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Engine blocks of modern passenger car engines are generally made of light metal alloys, mostly hypoeutectic AlSi-alloys. Due to their low hardness, these alloys do not meet the tribological requirements of the system cylinder running surface-piston rings-lubricating oil. In order to provide a suitable cylinder running surface, nowadays cylinder liners made of gray cast iron are pressed in or cast into the engine block. A newer approach is to apply thermal spray coatings onto the cylinder bore walls. Due to the geometric conditions, the coatings are applied with specifically designed internal diameter thermal spray systems. With these processes a broad variety of feedstock can be applied, whereas mostly lowalloyed carbon steel feedstock is being used for this application. In the context of this work, an iron-based wire feedstock has been developed, which leads to a nanocrystalline coating. The application of this material was carried out with the Plasma Transferred Wire Arc system. AlMgSi0.5 liners were used as substrates. The coating microstructure and the properties of the coatings were analyzed.

International audienceImproving sealing between rotating and stationary parts in aerospace gas turbines significantly increases engine performance by improving thermal efficiencies. To reach this aim, abradable seals are being incorporated into turbine casings. With an abradable seal, the blade tips incur into the shroud, thereby reducing the gap between the rotor and the coating to a minimum. These coatings are generally multiphase materials applied by thermal spray techniques and consisting in a combination of metallic matrix and additional dislocator phases with a controlled amount of porosity. The sealing effectiveness requires a combination of properties that are usually optimised empirically with thermal spray coatings generally made up from a range of two-phase powder mixtures. The present study intends to initiate a theoretical approach for the study of these materials aiming at developing a prediction strategy for structure improvement. Image analyses and finite element calculations were used to examine the effect of phase morphology on the mechanical behaviour of two reference abradable systems, namely AlSi-hBN and NiCrAl-Bentonite for compressor stages. Scanning Electronic Microscopy (SEM) was used to obtain a series of micrographs for coating characterisation. These micrographs were then treated to create equivalent images based on geometrical description of the inherent morphology. The resultant reduced images are used to carry out finite element calculations, in order to determine the mechanical properties of each coating. It is believed that this approach provides consistent results and is believed to be a reliable starting point for further coatings design

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Hydroxylapatite (HA) is one of the most important materials for human hard tissue implants. Until now, HA coatings are widely deposited on implants using atmospheric plasma spraying (APS). Due to the decomposition of HA and formation of amorphous phase during spraying, the crystallinity of APS coatings is usually below 70 %, although coarser spray powders such as one with a size distribution of -150 +45 lm are used. In this study a finer HA powder -80 +50 lm was sprayed using both a conventional APS process and the new "microplasma spraying" (MPS) process. The coatings were characterized in terms of their microstructure and crystallinity. It was found that the spray parameters influenced strongly the coating structure and phase composition. Despite the smaller particles, the HA content of APS coatings could be increased from 27 % to 72 % only by changing the spray parameters. Higher HA contents up to over 85 % could be obtained by microplasma spraying. It was found that textured coatings could form under certain conditions during both spray processes.Keywords: hydroxylapatite, coating, microplasma spraying, crystallinity Hydroxylapatit (HA) zählt zu den wichtigen Biowerkstoffen für Implantate zum Hartgewebeersatz. Bislang wird die Beschichtung der Implantate mit HA meist mittels atmosphärischen Plasmaspritzverfahren durchgeführt. Aufgrund der Zersetzung von HA und Bildung einer amorphen Phase beim Spritzen liegt die Kristallinität einer APS-Schicht normalerweise unter 70 %, selbst wenn gröbere Spritzpulver mit einer Kornfraktion im Bereich von -150 + 45 lm verwendet werden. Im Rahmen dieser Arbeit wurde ein feineres Pulver -80 +50 lm sowohl mittels APS-Verfahren als auch mittels des neuen Mikroplasmaspritzverfahrens (MPS) gespritzt. Die Schichten wurden im Bezug auf ihre Mikrostruktur und Kristallinität untersucht. Es wurde festgestellt, dass die Spritzparameter sowohl die Schichtstruktur als auch die Phasenzusammensetzung der Schicht stark beeinflussen. Trotz der kleineren Spritzpartikel konnte der HA-Gehalt der APS-Schicht durch Variation der Spritzparameter von 27 % bis auf 72 % erhöht werden. Mittels des MPS Verfahrens konnte ein höherer HA-Gehalt bis über 85 % erzielt werden. Unter bestimmten Spritzkonditionen entstand eine Texturstruktur in der Schicht sowohl beim APS als auch beim MPS.