Investigation of scratch resistance of thin carbon overcoat media using micro scratch testing

This paper investigates the scratch resistance of thin carbon overcoat media using a novel micro scratch testing method. Ramp loading was applied to a carbide blade, scratching along a rotating hard disk surface and the load corresponding to the penetration of the carbon overcoat, referred to as the critical load, was used as the measure of scratch resistance. The contact electric resistance (CER) at the cutting point of the blade/media interface was monitored through the scratch process and the critical load was determined when the CER dropped to zero. It has been found that CER monitoring is a very accurate and reliable way of determining the critical load. Scratches were characterized using scanning electronic microscopy (SEM) and it has been found that at the critical point the carbon overcoat was delaminated, peeled off, or plowed away. The micro scratch testing has shown to have the sensitivity to differentiate the effect of carbon thickness, carbon type, lubricant, and substrate type on media scratch resistance.