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The FeCuAl-Al2O3 coatings deposited by means of supersonic technique - microstructure and properties

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In the past few years it has been scientifically and technically demonstrated that the employment of nanostructured materials to produce high performance surfaces is a winning approach for creating coatings with exceptional properties: low friction, and high resistance to wear, temperature, and chemical attack [1÷3]. Advanced, multifunctional nanophased powder systems can be produced using high energy milling technology. This technology exploits mechano- chemical synthesis principles, and simultaneously manages to induce material property improvements such as a fine phase distribution and crystal size refinement [4]. It is necessary to adopt a deposition process which does not damage the nanostructure of starting milled materials (i.e. exposing them to high temperature for prolonged time) in order to take advantage of improved properties. In the coating sector, thermal spray technology is commonly used to produce high thickness coatings in the defense, aerospace and gas turbine industries [5÷7]. Particle velocity and particle temperature, together with substrate temperature, are the most important parameters affecting the deposit formation. Thus, the “Cold Gas Spraying" technology, which uses purely kinetic effects to deposit powders, fulfils the requirement of not damaging the nanostructure, even if it sometimes presents some technical limitations that need to be overcome[7÷9]. Various factors are responsible for the quality of the coating and it’s surface in terms of corrosion and wear resistance. Bonding between sprayed powder particles markedly affects the cohesion and mechanical properties of the coating. In the present study, FeCuAl-Al2O3 (FAC-Al) powder was used to prepare coatings by cold spray process. The aim of this work was to investigate the microstructure of the FeCuAl-Al2O3 coatings obtained by supersonic cold gas spraying of micropowder prepared by the high energy milling of the commercially availa[...]

Structural and chemical investigation into Ti/TiC coatings deposited with Cold Gas Spraying (CGS)

  Nanostructured materials and coatings are a main subject in research and development thanks to their good physical and mechanical properties compared to crystalline materials [1]. Cold Gas Spraying (CGS) is a low-temperature method with deposition carried out in the solid substrates relative to conventional thermal spray [2]. The deposition is achieved through powder acceleration to supersonic velocities in the de Laval type nozzle [3] (Fig. 1). The technique was developed in the Institute of Theoretical and Applied Mechanics of the Russian Academy of Science in Novosibirsk [3]. The coating materials are injected into the carrier gas stream in nanopowder form at the inlet of the de Laval nozzle. It is accelerated in gas stream and propelled to the substrate with high velocities. In the special chamber gas is heated to temperature lower than the powder material’s melting point, before entering the nozzle [4]. Only particles which reach the velocity higher than the critical velocity could be deposited onto a substrate [5]. The low-temperature method, the very short time scales and the use of more or less inert carrier gases (nitrogen, helium) make the Cold Gas Spray technique useful for applications where it is vital to avoid oxidation, maintain stoichiometry and to retain properties of the powder in the coatings. In comparison to conventional thermal spraying, CGS has the another advantage of being simple to implement [6]. In the coatings titanium was used as a plastic binder. The hard titanium carbides improve wear resistance. The aim of this work is to present the results of microstructural and compositional investigation into Ti/TiC coatings deposited by means of supersonic spray[...]

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