Current-carrying Friction Properties Of Graded Copper-carbon Composites

Based on the non-uniformity of the current-carrying friction damage surface,the spark plasma sintering process was used to prepare horizontally gradient coppercarbon composites and uniform copper-carbon composites,which were paired with QCr0.5 chrome bronze.The test was carried out on a self-made pin-disc mode highspeed current-carrying friction and wear tester HST-100.After the test,the morphology and the wear morphology of the friction surface were analyzed using the JSM-56l0 LV scanning electron microscopy,Nano Focus ? surf surface 3D topography instrument and LEICA DIM 8 inverted microscope.In addition,the composition of the friction surface was analyzed using an energy dispersive spectrometer to compare the current-carrying friction and wear performance of a horizontally gradient coppercarbon composite.The results show as follows:1.Horizontally graded copper-graphite composites based on the spark plasma sintering technology are tightly bonded between the different layers.The graphite in each layer is evenly distributed and the interface between copper and graphite is tightly combined.Moerover,compared with the uniform copper-carbon composites,the horizontally gradient copper-carbon composites have little difference of relative density,electrical conductivity and hardness.Thus,it is appropriate to serve as the current-carrying friction materials.2.Comparative investigation of the 5 wt.% C uniform copper-carbon composites,7.5 wt.% C uniform copper-carbon composites,10 wt.% C uniform copper-carbon composites and horizontally gradient copper-carbon composites is conducted.From the average friction coefficient,the average friction coefficient of the uniform coppercarbon composite material gradually decreases with the increase of the carbon conten t.Furthermore,the average friction coefficient of the horizontally gradient coppercarbon composite material is similar with the 10 wt.% C uniform copper-carbon composite.Additionally,from the aspect of wear rate,the wear rate of uniform coppercarbon composites gradually decreases with the increase of carbon content,the wear rate of horizontally gradient copper-carbon composites have little difference with the uniform copper-carbon with carbon content of 10 wt.% C.When it refers to the dynamic friction coefficient,the fluctuation of the dynamic friction coefficient of the uniform copper-carbon composites gradually decreases with increasing carbon content,and the gradient copper-carbon composites have the smallest fluctuations.From the perspective of electrical conductivity,the current-carrying efficiency and currentcarrying stability of the material increase with the increase of carbon content.The current-carrying efficiency and current-carrying stability of the graded copper-carbon composites are similar with a carbon content of 10% carbon composites.Based on the friction mechanism of the uniform copper-carbon composites,the arc erosion area is gradually decreased as the carbon content increases.Arc erosion not only exists in the exit area of the worn surface and the edge of the specimen,but also in other locations,and it is mainly strip-shaped arc erosion.The wear mechanism of the uniform coppercarbon composites is mainly mechanical wear and arc erosion.While the arc erosion area of the horizontally gradient copper-carbon composites is mainly concentrated in the friction and wear exit area,and its wear forms are mechanical wear and arc erosion,especially the mechanical wear.From the above analysis,it can be seen that the performance of the gradient copper-carbon composite material is the best.Its wear mechanism is mainly mechanical wear.Arc erosion exists only in the exit area.3.By studying the effect of the speed on the frictional properties of the currentcarrying copper-carbon composites,as the friction speed increases,the friction coefficient and wear rate tend to decrease first,and then increase but decrease at last.And when the friction speed is 50 m/s,the friction coefficient and wear rate of the horizontally gradient copper-carbon composite materials have reached the lowest value.From the current carrying performance of the material during the friction test,both the current-carrying efficiency and the current-carrying stability of the sample show a trend of increasing and then decreasing.The current-carrying efficiency is stable between 72% and 87%,and the current-carrying stability is between 72% and 78%.From the analysis of the wear mechanism,with the increase of the linear velocity of friction,the arc erosion area of the friction surface gradually decreases,and the position of the arc ablation gradually approaches the exit area.Furthermore,the types of the arc erosion are mainly melting and splashing.With the increase of friction speed,the roughness of the horizontally graded copper-carbon composites has not increased significantly.At the same time,the wear mode of the horizontally graded coppercarbon composites is mainly mechanical wear,and there is only a small degree of arc erosion.Gradient copper-carbon composite material possesses more obvious advantages of the high speed carrier flow friction and wear.In this paper,according to the current-carrying friction and wear tests,it is verified that the gradient copper-carbon composites can improve the current-carrying friction properties.It is significant to study the direction of material's current-carrying friction and erosion resistance,and it can enriches current-carrying tribology theory.