Physical characteristics of Atmospheric Plasma Sprayed (APS) Alumina coating and Low Pressure Plasma Sprayed (VPS) Alumina coating were investigated. High purity Alumina powder was used for thermal spraying in this test. As electrical properties, the volume resistivity, dielectric constant, and the dielectric breakdown voltage were measured at R.T. to 873K. And the coefficient of thermal expansion, and the thermal conductivity were measured at also R.T. to 873K, as thermal properties. Mechanical properties, such as the Young’s modulus, the bending strength, and the cross-sectional hardness value were measured at R.T. As a test result, the Alumina coatings using both APS and VPS have similar properties except for the cross-sectional hardness value that was higher when sprayed by VPS.

Goal of this work is to homogenize properties of three-cathode plasma sprayed coatings on basis of advanced diagnostics and numerical simulations. After a brief description of the general approach to achieve this objective, selected aspects of the current work are presented. Thereby the paper is focused on the self developed suspension injection TriplexII setup, in the special determination of the plasma and in measurement plus presentation of the suspension-particle-behavior. In the suspension plasma diagnostic part (CT-Computed Tomography) the different temperature profiles and geometries are shown and discussed. Additional the suspension-particle-behavior are more explained with the PIV (Particle Image Velocimetry), High-Speed-Camera and AccuraSpray-g3 results, which are calculated and presented with special image processing algorithm. The last part of the paper describes the suspension coating analysis and concludes with an outlook for future measurements of the self developed SPS-TriplexII setup.

Yttria doped zirconia has been widely employed as electrolyte materials for solid oxide fuel cells (SOFCs). Plasma spraying is a cost-effective process to deposit YSZ electrolyte. In this study, the 8 mol % Y 2 O 3 stabilized ZrO 2 (YSZ) layer was deposited by low pressure plasma spraying (LPPS) and atmospheric plasma spraying (APS) with fused-crushed and agglomerated powders to examine the effect of spray method and particle size on the electrical conductivity and gas permeability of YSZ coating. The microstructure of YSZ coating was characterized by scanning electron microscopy and X-ray diffraction analysis. The results showed that the gas permeability was significantly influenced by powder structure. The gas permeability of YSZ coating deposited by fused-crushed powder is one order lower in magnitude than that by agglomerated powder. Moreover, the gas permeability of YSZ deposited by LPPS is lower than that of APS YSZ. The electrical conductivity of the deposits through thickness direction was measured by potentiostat/galvanostat based on three-electrode assembly approach. The electrical conductivity of YSZ coating deposited by LPPS with fused-crushed powder of small particle size was 0.043 S × cm-1 at 1000°C, which is about 20% higher than that of APS YSZ with the same powder.

In this study, a TiO 2 (anatase) nanopowder suspension was processed by high velocity suspension flame spraying (HVSFS). The resulting coatings were characterized and compared to conventional HVOF and atmospheric plasma sprayed layers. It is shown that the HVSFS operating parameters can be adjusted to achieve dense titania with a near nanostructure and homogeneous distribution of anatase and rutile phases. These coatings have lower pore interconnectivity and higher wear resistance than the APS and HVOF layers. Alternatively, large unmelted agglomerates of anatase nanoparticles can be embedded in the coating, increasing the porosity and anatase content for enhanced photocatalytic efficiency.

This study investigates the influence of plasma gas composition on deposition efficiency achieved during atmospheric plasma spraying and the properties of the resulting deposits. In the experiments, ternary mixtures of argon, hydrogen, and helium are used in different combinations and flow rates to spray Al 2 O 3 -TiO 2 and ZrO 2 -Y 2 O 3 powders on test substrates while measuring deposition efficiency. Several coating properties are measured, including porosity, hardness, and bond strength, and correlated with plasma gas ratios. Paper text in German.

We present the results of an investigation of the effects of a travelling magnetic field (TMF) on the plasma flow using a commercial program package. The argon plasma generation in the electric arc and the Lorentz force induced by the TMF are simulated with specific equations, which are derived from the magnetofluiddynamic equations using appropriate simplifications. First calculations confirm the predicted effects.

Understanding the particle injection into the gas flow issuing from an APS torch is necessary to optimize the spraying parameters. In order to solve numerically this task, the distribution of gas velocity and temperature at the torch outlet is required. In this work this is achieved by developing a model which not only delivers the solution for the electrically charged gas flow within the torch, but also includes the thermodynamical condition of minimum entropy production. This additional condition fixes the size of the electric arc inside the torch, whose radius is particularly responsible for the form of the calculated velocity and temperature profiles at the torch nozzle. The velocity and viscosity of the gas flow near the torch outlet mainly control the trajectory of particles injected into the gas flow. For the typical gas mass flow and torch power used in APS, the resulting temperatures at the gas core are slightly above the ionization temperature of the gas species. The radial location of the viscosity maximum corresponding to the ionization temperature is calculated, since this maximum strongly influences the particle trajectory. Finally, the influence of plasma fluctuations on the heat transfer to the injected particles is discussed.

