Study On Electrical Contact Fretting Wear Mechanism Of Copper/Brass Under Different Suface Roughness And Oxidation Conditons

The electrical connector has the function of connecting or disconnecting the current,and is an indispensable part of various electrical circuits.Due to the influence of the external environment and working conditions,the fretting wear of electrical connector contacts under the live state has become a key bottleneck affecting the reliability,stability,accuracy and service life of electrical connectors.In this paper,a series of electrical contact fretting wear tests were carried out around red copper/brass（face/point contact mode）using the self-developed electric contact fretting wear test equipment.Special attention is paid to such characteristic parameters as friction coefficient,friction dissipation energy,tangential stiffness,wear volume,contact resistance,micro morphology and composition of wear scar.By simulating the actual working conditions,the evolution laws of the chemical and physical processes of contact surface oxidation,adhesion（transfer）,stacking,delamination,etc.under different oxidation conditions and surface roughness in fretting wear of electrical contact materials were systematically studied,and the internal relationship and mechanism between fretting damage,oxidation characteristics and contact resistance were further revealed.The research results not only clarify the main factors of electrical contact failure of copper but also enrich and improve the oxidation mechanism of,providing a theoretical support for promoting the extensive application of copper-based materials in the field of electrical contact.The main conclusions are as follows:1.Effect of surface roughness on fretting wear behavior of electrical contact（1）The electrical contact characteristics are positively correlated with the material surface roughness（R_a）,that is,the greater the Ra,the better the electrical contact performance.The test results show that when R_a=0.09μm-3.09μm,the electrical contact life increases with the increase of R_a.（2）Third bodies such as debris on rough surfaces are easy to be removed by local large stress of convex points or distributed in valleys.The contact points are free of foreign matters and keep low contact resistance;The smooth surface of the third body is easy to accumulate and adhere to the wear area,blocking the direct contact between the matrix,resulting in increased contact resistance.（3）Different initial surface roughness achieves different balance roughness due to the difference of wear conditions,and balance roughness determines the physical morphology of wear surface.2.Effect mechanism of oxidation treatment temperature on electrical contact performance（1）The influence of oxidation products on wear characteristics under different oxidation treatment temperatures:at room temperature,there are less oxides on copper surface,and the wear resistance is the worst;After oxidation treatment at 200℃,a thin Cu₂O film with hole structure was formed on the copper surface,and the wear resistance was the best;After oxidation treatment at 400℃,a thick Cu O film is formed on the surface of copper,which is easy to peel off,but the next layer is Cu₂O,with medium wear resistance.Research shows that the oxidation film containing Cu⁺has the function of reducing wear and lubrication.（2）The difference in composition and structure of oxide film under different oxidation treatment temperatures leads to different wear resistance during electrical contact fretting wear,which affects the morphology and distribution of the third body:after room temperature oxidation treatment,the surface is seriously damaged,and the third body mainly adheres（transfers）and accumulates;After oxidation at 200℃,the surface is slightly damaged,and the wear debris generated by fretting is less and evenly distributed;After oxidation at 400℃,the surface oxides mainly peel off in the form of layers.Adhesion（transfer）,stacking and peeling will cause the increase of contact resistance.Therefore,the electrical contact fretting wear performance is the best after oxidation at 200℃.3.Electrical contact fretting wear performance under different oxygen atmospheres（1）In the complete slip zone,according to the magnitude of friction energy dissipation,the damage severity is in the order of 10%O₂>30%O₂>20%O₂,and the friction coefficient is in the order of 30%O₂>10%O₂>20%O₂.Under the same displacement amplitude,the instantaneous peak value of contact resistance is the largest and fluctuates violently in 30%O₂environment,and the instantaneous peak value of contact resistance is the smallest in 20%O₂environment,and the electrical contact life is the longest.（2）The relative content of O element on the wear area:30%O₂>10%O₂>20%O₂,indicating that the oxidation degree is not linear with the oxygen content in the environment,and the wear will aggravate the oxidation.Therefore,10%O₂ is more serious than 20%O₂.The difference of contact resistance caused by the different morphology and distribution of the third bodies such as oxides and wear debris in the wear zone:block peeling under 10%O₂environment,a small amount of adhesion and accumulation under 20%O₂ environment,aggregation in 30%O₂ environment.The electrical contact performance is 20%O₂ best,10%O₂ second,and 30%O₂ worst.The results show that oxygen content and degree of wear in the environment,together,dominate the fretting wear performance of copper-based materials.4.Electrical contact failure mechanism of copper-based materials in several surface interface states（1）It is found that the tangential stiffness of copper-based materials is large and the electrical contact performance is good in the partial slip region;In the complete slip region,the tangential stiffness is small,and the electrical contact performance is poor.The tangential stiffness of slip zone can be used to judge the change of friction force,compare the degree of surface damage,and evaluate the electrical contact performance.（2）Different oxidation conditions（oxygen containing atmosphere,oxidation treatment temperature）and initial surface morphology lead to different fretting damage and deformation degree,which leads to the difference of wear debris morphology.Peeling,stacking and agglomeration form a large third body,which increases the contact resistance and even opens the circuit,leading to the electrical contact failure of copper-based materials.Therefore,the direct reason that affects the electrical contact performance under several surface interface states is the physical factors such as the shape,size and distribution of the third body.