Abstract Unlike their metal counterparts, composite structures do not readily conduct away the electrical currents generated by lightning strikes. Cost reduction and expected production growth of the next middle range airplanes require automated manufacturing process of polymer components. The development of an automated technology to metallize polymer based composite for lightning strike protection is the aim of the CO3 project (EU Grant agreement: ID831979). In this study, thermal and electrical conductivities of composites were achieved by cold spray deposition of Cu or Al coatings. Critical points to be addressed were substrate erosion during cold spray, lack of polymer-metal adhesion and poor deposition efficiency. Several strategies were tested: i) a thin polymer film was cocured at the substrate surface before cold spraying, to enable implantation of metallic particles in the film, helping coating build-up and protecting the fibers of the composite. ii) Cold spraying a mix of metal and polymer powders to improve coating adhesion and prevent fiber damage. iii) Supercritical Nitrogen Deposition technology, prior to cold spray, to mechanically anchor metallic particles into the polymer. Subsequent cold spraying of purely metallic coatings was more efficient and showed better adhesion. All coatings were tested in terms of adhesion strength and electrical conductivity.

Abstract Thermally sprayed ceramic coatings can be used for wear protection as well as thermal and electrical insulation. When exposed to environments with high humidity, the water absorption of the ceramic coating has a tremendous impact on the electrical insulation. In thermally sprayed ceramic coatings, water can easily be absorbed by the porous microstructure of the coating. A general result of the water absorption is the reduction of the dc resistivity. However, in the high frequency regime of ac loads, contrary results were observed for sealed Al 2 O 3 coatings on steel substrates. Specimens exposed to high air humidity have shown an increased ac resistance compared to dry specimens if frequencies above 1 MHz are considered. To analyse this phenomenon, a novel measurement technique was developed to investigate the influence of the water absorption of detached ceramic coatings on the ac resistivity at high frequencies. Moreover, the water absorption of the ceramic is measured gravimetrically. To ensure the results are also applicable to ceramic coatings on substrates, the morphology of the coating was analysed using electron microscopy and compared to reference specimens deposited on steel substrates from [1].

Abstract Microstructure and physicochemical properties of a thermally sprayed coating depend on the dynamics of the particles interacting with the spray jet. This is especially the case for electrical properties. In this study, different spraying processes were used to spray p-type and n-type half-Heusler powders. Thermoelectric powders, Hf20Zr75Ti05CoSb80Sn20 (p-type) and Hf60Zr40NiSn98Sb02 (n-type), were selected due to their interesting electrical properties. The spray processes were evaluated based on coating composition and mechanical property measurements. The only coatings of practical interest were those that were plasma sprayed and they were examined in detail to assess the effect of process parameters on coating properties.

Abstract Stabilized bismuth oxide with fluorite structure is considered a promising electrolyte material for intermediate temperature solid-oxide fuel cells (SOFCs) due to its high oxygen ion conductivity. The ternary system, Bi2O3-Er2O3-WO3, is of particular interest because it is ionically conductive as well as thermally stable. This study investigates the quality of Bi2O3-Er2O3-WO3 (EWSB) electrolyte produced by plasma spraying. The phase structure and cross-sectional microstructure of plasma-sprayed EWSB were characterized by XRD and SEM. The as-sprayed EWSB was found to have a dense microstructure with well bonded lamellae. XRD analysis showed the formation of EWSB with δ-phase and a trace of β-phase, while the β-phase disappeared after annealing at 750°C for 10h. Electrical property tests revealed that the plasma-sprayed electrolyte also had excellent ionic conductivity (0.26 S cm-1 at 750 °C), making it a strong candidate for use in SOFCs at intermediate temperatures.

Abstract This paper discusses the application of electrical insulation on glass ceramic. Morphology of splats, phase transformation, mechanical and electric properties of plasma-sprayed ceramic coatings on glass ceramic are studied. It is observed that the preheating of substrate during deposition of glass ceramic is necessary, since bounding mechanism between coating and glass substrate is mainly of chemical nature. However, high preheating temperature causes also large residual stress in the coating. In order to reduce those, substrate cooling must be activated starting the second deposition step. Further spray parameters such as plasma power and powder feed rate must be also reduced in order to reduce the residual stress in the coating. Paper includes a German-language abstract.

