Extraordinary macroscale lubricity of sonication-assisted fabrication of MoS2 nano-ball and investigation of in situ formation mechanism of graphene induced by tribochemical reactions

We first fabricate MoS 2 nano-ball in isopropanol using sonication-assisted method. We systematically probe the lubrication mechanism of MoS 2 nano-ball in isopropanol. Hydroxylated MoS 2 nano-ball could effectively reduce the contact area for GCr15 steel balls and possess superior load-capacity and make the tribosystem achieve ultra-low friction and wear under 98 or 196 N and 600 rpm. For comparison, the lubricity of tribosystem sliding in isopropanol is conducted. Interestingly, graphene layers are formed sliding under 196 N and 600 rpm, the graphene-based transfer film on GCr15 steel ball makes the lubrication condition fast transfer from mixed lubrication condition to full film lubrication condition, which results in high friction and wear. The formation mechanism of graphene is discussed and proposed in details.