Intermediate temperature - solid oxy-fuel cells (IT-SOFCs) include in their design a solid electrolyte layer made of yttria-partially stabilized zirconia (Y-PSZ), an ionic conductor, through which oxygen ions diffuse. This layer needs to fulfill several characteristics among which a low leakage rate corresponding to a non-connected pore network and a low level of stacking defects such as microcracks or globular pores. Moreover, the thickness of this layer needs to be as low as possible (about 20 µm) in order to limit ohmic losses. Suspension plasma spraying (SPS) appears as a potential technological route to manufacture such layers structured at micrometric or sub-micrometric scales. In SPS, a stabilized suspension, made of a liquid, solid particles and a dispersant, is injected within the plasma flow. The liquid is very quickly fragmented and then vaporized and the individual particles, or the particle agglomerates, depending on the average size and morphology of the solid feedstock, are heated and simultaneously accelerated towards the substrate surface where they impact, spread and solidify, analogously in a first approximation to larger particles, to form a layer. The architecture of the layer is very closely related to plasma operating parameters (from which derive plasma flow stability), from the suspension characteristics, in particular the feedstock particle size distribution and from the suspension injection parameters. This work aims at presenting recent developments made to optimize some of these operating parameters to maximize the electrolyte layer characteristics.

Thermal spraying technologies take part in the current worldwide scene as serviceable and profitable technologies for a wide range of intents. The growing adoption of those techniques has driven companies to progressive investments in efforts to reach innovative designs and market needs. Wear resistance is among the desired features which certain components must be able to provide while performing. In this context tribology has an outstanding importance, where the adoption of suitable materials and operational parameters jointly contribute for a longer lifetime of parts. This contribution presents a comparison of AISI 1045 (DIN C45) steel surfaces coated by means of arc spray process, employing cored wires as feedstock. Corresponding light microscopy, SEM-EDX, 3Dprofilometry, hardness and ball-on-disk analyses were conducted to understand the tribological behaviour of two unlubricated iron-based layers with and without carbides reinforcement. The results point out equivalent thickness, porosity and as-sprayed roughness for both coatings. Higher hardness and lower friction coefficients for the carbide free coating as well as a downward trend considering the coefficients of friction for coated and uncoated surfaces under heavier loads.

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.

Nanostructured and conventional Al 2 O 3 powders have been plasma sprayed, under the same parameters, to produce coatings on 304 stainless steel. The nanopowder was fabricated by mechanical attrition techniques and composed of agglomerates of nanoparticles, whereas the conventional powder consisted of solid granules. In order to maintain the beneficial effect of the nanostructure in the final coating, a fraction of the powder’s nanostructure should be retained in the coating after spraying. Dissimilarities were observed between the two types of coating, regarding porosity, roughness, deposition efficiency and α-Al 2 O 3 to γ-Al 2 O 3 proportions, which are related with the different percentages of semimolten particles in the coatings. The nanocoatings retained a higher percentage of semimolten particles than the conventional coatings, owing to the higher porosity of the nanoparticle agglomerates, as compared to the conventional solid granules. The molten part of both conventional and nanostructured coatings consisted of γ-Al 2 O 3 of columnar morphology. In order to investigate the mechanism of the melting front advance into the particle interior during their presence in the plasma stream, the particles were sprayed directly into distilled water. The nanoparticles mainly formed hollow spheres, whereas the conventional particles mainly formed compact spheres. The internal porosity of the solidified nanoparticle agglomerates, which affected the overall coating porosity, was linked to the hollow sphere phenomenon.

In order to achieve SOFC at reduced costs, atmospheric plasma spraying (APS) could be an attractive technique. However, it is difficult to elaborate plasma sprayed coatings with the appropriate porosity for the electrodes and full density for the electrolyte. The spray process has been adapted by providing a suspension as feedstock material. SPS shows important advantages over APS, since it is now possible to spray finer powders to obtain either a thin (10 µm) dense layer as electrolyte or thick and finely structured porous layers for the electrodes. Nevertheless some questions still remain before considering manufacturing SOFC by SPS. The major one is to understand the influence of the suspension and the injection parameters on the drops formation and transformation in plasma before impinging upon the substrate as well as of the suspension characteristics (formulation, particle size and amount, viscosity, surface tension,...). To answer these questions, suspensions based on nickel oxide (NiO) and YSZ (yttria stabilized particles) have been prepared and functional layers have been produced by SPS. This work is compared with previous studies of YSZ sprayed suspensions.

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.

HVOF-sprayed carbide based coatings such as WC/Co or Cr 3 C 2 /NiCr are industrially well established for wear and corrosion protection applications. Due to their high carbide content of typically 75 wt.-% and more, they are providing a very high hardness and excellent wear resistance. Unfortunately costs for matrix materials like Ni or Co underlie strong fluctuations and are significant higher compared to iron. Therefore an alternative concept to the conventional carbides is based on TiC-strengthened low cost Fe-base materials, which are already in use for sintering processes. Depending on the carbon content the Fe-base material can additionally offer a temperable matrix for enhanced wear behaviour. Within this study the sprayability of TiC-strengthened Fe-powders with a gaseous and a liquid fuel driven HVOF-system has been investigated. The resulting coatings have been analysed with respect to microstructure, hardness and phase composition and compared to galvanic hard chrome, HVOF-sprayed and remelted NiCrBSi and HVOF-sprayed Cr 3 C 2 /NiCr (80/20) coatings as well as sintered Fe/TiC reference materials. Furthermore the Fe/TiC coatings have been heat treated to proof the retained temperability of the Fe-matrix after thermal spray processing. For determination of wear properties tribometer tests have been conducted. Currently the corrosion resistance of the sprayed Fe/TiC coatings is investigated as well the wear behaviour in a practical hydraulic test bench.

