Measurements of the wear of a thin film disk

A test designed to simulate worst-case start-stop contacts is described. It combines controlled contact stresses with well-defined flying. Magnetic readback and optical methods are used to characterize the damage. Two failure modes are observed: in one, the disk is overstressed and it fails rapidly; the other mode of failure occurs for lower stresses. Contacts induce changes which increase with repeated contacts until failure occurs. Changes in the magnetic signal and in the reflected light intensity and ellipticity are reported. The optical phenomena are attributed to the overcoat being worn thin. The average depth of the trough is found to be similar to the loss of overcoat thickness. Failure is similar to that observed with higher stresses. It is characterized by an increase in light scattering, by a nonlinear and irregular increase in wear with increasing number of contacts, and by spreading of the damage to other areas. These phenomena are shown to be delamination and three-body wear. The magnetic measurements prove to be a sensitive detector of mechanical head/disk interaction, showing changes before overcoat thinning could be detected.<
>