Abstract Various silicate materials have been examined with regard to sprayability, composition, micro-structure as well as mechanical and thermal properties. This paper deals with the dielectric properties. Synthetically produced mullites, steatites, and spodumens, as well as natural olivine forsterites, are processed using water stabilized plasma system. The layers are peeled off, sanded, and polished to obtain plane-parallel plates with smooth surfaces. Such samples, the monoblock capacitor principle, are tested in alternating voltage fields in the low voltage range using an RCL meter. Volume specific resistance, capacitance, and voltage drop are measured. This enabled the relative conductivity to be calculated. It is observed that this relative conductivity of plasma-sprayed silicates is stable in the entire range between 200 Hz and 1 MHz. The suitability for insulation is discussed in comparison to solid material of the same composition. Paper includes a German-language abstract.

Abstract The denser structure of HVOF-sprayed aluminum layers compared to APS-sprayed ones opens up high-quality application possibilities, especially in the form of electrical layers in semiconductor applications. This paper presents the effect of fuel gas/oxygen ratio on melting level of the particle, total gas flow, and particle flux in terms of coating thickness per pass on the electrical properties of the coatings. A large number of spray parameters are changed for more detailed investigations. Splats are created to investigate the relationship between diagnostic data, melting behavior, and the interactions between droplets and substrate in the case of aluminum particles. Paper includes a German-language abstract.

Abstract Semiconductor manufacturing apparatuses have begun to employ dry processes instead of conventional wet processes, based on the associated benefits in terms of automation, productivity, and environmental protection. This paper investigates the methods for forming an oxide-based dielectric ceramic layer on the aluminum base, a layer that has high adsorptive and stable electric properties. It discusses the electrostatic chuck, and describes the relationship between the characteristics of the aluminum oxide-titanium dioxide coating formed by the low-pressure plasma-spraying method and the resulting performance of the electrostatic chuck. The advantages of deoxidation and the change in the specific resistance of titanium dioxide during the spraying process were used to produce the layer. Paper includes a German-language abstract.

Abstract A numerical model is developed to study the effects of the contact resistance, droplet impacting droplet temperature, and substrate temperature on the droplet solidification rate and temperature of the droplet under the condition when the substrate can melt and re-solidify. Two-dimensional simulations show that the interface velocity is small in the area of poor contact with an irregular solidification interface shape. During the impact of Molybdenum on a steel substrate, Mo solidifies while the steel substrate melts.

Abstract 316L stainless steel and Hastelloy C alloy powders were sprayed by an HVOF apparatus onto mild steel substrates. The microstructure, pore size distribution, composition and corrosion resistance of thus obtained coatings were evaluated experimentally. Corrosion resistance in sea-water was examined by monitoring the impedance and corrosion potential of samples immersed in artificial sea-water at 300 K over a period of more than 3 months and also by polarization measurement. It was found that the stainless coatings composed mainly of plastically deformed particles and some splats which were molten at the impact. By increasing the combustion pressure, the porosity as measured by mercury porosimeter could be reduced to below 1%. In comparison, Hastelloy C deposits sprayed under the standard condition were so dense that its porosity could not be measured by the porosimeter. The polarization curve and the results of impedance monitoring both exemplified that the Hastelloy C coatings possess much superior corrosion resistance to the stainless coatings in sea-water, which was attributed to the higher density and better adhesion of the Ni-base alloy coatings.

