Effects of tungsten pre-implanted layer on corrosion and electrochemical characteristics of amorphous carbon films on stainless steel

Amorphous carbon (a-C) films have been deposited on untreated and W pre-implanted (20 kV, 3 x 10(17) ions/cm(2)) stainless steel substrates by plasma immersion ion implantation and deposition (PIII D). X-ray photoelectron spectroscopy indicates that the transition layer consists of tungsten carbide (WC) and C. The corrosion behavior of the coatings is investigated electrochemically in 37 +/- 1 degrees C simulated body fluids. In comparison with the a-C films, the a-C films with a W pre-implanted layer exhibit more positive open-circuit potentials, lower corrosion current density, and higher protection efficiency as indicated by potentiodynamic polarization tests. Electrochemical impedance spectroscopy reveals that the W pre-implantation layer increases the corrosion resistance of the a-C coatings in test solutions. The continuous structure caused by W preimplantation layer is believed to not only offer good adhesion between the a-C film and steel substrate but also act as a barrier to mitigate penetration of water molecules and ions. (c) 2008 Elsevier B.V. All rights reserved.