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ZDDP tribofilm formation on non-ferrous surfaces

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Title: ZDDP tribofilm formation on non-ferrous surfaces
Authors: Ueda, M
Kadiric, A
Spikes, H
Item Type: Journal Article
Abstract: The current trend for using lower viscosity lubricants with the aim of improving fuel economy of mechanical systems means that machine components are required to operate for longer periods in thin oil film, boundary and mixed lubrication conditions, where the risk of surface damage is increased. In addition, non-ferrous materials are increasingly being introduced in machine components to reduce wear and increase efficiency. Thus, understanding of the ZDDP antiwear tribofilm formation on both ferrous and non-ferrous surfaces is increasingly important in order to formulate lubricants that give desired antiwear performance with both types of materials. In this paper the effect of ferrous and non-ferrous rubbing materials, namely, steel, Si3N4, WC, SiC and a-C:H DLC coating, on ZDDP tribofilm formation was investigated. Among non-ferrous materials, it was found that ZDDP tribofilms were formed on Si3N4 and WC in the boundary lubrication regime, but almost no tribofilms were formed on SiC and a-C:H DLC. In addition, although tribofilms formed on some non-ferrous surfaces, they were easily removed under boundary lubrication by direct asperity contact because of their weak adhesion to the substrate. This tribofilm removal makes quantification of ZDDP tribofilm formation rate on non-ferrous surfaces under boundary lubrication conditions difficult. By contrast, under high shear stress EHL conditions, thick tribofilms formed without film removal with the tribofilm thickness being the greatest for steel, followed by Si3N4 and then WC, with no tribofilm formation observed on SiC and DLC. QCM results suggest that ZDDP tribofilm formation might be considerably affected by the extent to which ZDDP adsorbs on the substrate surface. The chemical properties of tribofilms are discussed and a possible mechanism by which ZDDP forms tribofilm on non-ferrous surfaces is suggested. This study has practical implications for ways in which non-ferrous surfaces can be protected from wear via lubricant formulation.
Issue Date: 15-Oct-2020
Date of Acceptance: 23-Sep-2020
URI: http://hdl.handle.net/10044/1/83513
DOI: 10.2474/trol.15.318
ISSN: 1881-218X
Publisher: Japanese Society of Tribologists
Start Page: 318
End Page: 331
Journal / Book Title: Tribology Online
Volume: 15
Issue: 5
Copyright Statement: © 2020 Japanese Society of Tribologists. This article is distributed under the terms of the latest version of CC BY-NC-ND defined by the Creative Commons Attribution License.
Sponsor/Funder: Engineering & Physical Science Research Council (EPSRC)
Funder's Grant Number: EP/P030211/1
Publication Status: Published
Open Access location: https://doi.org/10.2474/trol.15.318
Online Publication Date: 2020-10-15
Appears in Collections:Mechanical Engineering
Faculty of Natural Sciences

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