An Electrochemical Impedance Evaluation and Laser Irradiation Effects on the Electronic Structure of Silicon Containing Diamond-Like Carbon Coating

Report No. ARL-TR-2466
Authors: Costas G. Fountzoulas and John V. Kelley and Garry P. Halada
Date/Pages: May 2001; 24 pages
Abstract: Hard, adherent, 2-micro-thick lubricious silicon containing diamond- like carbon coatings (Si-DLC) were synthesized by 40 keV Ar+ ion beam-assisted deposition (IBAD) of tetraphenyl-tetramethyl-trisiloxane oil on two, 5-cm x 5-cm x 0.64-cm-thick 4340 steel substrates. Two different substrate surface finishes were examined, one polished and one 600-grit finish (unpolished). The corrosion resistance of the Si-DLC coating was evaluated by electrochemical impedance spectroscopy (EIS) in a O.005N concentration sodium chloride (NaCl) solution. Low-frequency impedance data from each of the coatings were compared with those of bare steel. The Si-DLC coating deposited on the polished substrate performed slightly better than the one deposited on the unpolished surface. Overall, the Si-DLC coating did not appear to offer very much corrosion protection to the steel. This was manily attributed to the presence of defects in the coating. Furthermore, to study the effect of radiation on the electronic structure of the Si-DLC coating, three Si-DLC coatings synthesized under the same deposition conditions on silicon substrates at various oil precursor temperatures were irradiated by a 335-mn wavelength, 0.37 W, pulsed YAG laser at 35 kHz Corrosion and irradiation results and procedures to minimize the pinhole density in the Si-DLC coating are discussed in detail.
Distribution: Approved for public release
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Last Update / Reviewed: May 1, 2001