<i>In Situ</i> Raman-SLIM Monitoring for the Formation Processes of MoDTC and ZDDP Tribofilms at Steel/Steel Contacts under Boundary Lubrication

Abstract

In this study, the formation processes of molybdenum dithiocarbamate (MoDTC) and zinc diallyldithiophosphate (ZDDP) tribofilms were investigated using an in situ Raman-space layer imaging method (SLIM) tribometer under boundary lubrication. According to the results, the ratio of the PO x and P-O-P bonds in the tribofilms was almost the same as the film thickness behavior calculated from the SLIM images. Hence, the the time-dependence chemical composition change of the tribofilms of phosphate related bonds in the tribofilms is considered a factor in the growth of ZDDP tribofilms. Moreover, the presence of MoDTC in the ZDDP solution contributed to the formation of phosphate compounds with a relatively high ratio of P-O-P links, such as ultra-phosphate glasses. This mechanism is attributable to the friction-reduction effects of MoS 2 on the tribofilm, which can contribute to maintaining a suitable condition for the formation of relatively high P-O-P-link-ratio tribofilms.

Active control of Lubricant Flow Using Dielectrophoresis and Its Effect on Friction Reduction

“…Shi et al found that similar low friction mechanism was observed on the graphene/copper/hydroxypropyl-methylcellulose coating [26]. Additives in oil lubricants, which are also widely used in industry, generate additive-derived tribofilms on sliding surfaces due to sliding heat and high shear stress at the real contact area, resulting in high wear resistance and low friction [27][28][29][30][31][32][33][34][35]. Both systems can be reconsidered as excellent systems designed to transition to the desired state (e.g., low friction surfaces) upon the occurrence of the phenomenon to be controlled (e.g., friction).…”

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. − …”

Friction Coefficient Dynamics of Tribological Coatings from Engine Lubricants: Analysis and Interpretation

“…Measurements of film thickness are commonly carried out by spacer layer interferometry and electrical contact resistance methods for in situ measurements, and atomic force microscopy, scanning electron microscopy, and transmission electron microscopy for ex situ measurements [18,22,23]. The predictions of the lubricating film thickness are developed from tribochemical models of film growth, experimental parameters of film removal, elastoplastic models of viscous films over rough surfaces, the Reynolds equation, and mass balance models [9,10,17,20,24,25]; the measurements of the coefficient of friction are in general carried out from tribological devices that measure friction force [6,13,22,[26][27][28][29]. Friction coefficient predictions are developed from multi-scale roughness and linear models of friction as a function of coated surfaces [2,29,30].…”