Friction-reduction and anti-wear properties of polyalphaolefin oil with Mo-DTC additive enhanced by nano-carbon materials

Polyalphaolefin (PAO) oil is one of the most commonly-used based oil to decrease the fuel energy consumption of mechanical systems, like vehicles. Nevertheless, it heavily relies on environmental toxic organic additives with sulfur, phosphorus, and/or chlorine. Accordingly, nano-carbon materials, such as nano-diamond (ND), onion-like-carbon (OLC) and graphene (Gr.), was adopted to develop a novel kind of environmentally-friendly PAO-based lubricants with low toxic additives. Synergetic effects between nano-carbon materials and MoDTC additives were investigated to enhance friction-reduction and anti-wear performances of PAO oil with molybdenum di-thiocarbamate (MoDTC) additive. Experimental results show that ND and OLC additives are effective in the enhancement of friction-reduction and anti-wear performances of self-mated AISI 52100 steels lubricated under poly-alpha-olefin (PAO) oil with Mo-DTC additive, due to the formation of tribo-film consist of MoSx, polishing, ball-bearing and reinforcement effects of nano-particles. Via the addition of ND or OLC additive with a content of 0.05 wt.%, the optimized dosage of MoDTC additive can be significantly decreased from 1 to 0.1 wt.%. Friction coefficient of self-mated AISI 52100 steels lubricated under PAO oil with 0.1 wt.% Mo-DTC and 0.05 wt.% ND additive is about 0.05, approximately equal to that lubricated under PAO oil with 1 wt.% Mo-DTC additives. Moreover, ND additive resulted in a lower friction coefficient, better wear resistance (about 2.3 × 10− 16 m3/N m) and shorter duration of run-in period than OLC additive in PAO oil with MoDTC additive. Graphene is not helpful to enhance the friction-reduction and anti-wear performance of PAO oil with or without MoDTC, due to the absence of polishing, ball-bearing and reinforcement of nano-particles effects. Although, individual addition of OLC additive in PAO oil also caused friction-reduction effectiveness, serious wear damage occurred attributed to the abrasive of nano-particles.