Observations on electrochemical and environmental corrosion tests for cobalt alloy disc media

The corrosion resistance of cobalt alloy magnetic recording media was studied using both electrochemical and accelerated business environment corrosion testing. The electrochemical test was found to correlate reasonably well with the environmental test. Examination of various cobalt alloy discs, after exposure to the environmental test, showed similar corrosion product sizes, the presence of sulfur and oxygen in the corrosion products and different corrosion morphologies. A carbon overcoat served to improve a disc's corrosion resistance by inhibiting the lateral growth of corrosion products across the disc surface. Generally, Co-Cr media are the most corrosion resistant, followed by Co-Ni and Co-P, in decreasing order.