Study Of The Effect Of Surface Topography On Tribology Behavior Of PTFE/nano-SiO₂ Composites

Solar energy,as a clean energy,is widely used in social activities and production.Disc solar thermal power generation is the most efficient thermal power generation technology.Stirling engine,the core part of disc solar thermal power generation system,is a closed cycle reciprocating engine with external heating,which has the advantages of high thermal efficiency,low noise and little pollution.However,due to the influence of severe working conditions such as high temperature,high pressure and alternating load,the piston ring is easy to wear,resulting in the leakage of working medium,reducing the efficiency of solar thermal power generation.Therefore,improving the wear resistance of piston ring has become an urgent problem to be solved.Aiming at the problem that the piston ring of Stirling engine is easy to wear under the harsh working condition,the friction pair composed of the piston ring and the cylinder is taken as the research object,and the relevant work on the influence of the surface topography on the friction and wear characteristics of the sealing material is carried out.Simplifying the friction between piston ring and cylinder to"pin-disc"reciprocating friction model,the effects of dual surface topography（surface roughness and texture）on the friction and wear behavior,friction transfer characteristics,transfer film morphology,and contact surface stress distribution of nano-filled modified PTFE composites are investigated under dry friction conditions.In this thesis,the PTFE composite material modified by nano-SiO₂ is prepared by cold pressing and hot sintering process.The tribological characteristics between PTFE composite material and dual steel disc（GCr15）with different surface topography are evaluated by LSR-2M reciprocating friction and wear tester.The morphologies and chemical composition of the transfer film and the abrasive particles are characterized by optical microscopy（OM）,scanning electron microscopy（SEM）and energy dispersive spectrometer（EDS）.The contact model of friction pair is established by finite element method（FEM）.Combined with theoretical calculation,the friction and wear mechanism of PTFE composite is investigated from the microscopic level.The main conclusions are drawn from above investigation as following:（1）The friction coefficient（COF）of PTFE composite increases with the increase of dual surface roughness,and the wear volume matches the dual surface roughness.The reasonably matched friction pair can effectively promote the friction transfer of the composite,and form a transfer film with high coverage,uniform,continuous and consistent with the sliding direction on the dual surface,which is beneficial to reduce the friction of the material wear.（2）The texturing surface increases the COF and reduces the wear rate of the material.When the pin（99.5wt.%PTFE+0.5wt.%nano-SiO₂）slides on the surface of A₂B₄C₁ texture,the COF increases by 5.6%,and the wear rate decreases by 64.3%compared with the smooth pair,which significantly improves the wear resistance of the material.（3）The stress distribution of the textured surface is more uniform than the smooth surface,which increases with the increase of groove width and friction angle,and decreases with the increase of groove spacing.Summarily,reasonable texture parameters and friction angle can effectively improve the stress distribution of the contact surface.In summary,under dry friction conditions,surface texture can effectively improve the wear resistance of sealing materials,increase the service life of seals,enhance the sealing performance of Stirling engine,and thereby promote the thermal power generation efficiency of disc solar energy,increase the utilization rate of solar energy,which is of great significance for the efficient use of clean energy.