CORROSION BEHAVIOR OF SPUTTER-DEPOSITED CO-BASE ALLOY-FILMS IN NEUTRAL SOLUTIONS

The corrosion behavior of three kinds of sputter-deposited Co-base alloy thin films-whose compositions are almost the same as those of the currently used magnetic recording hard disks-has been studied by electrochemical methods and X-ray photoelectron spectroscopy analysis. The alloys suffer general corrosion in a 0.5 M NaCl solution and pitting during anodic polarization in borate-boric acid solutions containing Cl- ions with pH 8.4 at 30-degrees-C. The corrosion resistance decreases in the following order: Co-12Cr-2Ta>Co-24Ni-5Cr much greater than Co-10Pt-9Ni. The high corrosion resistance of the Co-12Cr-2Ta alloy film is based on the formation of a Cr- and Ta-enriched surface film. The C overcoat is incomplete and it may enhance localized corrosion through pores in the overcoat, as a result of the galvanic interaction between electrically conductive C and Co-base alloy films.