The effect of temperature on electrochemical behavior for Cu-Al-O coatingsprepared by CVD

The electrochemical behavior of two kinds of Cu-Al-O coatings prepared by C VD 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 degrees C has lower resistance against anodic polarization than the coating achieved at 800 degrees C. Alternatively, the former exhibits rather highe r susceptibility to hydrogen evolution than the latter. The atomic hydrogen evolves at the surface of the coating and penetrates deeply into the coati ng resulting in initiation of hydrogen bubbles. With the increase of hydrog en pressure in bubbles, they grow continuously leading to hydrogen-induced cracking ultimately at the moment when the hydrogen pressure reaches a crit ical value. Essentially, the susceptibility of hydrogen-induced cracking fo r coatings should be attributed to the temperature that prevailed during CV D. Higher temperature can evidently enhance the resistance against hydrogen -induced cracking. (C) 2000 Elsevier Science Ltd. All rights reserved.