The Enhancement of Corrosion Resistance of Titanium in High Temperature Acidic Solutions by Microarc Oxidation
Microarc oxidation technique (MAO) is an electrochemical process which can be used to make ceramic coatings on the surfaces of titanium and its alloys. In this investigation samples of a commercially pure titanium (TA3) were anodized in 30g/L NaAlO2 solution under 280V voltage for 75 minutes to form a 3-10µm coating. XRD analysis showed that the main phase of the coating is TiAl2O5. Samples of the titanium and the MAO treated titanium were immersed in HCl and H2SO4 acid solutions at 250°C in an autoclave. Results show that in 0.1 mol/L concentration both the titanium and the MAO treated titanium have good corrosion resistance in the acid solutions. However, in 1 mol/L concentration the titanium samples completely dissolved in 24 hour immersion. The MAO-treated titanium samples did not dissolved away although some degree of weight losses took place. SEM shows that there are corrosion products on the surfaces of MAO treated titanium samples. XRD analysis showed that the corrosion products are titanium oxides (rutile and anatase). A corrosion resistance mechanism, which is based on the synergic protection of aluminum titanium oxides and titanium oxides for the titanium substrate, is proposed for explaining the enhancement of the corrosion resistance.
H.S. Lee, I.S. Yoon and M.H. Aliabadi
J. S. Lu and C. Lu, "The Enhancement of Corrosion Resistance of Titanium in High Temperature Acidic Solutions by Microarc Oxidation", Key Engineering Materials, Vols. 385-387, pp. 777-780, 2008