Corrosion Study in Tbfecocr Amorphous Magneto-Optical Films

(Tb20Fe65Co15)94Cr6 film shows high corrosion resist. ance with good magneto-optical properties, Hc = 4.8KOe, 9k = 0.3dcg, Ku= 1.4xl06 erg/cc, and Tc=230C. Pit corrosion in IN-NaCI aqueous solution and wet corrosion in 85°C and 85% RH atmosphere are studied for TbFeCo films with and without Cr addition. It ‘vas suggested that pit corrosion occurs by a chemical reaction between anodic pit wall and cathodic film surface, resulting in a piling up of corroded products inside the pies, On the other hand, wet corrosion in TbFeCo and TbFeCoCr films shows bubble-chain-like morphology, similar to conventional filiform corrosion observed in a coated film. This seems to take place by discontinuous movement of anodic reaction area ahead of the bubbles. © 1990 IEEE