Titanium alloys are used in different industries like biomedical, aerospace, aeronautic, chemical, and naval. Those industries have high requirements with few damage tolerances. Therefore, they are necessary to use materials that present fatigue, mechanical, and corrosion resistance. Although Ti-alloys are material with high performance, they are exposed to corrosion in marine and industrial environments. This research shows the corrosion behavior of three titanium alloys, specifically Ti CP2, Ti-6Al-2Sn-4Zr-2Mo, and Ti-6Al-4V. Alloys were exposed on two electrolytes to a 3.5 wt % H2SO4 and NaCl solutions at room temperature using cyclic potentiodynamic polarization (CPP) and electrochemical noise (EN) according to ASTM G61 and ASTM G199 standards. CPP technique was employed to obtain electrochemical parameters as the passivation range (PR), corrosion type, passive layer persistence, corrosion potential (Ecorr), and corrosion rate. EN was analyzed by power spectral density (PSD) in voltage. Results obtained revealed pseudopassivation in CPP and PSD exposed on NaCl for Ti-6Al-2Sn-4Zr-2Mo, indicating instability and corrosion rate lower. However, Ti-6Al-4V presented the highest corrosion rate in both electrolytes. Ti-6Al-2Sn-4Zr-2Mo revealed pseudopassivation in CPP and PSD in NaCl, indicating a passive layer unstable. However, the corrosion rate was lower in both solutions.

Custom 450 stainless steel and AM 350 stainless steel are both precipitation hardening stainless steels, which are widely used in a variety of aerospace applications. The former steel exhibits very good corrosion resistance with moderate strength, whereas the latter is used for applications requiring high strength along with corrosion resistance. In this study, the corrosion behavior of CUSTOM 450 and AM 350 stainless steels passivated in (a) citric acid and (b) nitric acid solutions for 50 and 75 min at 49 and 70 °C, and subsequently exposed in 5 wt. % NaCl and 1 wt. % H2SO4 solutions are investigated. Two electrochemical techniques were used: electrochemical noise (EN) and electrochemical impedance spectroscopy (EIS) according to ASTM G199-09 and ASTM G106-13, respectively. The results indicated that passivation in nitric acid made the surface prone to localized corrosion. Statistical and PSD values showed a tendency toward pitting corrosion. On the whole, passivated CUSTOM 450 stainless steel showed the best corrosion behavior in both, NaCl and H2SO4 test solutions.

This research aimed to conduct a passive layer state study on martensitic and semi-austenitic precipitation hardening stainless steels (PHSS) passivated in citric acid and nitric acid baths at 49 and 70 °C for 50 and 75 min and subsequently exposed in 5 wt.% NaCl and 1 wt.% H2SO4 solutions. Corrosion behavior of the passivated material was observed by using potentiodynamic polarization (PP) according to the ASTM G5-11 standard. The microstructural analysis was performed by optical microscopy and scanning electron microscopy (SEM), while the passivated layer was characterized by X-ray photoelectron spectroscopy (XPS). The results indicated that the semi-austenitic-NA-50 min-70 °C sample showed the best corrosion resistance behavior in both solutions. The XPS characterization confirmed that the martensitic and semi-austenitic surface film presented a mixture of chemical compounds, such as Cr2O3 and Fe(OH)O, respectively.