Origin of the tribofilm from MoS_(2) nanoparticle oil additives: Dependence of oil film thickness on particle aggregation in rolling point contact  

作　　者：Hongxing WU Liping WANG Guangneng DONG 

机构地区：[1]State Key Laboratory of Solidification Processing,Center of Advanced Lubrication and Seal Materials,Northwestern Polytechnical University,Xi’an 710072,China [2]Petro China Lanzhou Lubricating Oil R&D Institute,Lanzhou 730060,China [3]Key Laboratory of Education Ministry for Modern Design and Rotor-Bearing System,Xi'an Jiaotong University,Xi'an 710049,China

出　　处：《Friction》2021年第6期1436-1449,共14页摩擦（英文版）

基　　金：This work was supported by the Fundamental Research Funds for the Central Universities(31020195C001,3102019QD0413,3102019ZD0403);The suggestions from Q.Jane Wang at Northwestern University are appreciated.Hongxing Wu also acknowledges the scholarship support from the China Scholarship Council(CSC,No.201606280181).

摘　　要：The lubrication effectiveness of MoS_(2) nanoparticles as an oil additive remains unclear,restricting its application in industry to reduce friction.The goal of this work was to explore the lubrication mechanism of MoS_(2) nanoparticles as an oil additive.In this study,the oil film thickness behaviors of MoS_(2) nanoparticles in poly-alpha olefin(PAO4)base oil,PAO4 with 3 wt%dispersant(polyisobutyleneamine succinimide,PIBS),and 0W20 engine oil were investigated using an elastohydrodynamic lubrication(EHL)testing machine.Following the EHL tests,the flow patterns around the contact area and the tribofilm covering rate on contact area were studied using optical microscopy to understand the lubrication mechanism.The results indicate that both the dispersant and nanoparticle aggregation significantly affected the oil film thickness.The expected oil film thickness increase in the case of 0.1 wt%MoS_(2) in PAO4 base oil was obtained,with an increase from 30 to 60 nm over 15 min at a velocity of 50 mm/s.Flow pattern analysis revealed the formation of particle aggregation on the rolling path when lubricated with 0.1 wt%MoS_(2),which is associated with a tribofilm coverage rate of 41.5%on the contact area.However,an oil film thickness increase and particle aggregation were not observed during the tests with 0.1 wt%MoS_(2) blended with 3 wt%PIBS as the dispersant in PAO4 base oil,and for 0.75 wt%MoS_(2) in 0W20 engine oil.The results suggest that nanoparticles responsible for tribofilm formation originated from aggregates,but not the well-dispersed nanoparticles in point contact.This understanding should aid the advancement of novel lubricant additive design.

关 键 词：nanoparticle lubrication oil film thickness flow pattern particle aggregation 

分 类 号：TH117.22[机械工程—机械设计及理论] TB383.1[一般工业技术—材料科学与工程]