An experimental and analytical study of the effect of water and its tribochemistry on the tribocorrosive wear of boundary lubricated systems with ZDDP-containing oil (original) (raw)
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ZDDP and MoDTC interactions in boundary lubrication--The effect of temperature and ZDDP/MoDTC ratio
Tribology international, 2006
Tribofilms formed under boundary lubrication from ZDDP and MoDTC additives alone or in different ratios in the lubricant have been studied. The tribological performance is linked to the tribofilm properties and consequently to the lubricating conditions. Tribofilms are formed using a reciprocating pin-on-plate tribometer. Surface sensitive analytical techniques, such as energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS) have been used for tribofilm characterisation. The XPS peaks have been deconvoluted to characterise the species formed in the wear scar. The formation of species with different tribological properties, due to the decomposition of ZDDP and MoDTC molecules as a result of testing temperature, is shown. Surface analyses have shown that MoDTC decomposes, even in low-lubricant bulk temperature tests (30 1C), forming the same species as in high-lubricant bulk temperature tests (100 and 150 1C) but the tribofilms give different tribological performance. The effectiveness in friction reduction is shown to depend on the ratio between what are defined as high-and low-friction species in the tribofilm. r address: A.Morina@leeds.ac.uk (A. Morina).
Tribology International, 2017
Water ingress into the lubricant as a contaminant affects performance leading to an alteration in wear, corrosion and fatigue behaviour of the tribological components especially in the rolling element bearings. The current study addresses the tribochemical phenomena involved in micropitting in tribocorrosion systems where different levels of dissolved-water are present in a model lubricant. In this study the effect of different temperatures, water concentrations and relative humidities have been investigated on micropitting under rolling/sliding contacts. The influence of free and dissolved water on tribocorrosive micropitting is clarified. The tribochemical change of the reaction films is studied using X-ray Photoelectron Spectroscopy (XPS) which confirmed that the (poly)phosphate chain length and tribofilm thickness are reduced with increased dissolved-water level. 1. Introduction Water is known as an insidious lubricant contaminant [1, 2]. Water can enter into the lubricant through several sources including a humid environment [2-5] by absorption and condensation, leakage from heat exchanger [2], by-product of chemical reactions [2], free-water [2, 6, 7], etc. Depending on the extent of water ingress in the oil, beyond or within the oil saturation level, water can exist as free-water or dissolved-water, respectively. The saturation level of a lubricant, representing its hygroscopicity, depends on the physiochemical characteristics of the base stock, additive package, environmental parameters (relative humidity and temperature) [8] and oil condition [9]. Free-water in the lubricant forms an emulsion which has an inferior load carrying capacity [10] leading to deficient lubricant performance.
Tribology International, 2017
Wear performance of any tribological system can be influenced in a complex way by water contamination. Water can be the cause of steel corrosion which, in turn, can accelerate wear. It can decompose the additives in the oil and create a more corrosive environment which leads to the higher wear in the system. A key novelty of this study is to investigate the effect of relative humidity and the tribochemical changes on the tribological performance and tribofilm characteristics of boundary lubricated systems by means of designing a humidity control system integrated to the Mini Traction Machine (MTM) and Spacer Layer Interferometry Method (SLIM) for the first time. The system is capable of simulating rolling-sliding conditions continuously where lubricant can be contaminated with water. This paper is the first part of a two-part study and the theoretical aspects of the work is the subject of the second part of this investigation. It was observed that humidity hinders the tribofilm formation, especially at higher values of relative humidity and lower temperatures and it can significantly affect the wear process. The correlation between tribofilm thickness, water concentration, temperature and wear of the system was studied. The experimental results suggest that the higher the humidity, the higher the wear of the system and it is more noticeable at lower temperatures where the tribofilm in thinner. The surface chemistry of zinc polyphosphates was investigated as a function of humidity.
TRIBOLOGICAL BEHAVIOUR OF ZDDP ANTI WEAR ADDITIVE WITH AND WITHOUT CONTAMINANTS
iaeme
Zinc DialkylDithiophosphatesare being used as anti-wear and anti-oxidant additive in lubricants since late 1950s. They are undoubtedly the most used anti-wear additives in the world right now. In this study, the role of Zinc DialkyldithioPhospahte (ZDDP) on the performance of lubricant has been investigated. A lubricant has been prepared from commercially available base oil by adding ZDDP. The role of base oil with and without ZDDP has been investigated with the help of a Tribotester. Tribological performance of this base oil, with and without ZDDP has been again evaluated by introducing sand particles in it. The results of this study are discussed in this work
Wear, 1984
It is well known that in many tribological situations antiwear additives act by reaction film formation on contacting surfaces. In the present paper we describe our observations on the reaction film formed with a zinc dialkyl dithiophosphate and the wear particles. Detailed structural and chemical information has been obtained by using optical microscopy, scanning electron microscopy, transmission electron microscopy and X-ray energy spectrometry. The results show a clear connection between the reaction film material and the nature of the wear particles present in the lubricant; both a highly dispersed phase system and a layered structure are present. The origin of the wear particles is discussed in terms of crack initiation mechanisms.
The mutual interaction between tribochemistry and lubrication: Interfacial mechanics of tribofilm
Tribology International
A new mechanism for the action of antiwear tribofilms is proposed. The antiwear action of ZDDP additive is believed to be mainly due to the formation of tribofilms that reduce wear by chemical action. In this study, a mixed lubrication model is developed and tribofilm growth integrated into this model to simulate the effects of tribofilms on lubrication. The dynamic evolution of the contacting surfaces due to plastic deformation, wear and tribofilm growth continuously change the lubrication characteristics inside the contact. It is observed that the growth of tribofilm roughens the contact and increase contact severity. It was found that this roughness increase also helps to entrain more lubricant, resulting in thicker lubricant films. Therefore, the plot of the evolution of film thickness ratio (h central (t)/R q (t)) shows that the lubrication regime is improved by the presence of tribofilm. Therefore, not only the chemical presence but the physical presence of the tribofilm on the surfaces also helps to improve contact performance by retaining more lubricant and improving the lubrication regime.