Nano- and Micro-Tribological Investigations of Boundary Layers on Axial Bearing Washers Tested under WEC Critical Conditions

Abstract

The formation of boundary layers on bearing surfaces due to the operational conditions has a significant influence on bearing lifetimes and frictional properties. Zinc dialkyldithiophosphate is an anti-wear additive widely used in oil and grease formulations that forms beneficial surface boundary layers. Under certain circumstances, this additive can cause early bearing failure due to white etching cracks (WEC) formation. By influencing chemical reactions and diffusion processes, the boundary films are suspected to be a reason for the emergence of WECs. The properties of these layers under WEC critical and uncritical conditions are of interest. To gain knowledge of these layers, nano- and micro-tribological tests were performed. One possibility is to measure the hardness by nanoindentation and scratching on and into the layers by nano scratch tests. Another way is to perform local resolved micro-pin-on-disk tests. Additionally, ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) was performed on the bearing surfaces to conclude the chemical compositions of the boundary layers. In the focus was, if the measured properties of the layers can be correlated to the bearing’s early failures due to WEC, frictional properties of the whole system, and the wear on the surfaces.

Investigation on Graphene Platelet Based Dry Lubricating Film Formation in Tribological Contacts

“…This highlights the poorer lubricating property of fullerene dry lubricant under these conditions. In conclusion, when the normal load is 2 N, sliding speed is 1 mm/s, and the track length is 2 mm, the lubricating properties of 3-4 nm graphite and graphene platelets are nearly comparable to typical lubricated contacts, with a COF between 0.1 to 0.15 under similar test conditions [26,27].…”

Investigation of Graphene Platelet-Based Dry Lubricating Film Formation in Tribological Contacts

“…In this case, stiction through physical surface effects, such as adhesion and bonding, results in a friction coefficient higher than 1. In conclusion, when the normal load is 2 N, the sliding speed is 1 mm/s, and the track length is 2 mm, the lubricating properties of 3-4 nm nano-graphite and graphene platelets are nearly comparable to typical lubricated contacts, with a COF between 0.1 and 0.15 under similar test conditions [28].…”

“…In this case, stiction through physical surface effects, such as adhesion and bonding, results in a friction coefficient higher than 1. In conclusion, when the normal load is 2 N, the sliding speed is 1 mm/s, and the track length is 2 mm, the lubricating properties of 3-4 nm nano-graphite and graphene platelets are nearly comparable to typical lubricated contacts, with a COF between 0.1 and 0.15 under similar test conditions [28]. Through the comparison above, it can be determined whether or not pre-rolling has the greatest effect on the friction coefficient of the samples using 6-8 nm graphene platelets and 3-4 nm graphite dry lubricant.…”

Rolling Contact Fatigue and White Etching Cracks of Bearings

“…Nano-and Micro-Tribological Investigations of Boundary Layers on Axial Bearing Washers Tested under WEC Critical Conditions: The author presents a detailed study on the formation of boundary layers of Zinc-dialkyldithiophosphate under WEC critical conditions using high lateral surface spectrometry and nano-hardness measurements [12]. 6.…”