Magnetron sputter process for inner cylinder coatings

For various applications, it is necessary to coat the inner surfaces of components, for examples the inner cylinders of engines and the inner surfaces of bearings. For special sensors, e.g. for measuring accelerations, inner coatings are applied to achieve a special surface function, e.g. electrical conductivity. For most applications, coatings are required which exhibit a high homogeneity and an even thickness distribution, without any significant heat-up during the coating process.A magnetron-assisted sputtering process can be adjusted to fulfill these requirements. In the present paper, we will describe a depositioning set-up for which cylindrical permanent magnets are used — either inside a cylindrical sputter-cathode (post magnetron PM), or at the ends of the hollow cylinders or sleeves that are to be coated (ring magnetrons RM). For the study, copper cathodes of 2 or 4 mm diameter were used. The cylindrical substrates were made of aluminum alloy and had an inner diameter of only 10 mm. The paper includes theoretical considerations, evaluations of the magnetic fields, and a description of the set-up and the realization of the experiment, as well as the characterization of the coatings. Due to the high relevance for the function of precision sensors, the study also presents the structure and the thickness distribution of the inner cylindrical coatings.