Toward an understanding of overcoat corrosion protection

This paper presents detailed electrochemical investigations on the role of overcoat and lubricant in head and media corrosion protection. Depending on the types of metal to be protected, some types of overcoat materials can actually accelerate corrosion due to galvanic coupling effect. To eliminate such coupling, a true dielectric film needs to be used instead of the conventional hydrogenated carbon films. On the other hand, galvanic coupling is not always detrimental depending on the types of materials to be protected.

I. Introduction

Carbon overcoat has been used for head and media corrosion protection for over ten years. Along with the quest for higher areal density, the thickness of the overcoat has been reduced from over 20 nm to below 5 nm today [1]. To maintain the corrosion and wear performance, the overcoat materials have also been evolving with time, changing from sputtered amorphous carbon to hydrogenated carbon , nitrogenated carbon , and to most recently ion beam deposited carbon (IBC).