Electrochemical evaluation of the corrosion behavior of steel coated with titanium-based ceramic layers

Titanium nitride, titanium diboride and titanium boronitride with different boron content were deposited on a martensitic stainless steel from a gaseous mixture consisting of TiCl(4), H(2), N(2) and BCl(3) by chemical vapor deposition (CVD) at a reduced pressure of 600 mbar and a temperature of 900 degrees C. The morphology and composition of the coatings were characterized by SEM, XRD and XPS. The corrosion behavior of the coated steel samples was evaluated by potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS) in a 0.5 M sodium chloride solution. The results show that steel coated with TiB(2) and with TiBN with a boron content of 20% (TiBN-2) have the best corrosion resistance. TiB(2) coated steel, initially, has a higher corrosion resistance than the TiBN-2 coated samples. However, a decrease in impedance values with the immersion time was slower for the TiBN-2 coated steel than for the TiB(2) coated sample. The protectiveness of the deposited surface layers is mainly related to their morphology such as defects or pores. (C) 2010 Elsevier B.V. All rights reserved.