10 – 80 L/min. For non-Darcy flow with inertia effects in the porous media, the Dupuit and Forchheimer modification is employed with the experimental results to determine foam characteristics such as permeability (K), Ergun coefficient (CE) and the friction factor (f). To measure the heat-transfer performance of the metal foam filled channels, a length average Nusselt number is derived based on the local wall and fluid temperatures. Heat transfer was shown to have nearly doubled compared to that of a channel without a foam core.