AVS 47th International Symposium
    Surface Engineering Monday Sessions
       Session SE-MoA

Paper SE-MoA9
Thin Film Disk Contact Start/stop Durability Failure Model: Subcritical Interfacial Crack Growth

Monday, October 2, 2000, 4:40 pm, Room 201

Session: Coatings for Extreme Environments: Wear Resistant, Lubricious, Anti-corrosive, High Temperature Coatings
Presenter: R.L. White, IBM Corporation
Authors: R.L. White, IBM Corporation
V. Raman, IBM Corporation
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Analogous to fatigue failure in bulk materials, contact start/stop (CSS) failure of thin film disks is modeled as the progressive growth of interfacial cracks resulting from the cyclic tractions applied by intermittent slider-disk contact. Interfacial cracks eventually reach a critical dimension, resulting in film fracture or spallation and catastrophic failure of the head-disk interface. There are two bodies of evidence which support such a model. The first derives from scratch adhesion testing of mechanically textured disk media. The scratch data demonstrate that the same weibul statistics that can be fitted to CSS failures also describe the distribution of critical loads necessary to produce delamination of the disk metallurgy. Furthermore, a number of cases can be cited in which the critical loads can be correlated to start/stop durability, including the effects of hydrogenation on the start/stop durability of CHx overcoats. Secondly, this model provides for the semi-quantitative prediction of the effects of head-disk interface parameters which are in general agreement with empirical studies. The tractions applied at the head-disk interface are predicted to diminish with distance from the interface with a 1/d dependence. Since subcritical crack growth rate follows a power law relationship to stress intensity, start/stop failure statistics would be expected to show a power law dependence on carbon thickness. Data are presented demonstrating CSS life is proportional to the 3rd power of carbon thickness. The effects of CSS test temperature and slider size can also be rationalized based on the above model for CSS failure.