The corrosion behavior of sputter-deposited amorphous Fe-Cr-Ni-Ta alloys in 12 M HCl

Amorphous Fe-Cr-Ni-Ta alloys containing 7-75 at.% tantalum were successfully prepared by the D.C. magnetron sputtering method by using a target of commercial Type 304 stainless steel and high purity tantalum discs. The corrosion behavior of the Fe-Cr-Ni-Ta alloys in 12 M HCl at 30°C was investigated by immersion tests, electrochemical measurements and XPS analysis, and compared with that of Cr-Ta binary alloys. The corrosion rate of the sputter-deposited Fe-Cr-Ni-Ta alloys containing more than 19 at.% tantalum was more than six orders of magnitude lower than that of bulk Type 304 stainless steel and even lower than that of sputter-deposited tantalum metal, although the corrosion rate of the alloys was higher than that of the Cr-Ta alloys. The open circuit potentials of the Fe-Cr-Ni-Ta alloys are located in the passive regions of both chromium and tantalum, and all the alloys are spontaneously passivated. XPS analysis revealed that the passive films formed on the alloys by immersion in 12 M HCl were significantly rich in tantalum and chromium cations. The films were deficient in iron cation and the formation of homogeneous double oxyhydroxides containing mainly chromium and tantalum should be responsible for the high corrosion resistance of the alloys.