Investigation of the Scaling of Friction Coefficients from the Nano to the Micro Level for Base Materials and Coatings

Heimes, Norman; Pape, Florian; Konopka, Dennis; Schöler, Simon; Möhwald, Kai; Poll, Gerhard; Behrens, Bernd‐Arno

doi:10.1007/978-3-662-62138-7_17

Cited by 3 publications

(4 citation statements)

References 8 publications

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“…The Hertzian pressure could provide an explanation for the same increase in hardness despite the significantly lower normal force at the nano level. In the nano wear test, very high Hertzian pressures in the range of 12 GPa were achieved, while the Hertzian pressure in the micro-level sliding test was about 0.3 GPa [24]. Due to this very high point load, a hardness increase was also achieved at the nano level.…”

Section: Wear Track Analysismentioning

confidence: 90%

Investigation of the Hardness Development of Molybdenum Coatings under Thermal and Tribological Loading

et al. 2023

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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.

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Section: Wear Track Analysismentioning

confidence: 90%

Investigation of the Hardness Development of Molybdenum Coatings under Thermal and Tribological Loading

et al. 2023

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“…In terms of a reproducible and successful deposition of the coating on the steel substrate surface, the experience gained from previous investigations was taken into account [ 2 , 34 , 35 ]. Hardened rolling bearing steel AISI 52100 was used as the substrate for the coatings as cylindrical plates with a diameter of 14 mm and a height of 5 mm.…”

Section: Methodsmentioning

confidence: 99%

“…To determine the coating hardness, the test forces were varied to determine at which force the minimum penetration depth of 50 nm was exceeded. The steel substrate hardness is known from previous investigations [ 34 ], so that the layer hardness can be determined by exceeding the minimum penetration depth and it can be decided which of the two rules must be used. By analyzing the resulting penetration depth, the process parameters for the hardness measurement were determined.…”

Section: Methodsmentioning

confidence: 99%

“…The contact temperature on the nano level is the same as the ambient temperature as the speeds and contact areas are small. Due to the small contact areas, very high contact pressures of several GPa occur on the nano level, even with the smallest loads [ 34 ]. It must be investigated whether the boundary conditions on the nano level are sufficient to form an oxide layer in the wear surface or whether wear particles are enriched with oxygen and act as a transfer lubricant.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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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.

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

et al. 2022

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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.

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Investigation of the Scaling of Friction Coefficients from the Nano to the Micro Level for Base Materials and Coatings

Cited by 3 publications

References 8 publications

Investigation of the Hardness Development of Molybdenum Coatings under Thermal and Tribological Loading

Investigation of the Hardness Development of Molybdenum Coatings under Thermal and Tribological Loading

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

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

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