Ultralow-friction and wear properties of IF-WS2 under boundary lubrication

Abstract

Tested in boundary lubrication, inorganic fullerene-like WS 2 nanoparticles used as additives in oil present interesting friction reducing and anti-wear properties. A dispersion with only 1 wt% of particles leads, from a contact pressure of 0.83 GPa, to a drastic decrease of the friction coefficient below 0.04 and to very low wear. High resolution transmission electron microscopy (HRTEM), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Raman Spectroscopy and video imaging were used to explain the lubrication mechanisms. A structural modification of fullerene-like nanoparticles into sheets during the friction test was evidenced to be the main effect at the origin of these properties.

Formation of Anti-Wear Tribofilms via α-ZrP Nanoplatelet as Lubricant Additives

“…The weak van der Waals force between the discs is responsible for promoting shear resulting in low frictional force. Similar results have been observed by other sheet-like particles, such as MoS 2 [21], H-BN [22], and WS 2 [23]. The present research further proves the effectiveness of nanosheets with weak interfacial bonding.…”

Friction Modifier Additives

“…The IFs of main interest in tribology to date have been molybdenum and tungsten disulphides (IF-MoS 2 , IF-WS 2 ). Both of these have been shown to have friction-reducing and antiwear properties [230,231]. In situ high resolution SEM has identified three different mechanisms by which they reduce friction, as summarised in Fig.…”

“…In situ high resolution SEM has identified three different mechanisms by which they reduce friction, as summarised in Fig. 18 [231]. At low pressures, particle rolling can occur depending on the particles' shape and hardness.…”

Nanolubrication

“…The strategy is based on the direct feeding of the sliding interface with nano-particles of tribo-active phases (graphite, MoS 2 , fluorinated carbon species [28][29][30]) or precursors of tribo-active phases (precursor of lamellar phases such as, carbon nano-onions or nanotubes, metal dichalcogenide fullerenes, [31][32][33][34][35]) dispersed in lubricant base oils or greases to produce the tribo-film without reaction with the substrate surfaces. The main advantages of nano-particles are their sizes, in the nano-meter range, which is well adapted for a perfect feeding of the sliding interface and the possibilities of composite particle syntheses which can combine multiple properties such as friction reduction, anti -wear anticorrosion An other route, using nano-particles of two different reagents needing contact physical conditions to react has been successfully tested but with material presenting weak interest for tribologic applications [36].…”