Due to the increasing demand of low emission and fuel economy, friction modifiers have been widely used in lubricating compositions to adjust friction and wear properties of lubricants. Recent achievements in the application of friction modifiers for liquid lubricants (2007–present) are reviewed in this paper. There are three types of friction modifiers for liquid lubricants: organomolybdenum compounds, organic friction modifiers, as well as nanoparticles. The tribological properties and lubrication mechanisms of these friction modifiers are discussed. The problems and some suggestions for the future directions of research on friction modifiers are proposed.

A review of recent developments of friction modifiers for liquid lubricants (2007–present)

Boron compounds are widely used in a range of tribological applications such as friction modifiers, antioxidants, antiwear additives, and in many cases as environmentally friendly lubricants. The chemical nature and structure of boron compounds provide multifunctionality. They are used as (1) solid lubricants such as boric acid and hexagonal boron nitride, (2) liquid lubricants such as ionic liquids, (3) lubricant additives such as borate derivatives of various organic and inorganic compounds, and (4) coatings such as cubic boron nitride and different metal borides. Boron is also one of the most favorable elements for coatings and thin films in biotribological and biomedical applications. This review outlines the growing role of boron in lubrication over the past several decades, summarizes the main findings, and identifies future challenges related to boron chemistry.

Boron in tribology: from Borates to ionic liquids

In this article an engineering approach is described to model micropitting in rolling–sliding, heavily loaded lubricated contacts. The competitive mechanism between surface fatigue and mild wear is captured in the present approach as well as the effects of deterministic surface microgeometry (e.g., roughness). The fatigue model is based on the Dang Van fatigue criterion and the mild wear model uses a modified Archard approach. The complete modeling scheme is validated experimentally first using laboratory-controlled conditions, where the surface topography is varied as well as the operating conditions in the contact. Then the model is applied to describe the behavior of full-bearing tests. The behavior of the model agrees well with the experimental observations, qualitatively.

Micropitting Modelling in Rolling–Sliding Contacts: Application to Rolling Bearings

https://spiral.imperial.ac.uk/bitstream/10044/1/55847/5/1-s2.0-S0043164817309535-main.pdf

Prediction of micropitting damage in gear teeth contacts considering the concurrent effects of surface fatigue and mild wear

A descriptive model of wear evolution in rolling bearings

Effect of lubricants on micropitting and wear

Previous studies have shown that many anti-wear additives have a tendency to aggravate micropitting damage in hard steels subjected to rolling sliding contact at low lambda values. This is apparently because anti-wear additives suppress the gradual smoothing of the rough surfaces that takes place when a pure base stock is used under mild conditions. However, in practice, it is common to combine anti-wear and friction modifier additives in formulated oils, a combination that leads to reduced boundary friction. In the work described in this article, we added a common friction modifier agent, a molybdenum bis-diethylhexyl dithio-carbamate (MoDTC), to an oil containing an anti-wear additive, a secondary zinc dialkyl-dithio-phosphate (ZDDP) in a mineral base-stock. We examined micropitting behavior using a disc tester. The oil with both MoDTC and ZDDP showed initial micropitting that gradually disappeared with continued running, whereas ZDDP alone led to continuing severe damage. Analysis of the counter-discs ...

E. Lainé

Papers

Effect of lubricants on micropitting and wear

The Effect of a Friction Modifier Additive on Micropitting