For cold spraying, a method for the construction of the window of deposition and the selection of optimum process parameters is presented. Initially, particle impact velocity and the critical particle velocity for bonding are worked out and expressed explicitly in terms of key process and material parameters. Subsequently, the influence of particle velocity on coating characteristics is examined in view of the results of experiments and simulations. It has been found that main coating characteristics can be described as a unique function of the ratio of particle velocity to critical velocity, here referred to as g. Finally, coating properties are linked directly to primary process parameters via parameter selection maps, where contours of constant g are plotted on a plane of gas temperature versus gas pressure. Inferences of the presented method and the resulting parameter selection maps are discussed for the example of copper as feedstock material.
Titanium dioxide (TiO 2 ) coatings have potential applications in biomedical implants or as photo-catalytic functional systems. Cold spraying is a well-established method for metal on metal coatings. In cold spraying, the required heat for bonding is provided by plastic deformation of the impacting ductile particles. In contrast, few authors have investigated the impact phenomena and layer formation process for spraying brittle ceramic materials on ductile metal surfaces. In this study, the formation of TiO 2 coatings on aluminum, copper, titanium, and steel substrates was investigated by SEM, TEM, XRD, and Raman spectroscopy. The results show that the deposition efficiency depends on spray temperature, powder properties, and in particular on substrate ductility, even for impact of ceramic particles during a second pass over already coated areas. Ceramic particles bond to metallic substrates showing evidence of shear instabilities. High-resolution TEM images revealed no crystal growth or phase transitions at the ceramic/metal interfaces.
Cold spraying is a well-established coating technology for several materials and applications. The formation of dense microstructures occurs only by the plastic deformation of particles hitting the substrate with sufficiently high kinetic energies. Limited thermal influences well below the melting temperatures of respective spray materials and very short time scales make the process suitable for heat sensitive materials. For optimum spraying conditions and coating performance, a comprehensive understanding of the cold spray process and bonding mechanisms is required. This presentation summarizes the current model for coating formation based on adiabatic shear instabilities. Computer simulations visualize the bonding process and allow for extracting critical parameters that define the "window of deposition". For selected materials, a correlation between powder characteristics, particle impact conditions and coating properties is shown. Furthermore, the state of the art in spraying equipment is reviewed. Special emphasis is put on recent improvements that ensure better coating performance and widen the range of sprayable materials. Finally, different application examples are presented to elucidate the potential for a variety of coating and substrate materials.Keywords: Cold gas spraying / impact simulation / bonding mechanism / nozzle design / coating properties / Das Kaltgasspritzen ist als Beschichtungstechnologie für mehrere Werkstoffe und Anwendungen bereits etabliert. Dichte Schichtmikrostrukturen entstehen, indem Pulverpartikel mit hoher kinetischer Energie auf ein zu beschichtendes Substrat aufprallen und sich dabei stark plastisch verformen. Da die Prozesstemperaturen deutlich unter dem Schmelzpunkt des jeweiligen Materials liegen und die Prozessdauern sehr kurz sind, eignet sich dieses Verfahren auch für temperaturoder oxidationsempfindliche Werkstoffe. Für die Optimierung der Prozessparameter und Schichteigenschaften ist ein umfassendes Verständnis des Spritzprozesses und der Bindemechanismen notwendig. Diese Arbeit fasst zunächst das aktuelle Modell für die Schichtbildung zusammen, das auf adiabatischen Scherinstabilitäten basiert. Computersimulationen veranschaulichen den Bindeprozess und erlauben die Erfassung kritischer Parameter, die das sogenannte "Spritzfenster" definieren. Für ausgewählte Materialien wird der Zusammenhang zwischen Pulverparametern, Aufprallbedingungen und Schichteigenschaften gezeigt. Darüber hinaus wird der aktuelle Stand der Spritztechnik mit den bisherigen Entwicklungsstufen verglichen, insbesondere in Hinblick auf neuere Entwicklungen, die zu besseren Schichteigenschaften führen und die Palette spritzbarer Werkstoffe erweitern. Abschließend werden verschiedene Anwendungsbeispiele prä-sentiert, um das Potenzial für eine Vielzahl von Schicht und Substratwerkstoffen zu demonstrieren.
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