Effect of temperature on electrochemical behavior for Cu-Al-O coatings prepared by CVD

The electrochemical behavior of two kinds of Cu-Al-O coatings prepared by CVD at different temperatures was monitored anodically and cathodically in a solution of 0.1 M NaCl. The results show that the coating achieved at 700 °C has lower resistance against anodic polarization than the coating achieved at 800 °C. Alternatively, the former exhibits rather higher susceptibility to hydrogen evolution than the latter. The atomic hydrogen evolves at the surface of the coating and penetrates deeply into the coating resulting in initiation of hydrogen bubbles. With the increase of hydrogen pressure in bubbles, they grow continuously leading to hydrogen-induced cracking ultimately at the moment when the hydrogen pressure reaches a critical value. Essentially, the susceptibility of hydrogen-induced cracking for coatings should be attributed to the temperature that prevailed during CVD. Higher temperature can evidently enhance the resistance against hydrogen-induced cracking.