Normally the conventional thermal spray processes as the atmospheric plasma spraying (APS) have to use easily flowable powders in a size range between 10 and 100 µm. In contrast the suspension plasma spraying (SPS) makes it possible to process nano sized particles directly. Due to the use of nano materials new microstructures and properties could be generated. One point is the possibility to influence the porosity level, its size range and micro crack densities in a wide band. Microstructure features like the porosity and cracks serve as scattering centres and lead to changes of optical properties. Furthermore the thermal conductivity is affected by the porosity level. In this work yttria partially stabilized zirconia coatings were generated by the SPS and APS process. The influence of the different microstructures on the thermal conductivity, the hemispherical reflectance and transmittance for wavelengths between 0.3 to 2.5 µm has been investigated. Due to the higher porosity and crack level of the SPS coatings the thermal conductivity and hemispherical transmittance was significant reduced.

Thermal spraying and thixoforging technologies can be combined in a new manufacturing method for the production of light metal matrix composites. Laminated prepregs are produced by coating unidirectional fiber bundles with light metal matrix material. The prepregs are heated up and densified by thixoforging to near net-shape composites. Compared to conventional technologies for the integration of fibers in light metal matrices, like squeeze casting, hot pressing and diffusion bonding, this method offers the possibility to realize complex component geometries with short cycle times. Due to its high deposition rate and reduced thermal load on the substrate, the arc wire spraying technique is used for the coating of fiber bundles with the matrix material (AlSi6). The final fiber volume content of the MMC can be tailored by the thickness of the coating. Prior to the coating process, a continuous fiber strand is coiled on a cylindrical workpiece with adapted dimensions by using a winding unit provided with fiber guiding system. The speed and horizontal range of the fiber guide unit can be continuously varied in order to control overlapping and ensure homogeneous thickness of the fiber layer. An efficient air cooling system is installed in order to control the thermal load, which affects the formation of microcracks and influence the final residual stress distribution in the coating. An innovative method to wind and coat continuous fibers for manufacturing fiber reinforced light metal matrix composites will be presented.

Different post treatment methods are developed up to now to improve the properties of thermally sprayed coatings. In this work, arc sprayed aluminium coatings on aluminium substrates are post-treated by plasma electrolytic oxidation. To estimate the wear resistance of resulting oxide coatings, two abrasive wear tests (ASTM G65 and ASTM C1624) are carried out. Worn surfaces are examined by scanning electron microscopy in order to establish the wear mechanisms. These results of the abrasive wear tests are correlated with the parameters of the PEO process and the hence resulting micro structures of the coatings.

Near net shape coating is a trend in thermal spraying being aimed at for several years to lower costs through shortened spray time and reduced after treatment work. Because of better microstructure compared to conventional coatings, the thickness is often also reduced. To characterise the quality of those thin layer systems the standardized tensile adhesive test is not suitable, as the adhesion outweighs the cohesion by far due to reduced quantities of coating defects. To characterize the coatings behaviour under tensile stress, three-point bending tests were performed. As especially thin cermet coatings do not show abrupt catastrophic failure in bending tests, ultrasonic signals being emitted from cracks propagating through the coatings were taken during the tests. Three coating systems (Cr 2 O 3 , Cr 3 C 2 -NiCr and WCCoCr) were investigated in this work using fine grained feedstock powders with three different size distributions per system. The tests showed the negative influence of stress moments in case of the oxide ceramic and the embrittlement of the cermets, especially the Cr 3 C 2 -NiCr, with increasing spraying temperature regime due to increased formation of solid solutions and decarburization. It can be said, that the analysis of acoustic emission during bending tests gives valuable information about how to achieve thin wear and corrosive protecting coatings being qualified for high operational demands.

Thermal Spray processes are widely used to fabricate corrosion and wear resistant coatings respectively. However, these coatings have to be finished generally in subsequent steps, for example by turning, milling or grinding, to adjust the the required properties, e.g., surface roughness and accuracy. Up to now grinding is the most common post processing for wire arc sprayed coatings, but in recent years the hard turning technology gained high interest for coating treatment due to high machining efficiency. The aim of the present work is to enhance the machinability of different thermal sprayed coatings. DoE-based experiments regarding surface roughness, cutting forces and temperatures in the cutting zone had been carried out. Within the investigations a significant increase of hardness due to the hard turning process at Fe-Mn coatings had been verified. This effect, the force induced martensitic transformation, could improve the mechanical properties of the coating considerably. Based on the investigations presented in this paper, a deeper understanding of post processing of thermal sprayed coatings is given.

In this work, the microstructure of silver coatings obtained by cold spraying with a fine and a rather coarse powder were investigated. Cold-sprayed microstructures strongly depend on the deposition process parameters. These parameters have an influence on porosity, plastic strain, particle-to-particle bonding mechanisms. The originality of this study rests on the use of X-ray microtomography, which is shown to be a very powerful technique to investigate into cold-sprayed coatings. Several samples were machined from coatings by electro-discharge machining (EDM) then scanned using microtomography. Porosity fraction was determined by three-dimensional image analysis and compared to classical two-dimensional analysis of micrographs. A difference between the two methods was exhibited, which showed sample preparation effects. Consequently, X-ray microtomography seems to be well adapted to study cold-sprayed coatings thoroughly. Another result from this work was the characterization of the morphology of pores and deformed particles. Bonding mechanisms in cold spray could therefore be discussed. In addition, the knowledge on deformed particles allowed to simulate cold-sprayed coatings with build-up models. This will be done in a further work