Evolution of damage in MoS 2 -based dry film lubricants (DFLs) in fretting wear—The effect of DFL thickness and contact geometry

K Barman,K.T Voisey,P.H Shipway,G Pattinson

doi:10.1016/j.porgcoat.2016.12.022

K Barman, K.T Voisey + Show 2 more

Open Access

https://doi.org/10.1016/j.porgcoat.2016.12.022

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Abstract

Dry film lubricant (DFL) coatings are widely used to reduce coefficients of friction and damage in highly loaded contacts. This work investigates the behaviour of a commercially available MoS2-based DFL in a cylinder-on-flat contact geometry with a fretting amplitude of 300 µm. Cylinders with radii of 15 mm, 80 mm and 160 mm along with DFL thicknesses between 12 µm and 86 µm were utilized. Three stages in the lifetime of the system were investigated; in the first stage, the DFL wore with a volumetric rate that was proportional to the number of cycles (under a given load), until the thickness of the DFL was reached. In the second stage, a thin low friction surface layer existed, with its durability being proportional to the contact pressure. In the third stage, metal-metal contact resulted in short-term instabilities in the coefficient of friction and the DFL system was said to have failed.

Highlights

Mechanical vibration of highly loaded contacts can lead to fretting due to the resulting relative displacement between the two contacting bodies
energy dispersive X-ray analysis (EDX) analyses of the worn surfaces again reveal their mixed substrate/ Dry film lubricant (DFL) makeup, with Ti at wt% and Mo at wt% (t = 12 μm) and Ti at 27 wt% and Mo at 27 wt% (t = 62 μm). These observations together indicate that the identification of Stage II with a period where the surface in contact is comprised of a combination of the DFL and the metallic substrate material has general validity
The polymer-based DFL wears away until the substrate starts to come into contact; during this stage the coefficient of friction falls slowly

Summary

Introduction

Mechanical vibration of highly loaded contacts can lead to fretting due to the resulting relative displacement between the two contacting bodies. Longer lifetimes are associated with lower rates of wear of the lubricant film itself, and the desire for low friction and long lifetime are often (but not always) complimentary, since low friction leads to a reduction in frictional energy dissipation and to reduced wear [8]. Such low-friction coatings are more generally referred to as dry film lubricants (DFLs) and are used in a variety of industrial applications to reduce the coefficient of friction where conventional liquid lubricants are ineffective or cannot be readily deployed [9, 10]

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