Effect of Transfer Layer on Ultra Low Friction of CNx Coating under Blowing Dry Ar

Abstract

In order to clarify the ultra low friction mechanism of Carbon Nitride (CN x ) coatings under blowing dry Ar, thickness and area of transfer layers on mating surface were in-situ observed with an optical microscope during sliding against a sapphire hemisphere under blowing dry Ar. During sliding, thickness of transfer layer from CN x coating to a sapphire hemisphere increased and leaded to ultra low friction. When thickness and area of transfer layer was thick and small respectively, ultra low friction was observed. The result showed that the coefficient of friction decreased from 0.18 to 0.003 and remained constant throughout the friction test. It was confirmed the formation of a graphite-like transfer layer with Raman analysis and Auger Electron Spectroscopy (AES).

Stable and super‐low friction of amorphous carbon nitride coatings in nitrogen gas by using two‐step ball‐on‐disk friction test

“…On the other hand, although the formation of a uniform tribofilm on the wear scar of the ball surface is beneficial for obtaining super-low friction of CNx coatings in N 2 gas environment, the tribofilm is unstable, and it has been found that a random lost or detachment of tribofilm on the ball surface occasionally leading to high and unstable friction coefficients (μ > 0.3). 12 On the contrary, high and unstable friction coefficients were not observed in the current work when the contact material combination of self-mated CNx coatings was generated. Therefore, the stable and low friction behaviour of CNx/CNx in N 2 gas stream can be attributed to the formation of self-mated CNx coatings.…”

“…Two‐step friction test is proved to be an effective technique for obtaining the contact material combination of self‐mated CNx coatings, and it provides a new pathway for studying the potential outstanding tribological properties of self‐mated CNx coatings in N 2 gas environment. On the other hand, although the formation of a uniform tribofilm on the wear scar of the ball surface is beneficial for obtaining super‐low friction of CNx coatings in N 2 gas environment, the tribofilm is unstable, and it has been found that a random lost or detachment of tribofilm on the ball surface occasionally leading to high and unstable friction coefficients (μ > 0.3) . On the contrary, high and unstable friction coefficients were not observed in the current work when the contact material combination of self‐mated CNx coatings was generated.…”

Development of a new diamond-like carbon surface treatment method with electric discharge for short running-in and friction reduction

“…Generally, the transfer layers are generated through running-in, resulting in a decrease in friction. 34,37,40 Although an optical microscope is able to detect transfer layers, spectroscopic analysis (e.g. Raman spectroscopy, X-ray photoelectron spectroscopy, and reflectance spectroscopy) is required to analyze DLC structures.…”

“…Nitride doping is one well-known method to realize super-low friction and adhesion. [38][39][40][41] Transfer layers derived from carbon nitride (CNx) coatings show a high sp 2 fraction due to restructuring of the carbonaceous structure by the desorption process of nitrogen atoms. 40,42 The transfer layers with a high sp 2 fraction provide lower friction due to the lower shear strength of the graphite-like structures.…”

“…[38][39][40][41] Transfer layers derived from carbon nitride (CNx) coatings show a high sp 2 fraction due to restructuring of the carbonaceous structure by the desorption process of nitrogen atoms. 40,42 The transfer layers with a high sp 2 fraction provide lower friction due to the lower shear strength of the graphite-like structures. Other research studies show that the nitride-contained DLC coatings provide a smooth surface due to their tough structure, resulting in low friction under lubricating conditions.…”