In order to improve titanium corrosion behavior, we can increase the thickness of oxide layer on titanium surface during anodizing process and by electrochemistry. In this research, self-color anodizing of Ti in sulfuric acid was done, and anodizing layers were created in different colors. The highest value of chromaticity was 37.8 for the anodized sample in 10 V, and the lowest value was 8.6 at 15 V. The oxide layer thickness was calculated by optical method (light refraction). The anodic film thickness increased by increasing the anodizing voltage. The highest thickness of anodic film was 190 nm in sulfuric acid solution for the anodized sample in 80 V. Corrosion resistance of anodized Ti was studied by potentiodynamic polarization curves in biological solution of RingerÕs at 37°C. On increasing the anodizing voltage further, corrosion rate of the alloy increased from its lowest rate. The lowest rate of corrosion was for the sample anodized in 10 V, which was 0.96 3 10 23 mpy.

In this research, color anodizing of Ti-6Al-4V alloy was performed in phosphoric acid solution of 0.4 M concentration and within 30 s in different voltages (10-120 V) of a DC power supply. The effect of anodizing voltages on the color and thickness of anodized layers on Ti-6Al-4V alloy surface was surveyed. Thickness and refractive index of layers were measured by spectrophotometery and reflectance curves. According to the results, thickness of layers increased with increasing anodizing voltage and was in the range of 38-167 nm. Also the refractive index of anodic film was approximately constant at about 2 and increased inconsiderably with increasing anodizing voltage. Corrosion resistance of the anodized samples in 20 and 50 V was surveyed in physiological solutions of RingerÕs solution, Artificial Saliva solution, and RingerÕs + 150 mM H 2 O 2 solution at the temperature of 37°C by potentiodynamic polarization method. The anodized sample in 50 V indicated lower corrosion rate than the non-anodized sample as well as the sample which was anodized in 20 V in all solutions. The non-anodized sample indicated the highest corrosion rate of about 0.25 lA cm 22 .

Abstract:In this research slow strain rate testing (SSRT), scanning electron microscopy (SEM), hardness measurement, metallography and optical microscopy were used to investigate the effect of localized coating damage on stress corrosion cracking (SCC) resistance of API 5L Grade B steel. According to the results, by increasing the damaged coating surface area, resistance to SCC increased. This phenomenon had 2 reasons. Firstly, by reduction of damaged surface area of coating, the ratio of anode surface to cathode surface reduced and consequently the corrosion reduced. Other reason was reduction in toughness by reducing the area of damaged surface of coating which resulted in failure at lower stresses.