On the Role of Oxidation in Tribological Contacts under Environmental Conditions

Rolf Merz,Alexander Brodyanski,Michael Kopnarski

doi:10.1155/2015/515498

Abstract

Oxidation processes in tribological steel contacts are investigated, which are treated in a dry sliding, linear reciprocating model tribometer, by EDX (energy dispersive X-ray spectroscopy), AES (Auger electron spectroscopy), and HREFTEM (high resolution energy filtered transmission electron microscopy). Typical for steel contacts under environmental conditions is the feature that the counterparts are separated by oxide layers, which influence the tribological properties. And vice versa the tribological load will influence and change the oxide layers. The interaction of this dynamically coupled system was resolved by focussing the postexperimental surface analysis to long time stable balance states. As special challenge for the analyst of the tribological experiment under environmental conditions a postexperimental grown oxide layer covers the tribological induced changes and has to be distinguished from the tribological induced changes. Thick oxide layers, formed during the tribological load, were observed, which start to grow in form of islands and at the end separate the metallic bulk materials of the counterparts completely and avoid direct metal-metal contact. Thicknesses up to some microns strength, exceeding native oxide layers by magnitudes, were reached. Ploughing under fresh surface oxide and compacting and embedding of fresh oxidized debris particles were identified as main mechanisms responsible for the growing of these thick oxide layers.

Highlights

It is well known that the friction coefficient of metals is reduced due to oxide layer formation [1,2,3,4,5,6]
Ploughing under fresh surface oxide and compacting and embedding of fresh oxidized debris particles were identified as main mechanisms responsible for the growing of these thick oxide layers
Smaller particles were analyzed by high resolution energy filtered transmission electron microscopy (HREFTEM) with direct resolution of lattice planes

Summary

Introduction

It is well known that the friction coefficient of metals is reduced due to oxide layer formation [1,2,3,4,5,6]. In contrast even in the case of mild wear of steel the growing of up to some microns thick oxide layers is observed, which separate the metallic counterparts [6]. The forming of oxide layers due to compaction of oxide debris material is proposed as sufficient to explain the growing of thick oxide layers [6, 14]. This was confirmed in the actual study. The growing of thick oxide islands is due to the embedding of oxidized debris particles This was studied in detail by surface analysis

Experimental

Results and Discussion

Conclusion