Running-in behavior of a H-DLC/Al2O3 pair at the nanoscale

Pengfei Shi,Bin Zhang,Junhui Sun,Linmao Qian,Yunhai Liu,Junyan Zhang,Lei Chen

doi:10.1007/s40544-020-0429-5

Pengfei Shi, Bin Zhang + Show 5 more

Open Access

https://doi.org/10.1007/s40544-020-0429-5

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Abstract

Diamond-like carbon (DLC) film has been developed as an extremely effective lubricant to reduce energy dissipation; however, most films should undergo running-in to achieve a super-low friction state. In this study, the running-in behaviors of an H-DLC/Al2O3 pair were investigated through a controllable single-asperity contact study using an atomic force microscope. This study presents direct evidence that illustrates the role of transfer layer formation and oxide layer removal in the friction reduction during running-in. After 200 sliding cycles, a thin transfer layer was formed on the Al2O3 tip. Compared with a clean tip, this modified tip showed a significantly lower adhesion force and friction force on the original H-DLC film, which confirmed the contribution of the transfer layer formation in the friction reduction during running-in. It was also found that the friction coefficient of the H-DLC/Al2O3 pair decreased linearly as the oxygen concentration of the H-DLC substrate surface decreased. This phenomenon can be explained by a change in the contact surface from an oxygen termination with strong hydrogen bond interactions to a hydrogen termination with weak van der Waals interactions. These results provide new insights that quantitatively reveal the running-in mechanism at the nanoscale, which may help with the design optimization of DLC films for different environmental applications.

Highlights

As an unavoidable phenomenon for most as-fabricated mechanical parts during the initial operation, runningin alters the performance of the moving components and plays a crucial role at all size scales, from macroscale engines down to dynamic nano-devices [1,2,3,4,5,6,7,8]
3.1 Running-in of the H–Diamond-like carbon (DLC) film under vacuum Figure 2 shows the variation of the friction coefficient during running-in under vacuum
The discriminable nano wear of the hydrogenated diamond-like carbon (H–DLC) film formed after five reciprocating sliding cycles during running-in (Fig. 3(a))

Summary

Introduction

As an unavoidable phenomenon for most as-fabricated mechanical parts during the initial operation, runningin alters the performance of the moving components and plays a crucial role at all size scales, from macroscale engines down to dynamic nano-devices [1,2,3,4,5,6,7,8]. Diamond-like carbon (DLC) film is one of the most promising materials for reducing energy consumption and CO2 emission since it is capable of achieving super-low friction for sliding parts [9,10,11,12]. It is important to achieve a scientific understanding of the contact and friction mechanisms that occur during the running-in of a DLC film from the nanoscale to the macroscale. In previous running-in studies, tribological experiments on DLC films were usually performed at the macroscale and several mechanisms involving transfer layer formation, substrate graphitization [17,18,19], passivation theory [20,21,22], and native oxide removal [23,24,25] were proposed to explain the Friction 9(6): 1464–1473 (2021)

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