Tribological performances of copper perrhenate/graphene nanocomposite as lubricating additive under various temperatures

Abstract

• The copper perrhenate was synthesized via microemulsion reaction method, and then was coated on the surface of graphene using an ultrasonic method. • The copper perrhenate/graphene as oil additive exhibited excellent lubricating performance. • The protective layer consisted of copper perrhenate, remnant carbide and native oxide was formed at elevated temperatures. Herein, copper perrhenate (Cu(ReO 4 ) 2 ) was synthesized using a micro-emulsion method and adhered to graphene (Gr) using an ultrasonic process. Then, the as-prepared Cu(ReO 4 ) 2 /Gr composite was added into the synthetic oil as a lubricant additive with the help of ionic liquid to achieve enhanced dispersion stability within the base oil. The tribological performances of the Cu(ReO 4 ) 2 /Gr additive were investigated using four-ball tests and the ball-on-disk reciprocating configuration under various temperatures. The potential lubrication mechanisms of the Cu(ReO 4 ) 2 /Gr additive were performed using a series of characterization methods including XRD, Raman, SEM-EDS, TEM, DSC/TG, and XPS. The results of four-ball tests at room temperature indicated that the Cu(ReO 4 ) 2 /Gr additive could substantially improve the tribological performances of the base oil. The smallest coefficient of friction (COF) and wear scar diameter (WSD) values were 0.068 and 495 μm, respectively, when 0.05 wt% of Cu(ReO 4 ) 2 /Gr was added. Additionally, the graphene accelerated friction-induced heat transfer, which led to decreased friction and wear. The results of reciprocating friction experiments at elevated temperatures revealed that the Cu(ReO 4 ) 2 /Gr additive had excellent friction-reduction properties when the temperature was high. This could be attributed to the generation of a protective layer containing tribo-oxides from the alloy, some residual carbides and copper perrhenate induced by friction heat and stress. This protective layer was uniformly and stably covered on the worn surface, which could effectively alleviate direct contact between the rubbing pair.