Doping of Ultralow Friction Coatings for Reduced Sensitivity of Friction to Humidity and Improved Interfacial Adhesion (24080)
Northwestern researchers have created new wear-protective ultralow friction coating compositions, with reduced affinity for water adsorption, affording decreased surface friction in humid environments. The amorphous films are generated by conventional sputtering techniques on a variety of material surfaces. The coatings show great promise where low friction in humid environments, close proximity contact forces and humidity sensitivity are critical to performance, such as hard disk systems, MEMS/NEMS sliding surfaces, etc.
ADVANTAGES: The new coatings enable ultralow friction performance from dry to humid environments by decreasing surface moisture adsorption sensitivity. The coatings reduce short-ranged attractive forces inherently present in some systems such as hard disk drives and MEMS/NEMS and promise greater device tolerance to ambient humidity changes.
SUMMARY: Surfaces in relative motion and close contact (e.g. nanometer range) may generate moisture-induced meniscus and intermolecular adhesive forces, which can impair performance and device efficiency. Ultralow friction amorphous carbon coatings, while useful in these applications, are degraded by ambient moisture adsorption. New doped amorphous carbon coatings have been identified that significantly reduce surface moisture adsorption and accompanying interfacial friction. Thus, silicon substrates and chrome steel ball bearings, coated with a new doped hydrogenated carbon film exhibit significantly less moisture sensitivity (Fig. 1) and steady state coefficient of friction (Fig. 2) than comparable non-doped amorphous carbon coated materials. The ~ 500 nm films, coated by magnetron sputtering in vacuo (10-7 Torr), exhibit excellent adhesion without compromising coating hardness.
This invention provides ultralow friction wear-protective surfaces with reduced sensitivity of friction to humidity. Wide application to tribological components in relative sliding motion (e.g., gears and bearings) and in devices with close proximity moving surfaces (e.g., disk drives, MEMS/NEMS) is anticipated.
Yip-Wah Chung and Christina Freyman
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