Samaria-doped ceria (SDC) has become a promising material for the fabrication of intermediate-temperature, metal-supported solid oxide fuel cells (SOFCs). While typical SOFC materials, such as yttria-stabilized zirconia (YSZ), require high temperatures (> 700°C) to exhibit suitable ionic conductivity for high cell performance, SDC displays similar ionic conductivities at lower temperatures (600°C – 650°C). The atmospheric plasma spray (APS) process is a promising technique for manufacturing metal-supported SOFCs. In this study, the in-flight characteristics, such as particle velocity and surface temperature, of spray-dried SDC agglomerates were analyzed at various plasma spray conditions using the DPV-2000 in-flight particle sensor manufactured by Tecnar Automation. Coatings of SDC were applied on stainless steel substrates using a range of spray conditions, and their resulting microstructures and deposition efficiencies were analyzed. It was found that particle temperature could be related to the specific plasma energy, and that coating porosity was related closely to the measured average particle temperature.

The main purpose of this work is the development of mathematical and computer models for the integrated simulation of all stages of the atmospheric plasma spraying process (APS) with temperature dependent thermophysical and mechanical properties of the used materials and gases and experimental verification of the simulated results. The following mathematical models of APS were created: particle heating and movement in the plasma jet; coating structure formation; heat transfer and residual stresses in the coating-substrate system. The computer realization of these models enables us to model all stages of APS (integrated or separately). Databases of coating, substrate and plasma-gas substances include the temperature dependent properties. The model of APS is divided in 3 parts, which are connected by continuous data interface. Two dimensional approximation of plasma-gas velocity and temperature in the free plasma jet was used for computation of particle velocity, trajectory and temperature. This information was created with a special Graphic program module and included in database. Computer experiments for plasma spraying of Ah03 and ZrO 2 +8%Y 2 O 3 in Ar/H 2 plasma were carried out. The experimental verification of developed models with High-Velocity-Pyrometry (HVP) and Laser-Doppler-Anemometry (LDA) have shown the satisfactory precision of simulated results.

This paper evaluates two CFD tools for predicting particle speeds and temperatures during atmospheric plasma spraying. The investigation is based on varying two parameters: plasma current and gas flow rate. Although the tools differ in accuracy, both proved to be sufficient for optimizing industrial plasma spraying processes. A comparison of the results with experimental data showed the more advanced tool to be capable of predicting variations in particle characteristics when operating conditions change. Paper includes a German-language abstract.

This study analyzes the tribological behavior of nickel-graphite and aluminum-silicon-polyester thermal sprayed coatings and the effect of non-metallic compounds. Self-lubricating coating composites based on a metallic matrix with ceramic or polymeric filler phases show potential applications requiring high wear resistance and thermal stability at low cost. In some cases, the nickel-graphite layer may eliminate the need for external lubricants or lubricating systems. Paper includes a German-language abstract.

Studies on atmospheric plasma spraying have generally focused on the influence primary parameters such as gas flows and plasma current. However, the APS process is also influenced by a large number of disturbance variables including electrode wear, cooling system irregularities, and disruptions in powder injection. This study investigates both the cause and effect of each of these factors in the context of aluminum oxide spraying. Numerous measurements are made showing how electrode wear, cooling fluctuations, flow measurement inaccuracy, and variations in powder feed rates affect in-flight particle characteristics, deposition efficiency, and layer thickness. Paper includes a German-language abstract.

The excellent wear-resistant performance of cast iron coatings considerably depends on the formation of graphite structure with an inherent self-lubricating property. In the present study, two types of cast iron powders produced by gas- (GA) and water-atomization (WA) were deposited on an aluminium alloy substrate by atmospheric DC plasma spraying. WA powders are generally characterized by high oxygen content, irregular appearance and inexpensiveness compared with those of GA powders. Although alloying elements of silicon and aluminium work as a strong graphitizer and anti-oxidizer, graphite structures are not recognized in coatings sprayed with as-atomized high silicon and aluminium powders. Therefore, either pre-annealing of powders or post-annealing of coatings is required to achieve cast iron coatings containing graphite structure. A marked decrease in graphite occurs to the coatings with pre-annealed GA powder, since there exists precipitated graphite mainly on a GA powder surface. A short period of post-annealing is also valuable for graphitization. The weak oxide layers are observed in coating cross-sections with GA and WA powder, however, their oxidized levels are much lower than those with bearing steel powder containing low silicon and aluminium. Hence, graphitized cast iron coatings sprayed with inexpensive WA powder exhibit a splendid anti-wear performance.

The emergence of lanthanum silicate as an electrolyte is required to accelerate the development of synthesis techniques for intermediate temperature solid oxide fuel cells (ITSOFCs). Apatite-type oxide powders of La 10 (SiO 4 ) 6 O 3 have been elaborated through atmospheric plasma spraying (APS) using micro-scale mixtures of La 2 O 3 and SiO 2 powders. Granulometer and scanning electron microscopy analyses have indicated the result of high temperature reaction and rapid solidification in the evolution of multi-scale microstructure.

