Influence of Tipradius and Substrate on the Nanotribological Characterization of Thin DLC Coatings
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Influence of tipradius and substrate on the nanotribological characterization of thin DLC coatings Thorsten Staedler and Kirsten I. Schiffmann Fraunhofer Institute for Surface Engineering and Thin Films, Braunschweig, GERMANY
ABSTRACT In this work diamond-like carbon films deposited via plasma enhanced chemical vapor deposition with a thickness of 250nm on different substrates are characterized by nanoindentation and microscratching in combination with scanning probe microscopy. The substrates (SU8 photoresist, quartz glass, Si(100) and AlTiC ceramic) provide a wide range of combinations between film and substrate properties. The experimental configuration allows the testing of samples with loads between 1µN and 10mN and a high local resolution. The tribological response of the various film/substrate systems is analysed in two different ways. A single scratch test with linear increasing load and an oscillating wear tests at constant loads is used. The tip radii of the conical diamond tips utilized vary between 0.6 and 6µm. Both, the substrates as well as the tip radii, show a significant influence on the tribological behavior of the systems.
INTRODUCTION Hard protective coatings, such as diamond-like carbon (DLC) films, are commonly used as tribological coatings in the area of mechanical engineering in order to reduce friction and wear. The system is also interesting with respect to various applications in the hard disk as well as in the microsystems industry [1, 2]. The motivation of this work is an improvement of the tribological performance of different microelectromechanical systems (MEMS) especially linear actuators. In this case the tribological bearings are coated with DLC. As these bearings may consist of various materials it is the aim of this work to study the influence of the substrate on the mechanical as well as the tribological response of a film substrate system. In the case of a mechanical characterization of thin films the influence of the substrate is well-known even though not fully understood [3, 4, 5, 6]. It is only reasonable the substrate should also have an effect on the tribological response, but up to now only a few authors treated this topic [2, 7, 8]. In this work the influence of different substrates on the mechanical and tribological properties of thin DLC films in the low-load regime is analysed and discussed. Additionally the influence of the tip radius on the measured friction coefficient was studied.
EXPERIMENTAL SETUP The DLC films characterized in this work were deposited via a plasma enhanced chemical vapor deposition (PECVD) process on four different substrates: Al2O3-TiC ceramic (AlTiC), Si (100), fused silica and SU8 photoresist. In the case of SU8 photoresist a 100µm thick layer on
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top of a Si (100) wafer served as substrate. All substrates were coated in one single process with a film thickness of 250nm. The mechanical properties of the substrates as well as the coated systems were determined by nanoindentation using a Hysitron Nanoindenter/TriboScope in combin
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