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Influence of black oxide coating on micropitting and ZDDP tribofilm formation

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Title: Influence of black oxide coating on micropitting and ZDDP tribofilm formation
Authors: Ueda, M
Spikes, H
Kadiric, A
Item Type: Journal Article
Abstract: Micropitting is a type of surface fatigue damage that occurs in rolling-sliding contacts operating under thin oil film conditions. Application of black oxide (BO) coating to steel rubbing surfaces has been suggested as a potential approach to alleviate micropitting. This paper confirms that BO coatings can prevent micropitting and identifies the predominant mechanism by which this occurs. Micropitting tests were carried out using ZDDP solutions in a ball on disc tribometer. Micropitting was preferentially generated on the smooth balls and this was completely prevented by applying a BO coating to the rougher discs, regardless of whether the balls were coated or not. In contrast, when the rough discs were not BO-coated, micropitting was consistently generated on both BO-coated and uncoated balls. BO coating has about one quarter the hardness of the steel used and was found to be very rapidly removed from the surface asperity peaks at the onset of rubbing, despite the presence of ZDDP. This resulted in an almost immediate and very large reduction of the surface roughness of the discs and this prevented high asperity stresses that would normally initiate and propagate the surface fatigue cracks leading to micropitting. Parallel measurement showed that BO did not suppress tribofilm growth, so the ZDDP was able to protect against adhesive wear while not promoting micropitting. The insights presented here can help with the design of components and lubricants that are effective in controlling both sliding wear and micropitting.
Issue Date: 10-Jan-2022
Date of Acceptance: 4-Jun-2021
URI: http://hdl.handle.net/10044/1/92347
DOI: 10.1080/10402004.2021.1940407
ISSN: 1040-2004
Publisher: Informa UK Limited
Start Page: 1
End Page: 21
Journal / Book Title: Tribology Transactions
Volume: 65
Issue: 2
Copyright Statement: © 2021 The Author(s). Published with license by Taylor and Francis Group, LLC This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.
Sponsor/Funder: Engineering & Physical Science Research Council (EPSRC)
Funder's Grant Number: EP/P030211/1
Keywords: Science & Technology
Engineering, Mechanical
black oxide
rolling contact fatigue
0913 Mechanical Engineering
Mechanical Engineering & Transports
Publication Status: Published
Open Access location: https://www.tandfonline.com/doi/full/10.1080/10402004.2021.1940407
Online Publication Date: 2021-06-15
Appears in Collections:Mechanical Engineering
Faculty of Natural Sciences
Faculty of Engineering

This item is licensed under a Creative Commons License Creative Commons