In-Situ Observation of the Effect of the Tribofilm Growth on Scuffing in Rolling-Sliding Contact

Abstract

General reductions in lubricant viscosities in many machine components mean that the role of lubricant additives in forming tribofilms has become increasingly important to provide adequate surface protection against scuffing. However, the relationship between scuffing and the formation and removal of tribofilms has not been systematically demonstrated. In this study, a step-sliding speed scuffing test based on contra-rotation using MTM-SLIM and ETM-SLIM has been employed to observe concurrently tribofilm thickness and the onset of scuffing. The initial sliding speed used was found to significantly affect scuffing performance since it determines the extent to which a tribofilm can form before critical sliding speed conditions are reached. In general, additives that formed thicker tribofilms, especially ZDDPs and triphenyl phosphate, gave effective protection against scuffing, though their protective tribofilms were progressively removed at higher sliding speeds, eventually resulting in scuffing. Graphical Abstract

Influence of PMA on the anti-scuffing properties of AW/EP additives

“…All tests were carried out at least twice to verify repeatability. Further detail and rationale of each of the three stages, running-in stage, test stage and rest stage are described in [19]. It should be noted that tests on GTL4 +ZDDP solution with an initial sliding speed of 1.0 m/s and above gave scuffing immediately after the test started, while those starting below 1.0 m/s did not scuff even up to a sliding speed of 5 m/s.…”

“…In a previous study by the authors, the influence of initial sliding speed stage was studied by starting the main step-speed test sequence at different sliding speeds [19]. Results showed that for additive-free PAO, the sliding speed at scuffing was largely independent of the initial sliding speed used.…”

“…In a recent paper by the authors it was shown that the additive zinc dialkyldithiophosphate (ZDDP), that contains both S and P, in addition to being very effective in controlling wear, could also prevent scuffing of a heavily-loaded rolling-sliding contact as present in many machine components [8]. However, it could only do this if it was able to form a protective tribofilm under relatively mild conditions before the contact was subjected to more severe conditions.…”

Scuffing failure analysis based on a multidisciplinary coupling model and experimental verification

“…The substrate materials will be exposed and massive surface wear as well as severe lubrication failure, like scuffing, may occur [12,27]. Therefore, scuffing failure under boundary lubrication is controlled by the nature and effectiveness of the tribofilms formed on the surface [28,29]. The time for the final breakdown of the protective tribofilm is inversely dependent on the applied load and it was shown that higher contact loads resulted in premature breakdown of the tribofilm [27].…”

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

“…They used a high-frequency reciprocating rig compared to the base oil between steel/steel pair. In addition, Ueda et al reported the high anti-scuffing effects and the low friction of ZDDP tribofilm for metal/metal direct contacts [20]. The condition incorporating step load tests using the steel/steel pair was employed.…”