Exploring the potential of coal derived graphite as next generation lubricant additive for multifunctional applications

In the present study, the friction and wear characteristics of steel/steel contact under reciprocating sliding conditions were investigated using composite mixtures made from Polyalphaolefin 4 (PAO4) as base oil lubricant and North Dakota lignite-derived graphite (LG) as high-value carbon additive. The results show that addition of 1 wt% LG to PAO4 led to a reduction in the friction coefficient and wear volume by ∼15 % and ∼13 %, respectively. In addition, the oxidation induction time (OIT) at 160 °C was increased by ∼29 %, which further indicates good stability of the formulated composite lubricant against oxidative degradation. The primary wear mechanism on AISI 52100 steel flat and counter-body was found to be abrasive wear under high-contact stress reciprocating sliding conditions, where tribo-oxide films of 100–200 nm were observed on the wear tracks of 52100 steel surfaces using focused ion beam scanning transmission electron microscopy (FIB-STEM). Furthermore, cross-sectional analysis of the wear track of AISI 52100 steel revealed that 1 wt% of LG additive reduced the thickness of the sub-surface deformation zone by 44 %, which indicates higher load-bearing capacity and improved wear resistance.