Work of Adhesion Measurements of MoS₂ Dry Lubricated 440C Stainless Steel Tribological Contacts

Abstract

The tribological behavior of dry lubricants depends on their mechanical and physicochemical environment, making it difficult to predict in practice. Discrete Element Method-based modeling has been one successful approach to provide valuable insight into the tribology of dry lubricated contacts. However, it requires well-defined interactions between discrete elements, in particular between those simulating different materials. Measuring the properties governing those interactions, such as the work of adhesion (W), is therefore critical. The present work describes a method for measuring the W between AISI440C steel and MoS 2 -based coatings used in spacecraft. Using Atomic Force Microscopy local asperity and adhesion measurements, the W between steel microbeads and MoS 2 coatings is determined at different stages in its wear life. The distributions of W values in the worn coatings and pristine coatings agree well with earlier Time-of-Flight Secondary Ion Mass Spectroscopy studies on the physicochemistry of the samples, as well as contact angle measurements. Additional measurements between the same materials on a ball bearing from a real life-test unit of a spacecraft instrument also show a similar W distribution, suggesting that the approach used here provides relevant data for use in numerical simulations.

Role of chemical vs. physical interfacial interaction and adsorbed water on the tribology of ultrathin 2D-material/steel interfaces

“…interfacial shear strength (ISS) measurements were performed by using the generalized Maugis-Dugdale model fitting procedure proposed by Carpick et al based on the FFM (friction vs. normal load) data in dry conditions [22]. The fitting considered a local asperity on the 440C-Steel tip in contact with the surface which had a radius measured as ∼1.3 µm by using a reverse imaging procedure reported in the literature [23]. The tip was reverse imaged using the same cantilever holder used for FFM and adhesion tests to ensure the cantilever had the same inclination angle.…”

“…The contacting asperity was identified and the contact radius of the asperity was measured by emulating the geometrical interpenetration of the bead onto the topography of the 2D material surface. This approach was adopted from a previously reported study [23]. Details of the ISS procedure are provided in the SI (Supporting Information; Section S2) [22].…”

The Holy Grail in Platinum‐Free Electrocatalytic Hydrogen Evolution: Molybdenum‐Based Catalysts and Recent Advances

“…MoS 2 exhibits many intriguing properties, and is usually employed as a dry lubricant, transistor, logic circuit, sensor, and catalyst, and therefore has attracted intensive attention over the past decade . As a typical transition‐metal dichalcogenides (TMD) material, bulk MoS 2 generally crystallizes with a hexagonally packed layered structure, similar to graphite, of which the individual sheets are stacked weakly with an interlayer ∼6.5 Å van der Waals spacing . Such a crystal structure endows MoS 2 with a ∼2200 times faster carrier mobility along basal plane than perpendicularly between sheets .…”

Analysis of the Quality of Sulfomolybdenum Coatings Obtained by Electrospark Alloying Methods

“…The 2.5-μm-thick lubricating layer contains 4000 layers of (S-Mo-S) (see Figure 1 ). The sulfur layers, which form the surface of a molybdenum disulfide crystal, provide strong adhesion to a metal surface [ 9 , 10 ].…”