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running-in process of Si-SiO_(x)/SiO_(2)pair at nanoscale-Sharp drops in friction and wear rate during initial cycles

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Friction 2013年第1期1卷 81-91页

作者： Lei CHEN Seong HKIM Xiaodong WANG Linmao QIAN Tribology Research Institute National Traction Power LaboratorySouthwest Jiaotong UniversityChengdu 610031China Department of Chemical Engineering The Pennsylvania State UniversityUniversity ParkPennsylvania 16802USA

Using an atomic force microscope,the running-in process of a single crystalline silicon wafer coated with native oxide layer(Si-SiO_(x))against a SiO_(2)microsphere was investigated under various normal loads and displacement amplitudes in ambient air.As the number of sliding cycles increased,both the friction force Ft of the Si-SiO_(x)/SiO_(2)pair and the wear rate of the silicon surface showed sharp drops during the initial 50 cycles and then leveled off in the remaining cycles.The sharp drop in Ft appeared to be induced mainly by the reduction of adhesion-related interfacial force between the Si-SiO_(x)/SiO_(2)pair.During the running-in process,the contact area of the Si-SiO_(x)/SiO_(2)pair might become hydrophobic due to removal of the hydrophilic oxide layer on the silicon surface and the surface change of the SiO_(2)tip,which caused the reduction of friction force and the wear rate of the Si-SiO_(x)/SiO_(2)pair.A phenomenological model is proposed to explain the running-in process of the Si-SiO_(x)/SiO_(2)pair in ambient air.The results may help us understand the mechanism of the running-in process of the Si-SiO_(x)/SiO_(2)pair at nanoscale and reduce wear failure in dynamic microelectromechanical systems(MEMS).

关键词： nanotribology friction nanowear running-in process silicon atomic force microscope

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Tribological behavior of co-textured cylinder liner-piston ring during running-in

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Friction 2022年第6期10卷 878-890页

作者： Chenwei MIAO Zhiwei GUO Chengqing YUAN School of Energy and Power Engineering Wuhan University of TechnologyWuhan 430063China Reliability Engineering Institute National Engineering Research Center for Water Transportation SafetyWuhan 430063China

The running-in of cylinder liner-piston rings(CLPRs)is the most important process that must be performed before a marine diesel engine can be operated.The quality of running-in directly affects the reliability of a CLPR.The surface texture of a CLPR has been proven to significantly affect its lubrication performance.In this study,the tribological behavior of a CLPR during running-in is investigated.Three types of surface textures are generated on the CLPR via laser processing:dimple texture on piston rings,groove texture on cylinder liners,and co-texture on both sides.Subsequently,a series of tests are performed on a slice tester.A load of 300 N(1.64 MPa) is applied,and two speeds(50 and 100 rpm)are adopted.The CLPR running-in quality is characterized based on three parameters,i.e.,the friction coefficient,contact resistance,and wear topography.Experimental results show that,compared with a non-textured surface,the three types of surface textures mentioned above improved the friction performance during running-in.The lubricant supply capacity of the dimple texture on the piston ring,as a mobile oil reservoir,is stronger than that of the groove texture on the cylinder liner serving as a static oil reservoir.By contrast,the wear resistance of the dimple texture,as a movable debris trap on the piston ring,is weaker than that of the groove texture on the cylinder liner,which serves as a static debris trap.It is demonstrated that the co-texture combines the advantages of dimples and groove textures.Compared with non-textured surfaces,the friction coefficient decreased the most at 100 rpm(44.5%),and the contact resistance improved the most at 50 rpm(352.9%).The coupling effect provides the surface with improved running-in quality by optimizing the tribological performance,particularly at the dead center.This study provides guidance for the tribological design and manufacturing of CLPR in marine diesel engines.

关键词： marine diesel engine cylinder liner-piston ring running-in process co-texture tribological performance

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Load and velocity boundaries of oil-based superlubricity using 1,3-diketone

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Friction 2023年第5期11卷 704-715页

作者： Yuyang YUAN Tobias AMANN Yuwen XU Yan ZHANG Jingfu CHEN Chenqing YUAN Ke LI School of Transportation and Logistics Engineering Wuhan University of TechnologyWuhan 430063China Reliability Engineering Institute National Engineering Research Center for Water Transport SafetyMOSTWuhan 430063China Fraunhofer Institute for Mechanics of Materials IWM Freiburg 79108Germany

The clarification of the critical operating conditions and the failure mechanism of superlubricity systems is of great significance for seeking appropriate applications in industry.In this work,the superlubricity region of 1,3-diketone oil EPND(1-(4-ethyl phenyl)nonane-1,3-dione)on steel surfaces was identified by performing a series of ball-on-disk rotation friction tests under various normal loads(3.5–64 N)and sliding velocities(100–600 mm/s).The result shows that beyond certain loads or velocities superlubricity failed to be reached due to the following negative effects:(1)Under low load(≤3.5 N),insufficient running-in could not ensure good asperity level conformity between the upper and lower surfaces;(2)the high load(≥64 N)produced excessive wear and big debris;(3)at low velocity(≤100 mm/s),the weak hydrodynamic effect and the generated debris deteriorated the lubrication performance;(4)at high velocity(≥500 mm/s),oil migration occurred and resulted in oil starvation.In order to expand the load and velocity boundaries of the superlubricity region,an optimized running-in method was proposed to avoid the above negative effects.By initially operating a running-in process under a suitable combination of load and velocity(e.g.16 N and 300 mm/s)and then switching to the target certain higher or lower load/velocity(e.g.100 N),the superlubricity region could break through its original boundaries.The result of this work suggests that oil-based superlubricity of 1,3-diketone is a promising solution to friction reduction under suitable operating conditions especially using a well-designed running-in strategy.

关键词： macroscopic superlubricity 1,3-diketone oil running-in process load and velocity boundaries

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