Ion beam sputter coating of three-dimensional objects: rings, cylinders, and tubes

Abstract

Ion beam techniques as a surface modification and coating technique offer some advantages such as excellent controllability, versatility, and low process temperature. However, they suffer from a basic limitation, their line-of-sight character. Only the part of an object, which is turned towards the ion beam, can be treated properly. This is one of the reasons why the application of ion beam techniques to three-dimensional objects is quite limited. If one would like to take advantage of, as an example, the low process temperature of ion beam techniques for treatment of temperature-sensitive materials, but the objects were three-dimensional, special sample manipulators and/or ion beam guiding elements had to be used. However, in some cases comparatively simple set-ups can be used when they are especially designed for the substrate to be coated. The present paper describes different apparatus for ion beam sputter coating of rings, cylinders and tubes. They use conical sputter targets, which are placed inside the objects. In case of cylinders and tubes, a beam of energetic ions enters the object to be coated along its axis, impinges onto the target and sputters atoms onto the inner walls. In case of rings, in addition to the inner conical sputter target an outer hollow cone is used. Thus, the ring is completely covered. Rings, cylinders and tubes of aluminum and an aluminum alloy were coated at temperatures below 200 °C with several 10–100 nm thick protective films of carbon, niobium and aluminum. Electrochemical polarization measurements in sodium chloride solution showed that the coatings lead to a reduction in pitting corrosion which aluminum suffers from in aqueous media in the presence of aggressive anions.