CHARACTERIZATION OF ULTRA-THIN DLC COATINGS BY SEM EDX, AFM AND ELECTROCHEMICAL TECHNIQUES/

Characterisation of DLC coatings ion beam-deposited on to AlTiC substr ate (70 wt% Al2O3 + 30 wt% TiC) has been carried out. AFM and SEM anal ysis showed that the island-like topography of DLC-coated AlTiC substr ates is very similar to that of uncoated substrate, implying the full coverage of coatings without visible defects. Moreover, the island hei ght was found to increase on average either with film thickness or dep osition voltage due to the possible preferential growth of DLC on TiC and the possible preferential sputter etching of Al2O3 by energetic io ns at the initial film growth stage when deposited at increased voltag es. Electrochemical measurements showed that coating with relatively t hick DLC films (> 100 nm) at an ion beam deposition voltage of 200 V c an enhance significantly the impedance of sample/solution interface so as to increase the corrosion potential of the substrate. For a given film thickness, however, the impedance as well as the corrosion potent ial increase with deposition voltage up to 200 V and decrease thereaft er. This is attributed mainly to the kinetic energy-dependent microstr ucture of both DLC and the coating/substrate interface. Consequently, deposition of DLC under proper conditions can improve dramatically the corrosion resistance of AlTiC when used in a corrosive environment. ( C) 1998 Elsevier Science S.A.