Effects of fluoride concentration and elastic tensile strain on the corrosion resistance of commercially pure titanium

The corrosion resistance of commercially pure (CP) titanium in 1% NaCl divi ded by 0 similar to 1% NaF solution (pH = 6) under different elastic tensil e strains was investigated by using electrochemical impedance spectroscopy (EIS) measurement technique. The polarization resistance (Rp), which is inv ersely proportional to the corrosion rate, of CP titanium in the test solut ion was obtained from the EIS data. Different elastic tensile strains, name ly 0%, 1%, 2%, and 4%, were applied on the test specimens by using a tensil e test machine during the corrosion tests. Corrosion morphology was charact erized by using a scanning electron microscope. Surface chemical analyses w ere performed by using energy dispersive spectroscopy and X-ray photoelectr on spectroscopy. The results showed that the NaF concentration and the elas tic tensile strain had a statistically significant influence on the R-p (P <0.001). The R-p decreased on increasing the NaF concentration and the elas tic tensile strain. When the NaF concentration was lower than 0.01 %, the R -p value ( > 3.4 x 10(5) Omega cm(2)) was mainly ascribed to the formation of a protective titanium dioxide (TiO2) on the metal surface, regardless of the elastic tensile strain applied. However, when the NaF concentration wa s higher than 0. 1%, the protectiveness of TiO2 was destroyed by fluoride i ons, leading to severe corrosion of CP titanium. (C) 2001 Elsevier Science Ltd. All rights reserved.