Study On Tribological Properties Of PI Composites Filled With Two Fillers(PTFE/ACF)

Polyimide(PI),which has kinds of advantages,such as high and low temperature resistance,high mechanical strength,good radiation resistance,excellent dielectric properties,strong creep resistant ability and chemical stability and so on,has been widely used in the automotive,electronics,aerospace and other fields.However,its poor wear resistance and large friction coefficient limit its further application.In order to overcome the defects,PI composites are often prepared to improve its tribological properties through filling different additives into pure PI.The acquired PI composites can be used as tribological materials with high quality.In this paper,polyimide composites filled with polytetrafluoroethylene(PTFE)and activated carbon fiber(ACF)were prepared by hot compression molding process.The molding pressure,molding temperature,holding time,PTFE content and ACF content were taken as the main factors and each factor was set three levels.The mechanical property was set as the evaluation criteria with the method of orthogonal experiment to determine the optimal combination of the best hot pressing molding parameters to prepare PI composites.The mechanical properties of PI composites was tested and the influence of PTFE content and ACF content on the mechanical and tribological properties of PI composites were analyzed.Three-dimensional white light scanner and the scanning electron microscope were carried out to observe the microstructure of cross section and worn surface of PI composites to study its friction and wear mechanism.The orthogonal test and the tribological test of PI composites results showed that the best sintering process of the PI composites was molding temperature 360?,molding pressure 12.5MPa,50 min for thermal insulation and pressure,and then reduced to room temperature.PI composites filled with PTFE and ACF could significantly decrease the friction coefficient of PI composites.The composite filled with 20%PTFE,10%ACF had the minimum friction coefficient,about 1/4 that of pure PI.It showed that PTFE and ACF had obvious friction reduction effect.The mechanical properties and wear resistance of PI composites were both weakened with the increasing content of PTFE and ACF.It was analyzed that the low mechanical properties of PTFE reduced the strength of polyimide and the bonding strength between ACF and the matrix material decreased with the increasing content of ACF.The proper amount of PTFE and ACF can greatly improve the wear resistance of the composites and the composites with 15%PTFE,10%ACF had the best wear resistance,about 1/4 that of pure PI.It was concluded that PTFE was beneficial to the combination of ACF and PI because of their synergistic effect.The results also showed that the main wear mechanism of pure polyimide was adhesive wear,and the wear mechanism of PI composites were mainly slight abrasive wear through analyzing the surface morphology.