Use of FIB to Study ZDDP Tribofilms

Dawczyk, Joanna; Ware, Ecaterina; Ardakani, M.G.; Russo, Joe; Spikes, H. A.

doi:10.1007/s11249-018-1114-y

Cited by 19 publications

(20 citation statements)

References 27 publications

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“…To investigate tribofilm crystallinity using transmission electron microscopy (TEM), lamellae of ZDDP tribofilm cross sections were extracted using a Helios 600 NanoLab Focused Ion Beam (FIB) instrument. Before this, the ZDDP tribofilms were coated with a 50-70-nm gold layer to protect them from damage during gallium ion milling [14]. Table 3 shows the conditions used in the FIB process.…”

Section: Tribofilm Crystallinitymentioning

confidence: 99%

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On the Crystallinity and Durability of ZDDP Tribofilm

2019

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The current trend for using lower-viscosity lubricants with the aim of improving fuel economy of mechanical systems means that machine components are required to operate for longer periods in thin oil film, mixed lubrication conditions, where the risk of surface damage is increased. Consequently, the performance and durability of the tribofilms formed by antiwear additives, and in particular zinc dialkyldithiophosphate (ZDDP), the main antiwear oil additive used in engine oils, has become an increasingly important issue. In this paper, it is confirmed that ZDDP tribofilms are initially relatively easily removed by rubbing but that they become more durable during prolonged rubbing. FIB-TEM analyses at different stages of tribofilm formation show that during the early stages of rubbing only the tribofilm close to the steel substrate is nanocrystalline, while the outer region is amorphous and easily removed. However, after prolonged rubbing all regions of the tribofilm become nanocrystalline and able to withstand rubbing in base oil without being removed. XPS analysis shows that after extended rubbing the outermost polyphosphate structures change from longer-chain structures such as metaphosphate and polyphosphate to shorter-chain structures including orthophosphate. This depolymerization of ZDDP tribofilm from long-to short-chain phosphate and consequent nanocrystallization are driven by heat and shear stress. EDX analysis shows that this conversion is promoted by diffusion of Fe cation into the bulk of the tribofilm. The finding that ZDDP tribofilms evolve during rubbing from a weaker amorphous structure to a more durable nanocrystalline one has important implications in terms of the behaviour of ZDDPs at low concentrations, on non-metallic surfaces and at very high contact pressures, as well as for the development of ZDDP tribofilm, friction and wear models.

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Section: Tribofilm Crystallinitymentioning

confidence: 99%

“…Most previous research has found or assumed that ZDDP tribofilms consist primarily of amorphous and glassy zinc phosphates. However, using high-resolution FIB-TEM it has recently been shown that ZDDP tribofilms may have both nanocrystalline and amorphous structures [14].…”

Section: Introductionmentioning

confidence: 99%

On the Crystallinity and Durability of ZDDP Tribofilm

2019

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“…Tribofilm analysis is typically performed ex situ and ex post. For insight at the atomic and molecular level, X-ray photoelectron spectroscopy, X-ray absorption near-edge structure spectroscopy, time-of-flight secondary ion mass spectroscopy, and transmission electron microscopy, among others, are common practice (see, for example, [27][28][29][30]). Such ex situ studies have recently been complemented by in situ observations of tribofilm growth at the macroscale by integrating a tribometer in a synchrotron X-ray absorption spectrometer [31,32] and at the nanoscale through use of an atomic force microscope to both mechanically drive film growth and image that growth [33].…”

Section: Introductionmentioning

confidence: 99%

Tribochemistry: A Review of Reactive Molecular Dynamics Simulations

2020

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Tribochemistry, the study of chemical reactions in tribological interfaces, plays a critical role in determining friction and wear behavior. One method researchers have used to explore tribochemistry is “reactive” molecular dynamics simulation based on empirical models that capture the formation and breaking of chemical bonds. This review summarizes studies that have been performed using reactive molecular dynamics simulations of chemical reactions in sliding contacts. Topics include shear-driven reactions between and within solid surfaces, between solid surfaces and lubricating fluids, and within lubricating fluids. The review concludes with a perspective on the contributions of reactive molecular dynamics simulations to the current understanding of tribochemistry, as well as opportunities for this approach going forward.

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“…18 shows a magnified image of part of the film. These indicate that all of the film has a nanocrystalline structure, as also seen with the ZDDP film prior to rubbing in OFM solution [34]. EDX analysis of the FIB wafer shows that the film is comprised predominantly of O, P and Zn with some sulphur in the 30-nm closest to the steel substrate but none further away from the steel surface [37].…”

Section: Film Compositionmentioning

confidence: 94%

“…TEM was employed to investigate the structure of the ZDDP film and EDX to map the elemental composition of the lamellae. The process of TEM specimen preparation is fully described in [34].…”

Section: Focused Ion Beam (Fib)-transmission Electron Microscopy (Tem)mentioning

confidence: 99%

Ethoxylated Amine Friction Modifiers and ZDDP

2019

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The influence of a series of Ethomeens (ethoxylated alkylamine organic friction modifiers) on the durability and friction of tribofilms formed by a commercial blend of primary and secondary ZDDP in sliding/rolling contact has been studied. When pre-formed ZDDP tribofilms are rubbed in Ethomeen solution, boundary friction is reduced and some of the ZDDP film is removed. Ethomeens having just two ethoxy groups give lower boundary friction on ZDDP than those with 15 ethoxy groups, but result in much greater removal of the tribofilm itself. Based on XANES analysis, the film removed by both types of Ethomeen consists primarily of nanocrystalline orthophosphate. The level of boundary friction and its dependence on sliding speed, coupled with the dimensions of the molecules, suggests that the Ethomeens with two ethoxy groups may form quite closely packed vertical monolayers on ZDDP tribofilm surfaces, but that those with fifteen ethoxy groups cannot be close packed; yet they still reduce boundary friction significantly. The study shows that selection of an appropriate aminic friction modifier for use with ZDDP is a balance between its ability to reduce friction and its potentially harmful effect on a ZDDP tribofilm.

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Use of FIB to Study ZDDP Tribofilms

Cited by 19 publications

References 27 publications

On the Crystallinity and Durability of ZDDP Tribofilm

On the Crystallinity and Durability of ZDDP Tribofilm

Tribochemistry: A Review of Reactive Molecular Dynamics Simulations

Ethoxylated Amine Friction Modifiers and ZDDP

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