Differences in nano-topography and tribochemistry of ZDDP tribofilms from variations in contact configuration with steel and DLC surfaces

Abstract

In this work, we evaluated the effect of the counter-body material (the same or dissimilar) and contact configuration (moving or stationary body), at similar contact tribological conditions, on the tribochemical and nanotopography characteristics of adsorbed surface films. Zinc dialkyldithiophosphate (ZDDP), the best performing anti-wear additive, was used in self-mated steel/steel and DLC/DLC contacts, which were compared with mixed steel/DLC and DLC/steel contacts in 1-h and 6-h sliding tests. The macroscale (tribometer) and nanoscale (atomic force microscopy) friction, thickness, topography, and chemical (attenuated total reflection-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy) properties of the tribofilms were studied. The results revealed unexpectedly large differences in all the studied tribofilm parameters; this is because all the tribofilms are completely different; this includes the chemical composition, which is known to have a crucial effect on the nano- and macro-scale tribological properties. These results clearly demonstrate that the surface material, additives, and common contact operating parameters, that is, pressure, velocity, and temperature, crucially affect the ZDDP tribofilm as well as the position of the moving or stationary surface within the contact, and the material of the moving/stationary bodies.

Effect of Copper Nanoparticles Surface-Capped by Dialkyl Dithiophosphate on Different Base Oil Viscosity

“…Figure 1b illustrates the FTIR spectrum of CuDDP, with distinct C-H characteristic peaks (including CH 3 and CH 2 ) at 1380 cm −1 . Pertinent to this study are two pronounced absorption peaks near 1000 cm −1 , attributed to P-O-C at 636 cm −1 and P=S, indicative of the HDDP modifier's presence [27,28]. Figure 1c displays a TEM image and particle size distribution of CuDDP, revealing that the nanoparticles are spherical with an average diameter of approximately 5 nm, as shown in Figure 1d.…”

High Friction Mechanism of ZDDP Tribofilm Based on in situ AFM Observation of Nano-Friction and Adhesion Properties

“…Their findings are consistent with our experimental results. In addition, high friction of the ZDDP tribofilms is confirmed at the macroscale [12,21], regardless of the sliding pair. For example, the DLC/DLC and Si3N4/steel pairs.…”

“…We confirmed that there was a significant difference in shear strength between the steel and ZDDP tribofilm. Therefore, we assumed that the increase in friction force by the ZDDP tribofilm was caused by the [12,15,21]. Generally, the metal/metal friction is much higher, as reported by Bowden and Tayber [24].…”

“…In addition, Coga et al reported the high friction properties in the ZDDP solution for various types of sliding pairs, namely steel/steel, diamond-like carbon (DLC)/DLC, and steel/DLC. They used the sliding conjunctions of a ball on the disk reciprocating sliding tests [21]. Interestingly, they reported high friction in the ZDDP solution for various types of sliding materials on which the ZDDP forms tribofilms.…”

Impact of tribofilm on the anti-wear and friction-reduction properties of interfaces

“…Umer [25] reported that the nano-friction of the ZDDP tribofilm formed during the macro sliding test is higher than that of the no-worn steel surface. In addition, the high friction behavior of the ZDDP tribofilm has been consistently observed at the macroscale, irrespective of the sliding pair [18,26]. Kaisei Sato [27] utilized in situ Atomic Force Microscopy (AFM) to investigate the mechanism behind this high friction.…”