Low friction of metallic multilayers by formation of a shear-induced alloy

Ebru Cihan,Michael Stüber,Harald Leiste,Heike Störmer,Martin Dienwiebel

doi:10.1038/s41598-019-45734-7

Abstract

During sliding of metallic surfaces, the near surfaces undergo significant changes in terms of topography, composition and microstructure. Since friction and wear behavior of the materials are strongly influenced by sub-surface deformations, it is fundamental to investigate these effects. Therefore, the present study aims towards a better understanding of the behavior of friction depending on well-defined initial microstructures. By performing sliding experiments on Au-Ni multilayer samples under ultrahigh vacuum (UHV) conditions, we observe that the individual layer thickness of multilayer systems has a strong influence on friction behavior due to the transition in the dominant deformation mechanism near the surface. The experiments reported here provide a new route for lowering the friction force of metallic material systems in dry contact by providing more stable microstructures and alloy formation. Through ultrafine grains present in the alloy formed by mechanical mixing the number of grain boundaries strongly increases and hence, grain boundary-mediated deformation results in the low friction coefficient.

Highlights

Most machinery is constructed from technical alloys and even a slight reduction of friction and wear of their sliding parts has a huge economic impact
We carried out atomic force microscope (AFM) experiments to characterize the topography of the as-grown multilayer samples in order to see the effect of layer thickness on surface roughness, and it has been observed that the roughness increases only slightly with increasing layer thickness
Note that a significant pile-up has been observed in our measurements; and the critical indentation depth should vary for each multilayer sample due to different layer thicknesses having distinct hardness

Summary

Introduction

Most machinery is constructed from technical alloys and even a slight reduction of friction and wear of their sliding parts has a huge economic impact. It is extremely difficult to predict friction of metallic surfaces because when they are subjected to sliding friction, they develop new microstructures, phases or composition that are not present in the original material at the near surface[1,2,3] The development of these so-called ‘third bodies’ or tribomaterials[4] strongly influences the frictional and wear behavior of tribological systems and many examples exist for technical alloys and pure metals[5,6,7,8,9,10,11,12,13,14,15]. The deformation mechanisms can be quite complex, multilayer thin films are extremely promising for studying these mechanisms and can serve as model materials for tribological purposes to be able to clarify distinctive deformation processes which have strong relation with their friction behavior as we aim to demonstrate in this article

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Results

Conclusion