Atmospheric pressure PECVD based on a linearly extended DC arc for adhesion promotion applications

• Published in: Surface & coatings technology Vol. 234; pp. 8 - 13
• Main Authors: Kotte, Liliana, Althues, Holger, Mäder, Gerrit, Roch, Julius, Kaskel, Stefan, Dani, Ines, Mertens, Tobias, Gammel, Franz J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.11.2013
• Subjects: Adhesion layers; Atmospheric pressure PECVD; Atmospheric pressure plasma; Plasma surface treatment; Silicon dioxide films; Plasma surface treatment; Adhesion layers; Silicon dioxide films; Atmospheric pressure plasma; Atmospheric pressure PECVD
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2013.06.070

In the aircraft industry, an increasing demand for adhesion promotion layers for titanium based materials is observed to replace polluting and unhealthy substances. Plasma enhanced chemical vapour deposition (PECVD) at atmospheric pressure (AP) seems to be favourable for the deposition of thin silica-like layers. In this work, a linearly extended and scalable DC arc plasma source is used for PECVD of silica layers on Ti6Al4V. The influence of the precursor chemistry is evaluated for HMDSO and TEOS precursors. Using HMDSO, hydrophobic almost stoichiometric SiO2 coatings with a carbon content of 3at.-% to 5at.-% are deposited on the titanium alloy substrate. For TEOS, hydrophilic carbon-free stoichiometric SiO2 coatings are deposited. The dynamic deposition rate for TEOS is 3 times lower than that for HMDSO (up to 640nm•m/min). For the intended coating of slightly curved substrates, the film properties and deposition rates are studied for different working distances from 20mm up to 60mm. For 60mm the deposition rate is reduced by a factor 6 compared to 20mm, also the index of refraction of the film decreases from 1.45 at 20mm distance to 1.39 at 60mm. With increasing distance, the particle size and concentration on the surface increases and leads to less dense structures than in the case of shorter distances. The wedge test is used to evaluate the adhesion properties of the layer. The HMDSO-based coatings exhibit a good long-term durability and a high bonding strength comparable to that of the currently used standard pre-treatment, but without the use of harmful substances. •Atmospheric pressure plasma source based on a linearly extended DC arc•Working width from 80mm to 350mm with one plasma source•Plasma treatment of large area slightly curved components•Silicon dioxide coatings as adhesion layer for structural bonding of Ti6Al4V