Carbon nanomaterials (carbon nanotube, graphene, graphite, nanodiamond and fullerene) as lubricants have attracted a great interest in the field of not only their practical application but also theory. They are primarily used as boundary lubrication additives due to their fitness to a narrow gap between sliding surfaces under boundary lubrication condition. It is expected that more environmentally friendly lubricants can be possible by adopting the carbon nanomaterials instead of molybdenum, zinc, sulfur, phosphorus in additives. Fullerene, referring C60, mixture of C60/C70 or their derivatives, shows excellent performance as a lubricant additive applying for variety type of mechanical oils. Contrast to the other carbon materials, fullerene is remarkably unique behavior because it dissolves in oil. It suggests the lubricity of fullerene in oil has distinctive mechanisms in molecular level. Possible lubrication mechanism of fullerene is discussed based on experimental studies.

Tribological properties of fullerene dissolved oil were referred in the present study. Significant decrease of the friction coefficient and the wear car damage was found on the aluminum alloys and the aluminum alloy/steel pair lubricated with the fullerene dissolving mineral oi. An enhancement of the oil film duration resulting in dissolving fullerene was demonstrated with a corrosion experiment of the alloy steel. The decrease of the friction coefficient using dissolving fullerene oil was also confirmed with engine oils containing additives including the friction modifier. Therefore, it is concluded that the fullerene dissolving into the oil is effective means to decrease the friction coefficient and wear scar damage.

The boundary lubrication properties of the fullerene-added lubrication oils were measured on various substrate materials using a pin-on-disk friction tester, and the coefficient of friction change (Δμ) and wear scar width change (ΔW) with and without fullerene addition were evaluated. The results showed that the effects of fullerene addition differed depending on the material, even under the same sliding conditions. Specifically, the coefficients of friction and wear decreased for aluminum, duralumin (A2017P and A5052P), zinc, molybdenum, and bearing steel (SUJ2) (Group 1). For copper and bronze, the coefficients of friction and wear increased (Group 2). The coefficient of friction decreased, but wear increased for iron and stainless steel (SUS304) (Group 3). For magnesium, titanium, duralumin (A7075P), and nickel, no changes were observed with the addition of fullerene. To qualitatively verify the factors that cause the different effects of fullerene addition, as described above, the correlations between surface roughness, Youngʼs modulus, Mohs hardness, tensile strength, adhesion force, and Δμand ΔW were evaluated for all substrates. The results showed a high correlation with the adhesion force in Group 1. This suggests that fullerene is effective in reducing adhesion friction by intercalating between the metals. In particular, the higher the aluminum content, the more effective is the fullerene addition. However, no common characteristics were found for materials in which no effect was observed.

Regarding the effects of adding fullerenes to lubricating oils, we will explain recent basic spectroscopic research from two perspectives: liquid physical properties that lead to lubrication ability through the formation of fullerene aggregates, and the ability to trap radicals generated by degradation of lubricating oils. Regarding liquid properties, we will explain an aggregation model based on the results of measurements of the size of aggregates using visible-ultraviolet spectroscopy and dynamic light scattering methods, for two cases, in which fullerenes aggregate and in which they aggregate loosely. Regarding the radical trapping ability of fullerene, we will introduce the results of advanced ESR spectroscopic measurements using synchronized laser and pulsed ESR. We will discuss the effects of adding fullerene to lubricating oil based on the spectral identification of short-lived addition reaction products, the elucidation of the addition reaction mechanism, and the measured reaction rate constants for the addition of organic radicals to fullerenes.

ZnDTP is used in lubricating oils as an antioxidant to inhibit oxidation. However, the use of ZnDTP has been discouraged because it contains phosphorus, which has a high environmental burden, and a new multifunctional additive is required. Thus, fullerenes are attracting attention as a new multifunctional additive to replace ZnDTP. In this paper, we describe the radical scavenging effect of fullerenes and the structural changes of fullerenes associated with it. Also, we introduce a new degradation diagnostic method for fullerene-added oils. From our study, it was found that the lubricating oils with fullerenes exhibit a radical scavenging effect depending on the amounts of fullerenes. And the UV absorption spectrum decreased, and the color of the membrane patch changed by scavenging radicals. These consequences indicate that the double bond of the fullerenes is cleaved during the radical scavenging and the resulting fullerene reactants are trapped in the membrane filter. Thus, it is suggested the consumption of fullerenes can be easily detected by observing the change in hue.

The current status of the timing chain system of internal combustion engines for a conventional passenger car and an applicability of fullerene dissolved engine oil to improve the timing chain performance refers. Since the expansion of the hybrid power train systems results in the decrease of the engine temperature, and lack of the lubricant supplement to the timing chain system, novel additives accompanying without the chemical reaction are anticipated. Fullerene is one of the candidate additives to improve the tribological properties. A model experiment possible to perform service conditions of the timing chain system showed that the friction coefficient lubricated with the fullerene dissolved engine oil decreased. In addition, the decrease in the friction coefficient lubricated with fullerene dissolved engine oil containing friction modifiers was found.

Thermohydrodynamic lubrication (THL) models have been applied to predict the performances of journal bearings that support industrial rotating machineries. The final goal of this study is to propose a THL bearing design method of cylindrical journal bearings with two axial oil grooves by using the model expressions, which are derived from a database constructed by the THL performances and can predict the reasonably accurate bearing performances over a wide range of operating conditions and bearing specifications. In this article, an ALE (Arbitrary Lagrangian-Eulerian method)-based simplified THL model, which predicts the bearing performances from only four dimensionless numbers ―Sommerfeld number, bearing width-to-diameter ratio, Peclet number and Khonsari number ―, is employed for constructing a THL database of the bearing. In some cases, numerical oscillations concerning oil film viscosity make it impossible to obtain the numerally converged solution. However, the solution can be obtained by transforming the energy equation of the oil film so as to solve for the oil film viscosity, which results in the database for a wide range of the bearing design variables. The properties of the database are investigated and it is found necessary to derive the model expressions for the THL performances of the bearing.

Polyetheretherketone (PEEK) is a lightweight, high-performance thermoplastic widely used in aerospace and automotive industries for structural components. However, compared to metals, PEEK faces challenges in wear resistance, limiting its application in sliding components. This study seeks to improve the adhesion between PEEK and DLC by employing methane plasma ion irradiation to create functional groups, resulting in a tightly bonded transitional layer. This process involves surface cleaning, the formation of specific functional groups for a seamless transition layer, and the coating of the DLC layer, all achieved through a single-step carbon-based plasma interaction. To evaluate the impact of methane plasma, we varied ion energy and irradiation time, followed by DLC coating under identical conditions for Argon and Methane plasma treatments. Surface chemistry analysis using FT-IR and XPS techniques revealed a significant enhancement in adhesion with methane plasma ion irradiation, increasing the critical load by over twofold. This study conclusively establishes the effectiveness of methane plasma ion irradiation in enhancing adhesion between PEEK and DLC, thereby broadening the material's potential for use in sliding components.