Synergetic effect of metal sulfides and ZDDP on the lubricating performance of a PAO oil

PRIETO, G.; DENNEHY, J.; TUCKART, W. R.

Beijing

Conferencia; 10th Global Conference on Materials Science and Engineering; 2021

Bosen Academic Conference Services Ltd.

The current trend of increasing the power density of machinery and equipment implies a challenge for lubricating oils, mainly due to the increase in operating temperatures and contact stresses. To address this scenario, lubricating oils are additivated with compounds that protect the surfaces from direct metal-to-metal contact in boundary lubrication regimes. For this purpose, additives such as zinc dialkyldithiophosphate (ZDDP) have been traditionally used, thanks to their ability to form protective films on steel surfaces. Similarly, metal sulfides such as MoS2 and Bi2S3 can effectively reduce friction and wear by forming chemically bound layers to steel substrates. However, the joint action of metal sulfides and ZDDP has not been yet fully characterized.In this work, a PAO ISO VG 6 base oil was additivated with different combinations of ZDDP, MoS2, and Bi2S3. The formulated oils were tested using a Reichert test (Contact stress: 1.2 GPa; sliding speed: 1.7 m/s; sliding distance: 408 m). Both the fixed cylinder and the rotating ring in the Reichert test were made of AISI 52100 steel with a hardness of 62 HRC. During the tests, the friction force was continuously measured and the wear volume was determined using laser confocal microscopy. Wear scars were also characterized by employing Raman spectroscopy and SEM-EDS microscopy. The results have shown a strong synergetic effect between ZDDP and both metal sulfides, with a reduction in the wear volume ranging between 31 to 68% in comparison to each of the compounds tested separately.