Behaviour of boundary lubricating additives on DLC coatings

Abstract

The friction properties of a range of boundary lubricating additives in DLC-DLC rolling-sliding contact have been investigated. Two types of commercial DLC have been studied, one hydrogenated diamond-like and the other Cr-doped, nonhydrogenated and graphitic.The graphitic-type DLC coating initially gave very low boundary friction with additive-free base oil but after a few minutes of rubbing in thin film conditions friction rose to a higher value, similar to that produced immediately by the diamondlike carbon. Some organic friction modifiers were able to preserve this low boundary friction behaviour of the graphitic-type DLC for a full two hour rubbing test. One organic friction modifier, glyceryl monooleate produced a considerable reduction in friction with both types of DLC coating in intermediate speed, though notin very slow speed conditions. The additive molybdenum dithiocarbamate formed a low friction film on both DLC surfaces, with lower friction on the graphitic than on diamond-like carbon one. AFM measurements showed that this was due to the formation of regions of low lateral force on asperities within the rubbed track. ZDDP provided some reduction in friction on both DLC surfaces after rubbing but did not form thick ZDDP tribofilms like those generated on steel surfaces.

Lubrication of DLC Coatings with Two Tris(pentafluoroethyl)trifluorophosphate Anion-Based Ionic Liquids

“…DLC coatings are becoming quite widely used for machine elements in lubricated systems, especially in the automotive industry (He,et al (8); Gangopadhyay,et al (9)), as well as under high stress and/or under boundary or mixed lubrication regimes (Kalin,et al (10); Manier,et al (11)). Topolovec, et al (12) studied the friction properties of a range of boundary lubricating additives in DLC rolling-sliding contacts and analyzed how these coatings interacted with the various additives present in the formulated lubricants and the impact of additive-DLC interactions on friction and wear. Kalin,et al (10) studied the DLC-lubricant interaction and analyzed only DLC-DLC contacts in order to avoid the inevitable effects from interactions with other countermaterials such as steel.…”

In Situ Raman Observation of the Graphitization Process of Tetrahedral Amorphous Carbon Diamond-Like Carbon under Boundary Lubrication in Poly-Alpha-Olefin with an Organic Friction Modifier

“…It is natural to consider that the wear process increases the contact area and generates a conformal contact susceptible to strongly modify the contact parameters (contact pressure), which can be at the origin of the friction reduction process. Moreover, Topolovec-Miklozic reported that the formation of a GMO-derived tribofilm is needed by the contribution of a bulk fluid film [40]. This indicates that the increment of the contact area supported the formation of a GMO-derived tribofilm.…”

“…Owing to the considerable amount of research, it is well-known that the tribological behavior of a DLC film depends on various factors such as atmospheric conditions [1][2][3][4][5][6], counter-materials [7][8][9], and the type of lubricant [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. In particular, the tribological behavior of a DLC film is governed by graphitization of the DLC film under dry sliding conditions [24][25][26][27][28][29][30][31].…”

“…An "in contact" or "in situ (in lubro)" analysis is thus needed to clarify the effects of the graphitization on the tribological properties of DLC films under lubricated conditions. Moreover, it is expected that the lubricant additives strongly influence the graphitization process of DLC films under lubricated condition because the tribological properties of DLC films under lubricated conditions is governed by lubricant additives [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23].…”

Multiscale Friction in Lubricant-Surface Systems for High-Performance Transmissions Under Mild Wear

“…Kim et al [25] used a nano-indenter to investigate tribo-film hardness and elasticity of an ashless extreme-pressure additive generated through tribological tests. Topolovec-Miklozic et al [26,27] used a mini-traction machine (MTM) to investigate ZDDP tribo-film formation on DLC. After the surface was lightly cleaned with propanol, surface height and lateral force images measured using an AFM were used to gain an understanding of the tribometric results.…”