Tribofilms generated from ZDDP and DDP on steel surfaces: Part 1, growth, wear and morphology

Abstract

The growth and morphology of tribofilms, generated from zinc dialkyldithiophosphate (ZDDP) and an ashless dialkyldithiophosphate (DDP) over a wide range of rubbing times (10 s to 10 h) and concentrations (0.1-5 wt% ZDDP), have been examined using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) spectroscopy at the O, P and S K-edges and the P, S, and Fe L-edges. The physical aspects of the growth and morphology of the tribofilms will be presented in Part I and the chemistry of the films will be discussed in Part II. The major components of all films on 52100 steel are Zn and Fe phosphates and polyphosphates. The average thickness of these phosphate films has been measured using P K-edge XANES and XPS profiling. For ZDDP, a very significant phosphate film (about 100 Å thick) forms after 10 s, while film development for DDP is substantially slower. However, for both additives, the average film thickness increases to 600-800 Å after 30 min of rubbing, before leveling off or decreasing. The antiwear properties of pure ZDDP and in combination with DDP at different rubbing times and concentrations have also been examined. It was found that under all conditions, the performance of ZDDP as an antiwear agent is superior to that of DDP. However, DDP has no adverse effect on the performance of ZDDP when the two are mixed. The AFM results show that ZDDP forms larger and better developed ''pads'' than DDP at short rubbing times. At longer rubbing times, both films become more uniform. For the 1 h ZDDP films, the film thickness is surprisingly independent of the ZDDP concentration from 0.1 to 5 wt% ZDDP. The film thickness is also independent of the ratio of ZDDP/DDP concentrations.

WS2 nanoparticles – potential replacement for ZDDP and friction modifier additives

“…These results can be explained by considering other published results, which showed that the morphology of ZDDP derived tribofilms evolves with rubbing time to become smoother and more uniformly distributed [15,23].…”

A new insight into the interfacial mechanisms of the tribofilm formed by zinc dialkyl dithiophosphate

“…----Authors of the current manuscript recently reported a theoretical model with a hypothesis that formation and removal of the tribofilm happen simultaneously [35]. The hypothesis was based on the experimental observations of removal of the tribofilm and wear of the system even in the presence of fully-formed tribofilms [17,31,36]. The wear hypothesis was then validated against some wear measurements in experiments [37,38] and has shown good agreement.…”

“…The growth of ZDDP tribofilm on contacting surfaces has been subject of several studies [13,19,[27][28][29][30][31]. Fujita et al [32,33] studied the growth of ZDDP tribofilm using a Mini Traction Machine (MTM) and Spacer Layer Interferometry Method (SLIM).…”

A Semi-deterministic Wear Model Considering the Effect of Zinc Dialkyl Dithiophosphate Tribofilm

“…It was reported experimentally [16,[44][45][46] that, even in the areas where the tribofilm is fully formed, wear is occurring. It can be interpreted as partial removal of the tribofilm and at the same time formation of the film to restore the balance.…”