Corrosion Resistance of TiN-Coated Ti in an Acidic Fluoride Solution

Objectives:  It has been widely recognized that pure titanium and titanium alloys actively corrode in acidic gels and mouth-washes containing fluoride.  The purpose of the present study was to examine the effectiveness of TiN coating for preventing corrosion of pure titanium in an acidic fluoride solution at 37˚C. 

Methods:  The surface of a commercially pure titanium plate specimen (JIS type 2) was metallographically polished with colloidal silica suspension.  A TiN film (ca. 3 µm) was coated by arc ion plating at 400˚C under a N₂ atmosphere.  The corrosion behaviors of the TiN-coated titanium and the as-polished titanium plate specimens in a pH 4.0 solution containing 0.9% NaCl and 0.1% NaF were examined by corrosion potential measurements and potentiodynamic polarization measurements.  The amount of released titanium ions was determined by ICP after the specimens (n=4) had been immersed in the solution for 5 hours. 

Results:  The corrosion potential of the polished titanium dropped to -1,100 mV immediately after immersion, while that of the TiN-coated titanium was maintained at -250 mV for up to 30 hours of immersion. Potentiodynamic measurements demonstrated that the polished titanium actively corroded in the acidic fluoride solution, while the TiN-coated titanium was passive in potential regions from 0 mV to 800 mV vs. Ag/AgCl reference electrode.  The amounts of released titanium ions were 7.30 µg/mm² for the polished titanium and 0.02 µg/mm² for the TiN-coated titanium. 

Conclusions:  A TiN film is chemically stable in an acidic fluoride solution and is effective for increasing the corrosion resistance of pure titanium.  TiN coating by the arc ion plating method is useful for dental prostheses made of pure titanium and titanium alloys, especially for an oral implant abutment.