Abstract BaTiO3 has been successfully sprayed by HVOF to produce dense 25-150 µm thick deposits for use as dielectric and capacitive layers within prototype multilayer conformal electronics. Parameter optimization has been shown to play a critical role in the effective spraying of these materials as thin structurally homogeneous deposits. The affect of standoff distance and combustion chamber size on the phase structure of the coatings have been studied and related to the dielectric properties of the layer. The proportion of crystalline to amorphous phase was found to be critically dependent upon the degree of melting of the particles in the flame and the rate of cooling of the deposits. The crystalline/amorphous ratio is directly related to the dielectric properties of the layer with greater crystallinity giving higher values of dielectric constant. Microcracks and splat/splat interfaces are also believed to adversely affect the dielectric properties. The maximum dielectric constant (K) values achieved using the HVOF method for deposition have been in the range 70-115.

Abstract Ceria (CeO2) based electrolytes have been considered for use in solid oxide fuel cells (SOFC) for more than 20 years. There are however some limitations to this usage that this study has tried to address, indeed the study objective has been that of synthesizing and thermal spraying thin layers (50 - 100 µm) of doped CeO2 by the technique of suspension plasma spraying, using radio frequency (RF) plasma technology. Various dopant combinations and concentrations have been selected for this work in order to increase the useful partial oxygen pressure range for satisfactory ionic conductivity development, thereby increasing the anionic conductivity and preventing CeO2 reduction in fuel cell service. Ceria possesses the fluorite crystal structure at low temperatures but does not have enough oxygen vacancies to be a good ionic conductor. In ceria the cerium have 4+ oxidation state within the fluorite structure, and by substituting a certain amount of Ce4+ ions by trivalent dopant ions, oxygen vacancies are induced into the structure. Recent studies have demonstrated that at low temperatures doped ceria seems to be a better electrolyte than doped zirconia. Also, it seems that dopants with ionic radii close to Ce4+ ions give rise to better ionic conductivities. The doped ceria conductivity increases with the dopant concentration because more oxygen vacancies are created, but at higher concentrations vacancy ordering occurs which results in decreased ionic conductivity.

Abstract Plasma transferred arc (PTA) is now currently used for reclamation of worn materials or to provide wear or corrosion resistant coatings welded to the base material. Instead of injecting the powder in the molten pool created at the coated surface, another way to coat substrate surface before the PTA treatment has been studied. As the powder can not be simply deposited on the substrate surface because of the plasma flow which would blow it off before melting it, a tape casting process was used to obtain an adherent powder layer on the material surface. Its cohesion and adhesion to the substrate are due to the organic binder contained in the tape to form organic bridges between particles. In this paper, the electrical properties of NiCu (70/30) tapes deposited on cast iron substrates were first studied. It has been shown that the binder led to a low electrical conductivity of the layer. PTA treatment of the casted tapes has been carried out by starting the electrical arc on the metallic cast iron substrates. The process control by CCD camera allowed to observe that the NiCu particles fell in the melting pool created at the substrate surface. The study of the obtained alloy compositions has shown the drastic influence of the initial binder concentration in the tape. Moreover, before being treated by PTA, some NiCu tapes were heated in a furnace at 1100°C for 4 hours to remove the organic binder and sinter the layer. The coatings thus produced, which were characterized by a low electrical resistivity and a good adhesion to the substrate, were then treated by PTA. The surfacing alloy properties were compared to those obtained without heat treatment.

Abstract Thermoelectric (TE) power generation from waste heat is recently attracted much attention as one of energy-saving technologies. In this paper, Co-doped n-type iron silicide semiconductor was plasma sprayed under various spray conditions to find the optimum spray-forming conditions. Then Co-doped iron silicide TE device with thickness ranging from 3 to 5 mm and the area of over 100 cm square was produced in the form of a plate or on tube. The paper examines the microstructure and evaluates thermal and electric properties. Paper includes a German-language abstract.

Abstract This paper considers the problem of spraying the electrically conductive coatings on electrotechnical units for different purposes with the method of cold gas-dynamic spraying. It presents a general scheme of the spraying system, the characteristics of the spraying process and the main results of the property tests of electrotechnical units with coatings. The contact connections of copper bars provided with aluminum caps with protective coatings of copper, zinc, and nickel are tested. The paper demonstrates the conformity of the electrotechnical units injected using the CGS method with the requirements of the state standard. It was observed that while spraying the thin copper layer on aluminum caps by the CGS method the copper expenditurer 50 times decreases. The technical characteristics, with this, are close to the copper caps, and the cost is close to the aluminum caps. Paper includes a German-language abstract.

