Frequency-Time Domain Analysis of Electrochemical Noise of Passivated AM350 Stainless Steel for Aeronautical Applications

Precipitation-hardening stainless steel is frequently utilized in a variety of aerospace applications. While the latter steel is employed in applications demanding great strength and corrosion resistance, the former steel offers good corrosion resistance with moderate strength. In this work, the corrosion behavior of AM 350 stainless steel exposed to solutions containing 5% NaCl and 1% H2SO4 after being passivated in nitric acid and citric acid solution for 50 min each at 49 and 70 degrees C is examined. AM 350 stainless steel is precipitation hardening stainless steel, widely used in various aerospace applications. The former steel exhibits excellent corrosion resistance with moderate strength, whereas the latter is used for applications requiring high strength and corrosion resistance. In this study, AM 350 stainless steel corrosion behavior passivated in a) citric acid and b) nitric acid solutions for 50 min at 49 and 70 degrees C, and subsequently exposed in 5 wt. % NaCl and 1 wt. % H2SO4 solutions are investigated. The electrochemical technique used was electrochemical noise (EN), based on the ASTMG199 standards. Two data analysis techniques were employed for EN: the time-frequency domain (wavelets transform) and the power spectral density (PSD). The results showed a better behavior against corrosion of samples passivated in nitric acid in citric acid. Also, in NaCl electrolyte, the uniform process is the predominant behavior.