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Investigation of surface pre-treatments for the structural bonding of titanium

: Mertens, T.; Gammel, F.J.; Kolb, M.; Rohr, O.; Kotte, L.; Tschöcke, S.; Kaskel, S.; Krupp, U.


International journal of adhesion and adhesives 34 (2012), pp.46-54
ISSN: 0143-7496
ISSN: 1879-0127
Journal Article
Fraunhofer IWS ()
atmospheric pressure plasma; surface treatment; titanium and alloys; wedge test

This paper evaluates wet-chemical pre-treatments (alkaline etching, anodising) and a plasma treatment for structural bonding of titanium (Ti 6Al 4V). The main objective of this study is the comparison of the applicability of the plasma pre-treatment to wet-chemical treatments on titanium for structural bonding. In this context, an atmospheric pressure plasma device was used to deposit thin functional films from hexamethyldisiloxane (HMDSO) precursor on titanium. X-ray photoelectron spectroscopy (XPS) was employed to assess the chemical composition of the surface after different pre-treatments on the titanium substrate, while the morphology and the film thickness were investigated with scanning electron microscopy (SEM). The adhesion properties on titanium were evaluated by means of a wedge test in hot/wet conditions. After bonding tests the fracture surface and the failure loci were analysed. Using a long arc plasma generator and HMDSO precursor almost stoichiometric SiO 2 coatings were obtained on the titanium substrate. These coatings exhibit good long-term durability and bond strength compared to an alkaline etching in the wedge test. The investigated anodising process leads to oxide layers revealing a highly porous nanostructure. In contrast to the alkaline etching, the plasma derived coatings and the oxide layer produced by the anodising process exhibit a higher micro, respectively nano roughness, and hence a better long-term durability.