Browsing by Keyword "HVOF"
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Item Investigation of HVOF spraying on magnesium alloys(2006-12-04) Parco, Maria; Zhao, Lidong; Zwick, Jochen; Bobzin, Kirsten; Lugscheider, Erich; EXTREMATMagnesium alloys are promising alternatives to other lightweight alloys such as aluminum alloys due to their high specific strength and stiffness. However, the use of magnesium alloys is limited by their poor wear behaviour and corrosion performance. Recent studies have shown an enormous potential of thermal spray techniques for the surface modification of Mg alloys. The high particle velocities and moderate temperatures achieved by the High Velocity Oxy-Fuel (HVOF) flame spray process lead to very dense coatings with outstanding wear behaviour and superior bond strengths in comparison to other thermal spray processes. In this study, two Mg alloys AZ91 and AE42 were coated using the HVOF spray process. The substrates were compared in terms of the measured bond strength and the observed adhesion mechanisms of the coating. Furthermore, the coatings were characterized concerning their corrosion performance on AZ91 substrates. It was found that dense WC-Co coatings could be applied on Mg alloy substrates using the HVOF spray process. The high kinetic energy of the WC-Co particles led to a "self roughening" effect on the substrate, enabling the deposition on polished Mg alloy substrates. The coatings showed a very good adhesion to the substrates. The corrosion tests showed that the unsealed WC-Co coatings could not improve the corrosion performance of Mg alloys. In contrast, the duplex coating system with an Al bond coat improved significantly the corrosion resistance of Mg alloys. The sealed coatings showed a very good corrosion behaviour.Item Parameters Influencing the Photocatalytic Activity of Suspension-Sprayed TiO2 Coatings(2014-10) Toma, Filofteia Laura; Berger, Lutz Michael; Shakhverdova, Irina; Leupolt, Beate; Potthoff, Annegret; Oelschlägel, Kathrin; Meissner, Tobias; Gomez, José Antonio Ibáñez; de Miguel, Yolanda; TRAZABILIDAD CIRCULAR; MercadoPhotocatalytic properties of titania have been studied very intensively for a variety of applications, including air and water purification. In order to clarify the influence of the phase composition and other parameters, thermal spraying with suspensions was applied to produce photocatalytically active titania coatings starting from two commercially available anatase and rutile submicron powders. Aqueous suspensions containing 40% solids by weight were sprayed with an HVOF process using ethylene as the fuel gas. The spray parameters were chosen in order to produce mechanically stable coatings and to preserve a high content of the initial crystalline phases of the powders. The coating microstructures, phase compositions, and surface properties were characterized. The photocatalytic performance was evaluated by degradation of the pink dye Rhodamine B (RB) using two techniques: degradation of an aqueous solution of RB and discoloration of impregnated RB. All the coatings exhibited photocatalytic activity to varying degrees, depending on the phase composition as well as other factors, namely, the coating microstructure, surface morphology, surface hydroxylation, light absorption, and interaction with the pollutant.