A Review of Friction Performance of Lubricants with Nano Additives

Experimental Investigation of Engine Valve Train Friction Considering Effects of Operating Conditions and WPC Surface Treatment

Reduction in friction ensures fuel economy, control on emissions and durability of components in internal combustion engines. A modern gasoline internal combustion engine was instrumented to determine the friction values at the cam-roller interface considering the effects of surface treatment and engine operating state. A series of tests under different operating speeds and lubricant inlet temperatures were undertaken using both an original surface roller and a Wonder Process Craft (WPC) surface-treated engine roller. The results clearly revealed a substantial reduction in friction magnitude for the WPC surface-treated engine roller in comparison to the original roller while operating under similar conditions, indicating their strong potential for employment in engines. An increase in friction with the rise in temperature was also observed for both types of rollers, whereas increased lubricant entraining velocity due to higher operating speed had the opposite impact. A considerable reduction in frictional drive torque ranging from 8% to 28% was observed by employing the WPC-treated roller in comparison to original/untreated roller at various operating conditions, which signifies the strong potential for employment of WPC surface treatment in the roller/follower valve train engines.

Analysis of TiO2 Nanolubricant Influence in Micro Deep Drawing of Stainless Steel SUS301

To improve the quality of products produced from microforming, various nanolubricants have been applied in the field of micromanufacturing in recent years. In this paper, the effects of glycerol-based lubricant containing TiO₂ NPs (NPs) on micro deep drawing (MDD) of austenitic stainless steel (ASS) SUS301 were studied, and the lubrication mechanism involved was discussed. The MDD experiments were conducted with the SUS301 foils under dry, 1, 2, and 4 wt% TiO₂ NP lubrication conditions. The results show that the use of the TiO₂ nanolubricants can significantly improve the quality of the drawn cups in terms of decreased wrinkling and surface roughness. Besides, the concentration of TiO₂ NPs influences lubricity by reducing friction during the MDD process. The peak drawing force is the lowest when 2 wt% nanolubricant is applied, which drops to 72.54 N from 77.38 N under dry conditions. The micro cup drawn under 2 wt% TiO₂ nanolubricant has the best quality among those obtained under all the lubrication conditions. The lubrication mechanisms are derived from the mending effects of TiO₂ NPs and the formation of thin lubricant films associated with the open lubricant pockets (OLPs) and close lubricant pocket (CLPs) theory in the MDD. The CLPs function as reservoirs that retain lubricants to counteract the load pressure, whereas the OLPs lead to lubricant leakage due to the higher flow resistance. It was found that the lubricant film and NPs are insufficient at a low concentration (1 wt%), while the lubrication performance can be enhanced with increased NP concentration. However, there exist apparent agglomerations on the surface of the produced micro cup when using 4 wt% nanolubricant, which greatly deteriorates the lubricant performance in the MDD process. It is concluded that the lubricant containing 2 wt% TiO₂ NPs demonstrates the best lubrication performance during the MDD of ASS SUS301.

Organic-modified ZnS nanoparticles as a high-performance lubricant additive

Lubricants are essential in transportation vehicles and industrial machinery to improve the lifetime of moving components. Antiwear additives in lubricants significantly minimize wear and material removal due to friction. While a wide range of modified and unmodified nanoparticles (NPs) have been extensively studied as lubricant additives, fully oil-miscible and oil-transparent NPs are essential to improve performance and oil visibility. Here, we report dodecanethiol-modified oil-suspendable and optical-transparent ZnS nanoparticles (NPs) with a nominal diameter of 4 nm as antiwear additives to a non-polar base oil. The ZnS NPs formed a transparent and long-term stable suspension in a synthetic polyalphaolefin (PAO) lubricating oil. The ZnS NPs in PAO oil at 0.5 or 1.0 wt% concentration demonstrated excellent friction and wear protection. The synthesized ZnS NPs showed 98% wear reduction compared to the neat PAO4 base oil. For the first time, this report showed the outstanding tribological performance of the ZnS NPs benchmarked to the commercial antiwear additive zinc dialkyldithiophosphate (ZDDP) with an additional 40-70% wear reduction. Surface characterization revealed a ZnS-derived self-healing polycrystalline tribofilm (<250 nm), which is key to superior lubricating performance. Our results indicate the potential of ZnS NPs as a high-performance and competitive antiwear additive to ZDDP, which has broad transportation and industrial applications.

