Characterization and Modeling of Nano Wear for Molybdenum-Based Lubrication Layer Systems

Tribological Performance Evaluation of Greases on a Four-Ball Tester with Graphene Oxide Nanoparticles

Conventional greases have an exceptional place in the field of lubrication. They are unique in the sense of their areas of application and are very difficult to replace with other lubricating substances for the same reason. The advancements in the field of nanoparticles and the results they provide as an additive in greases have great scientific interest as they improve the tribological properties of greases to a great extent. The current work's aim is to synthesize a nanogripe using graphene oxide (GO) nanoparticles to lithium grease (Li grease), which will increase the tribological properties of the plain Li grease. Steps were taken to investigate the impact of variation of load on the frictional and wear characteristics of nanogrease. Synthesis of nanogrease and tribological evaluation were performed with a magnetic stirrer with a hot plate and a four-ball tester. Results indicated that nanogrease exhibits better tribological properties. It is also found that the antiwear and frictional properties of grease are not proportional to the wt % of GO nanoparticles. It is also detected that with the increase in load, the tribological properties of nanogrease increase.

Friction and Wear in Nanoscratching of Single Crystals: Effect of Adhesion and Plasticity

Friction and wear are two main tribological behaviors that are quite different for contact surfaces of distinct properties. Conventional studies generally focus on a specific material (e.g., copper or iron) such that the tribological result is not applicable to the other contact systems. In this paper, using a group of virtual materials characterized by coarse-grained potentials, we studied the effect of interfacial adhesion and material plasticity on friction and wear by scratching a rigid tip over an atomic smooth surface. Due to the combined effects of adhesion and plasticity on the nanoscratch process, the following findings are revealed: (1) For shallow contact where interfacial adhesion dominates friction, both friction coefficient and wear rate increase as the adhesion increases to a critical value. For deep contact where plasticity prevails, the variation of friction coefficient and wear rate is limited as the adhesion varies. (2) For weak and strong interfacial adhesions, the friction coefficient exhibits different dependence on the scratch depth, whereas the wear rate becomes higher as the scratch depth increases. (3) As the material hardness increases, both the friction coefficient and wear rate decrease in shallow and deep contacts.

Functionality Investigations of Dry-Lubricated Molybdenum Trioxide Cylindrical Roller Thrust Bearings

In addition to using conventional lubricants, such as oil and grease, rolling bearings can also be used with a dry lubricant. For example, the use of dry lubricant systems is necessary when the application of oils or greases is not possible (e.g., at high temperatures or in aerospace applications). The requirements of a solid lubricant are to reduce friction and wear of mechanical contact partners. In this work, a molybdenum-based coating system was applied by means of physical vapor deposition (PVD). The coating system consists of a molybdenum (Mo) reservoir with molybdenum trioxide (MoO3) as the top layer. The MoO3, which is particularly important for the run-in and the lubricating effect, is intended to continuously regenerate from the reservoir via tribo-oxidation. To determine the friction and wear behavior, cylindrical roller thrust bearings were used. Experiments demonstrated that the lubrication system is effective and that the frictional behavior has been improved. On the one hand, the frictional torque of the rolling bearings has been considerably reduced and, on the other, significantly extended operating times have been determined compared to unlubricated reference experiments. Simultaneously, material analyses have been carried out by means of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The investigations showed that the MoO3 was transferred to uncoated bearing components. This improved the tribological behavior and reduced abrasive and adhesive wear.