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

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.

Effect of Environment on Microstructure Evolution and Friction of Au–Ni Multilayers

“…As explained in detail in previous work [21], under welldefined UHV conditions the individual layer thickness of the Au-Ni multilayer systems has a strong impact on the resulting friction force. Under UHV, the multilayer samples with the thickness of 10 nm, 20 nm, and 50 nm showed a low COF, while the 100 nm sample resulted in much higher friction under the same sliding conditions.…”

“…However there is little difference for the 100 nm sample, where the mixing is not present in either UHV or N 2 . Note that the lower friction forces for thinner interlayer spacings under UHV was attributed to the final microstructure resulting from the mechanical mixing of Au and Ni [21]. This mixing is likely linked to the dominant deformation mechanism [24,25].…”

“…The COF values for the N 2 atmosphere were larger than that observed under UHV conditions, except the 100 nm sample. Error bars in d were determined by the fluctuations in friction behavior during sliding as shown in a and in [21] 20 nm to 40-45 nm during shearing, as shown in Fig. 4a.…”

“…In this article, we present a systematic experimental study of the frictional behavior of Au-Ni multilayer samples, with different interlayer spacing, under a well-controlled N 2 atmosphere, and present a comprehensive comparison with our previous UHV results [21]. Because Au and Ni are immiscible under certain conditions (e.g.…”

“…Because Au and Ni are immiscible under certain conditions (e.g. conditions provided during deposition of the layers in this study), they were chosen to analyze the effect of microstructure on friction [21]. We clarify what influence of the initial microstructure of these Au-Ni multilayer samples is observed in a dry N 2 environment.…”