Nanoscale wear and kinetic friction between atomically smooth surfaces sliding at high speeds

Abstract

The kinetic friction and wear at high sliding speeds is investigated using the head-disk interface of hard disk drives, wherein, the head and the disk are less than 10 nm apart and move at sliding speeds of 5-10 m/s relative to each other. While the spacing between the sliding surfaces is of the same order of magnitude as various AFM based fundamental studies on friction, the sliding speed is nearly six orders of magnitude larger, allowing a unique set-up for a systematic study of nanoscale wear at high sliding speeds. In a hard disk drive, the physical contact between the head and the disk leads to friction, wear and degradation of the head overcoat material (typically diamond like carbon). In this work, strain gauge based friction measurements are performed; the friction coefficient as well as the adhering shear strength at the head-disk interface are extracted;and an experimental set-up for studying friction between high speed sliding surfaces is exemplified.

Voltage assisted asymmetric nanoscale wear on ultra-smooth diamond like carbon thin films at high sliding speeds

“…A typical head-disk interface setup features the head flying on top of the disk similar to the one studied in ref. 6 , 28 . The disk is fabricated by depositing a magnetic multilayer film structure onto a glass substrate, then coated with 3 nm amorphous nitrogenated carbon (protective overcoat layer), and finally covered with a molecular layer of perfluoropolyether polymer lubricant (~1 nm thick).…”

“…For further insight, an in-situ monitoring of the wear is desired to gain better insight into the impact of electrochemical oxidation during sliding. The head disk interface has a unique feature with the micro-heater power calibrated precisely to measure the head overcoat wear depth in a continuous manner during the experiment (see Supplementary Information for more detail) 6 . Figure 1b shows the wear depth profile of the head carbon overcoat for the respective voltage condition as a function of time.…”

“…Wear is broadly classified in two categories: physical wear and progressive wear. Physical wear is further classified as adhesive, fatigue and abrasive wear which all lead to the formation or transfer of material across the sliding interface 1 2 3 4 5 6 . At macro or micro scale it follows Archard’s law describing fracture and plastic deformation with wear volume being proportional to both the applied load and sliding distance 7 8 9 .…”

Electrostatically Tunable Adhesion in a High Speed Sliding Interface

“…Maintaining good tribological properties such as low wear and stiction of such a high speed sliding interface at low clearance is critical for the long term reliability of hard disk drives [7]. Any contact between the head and the disk leads to friction and wear of the head overcoat layer, adversely impacting the disk drive performance [8][9][10][11].A unique way of reducing the friction during contact is through externally imposed oscillations of small amplitude and energy. Previous experimental and theoretical work to reduce the friction at a sliding interface explored the use of external excitation with either surface acoustic waves or electrostatic forces to modulate the out-of-plane or in-plane motion [12][13][14][15].…”

“…Maintaining good tribological properties such as low wear and stiction of such a high speed sliding interface at low clearance is critical for the long term reliability of hard disk drives [7]. Any contact between the head and the disk leads to friction and wear of the head overcoat layer, adversely impacting the disk drive performance [8][9][10][11].…”