Structure of the Passive Film formed on Fe-Mn-Si-Cr-Ni Shape Memory Alloy after Wet and Dry Corrosion Test

The corrosion resistance of an Fe-Mn-Si-Cr-Ni shape memory (16 Mn) alloy was estimated by the wet and dry corrosion tests, and the structure of the passive film formed on the alloy was examined by primary EELS (Electron Energy Loss Spectroscopy) using TEM (Transmission Electron Microscopy) analysis. The electrochemical behavior of 16 Mn alloy was investigated by EIS (Electrochemical Impedance Spectroscopy). 16 Mn alloy showed much higher corrosion resistance than the carbon steel (SM) in wet and dry corrosion tests. In EIS measurement following corrosion test, 16 Mn alloy had much larger value of corrosion resistance (Z(1mHz)) by forming the passive film as compared to SM. In AES (Auger Electron Spectroscopy) and XPS (X-ray Photoelectron Spectroscopy) analysis, the passive film of 16 Mn alloy was shown to contain Fe, Mn, Cr, Si and Ni. From TEM-EELS, the passive film was found to consist of 2 layers of a Cr Si-rich in inner and an Mn-rich outer layer of Fe oxide. It was found that 16 Mn alloy could maintain the passive film which composed of effective elements in the wet and dry environment.