THE BREAKDOWN MECHANISM OF DIAMOND-LIKE CARBON-COATED NICKEL IN CHLORIDE SOLUTION

The breakdown mechanism of chemical vapor deposited nickel (CVD Ni) co ated with 5 micrometers of diamond-like carbon (DLC) produced by plasm a source ion implantation (PSII) in chloride solution was investigated . PSII differs from traditional implantation techniques in that the ta rgets are placed directly in a plasma source and then pulse biased to produce a non-line-of-sight process to complex-shaped targets without complex fixturing. Electrochemical Impedance Spectroscopy (EIS) measur ements indicated the presence of small pores in the DLC presumably for med in the deposition process. These pores were also observed in the s canning electron microscope. These pores exposed a layer of CVD Ni imp lanted with carbon (C). EIS results were analyzed within the context o f an equivalent circuit model which incorporated three time constants representing the Ni-C implant layer, the DLC/solution interface, and t he pore/solution interface. Good correlation between CNLS fitting of t he impedance data and this circuit model was obtained. Upon immersion in chloride solution, the onset of breakdown of the DLC coating was ra pid. Breakdown failed to initiate in chloride solution buffered with s odium berate. Mixed potential theory was used to describe these result s and mechanisms for the initiation and propagation of coating failure in chloride solutions. Published by Elsevier Science Ltd.