IN view of the interest attaching to the vaporisation and diffusion of solids, the following observations may be worthy of record.

The Diffusion of Solids

Research into layered transition metal dichalcogenides (TMDCs), most notably those of molybdenum and tungsten disulfides, has become extensive, involving fields as diverse as optoelectronics, spintronics, energy storage, lubrication, and catalysis. The modification of TMDCs by transition metal doping can improve their performance in such applications and hence extend their potential for technological applications. This review concerns the synthetic strategies that have been used to incorporate transition metals into TMDCs and the applications of the resultant materials and relevant computational studies on the predicted properties of the doped materials.

http://pubsdc3.acs.org/doi/pdfplus/10.1021/acs.chemmater.6b00430

Synthesis, Properties, and Applications of Transition Metal-Doped Layered Transition Metal Dichalcogenides

The need for energy efficiency is leading to the growing use of additives that reduce friction in thin film boundary and mixed lubrication conditions. Several classes of such friction modifier additive exist, the main ones being organic friction modifiers, functionalised polymers, soluble organo-molybdenum additives and dispersed nanoparticles. All work in different ways. This paper reviews these four main types of lubricant friction modifier additive and outlines their history, research and the mechanisms by which they are currently believed to function. Aspects of their behaviour that are still not yet fully understood are highlighted.

/pdf/friction-modifier-additives-4p9xlprlx3.pdf

Friction Modifier Additives

This is the final version of the article. It first appeared from the Iron and Steel Institute of Japan via http://dx.doi.org/10.2355/isijinternational.ISIJINT-2015-430

Prevention of Hydrogen Embrittlement in Steels

Molybdenum disulfide (MoS2) is one of the most broadly utilized solid lubricants with a wide range of applications, including but not limited to those in the aerospace/space industry. Here we present a focused review of solid lubrication with MoS2 by highlighting its structure, synthesis, applications and the fundamental mechanisms underlying its lubricative properties, together with a discussion of their environmental and temperature dependence. The review also includes an extensive overview of the structure and tribological properties of doped MoS2, followed by a discussion of potential future research directions.

/pdf/solid-lubrication-with-mos2-a-review-17l0ksyp7y.pdf

Solid Lubrication with MoS2: A Review

Microstructural alterations in bearing steels during rolling contact cycling have been reported in the literature for more than half a century. These structural changes are primarily caused by the decay of parent martensite and have been designated as white and dark etching regions due to their preferential etching characteristics. One of the most striking features of the white etching bands is their repeatable directionality, which has puzzled investigators for decades. Despite numerous attempts, a satisfactory explanation for the orientation of these bands is still not available. In this article (Part 1), an overview of the phenomenon is presented with detailed discussion of various experimental observations from the literature. The article also examines the previous approaches adopted to explain white etching bands and address their limitations. In Part II of the article, a J2-based elastic–plastic finite element model coupled with a carbon diffusion model is developed that directionally predicts the o...

Microstructural Alterations in Bearing Steels under Rolling Contact Fatigue Part 1—Historical Overview

In this work, the tribological behavior of Ti-containing MoS2 film is studied under sliding and rolling contacts. Ti-MoS2 films deposited on AISI 52100 and M50 specimens contain ∼16 at% Ti are slightly substoichiometric in sulfur and have an amorphous structure. Experiments show that the friction and wear performance of Ti-MoS2 films is influenced by humidity and temperature.For the first time, the rolling contact performance of Ti-MoS2 films was evaluated using a thrust bearing tribometer and ball-on-rod tribometers at ∼1 GPa Hertzian contact stress. Rolling contact measurements performed in humid air indicate that the useful life of Ti-MoS2 as a solid lubricant depends upon the amount of coating material retained in the contacts. Results of the rolling contact experiments performed in a vacuum indicate that Ti-MoS2 film on balls may function extremely well as a solid lubricant for ball bearings operating in vacuum.

