Friction and Wear Properties of Tetrahedral Si-Containing Hydrogenated Diamond-Like Carbon Coating under Lubricated Condition with Engine-Oil Containing ZnDTP and MoDTC

Abstract

In this study, we investigated tribological properties of "tetrahedral" Si-containing hydrogenated DLC coating (TMS coating) during sliding against steel or cast-iron lubricated with engine-oil containing MoDTC and ZnDTP additives. TMS coatings derived from only tetramethylsilane were prepared using PACVD with high-bias process. TMS coating had the highly carbon sp 3 bonded structure induced by Si (over 20 at.%) with high hydrogen content (30 at.%). TOF-SIMS analysis showed that TMS coating could form the additive-derived tribofilm on both of the non-ferrous coating surface and the ferrous counter surface to promote Mo-sulfide formation effectively, leading a low friction coefficient. The tribo-chemical reactions were related not only to Mo-sulfides formation, but also reduction of Mo-oxides. Mo-oxides could react with DLC material and induce hydrogen evolution and transformation into further weak carbon structure, causing an increasing wear of hydrogenated DLCs. TMS coating showed no significant wear in spite of plenty hydrogen content. Si induced sp 3 bond and could act so as not to induce clustering of the sp 2 phase. This could inhibit increasing wear of the DLC in the presence of MoDTC. The effectiveness of TMS coating in friction and wear behavior was shown to depend on tribo-chemical reactions and transformation of carbon bond structure.

Diamond Like Carbon Films Containing Si: Structure and Nonlinear Optical Properties

“…It should be mentioned, that an increase of the oxygen atomic concentration with Si amount in DLC:Si films was reported by other authors, too [12,18]. In numerous studies, relatively large amounts of oxygen, comparable with the present study or even higher, were reported for both hydrogenated [18,20,21] and hydrogen-free [12,17] DLC:Si films. In other case, O atomic concentration increased for DLC:Si films deposited by plasma-enhanced chemical vapor deposition from tetramethylsilane (TMS) only in comparison with the films deposited from the mixture of C 2 H 2 and TMS [18].…”

“…It should be mentioned that such behavior was reported in numerous studies for both hydrogen-free and hydrogenated DLC films containing silicon or SiO x [8,[33][34][35][36]. G peak position downshift to 1505 cm −1 [21], 1495 cm −1 [23], 1480 cm −1 [12] and even as low as 1460 cm −1 [17,19] was reported. In those studies, the changes were explained by the increased sp 3 /sp 2 carbon bond ratio.…”

“…Thus, Figure 9a-c provides in some way contradicting information of changes in the amount of sp 3 carbon phase. In addition, according to Komori et al [17], the D/G ratio in the case of hydrogenated DLC:Si film is lower than the D/G ratio of the Raman spectra of tetrahedral amorphous carbon film. Thus, it should be supposed that sp 3 /sp 2 carbon bond ratio in that case is higher in DLC:Si film than that in tetrahedral amorphous carbon film.…”

“…Properties of DLC films can be additionally controlled by introducing chemical elements other than carbon or hydrogen [1,[3][4][5][6][7][8]. Particularly, silicon is one of the most often used DLC dopants [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Reduced internal stress and friction coefficient, as well as increased thermal resistance, while keeping high hardness of Si doped diamond-like carbon films were reported [9].…”

A Study on the Tribofilm Growth and Tribological Properties of Tribofilms Formed from Zinc Dialkyl Dithiophosphate (ZDDP) and Molybdenum Dialkyl Dithiocarbamate (MoDTC)

“…Nanoindentation, nanoscratch and atomic force microscopic (AFM) phase-image measurements have been used to study the nanometer-scale mechanical/structural properties of the tribofilms [10][11][12]. X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption spectroscopy (XANES), Auger electron spectroscopy, and time-of-flight secondary ion mass spectrometer (TOF-SIMS) have been used to determine the chemical structure of the tribofilm layer [13][14][15][16][17]. Research work has indicated that tribofilms that are formed from ZDDP consist of rough, patch, pad-like features that are composed of pyro-or orthophosphate glasses in the bulk, with an outer nanoscale layer of zinc polyphosphates and a sulfurrich layer near the metal surface [1,18,19].…”