Friction Properties of the DLC Film with Periodic Structures in Nano-scale

Abstract

Reduction of friction at very low normal loads and for very small contact areas is important for the development of micro devices. High performance hard coatings such as diamond-like carbon (DLC) films and improved surfaces with nanostructures are being investigated with respect to their friction reduction properties. Previously, difficulties associated with the production of nano-scale periodic structures in DLC films have prohibited the study of such films. In the present study, the friction properties of the DLC film with periodic structures were investigated at the nano-scale using an atomic force microscope (AFM). These periodic structures were generated on the surface of the DLC film by means of a femtosecond (fs) laser having the fluence near the ablation threshold. Friction tests were carried out under normal loads ranging from 20 nN to 130 nN, and the frictional directions were 0°, 45° and 90° (relative to the line along which the periodic structures were created). The lateral force of the DLC film with the periodic structures was lower than that of the film without the periodic structures. We have concluded that decreases in adhesive forces produce significant decreases in lateral forces for the same normal loads.

Possibilities of Dry and Lubricated Friction Modification Enabled by Different Ultrashort Laser-Based Surface Structuring Methods

“…A recent study reveals that about 23% of the world's energy consumption and 8120 Mt/year of CO 2 emission are caused by these tribological effects, in turn posing the necessity for wear and friction control [1]. While laser-based surface functionalization has already been intensively studied during the last decade, femtosecond laser technology has recently expedited surface structuring on different length scales to advance tribological properties [2][3][4][5][6][7]. In terms of laser surface texturing, different methods are available to modify the friction behaviour.…”

The spatial emergence of laser-induced periodic surface structures under lateral displacement irradiation conditions

“…In [152] a reduction of friction force for nN loads has been observed and in [153] tested under F N of 2 N and 10 N as well. Reasons for different results could be due to different measurement conditions, under which the load dependence was not explicitly determined, and different laser systems for structure generation.…”

“…Scope of research 9 that a certain pulse overlap between successive pulses is required, to extend structures in one direction. Recently, this topic gained interest, because potential prospects are seen in the field of surface functionalisation, such as tribology [152,153], optics [154,155], wettability [156,157] and biomechanics [158]. In the frame of this research, also other type of LIPSS, as HSFL, have been applied and different irradiation conditions have been studied.…”

“…Empirically, the laser power is selected such that a peak fluence around the ablation threshold and the displacement velocity such that a pulse overlap for a homogeneous structure is obtained [152,153,155,159]. For irradiation conditions where the displacement applied was too small, an "over-hatch" effect has been observed [159], resulting in the disappearance of LIPSS.…”

“…The influence of femtosecond initiated LIPSS was investigated by Mizuno et al [152] and the reduction of lateral force as well as decrease of adhesive force was found. Another study reports a decrease of friction for full and increase for partially structured areas [153].…”