Tribofilm Formation, Friction and Wear-Reducing Properties of Some Phosphorus-Containing Antiwear Additives
- PDF / 5,183,907 Bytes
- 24 Pages / 595.276 x 790.866 pts Page_size
- 6 Downloads / 161 Views
ORIGINAL PAPER
Tribofilm Formation, Friction and Wear‑Reducing Properties of Some Phosphorus‑Containing Antiwear Additives Juli Felicio Luiz1 · Hugh Spikes1 Received: 22 April 2020 / Accepted: 21 June 2020 © The Author(s) 2020
Abstract The film-forming, friction and wear properties of a range of model and commercial ashless P and P/S antiwear additives have been studied. A method has been developed for removing the tribofilms formed by such additives in order to effectively quantify mild wear. In general the P/S additives studied formed thinner tribofilms but gave lower wear than the S-free P ones. In extended wear tests, three P/S additives gave wear as low, or lower, than a primary zinc dialkyldithiophosphate (ZDDP). For almost all lubricants tested the wear rate measured in short tests was considerably higher than that in long tests due to the greater contribution of running-in wear in the former. This highlights the importance of basing antiwear additive choice on reasonably long tests, where running-in becomes only a small component of the wear measured. It has been found that for both P and P/S ashless additives the addition of oil-soluble metal compounds based on Ti and Ca boosts tribofilm formation and can lead to very thick films, comparable to those formed by ZDDP. However, this thick film formation tends to be accompanied by an increase in mixed friction and also does not appear to reduce wear but may even increase it. Keywords Antiwear additive · Ashless additive · SAPS · Friction · Wear · Tribofilm
1 Introduction Metal-free organophosphorus-containing compounds have been used as antiwear additives in aviation, transmission and hydraulic oils for many years. However, there is now considerable interest in employing them in crankcase engine oils, to replace, wholly or in part the currently used antiwear additive zinc dialkyldithiophosphate (ZDDP). This paper describes a study of the tribofilm-forming, friction and wear properties of a range of phosphorus- and phosphorus/ sulphur-based additives in rolling-sliding contact conditions. In all cases their performance is compared to that of a conventional ZDDP additive. The aims of the study are twofold: firstly to assess the extent to which these additives can match the wear-reducing performance of ZDDPs in rolling-sliding contacts such as are present in sliding cam-follower components, and secondly to learn more about the nature of the tribofilms formed by these metal-free, ashless additives and thus how they
* Hugh Spikes [email protected] 1
control wear. It should be noted that there is interest not just in seeking replacements for ZDDP but also to further understand the film formation, friction and wear performance of phosphorus-based antiwear additives in transmission oils.
2 Background 2.1 ZDDPs Zinc dialkyldithiophosphates (ZDDPs) have been the principal antiwear additives in crankcase engine oils for the last eighty years [1]. They are extremely versatile and cost-effective additives, exhibiting antioxidant, corrosion inhibitor and
Data Loading...
