Graphene-Reinforced Lithium Grease for Antifriction and Antiwear

Abstract

Graphene has attracted tremendous attention as a promising additive in lubricants due to its unique lamellar structure and excellent mechanical strength. Yet, unlike its use in oil and water lubricants, the amount of graphene additive should be considered when it is introduced into the grease which is a two-phase colloid. In this work, graphene was added into the lithium grease in different concentrations, and lubrication behaviors were investigated using a four-ball testing method under various operating conditions. Prior to the four-ball friction tests, graphene and grease materials were characterized by scanning (SEM) and transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and Raman spectroscopy. Friction test results demonstrate that the graphene concentration in grease varies at different tribological contact conditions to reach the optimum lubrication behavior. On the basis of the results from friction tests and worn scar morphology analysis, a lubrication mechanism was proposed to better understand the interactions among grease elements, e.g. graphene, thickener, and base oil, during the shearing process. It is believed that thickener soap actively participates in the lubrication process at low speeds by releasing enough oil into the friction contacts under high load. Meanwhile, less graphene concentration is required to strengthen the base grease by inhibiting and avoiding severe wear. High rotational speeds negatively affect the “oil-bleed” capability of thickener under lower contact loads due to the churning loss at high centrifugal force. Thus, extra graphene additives are required to retain more oil and separate the contact surfaces. This, in turn, promotes the formation of protective tribofilm on the interface which is the key to the enhancement of antifriction and antiwear performance.

Fundamental Evaluation of Sealability of Greased Metal-to-Metal Seal on Premium Threaded Joints at High Pressure and High Temperature

“…In addition, it was shown that solid additives in the grease can enhance the capability of oil retention by interacting with Fig. 10 Results of TG-DTA of the grease thickener [25]. As the grease applied in this study contained the large amount of solid additives, the sealability by this grease could be also enhanced because of the increase in the capability of the base oil retention.…”

Synergistic lubrication effects and tribological properties of graphene/oil-based lubricant systems

“…In summary, the μ value of the lubrication system with G is smaller at higher velocities. This may be due to the high-velocity shearing being more conducive to the spontaneous deposition of G on the friction interface [25]. Hence, a physical transfer film is formed to prevent direct contact between the GCr15 steel block and the ball.…”

Silver/Graphene Nanocomposite as an Additive for Aqueous Lubrication

“…In addition, the enhanced wettability of nanofluids contributed to improving tribological properties. Wu et al and Lin et al reported that graphene , and graphene oxide (GO) as nanoadditives contributed toward enhancing friction reduction and wear resistance for Si 3 N 4 /steel sliding pairs. The interfacial tribological properties between SiC and Si 3 N 4 ceramics lubricated by a graphene aqueous solution were investigated by Yuan et al, and it was found that the self-developed graphene exhibited an ultralow FC of 0.009 and an ultralow wear rate of 1.69 × 10 –7 mm 3 /N·m.…”

“…In addition, the enhanced wettability of nanofluids contributed to improving tribological properties. Wu et al and Lin et al reported that graphene 30,31 and graphene oxide (GO) 32 by Yuan et al, 33 and it was found that the self-developed graphene exhibited an ultralow FC of 0.009 and an ultralow wear rate of 1.69 × 10 −7 mm 3 /N•m. However, the weak dispersity of graphene in an aqueous solution creates a crucial challenge for its further application.…”