As a result of global economic and environmental change, the demand for innovative, environmentally-friendly technologies is increasing. Employing solid lubricants in rolling contacts can reduce the use of environmentally harmful greases and oils. The aim of the current research was the development of a solid lubricant system with regenerative properties. The layer system consisted of a molybdenum (Mo) reservoir and a top layer of molybdenum trioxide (MoO₃). After surface wear, Mo is supposed to react with atmospheric oxygen and form a new oxide. The determination of the wear volume of thin layers cannot be measured microscopically, which is why the wear behavior is initially determined on the nano level. In this work, single Mo and MoO₃ coatings prepared by physical vapor deposition (PVD) are characterized by nano testing. The main objective was to determine the wear volume of the single coatings using a newly developed method considering the initial topology. For this purpose, nano-wear tests with different wear paths and normal forces were carried out and measured by in situ scanning probe microscopy (SPM). Based on the characteristic values determined, the coefficient of wear was determined for wear modeling according to Sarkar. The validation of the wear model developed was carried out by further wear tests on the respective mono layers.

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.

The increasing global demand for innovative and environmentally friendly lubricants can be met through the use of solid lubricants. By switching from conventional lubricants such as various oils or grease to solid lubricants, new scopes of application can also be opened up. The main requirements for solid lubricants are a reduction in the coefficient of friction (CoF) and an increase in wear resistance. Due to the favourable material properties, molybdenum (Mo) coatings fulfil the tribological requirements and are therefore promising solid lubricants which can be applied via physical vapour deposition (PVD). In this work, the impact of substrate temperature on the hot hardness of deposited Mo coatings was determined. The specimen with the highest hot hardness was then tribologically examined both at the micro and nano level. Through an analysis of the wear tracks by means of nanoindentation and scanning electron microscopy (SEM), it was possible to detect the influence of the tribological load separately from that of the thermal loads. The results showed that the tribological load influenced the Mo coating by significantly increasing its hardness. This was achieved due to the work hardening of the Mo layer leading to an increase in the wear resistance of the coating.

Bearings play a crucial role in a broad range of engineering applications, such as automotive, aerospace and renewable energies. Particularly when it comes to larger and/or hard to replace/repair bearings, such as those in wind turbines, condition monitoring and load control are essential due to their complex and expensive conditions for maintenance and repair. Conventionally, different sensors are used, which are typically positioned outside of the bearing. Thus, a rather low depth of information is achieved, and the bearing condition cannot be assessed optimally. Therefore, this article focuses on the production and evaluation of directly deposited thin-film strain sensor arrays on a rolling bearing within and close to the tribomechanical contact between roller and raceway. The sensor production was carried out using sputtering, photolithography and etching processes. After the static strain gauge characterization concerning temperature, strain and pressure sensitivity on different substrates, a sensor-integrated 81212 thrust roller bearing was investigated in an FE8 bearing test rig. After data processing, the dynamic measurements with a maximum Hertzian pressure of 1 GPa revealed negative sensor resistance changes of up to −1.4 ‰ in the tribomechanical contact and up to 3.8 ‰ positive resistance change right next to the contact zone. Due to the fact that these sensors were subject to wear, sensors were also positioned at a greater distance from the contact that still showed a measurable signal of 0.5 ‰ resistance change that can be used after critical loads when their signal has been correlated to the other sensors in the contact zone when the latter are worn. Furthermore, the time-resolution enables the precise measurement of the rotational speed, and deviations in the roller geometries can be detected as well due to different sensor amplitudes. The location-resolved measurements allow important information about the tribomechanical contact to be derived in real-time, thus enabling intelligent component control, for example concerning rotational speed, lubrication and load before a damage occurs.