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

Abstract

The present paper proposes a new treatment method for diamond-like carbon (DLC) coatings using electric discharge. DLC coatings exhibit excellent mechanical and tribological properties due to their unique carbonaceous structure. Several surface treatment methods were presented to achieve short running-in and low friction. However, in-situ surface treatment is needed to extend the life of machines and maintain their performance. Here, we propose an electric discharge treatment with a simple electrical circuit. As a result, the friction coefficient drastically drops from 0.3 to 0.11. Interestingly, the drop starts shortly after the discharge starts. Consequently, the running-in is shortened to about 6-m sliding compared to no discharge condition, which does not show any running-in more than 68-m sliding. Raman analysis reveals that a transfer layer on the ball surface is composed of carbonaceous material and the structure exhibits graphite-like characteristics. However, there is visible damage on the DLC surface. Another friction test shows a very low friction coefficient of 0.04 using a transfer layer-covered ball and a new DLC disk with a smooth surface. In conclusion, the combination of a transfer layer and smooth DLC surface is needed to exhibit excellent tribological performance, indicating the importance of less damage treatment. Next, pulse discharge treatment is demonstrated to achieve less damage to the DLC coating. As a result, the pulse discharge method reduces friction and surface damage. In conclusion, the proposed treatment methods using electric discharge not only show the potential for reducing friction, but also the feasibility of in-situ treatment during machine operation.

A review of advances in tribology in 2020–2021

“…Design and fabrication of WC/DLC multilayer coatings with optimized interface characteristics and superior surface protection were proposed by Nemati et al [545]. A new DLC surface treatment method was developed with electric discharge for short running-in and friction reduction [546].…”

Superlubricity with Graphitization in Ti-Doped DLC/Steel Tribopair: Response on Humidity and Temperature

“…Ti-DLC made adhesion between ferrous metal and the transfer layer better, resulting in a high C / C contact ratio and low friction. In addition to the formation of a carbonaceous transfer layer, the friction performance of DLC is highly environmentally sensitive: lubricating fluid (i.e., gas, − gel, and liquid), operating temperature, , humidity, and additives. − …”

Influence of defects in sp2-bonded network of diamond-like carbon on silica scale adhesion in geothermal power plants

“…DLC is a carbon-based amorphous thin lm with diamond-and graphite-like structures (with sp 3 and sp 2 bonding, respectively [7]; moreover, it is resistant to corrosion and wear [8,9] and exhibits a low friction coe cient in non-lubricant systems [10][11][12][13][14][15]. So, it is expected to experience low interaction forces with mating materials, and low adhesion performance in the case of silica scale may be expected.…”