Characterization of nano-wear mechanisms of hard disk coatings

The wear mechanisms of carbon coated computer hard disks with laser-textured “LT” and mechanically-textured “MT” surfaces were characterized after contact start/stop “CSS” cyclic tests. Various analytical and mechanical testing techniques were employed to study the changes in topography, roughness, chemical elements, mechanical properties, and friction characteristics of the coating and lubricant. These techniques include: the atomic force microscopy “AFM”, continuous nano-indentation test, nano-scratch test, time-of-flight secondary ion mass spectroscopy “TOF-SIMS”, and Auger electron spectroscopy “AES”. The CSS test at 15 k cycles resulted in tangible reductions of surface roughness of approximately 3.0 nm and 5.8 nm, respectively, for the LT bump and MT zone. The elastic modulus and hardness values increased after the CSS test, indicating strain hardening of the top coating layer. A critical load was identified for adhesion failure between the magnetic layer and the Ni-P layer. The TOF-SIMS analysis also revealed reductions in the intensities of all lubricant elements, indicating wear of the lubricant applied on the disk surface. All foregoing results confirm the usefulness of the characterization techniques employed to detect the subtle changes in disk surface characteristics.