Abstract This paper presents the electrochemical characterization of a chromium carbide-NiCr coating applied using high-speed flame spraying. It examines the behavior of the complete system, the steel, the steel coating, and the coating immersed in NaCl solution alone. The paper discusses electrochemical measurement methods such as the measurement of polarization resistance, anodic polarization, and open circuit potential. The tests are compared with each other and with results from metallographic examinations. The structure was characterized by light and scanning microscopy. In addition, an analysis of the residual water was carried out using an ICP technique. The paper also includes a study of the various mechanisms that could affect the behavior of such coating types in a corrosive environment. Paper includes a German-language abstract.

Abstract This paper presents the results of metal dielectric multilayer structures based on aluminum alloys and several oxide ceramics respectively. It investigates thermomechanical and dielectric properties with regard to the use of different powders for thermal spraying as well as a high and a low energy gun for atmospheric spraying. The experimental work of this study is divided into two main parts: the selection of materials and the development of promising coating systems and the manufacturing and testing of novel ozonizer tubes. The investigated coating systems are analysed focusing the application in ozonizers. Therefore, a metallic electrode, an oxide ceramic and the dielectric properties of the metal-ceramic-composite are analysed. Finally, the appropriate metal-ceramic composites are tested in an ozonizer. Paper includes a German-language abstract.

Abstract Different oxides layers have been studied by friction in natural sea water medium under the same conditions (Cr 2 O 3 , Al 2 O 3 , Al 2 O 3 + Cr 2 O 3 ). The evolution of different parameters have been analyzed: friction coefficient, electrochemical potential, degradation of the layers in the contact, impedance spectroscopy. The main result observed is concerned by the cracking of the coatings under stresses, in such a way interconnection paths are rapidly present between the substrate and the sea water medium through the layers. The coating impregnation process by epoxy, before the tribocorrosion tests, improve the protection of the substrate against the corrosion.

Abstract Physical properties of coatings based on Fe-B, Fe-Ni-B, Fe-Cr-P-C, Fe-Ni-Si-B, Ni-P, Ni-Nb and Co-Fe-B-Si, deposited by the methods of flame, plasma-arc, and detonation spraying were investigated. The coatings have mostly the amorphous structure with the volume content of the amorphous phase equal to 75-95 %. Values of the distribution and temperature coefficients of electric resistance of the coatings, depending upon a method and conditions of spraying, as well as upon their treatment parameters, were determined. Comparative studies of these coatings and thin amorphous strips produced by the melt spinning method were conducted. The amorphous coatings of ferromagnetic iron and cobalt alloys are shown to be magnetically soft materials and are characterized by a high magnetic induction combined with a high magnetic permeability. As compared with the amorphous strips, Curie temperature of the amorphous ferromagnetic coatings is by 50-140 K higher and their anisotropy of magnetic properties is lower.

Abstract The atmospheric pressure plasma spray processes for functional layers of the tubular solid oxide fuel cell are developed to build a fuel cell structure consisting of air electrode, ceramic electrolyte, and fuel electrode. Further more the characteristics of each film are also investigated. The layers of LSM (La 0.65 Sr 0.35 MnO3) air electrode and Ni/8YSZ fuel electrode have porosities of 23 ~32 % sufficient for supplying fuel and oxidant gases efficiently to electrochemical reaction interfaces. The measured electrical conductivities of the electrodes are higher than 90 S/cm at 1000 °C, which satisfy the requirement as the current collecting electrodes. The YSZ electrolyte film has a high ionic conductivity of 0.07 S/cm at 1000 °C, but shows a bit too porous to block the oxygen molecule penetration through it. A unit tubular SOFC is fabricated by the optimized plasma spray processes for depositing each functional film and forming a porous cylindrical supporting tube of the cell, and turns out to have a promising capability of electricity generation.