An Asperity-Based Fractional Coverage Model for Solid Lubricant Film Transfer on a 3D Surface

Topography data was obtained from an aluminum thin film deposited unto a substrate. Using this 20 μm × 20 μm specimen, an asperity-based fractional coverage model was used to predict (1) the friction coefficient at a pad/disk interface (2) the thickness of deposited lubricant film and (3) the wear factor for a compacted lubricant pellet in sliding contact. The fractional coverage varies with time and is a useful modeling parameter for quantifying the amount of third body film covering the disk asperities. The model was based on a previous 1-D control volume fractional coverage model which was used to glean tribological parameters including friction coefficient and wear factor. In this model, the wear rate of the pellet, pad friction coefficient, and lubricant thickness can be determined as a function of the pellet load, slider pad load, disk speed, and material properties. Steady-state results from the model adequately predict the self-repairing and self-replenishing nature of powder lubrication as a function of topography.