Sealing performance of thin amorphous carbon films formed by ion beam assisted deposition at low temperature for protection of aluminium against aggressive media: the influence of the ion energy

Thin films of amorphous carbon (a-C) are well known for their low intrinsic microporosity. Being stable against aqueous media, they can be used for sealing metals against aggressive wet environment. Such a metal is aluminum. Its main advantage is its low weight at a comparatively high strength. Its disadvantages are its poor tribological features and its susceptibility to pitting corrosion. a-C films are very suitable for handling this problem. However, for some of the aluminium alloys the coating process temperature has to be kept low (<150 °C) in order to avoid detrimental structural changes. Such low process temperatures can be maintained when ion beam techniques are applied. Ion beam assisted deposition (IBAD) has been used to deposit a-C films on aluminium by electron beam evaporation of graphite under concurrent argon ion beam irradiation at room temperature. The sealing properties and microporosity of the films in chloride-containing water were examined by electrochemical polarization techniques. The results show that a-C films can effectively improve the corrosion performance when appropriate deposition process conditions are used. An increase in film thickness and in ion energy leads to a reduction in corrosion.