Nano-mechano-electrochemistry of passive metal surfaces

摘要

In situ nanoindentation tests were performed to evaluate the mechanical properties of the iron (100) and (110) surfaces passivated potentiostatically for 1 h in pH 8.4 borate solution after or without immersion in 5 X 10 ~(-2) M K_2Cr_2O_7 solution for 24 h. It was found from the measured load-depth curves at a maximum load of 400 μN that the hardness (3.2-3.3 Gpa) of the passivated iron (110) surfaces was larger by 10% than that (2.9-3.1 Gpa) of the passivated iron (100) surfaces. Moreover, the hardness of the passivated iron (100) and (110) surfaces increased slightly with increasing formation potential of passive film, which was ascribed to the presence of passive film. The dichromate treatment increased the hardness of the iron (100) and (110) surfaces to some extent. The loading discontinuity appeared frequently at a load of about 90 μN in the load-depth curves for the passivated iron (110) surfaces as compared with the passivated iron (100) surfaces. The loading discontinuity in the load-depth curves for the iron (110) surface, however, disappeared completely due to the dichromate treatment. Keywords: nano-mechano-electrochemistry; in situ nanoindentation; iron (100) and (110) surfaces; passive film; mechanical properties