Tribological Performances Of Si₃N₄-PTFE-EP Self-lubricating Composites Prepared By High Pressure Compression Molding

The ceramic-polymer composites combine the advantages of high ceramic strength and excellent polymer lubricity,which significantly improves the mechanical properties and tribological properties of single material.It has multiple design spaces to meet the special needs of tribological engineering applications.The preparation of existing ceramic matrix composites usually relies on high temperature,while polymer matrix composites are just limited by high temperature.Therefore,high temperature is the key problem that restricts the preparation of ceramic-polymer composites in arbitrary proportion.In this paper,the high pressure molding process is proposed to reduce the dependence of ceramic materials on high temperature and realize the densification of ceramic-polymer composites.A low friction and wear Si₃N₄-PTFE-EP?ceramic-polymer?self-lubricating composite material was prepared with silicon nitride?Si₃N₄?and polytetrafluoroethylene?PTFE?as the matrix phase,and an appropriate amount of epoxy resin?EP?was added.The physical and chemical properties of Si₃N₄-PTFE-EP self-lubricating composites were analyzed by the modern characterization technology.And the tribological performances and mechanisms of Si₃N₄-PTFE-EP self-lubricating composites were explored by the ball-disc friction and wear tester and white light confocal microscope.The preparation process and ratio design of Si₃N₄-PTFE-EP self-lubricating composite with Si₃N₄ particle size of 1?3?m were studied by tribological experiments.The reasonable preparation parameters were:the binder was EP,the dosage was 0.15g,the high-pressure pressure was 5GPa and the pressure holding time was 20min.The wear rate of 70Si₃N₄-30PTFE-EP composite reached 10^-7mm³?Nm?^-1,and the friction coefficient of 30Si₃N₄-70PTFE-EP composite was about 0.06.The wear forms of Si₃N₄-PTFE-EP composites gradually changed from abrasive wear to adhesive wear with increasing PTFE mass fraction,and fatigue wear always existed.By studying the tribological properties and particle dispersion of Si₃N₄-PTFE-EP composites with particle sizes of 20nm,100nm,500nm,1?3?m and 10?m,it was found that hydrolysis treatment of 20nm Si₃N₄ could improve the grafting rates of silane coupling agent KH560 and the dispersions of 20nm Si₃N₄ in organic solvents.Furthermore,the grafting rates decreased with the increase of Si₃N₄ particle size.The tribological behaviors of 70M-Si₃N₄-30PTFE-EP and 30M-Si₃N₄-70PTFE-EP composites with different Si₃N₄ particle sizes after surface modification?M-Si₃N₄?are slightly different.The difference is that the smaller the Si₃N₄ particle size,the easier it is to form a rolling effect between the 70M-Si₃N₄-30PTFE-EP composite and the counterpart ball,which has a certain effect on reducing the friction coefficient.Generally speaking,the number of Si₃N₄ particles peeled off during the friction process gradually decreases with the increase of Si₃N₄ particle size,thus showing better tribological performance.In particular,the 70Si₃N₄-30PTFE-EP and30Si₃N₄-70PTFE-EP composites of Si₃N₄ particle size of 10?m have the best tribological properties under load of 5N and sliding speed of 3cm/s.