Corrosion properties of TiC films prepared by activated reactive evaporation

Abstract

Potentiodynamic measurements were used to test the corrosion properties of titanium carbide (TiC) films. The films were deposited by the activated reactive evaporation process which consists of electron beam evaporating titanium at a rate of 0.22 g min -1 in the presence of a d.c. discharge of C 2H 2. Pressure was maintained at 1 × 10 -3 Torr during deposition. The films were deposited onto quartz substrates held at 400 °C. By growing films on an insulating substrate the inherent corrosion properties of TiC films without any substrate contribution can be evaluated. The thickness and grain size of the films, which had a slight (111) texture, were 4 μm and 2 - 3 μm respectively. The TiC films were highly corrosion resistant. Activity in the polarization curve was obtained only in a strong electrolyte (1 M HCl). Neither sulphuric nor perchloric acid could activate the film. The passivation potential and critical current density (current density at the passivation potential) in 1 M HCl were 710 mV ( vs. the saturated calomel electrode (SCE)) and 60 μA cm -2 respectively. The passive potential and passive current density were 900 mV (SCE) and 20 μA cm -2 respectively. The passive potential range was 900 mV up to at least 6000 mV (SCE). The oxygen overpotential was high (more than 5000 mV) for the TiC film and comparable with that for titanium.