Tribological Performance and Coating Characteristics of Sputter-Deposited Ti-Doped MoS2 in Rolling and Sliding Contact

Smearing damage was created on cylindrical roller bearings (CRBs) using a laboratory test protocol that required alternating the load zone direction according to a square wave function. The experimental goal was to compare the wear protection afforded by various surface treatments, including vibratory superfinishing (ES20), black oxide treatment, and special tungsten carbide–reinforced amorphous hydrocarbon roller body coatings (WC/a-C:H). The only bearing treatments that did not smear in these severe tests were the WC/a-C:H bearings. Black oxide and ES20 bearings experienced smearing with the same frequency as untreated bearings, albeit to different degrees of microscopic damage. The test rig was instrumented to measure cage slip, which provided insight about the roller–raceway slip dynamics during the tests via kinematic calculations. The CAGEDYN bearing dynamics model was used to simulate the experimental smearing test conditions, and it provided encouragement that accurate prediction of smearing risk ...

Prevention of Smearing Damage in Cylindrical Roller Bearings

Tribological thin-film coatings can enhance the performance of mechanical components such as bearings and gears. Although a lubricant is present in most applications, the interactions of the lubricant with the coated surfaces are not always well understood. In the present study, Stribeck curves (i.e., traction coefficient vs. dimensionless film thickness λ) were generated for lubricated rolling contact between coated and uncoated surfaces. Chromium nitride, tungsten carbide–reinforced amorphous hydrocarbon, and silicon-incorporated diamond-like carbon coatings were evaluated. Compositions, hydrogen concentrations, Raman spectra, and surface energies are reported for the films. A ball-on-flat test configuration was used in 5%, 50%, and 100% slide-to-roll conditions. The test lubricant was a polyalphaolefin containing rust and oxidation inhibitor additives only. Differences in traction performance were observed for different coating types. Traction coefficients decreased at high λ with increased hydrocarbon...

Traction of Lubricated Rolling Contacts between Thin-Film Coatings and Steel

Solid lubricant coatings are commonly employed in mechanical systems operating in environments where oil or grease lubrication is not feasible. In particular, solid lubricant coatings are currently being used in rolling element bearings operating in vacuum environments and/or at high temperatures. Although numerous studies have reported the tribological performance of these materials in sliding contact, few if any studies have reported their performance in rolling contact. Since the functional lifetimes of solid lubricant coatings in rolling element bearings are derived from sliding contact experiments, it is beneficial and important to understand if the actual performance of the coatings in rolling contact bears a relationship to their sliding contact performance. In this work, Sb 2 O 3 /Au-doped MoS 2 coatings are deposited onto AISI 52100 and M50 specimens by magnetron sputtering. Mechanical properties are studied by scratch tests and nano-indentation techniques; microstructural analysis is undertaken with Raman spectroscopy and transmission electron microscopy. Friction and wear measurements are performed on specimens in both unidirectional and reciprocating sliding, using ball-on-flat tribometers in both vacuum and humid environments. Friction coefficient values as low as ~ 0.04 and as high as ~ 0.14 are measured at different contact stresses, and depend greatly upon the test environment. Functional lifetimes of the coatings are obtained from rolling contact tests performed in a thrust ball bearing tribometer in standard laboratory conditions.

An investigation of material and tribological properties of Sb2O3/Au-doped MoS2 solid lubricant films under sliding and rolling contact in different environments

Ryan D. Evans

Papers

Microstructural Alterations in Bearing Steels under Rolling Contact Fatigue Part 1—Historical Overview

Tribological Performance and Coating Characteristics of Sputter-Deposited Ti-Doped MoS2 in Rolling and Sliding Contact

Prevention of Smearing Damage in Cylindrical Roller Bearings

Traction of Lubricated Rolling Contacts between Thin-Film Coatings and Steel

An investigation of material and tribological properties of Sb2O3/Au-doped MoS2 solid lubricant films under sliding and rolling contact in different environments