Effect of Environment on Microstructure Evolution and Friction of Au\u2013Ni Multilayers

Ebru Cihan,Nicolas Argibay,Katherine Jungjohann,Michael Chandross,Martin Dienwiebel

doi:10.1007/s11249-019-1245-9

Abstract

We present results from a systematic investigation of environmental effects on the frictional behavior of Au–Ni multilayer films of varying interlayer spacing. The current results, sliding against ruby spheres in a dry N2 atmosphere, are compared to prior work on the tribological behavior of these materials under ultra-high vacuum (UHV) (Cihan et al. in Sci Rep 9:1–10, 2019). Under both conditions, there is a regime of high friction when the interlayer spacing is large and a regime of low friction when the spacing is small. The low friction regime is associated with a critical grain size below which grain boundary sliding is expected to be the dominant mechanism of deformation. A shear-induced alloy formation (60–65 at.% Ni in Au) and a concomitant low friction coefficient was observed with multilayer spacings of 20 nm and lower under UHV. A distinct microstructure was found in dry N2, and is attributed to different interfacial characteristics due to adsorbed species; rather than mixing between Au and Ni layers, only the uppermost Au layers were affected by shearing. These observations are coupled with the friction and wear behavior of multilayer samples sliding under different environments.

Highlights

The environmental conditions under which tribological materials operate in industrial applications are generally not the same as those used during the process design
A 1 mN normal load was applied on an inert ruby sphere (3.2 mm in diameter) and slid against a flat silicon wafer coated with Au–Ni multilayers at 33 μm/s for 100 reciprocating cycles, using a stroke length of 1 mm
The friction coefficient drops after the first few cycles, and for some multilayer samples the coefficient of friction (COF) decreases gradually (e.g., 10 nm layer spacing), while for others it decreases suddenly

Summary

Introduction

The environmental conditions under which tribological materials operate in industrial applications are generally not the same as those used during the process design. The environment can have a profound impact on the friction and wear of the contacting material surfaces, as adsorbed contaminants can cause changes at the asperity level and so-called third bodies [3] are generated with different chemical compositions and morphologies [4]. The subsurface microstructure is affected by structural modifications due to the large plastic strain gradients generated during sliding of the surfaces in contact. These instabilities can lead to folding or cracking at the subsurface. At higher sliding cycles the COF may increase [17] due to delamination of this tribomaterial

Methods

Results

Discussion

Conclusion