Super low to high friction of turbostratic graphite under various atmospheric test conditions

Effect of Transfer Layer on Ultra Low Friction of CNx Coating under Blowing Dry Ar

“…The influence of relative humidity and O 2 on friction coefficient is considered very minimum in this experiment. High humidity and oxygen can cause high friction during friction test, as reported elsewhere [3,16,19]. As an inert gas, dry Ar gas flowed into the disorderly graphite structure without involving chemical interaction which attributed to the passivation of dangling covalent bonds [16].…”

“…As an inert gas, dry Ar gas flowed into the disorderly graphite structure without involving chemical interaction which attributed to the passivation of dangling covalent bonds [16]. This caused the atomic displacements from disorder into inter-lamellar layer of the lattice, which provided a highly slippery layer for super low friction, as reported elsewhere [19]. Since, no transfer layer was attached to the wear track of the CN x coating and the strongly adherent surface of the transfer layer on the sapphire hemisphere, it is suggested that a super low friction mechanism on the CN x coating against the sapphire hemisphere was provided by a low shear strength between the graphite-like transfer layer and the CN x coating.…”

“…The Raman spectra of the transfer layer and the wear debris, as shown in Fig. 10, proved that the transfer layer had graphite-like structures, which contributed to the super low friction during the friction test [18,19]. AES analysis showed that no Ar molecule was found on the test specimen after the sliding test.…”

Friction anisotropy in boronated graphite

“…Moreover, low friction in graphite is due to the passivation of dangling bonds by reactive gases [7][8][9][10][11][12][13]. In argon environment, super low value of friction coefficient in turbostratic graphite is attributed to self-organization and superficial mobility of crystallites at contact interface [9]. Even without chemical http://dx.doi.org/10.1016/j.apsusc.2014.…”

“…In ambient atmospheric conditions, friction coefficient is found to systematically decrease with increase in relative humidity. Increase in relative humidity provides passivation of interacting dangling bonds on the sliding surfaces resulting to decrease in friction coefficient [9]. Low friction coefficients with the values of ∼0.02 and ∼0.1 in graphite were measured when slided against Si 3 N 4 and SiC balls, respectively [14].…”