| Friction and wear occur in almost all relative moving part,and it is often the main cause of energy loss,system failure,and so on.Because of its good self-lubricity and electrical conductivity,carbon materials are often used with metal as the primary choice for power transmission of moving parts,and are widely used in rail transportation,aerospace,power systems and other fields.Nowadays,in the pursuit of higher speed and larger capacity transmission in all walks of life,the wear of sliding electrical contact pairs becomes more and more serious,and the security and stability of the system is greatly challenged.For carboncopper(C-Cu)sliding electrical contact pairs,the physical and chemical properties of interface materials determine the characteristics of the current carrying friction and wear,and the interface oxidation is the core factor for the performance transformation of the interface material.On the one hand,the interface oxide film is an important component of boundary lubrication,which can reduce the mechanical damage of the system.On the other hand,the oxide film hinders the transmission of current and aggravates electrical damage such as arc erosion.In addition,due to the lack of the lubrication and isolation of the oxide film,the interface roughness is greatly improved,the effective contact spots used to conduct current are reduced,and the good electrical contact performance is also difficult to maintain.At present,the laws of interfacial oxidation of C-Cu sliding electrical contact pairs and the complex competition mechanism of interfacial oxidation on the influence of electrical contact properties and tribological properties are not clear.The relevant work is urgently needed.The recovery of single discharge energy at large current is related to the oxidation of the carbon materials.Therefore,this paper focuses on the oxidation of the C-Cu contact interface during current-carrying friction.Based on the tribology and electrical contact theory,the variation of interfacial oxidation with temperature and oxygen content was studied.The correlation mechanism between interfacial oxidation and electrical contact performance was proved.The competitive mechanism of interfacial oxidation in the damage of the contact pairs was analyzed.And finally,a wear reduction method based on interfacial oxidation regulation by the magnetic field was proposed.Firstly,based on the control system of the interface temperature,the variation of the contact resistance,discharge frequency/energy,friction coefficient,wear loss,surface morphology and interface chemical composition with interface temperature were analyzed.The interfacial oxidation characteristics at high temperature and its influence on electrical and tribological properties of C-Cu contact pairs were investigated.It is found that the effect of interface temperature on contact resistance is the result of competition between intensified interfacial oxidation and material softening.The friction coefficient decreases with the interface temperature,which is related to the decrease of friction work caused by oxidation and material softening during micro-cutting.The high interface temperature can inhibit the wear,which is mainly reflected in the inhibition of delamination wear and discharge erosion.However,the severe oxidation of carbon materials under high current and high temperature will lead to severe damage of carbon slider.Secondly,based on the atmosphere control system,the dynamic fluctuation characteristics of contact resistance and friction coefficient are analyzed by adjusting the oxygen content and air pressure.The relationship between wear loss and surface morphology and interface material composition was studied.The evolution of electrical contact characteristics of C-Cu contact pairs in pantograph and overhead contact wire system under low oxygen and low pressure was analyzed.The abnormal wear mechanism of carbon sliderr is revealed.It is found that the fluctuation of contact resistance is more obvious at low pressure,which is related to the deterioration of self-lubricating performance of carbon materials and the higher dependence of the steady contact state on the interfacial oxide layer.It is found that interfacial oxidation is highly correlated with interfacial debris.Low pressure and low oxygen lead to higher friction coefficient,but the friction coefficient undergoes a significant run-in stage at low pressure,which is related to the time needed for the formation of a lubricated and stable oxide layer at the interface.The abnormal wear mechanism of carbon slider under low pressure and low oxygen is the severe adhesion wear and discharge erosion caused by the decrease of interface lubricity.Finally,the vertical constant magnetic field was used to regulate the oxidation characteristics of the carbon-copper interface,and the variation rules of friction coefficient,wear quantity,contact resistance,discharge energy and current-carrying efficiency with the intensity and polarity of the magnetic field were analyzed.The influence mechanism of magnetic field on the friction and wear performance of C-Cu contact pair with current load was revealed.The results show that the magnetic field promotes the growth of oxide film on the contact interface and accelerates the removal of hard abrasive debris from the friction interface under current loading condition,and the effects of friction and wear reduction are obvious.Within a certain range of magnetic induction intensity,the friction coefficient of CCu contacts decreases by 15.14%,and the wear loss of carbon slider decreases by 89.83%. |
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