Operando tribochemical formation of onion-like-carbon leads to macroscale superlubricity

Diana Berman,Alexander Zinovev,Ali Erdemir,Anirudha V Sumant,Subramanian K R S Sankaranarayanan,Badri Narayanan,Mathew J Cherukara

doi:10.1038/s41467-018-03549-6

Diana Berman, Alexander Zinovev + Show 5 more

Open Access

https://doi.org/10.1038/s41467-018-03549-6

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Abstract

Stress-induced reactions at the sliding interface during relative movement are known to cause structural or chemical modifications in contacting materials. The nature of these modifications at the atomic level and formation of byproducts in an oil-free environment, however, remain poorly understood and pose uncertainties in predicting the tribological performance of the complete tribosystem. Here, we demonstrate that tribochemical reactions occur even in dry conditions when hydrogenated diamond-like carbon (H-DLC) surface is slid against two-dimensional (2D) molybdenum disulfide along with nanodiamonds in dry nitrogen atmosphere. Detailed experimental studies coupled with reactive molecular dynamics simulations reveal that at high contact pressures, diffusion of sulfur from the dissociated molybdenum disulfide led to amorphization of nanodiamond and subsequent transformation to onion-like carbon structures (OLCs). The in situ formation of OLCs at the sliding interface provide reduced contact area as well as incommensurate contact with respect to the H-DLC surface, thus enabling successful demonstration of superlubricity

Highlights

Stress-induced reactions at the sliding interface during relative movement are known to cause structural or chemical modifications in contacting materials
We demonstrate that in dry environment when two dimensional (2D) MoS2 layers are combined with nanodiamonds in an alcohol solution and drop-casted onto the SiO2/Si substrate surface and slid against H-DLC16 coated surface, the tribochemical reaction manifest formation of large onion-like carbon structures (OLCs) scrolls in situ directly at the sliding interface leading to superlubricity
Through detailed experimental investigation combined with molecular dynamics simulations, we elucidate the mechanism of OLC formation and show that a mechanical stress-induced tribochemical reaction at the nanoscale is responsible for dramatic changes at the tribological interface leading to superlubricity at the macroscale

Summary

Introduction

Stress-induced reactions at the sliding interface during relative movement are known to cause structural or chemical modifications in contacting materials. Our observations suggest a tribochemically driven mechanism of OLCs formation in the tribolayer from a mixture of MoS2 with nanodiamonds at sliding interfaces as shown in the schematics in Fig. 2a–d (and Supplementary Figure 1), leading to decreased friction values from high values down to near zero.

Results

Conclusion