Tribological Properties of Cu-MoS2-WS2-Ag-CNT Sintered Composite Materials

In this work, in order to produce Cu-MoS₂-WS₂-Ag-CNT self-lubricating materials, powder metallurgy was used. Several different compositions containing single solid lubricant MoS₂, WS₂, Ag and CNTs as well as multi-component lubricants in the copper matrix were prepared. Friction and wear tests were carried out using the pin-on-disc method at room temperature. Light microscopy (LM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were used to characterize the wear mechanism of sintered materials. The tribofilm on the worn surfaces of sintered materials and counter-specimens was observed. The influence of single solid lubricants and the synergistic interaction of two, three or four solid lubricants on tribological properties of sintered composite materials were determined.

Development of Doped Carbon Quantum Dot-Based Nanomaterials for Lubricant Additive Applications

The development of advanced lubricants is essential for the pursuit of energy efficiency and sustainable development. In order to improve the properties of lubricating fluids, high-performance lubricating additives are required. In recent research studies, carbon nanomaterials such as fullerenes, carbon nanotubes, and graphene have been examined as lubricating additives to water or oil. Lubricating oils are well known for the presence of additives, especially friction-reducers and anti-wear additives. As part of this work, we have studied the advancement in the research and development of carbon dot (CD)-based lubricant additives by presenting a number of several applications of CD-based additives. We have also highlighted the friction-reducing properties and anti-wear properties of CDs and their lubrication mechanism along with some challenges and future perspectives of CDs as an additive. CDs are carbon nanomaterials that are synthesized from single-atom-thick sheets containing a large number of oxygen-containing functional groups; they have gained increasing attention as friction-reducing and antiwear additives. CDs have gradually been revealed to have exceptional tribological properties, particularly acting as additives to lubricating base oils. In our final section, we discuss the main challenges, future research directions, and a number of suggestions for a complete functionalized or hybrid doped CD-based material.

Tribological Behavior and Wear Mechanism of Ni-Nano TiO2 Composite Sintered Material at Room Temperature and 600 °C

In the present work, Ni-10 wt.%TiO2 self-lubricating composite sinters were prepared via a powder metallurgy. Commercially available powder of nickel and non-commercial nanometric titanium dioxide (approx. 30 nm size) produced by the microwave method was used. The produced sinters were characterized by evenly distributed TiO2 particles in a nickel matrix and a hardness of approx. 110 HV5. Pin-on-disc wear tests at room temperature and 600 °C were carried out. Light Microscopy (LM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-Ray Diffraction (XRD) were used to characterize the wear mechanism of sintered materials. The coefficient of friction of the Ni-10 wt.% TiO2—Inconel®625 friction pair tested at room temperature was approx. 0.52. At the test temperature of 600 °C, the same friction pair had a friction coefficient of 0.35. The main wear mechanisms in dry friction conditions at 23 °C were cutting and ploughing. At the test temperature of 600 °C, formation of tribofilm on the surfaces of the friction pair was observed, which reduces the wear by friction.

Increasing Wear Resistance of Heavy-Loaded Friction Pairs by Nanoparticles in Conventional Lubricants: A Proof of Concept

This paper provides experimental data on the effective use of a new lubricating composition, which includes industrial oil of any brand with the addition of a nanometal of the component of a friction pair, which has a lower hardness. It is shown that this composition significantly reduces the wear resistance of the rails and wheels of rolling stock during operation, prevents electrochemical corrosion of the friction pair wheel–rail and, most importantly, stabilizes the coefficient of friction at the optimum level after a relatively short operating time. The experiments were performed on the friction pair, “sample of the bandage material of the railway wheel—a sample of the rail material”, with a ratio of hardness of the bandage material (Rockwell hardness, HRC scale—35.3) to the hardness of the rail material of 1.1. Test results show that in the case of industrial lubricant, the BioRail brand, with the addition of a nanomaterial friction pair with lower wear hardness of the rail metal sample, after three hours in operation the wear was practically not observed. Moreover, the average value of the friction coefficient for three hours of operation was maintained at the level 0.25, which is optimal for the friction pair wheel–rail. Similar experiments using only the same lubricant brand showed much worse results.