Susceptibility to Pitting Corrosion of Ti-CP2, Ti-6Al-2Sn-4Zr-2Mo, and Ti-6Al-4V Alloys for Aeronautical Applications

Abstract

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.

Electrochemical Corrosion of Titanium and Titanium Alloys Anodized in H2SO4 and H3PO4 Solutions

“…EN data was processed with a program made in MATLAB 2018a software (Math Works, Natick, MA, USA). It removes the trends with a polynomial grade 9 and fast Fourier transform (FFT) with a Hann windowing [36,37,[62][63][64][65][66].…”

“…Past research [35,36] have demonstrated the titanium behavior in different media and shown that the passive layer generated by the natural process can be weakened due to the diffusion of different ions such as Cl − . A non-uniform passive layer will allow Cl − , Br − , or OH − ions' diffusion through the oxide layer, increasing the corrosion rate [37,38].…”

“…High energy in crystals from D1 to D3 is related to metastable pitting. Crystals from D4 to D6 are related to localized corrosion, and crystals from D7 to D8 are related to long process corrosion (diffusion or general corrosion) [36,37].…”

Electrochemical Behaviour of Ti and Ti-6Al-4V Alloy in Phosphate Buffered Saline Solution

“…Titanium and its alloys possess excellent properties such as low density, good formability, high specific strength and corrosion resistance, weldability and biocompatibility, making them desirable materials, which finds applications in different important areas such as automobile, aerospace, chemical and petrochemical industry, military and medicine [1][2][3][4][5]. Titanium and its alloys are the primary materials for biomedical and dental implant applications.…”

“…Titanium and its alloys are the primary materials for biomedical and dental implant applications. Almost 50% of titanium alloy production refers to Ti-6Al-4V alloy, the most used titanium alloy globally [2]. For biomedical applications, corrosion behavior is one of the most important criteria because the human body is an aqueous electrolyte that contains different ions such as Cl − , PO 4 3− , HCO 3 − , OH − , Ca 2+ , Mg 2+ , H + , K + , Na + etc.…”