MECHANICAL-PROPERTIES AND MICROSTRUCTURAL ANALYSIS OF A DIAMOND-LIKE CARBON COATING ON AN ALUMINA GLASS COMPOSITE/

We investigate the mechanical and microstructural properties of a diam ond-like carbon coating (DLC) which is deposited by plasma enhanced ch emical vapor deposition (PECVD) onto an alumina/aluminosilicate glass composite used for biomedical applications, Ball-on-ring tests yield a fracture strength that is essentially influenced by the surface topol ogy/roughness. The surface topology of the coating is investigated by atomic force microscopy (AFM). Tribology tests and nanoindentation rep resent the wear resistance and hardness; these are properties that are mainly influenced by the microstructural properties of the DLC coatin g. This microstructure is investigated by transmission electron micros copy (TEM) and analyzed by parallel electron energy loss spectroscopy (PEELS). For the general applicability of the coated composite, the in terfacial adhesion of the DLC coating on the comparably rough substrat e (roughness amplitudes and wavelengths are in the micrometer range) i s important. Therefore, we focus on TEM investigations that show the i nterface to be free of gaps and pores that we, together with a charact eristic microstructure adjacent to the interface, relate to the excell ent adhesion. The interlayer consists of a high density of SiC grains, part of them directly bound to the substrate, and part of them bound to other SiC grains, This interlayer is followed by an essentially dif ferent region of the coating as concerns the microstructure; this regi on consists of nanocrystalline diamond particles embedded in an amorph ous carbon matrix. It is this heterogeneous microstructure to which we attribute (i) the good adhesion based upon the interface stabilizing SiC grains, and (ii) the high hardness and wear resistance based upon the diamond nanocrystals in the coating.