Study On Friction And Wear Properties Of Copper-Graphite Lamellar Materials

Copper based friction material is a key material used for making rail transit vehicle brake.which is composed of Cu,Fe,SiO2,graphite,etc.Thanks to the synergetic effects of these components with different properties,the goal to get desired COF(coefficient of friction)and wear resistant properties is achieved.However,it is not beneficial to analyze the influence that a specific component have on the friction and wear properties due to the interaction between the components.To clarify the damage mechanism of different components in the friction process,a combined lamellar method is employed in this article,where Cu serving as the base material and graphite as the lubricant element.By conducting tests at constant speed,the formation process of Cu,graphite components and their third body are studied,at the same time,the COF is tested under different conditions.The results shows that:During the friction process,the formation of third body is different which Cu and graphite components involved in wear.Cu component forming massive third body by adhesion and plowing,it has good flowability and scalability,covering the surface of graphite to reduce the content of graphite component that actual participate in friction.Graphite component producing fine particles entrained in the third body of Cu by crushing,and with the flow of the third body,covering the surface friction,lubricates and isolation.For the lamellar material composed of copper and graphite,the friction changes and stability of COF have intimate relationship with the direction.When the friction is parallel to the plies,the COF and fluctuation degree is high,moreover it is long distance to reach a steady stage of friction.It is all due to the small degree of mixing and the adhesion of Cu third body increases both COF and the degree of fluctuation.When it comes to perpendicularconditions,the COF and fluctuation degree is low and easy access to the stable phase,which is due to the dispersion of graphite third body serves to decrease COF and increase stability.The impact of friction time to Cu and graphite lamellar material associated with the friction speed.When the speed is relative low,COF keeps increasing due to sufficient ploughing of hard abrasive with friction time.Whereas,the increasing COF is mainly caused by adhesion between the metals under high speed conditions.Meanwhile,the lubricity and thermal conductivity of graphite decrease the friction heat on the interface and heat lose,which defer adhesive wear.Since the content of graphite play an obvious role in the shape,homogeneity,continuity of the third body on the friction surface.With the increasing of content of graphite,On the one hand,more graphite wear occurs and participate in the formation of the third body,thus increasing the thickness of the third body is continuous and more compact;on the other hand,a third layer containing a large amount of graphite reduce the plastic deformed of Cu substrate driven by the external force,reducing the adhesion between metal matrix and the discs,so that plowing and adhesion phenomenon remission.