The potential of atmospheric plasma spraying (APS) technology has been investigated for the manufacture of anode, electrolyte and cathode of a solid oxide fuel cell. As substrates tape-casted or commercial available porous plates both made of a FeCr-alloy were used. The functional layers were applied by atmospheric plasma spraying, however, it turned out that screen printed LSCF cathodes performed better than thermally sprayed versions. Anode layers with high electrochemical activity could be produced by APS using separate injections of NiO and YSZ powders. The manufacturing of gas-tight electrolyte layers was a key-issue of the present development. With adequate processing conditions and advanced gun technology it was possible to produce highly dense ceramic coatings with a very low amount of micro-cracks and pores. These electrolytes gave high open cell voltages above 1 V corresponding to the low measured leakage rates (<10-3 mbar*l/s) of the rather thin (<50 µm) coatings. Additional layers have been applied to reduce the interdiffusion especially of species from the metallic substrates into the anode. These layers could significantly reduce degradation of the cells. SOFCs with a power density at 800°C well above 0.7 W/cm² could be produced by the developed technology.

The disadvantage of plasma torches using conventional single cathode techniques is the occurrence of azimuthal and axial instabilities inside the plasma torch. This causes electrical power fluctuations which result in inhomogeneities of the plasma jet enthalpy and with that an uneven plasma particle interaction. Hence, variations in particle properties occur and consequently an uneven coating quality is produced. Using the triple-cathode technique these electrical power fluctuations were successfully reduced, resulting in a stationary plasma flow. Thus this technique appears to offer the potential to homogenize coating properties. Similar results have been shown for plasma torches with triple anode arrangements. The goal of this research group is to homogenize properties of plasma sprayed coatings using of 3-cathode and 3-anode technologies based on numerical simulations. The approach used is to subdivide the complete APS process into the areas plasma torch, free jet as well as coating formation and characteristics. By simulation of the individual areas and combination with experimental results the corresponding process parameters will be obtained for the desired coating properties.

In this work numerical simulation results of the impact and solidification of molten PYSZ-particles on flat and rough substrate surfaces are presented. This investigation deals with the effect of the particle state prior impact, particle diameter and substrate roughness, on splats spreading behaviour and final morphology. The particles have a diameter range between 20 – 60 µm. Particle initial conditions prior to impact: speed, temperature and melting state, are taken from previous simulation modelling approaches of particle accelerating and heating. Simulations of fluid dynamics, heat transfer and solidification during the particle impact were performed using computational fluid dynamics. Tracing of free surfaces determinates volume of fluid method. Heat flux at the particle-substrate interface and temperature dependent liquid phase viscosity of PYSZ are studied and discussed. Simulated splat morphologies are compared with experimentally obtained splats.

An optimised de-Laval-type-contour for the Atmospheric Plasma Spraying (APS) with respect to the thermal and deposition efficiency as well as to the arc voltage fluctuations and the sound level of the plasma torch is presented. Investigations of the plasma gas dynamics and two different feedstock materials (Al 2 O 3 (fused and crashed) and Cr 2 O 3 (agglomerated and sintered)) have been done to promote the industrial utilization of convergent-divergent nozzles for the APS.

Laser-assisted atmospheric plasma spraying (LAAPS) is a new one-step coating process performed in air whereby the laser beam interacts with the plasma torch at the substrate or coating surface during deposition to generate a coating that is metallurgically bonded to the substrate. This hybrid process was developed in order to combine the specific advantages of APS and laser cladding. In this paper, the development of a hybrid gun for coating internal surfaces of tubes and cylinder bores by LAAPS is presented. The process was optimized for spraying AlSi30 coatings on internal surfaces of aluminum alloy cylinder bores. Single-pass coatings with thicknesses of 300-400 µm and metallurgical bonding to the substrates can be realized by applying an optimized parameter set. The dependence of coating microstructure on spray parameters was investigated by metallographic preparation and optical microscopy. Surface pretreatment must be performed to eliminate the strongly adhering oxide layer on the aluminum alloy substrate and to attain metallurgical bonding of coating to substrate.

Lightweight materials play a special role thanks to their low density. In recent years considerable development has been conducted using Al, Mg and their alloys. The increasing use of these materials enlarges the requirements related to the high wear resistance accompanied by good formability and ductility as well as the high corrosion resistance. A fulfillment of such demands can be attained through surface treatments. Among the currently available wide variety of surface treatment processes thermal spraying techniques play an important role. This study presents a comparison of light weight materials coated through Detonation-Gun and Atmospheric Plasma Spraying Processes. The influence of coating parameters, coating type and coating thickness on tribological properties are studied. The behavior of coatings under different bending angle regarding cohesion and adhesion is analyzed. Corresponding SEM- and LM-analyses are conducted to understand the underlying mechanisms.