Preparation And Properties Of Gr/CuCr Composite Materials For Electrical Contact

CuCr(copper-chromium alloy)belongs to the immiscible alloy series.Cu Cr alloy with high Cr content(CuCr25~CuCr50)not only maintain the characteristics of high conductivity and high conductivity of Cu components,but also play the characteristics of high melting point,high hardness and oxygen affinity of Cr components.It is the preferred contact material for medium and high voltage circuit breakers and vacuum switches.With the development of national electric power and the increase of contact material market demand,CuCr contact material also has higher performance requirements.Therefore,to solve the problems of Cr phase coarseness,Cr phase segregation and meet the requirements of high conductivity and high strength of CuCr contact material has become a hot spot and trend in recent years.According to the requirements of the comprehensive properties of the electric contact materials for medium and high voltage vacuum switches,this paper aims at the problems of Cr phase coarseness and Cr phase segregation in CuCr alloy by mixing powder and constructing Cr@Gr(Cr@graphene).In the process of core-shell structure,graphene(Gr)was added as the reinforcing phase,and the Gr/CuCr composite was prepared by vacuum hot pressing sintering and vacuum arc melting.The effects of three chemical coating processes on the construction of Cr@Gr core-shell structure were investigated by means of metallographic microscope and scanning electron microscope analysis,and the influence of Gr and Cr@Gr core-shell structure on Cr refinement in Gr/CuCr composites was studied;the interface between CuCr and Gr observed by Transmission Electron Microscope;The electrical conductivity,Brinell hardness and arc erosion resistance of Gr/CuCr composite were tested by metal conductivity tester,Bloch hardness tester and self-made three-phase AC relay,and the effect of Gr on the hardness and conductivity of Gr/CuCr composite was studied.In this paper,we investigated the effects of dopamine(DA)surface self polymerization,KH550(silane coupling agent)electrostatic self-assembly and BSA(bovine serum albumin)self-assembly on the Cr@GO.The influence and law of core-shell structure show that dopamine coating is a relatively better coating process,and graphene oxide mass: chromium powder mass is 3:300 obtains complete coating Cr@GO Structure.The Cr@GO core-shell structure was reduced to obtain the Cr@Gr core-shell structure.The arc/smelting method was used to prepare the Gr/CuCr25 composite material.The Brinell hardness and electrical conductivity of the smelted CuCr25 Gr composites were 104.5 and 28.5Ms/m,which were 6.2% and 15.3% higher than CuCr25,respectively.The average particle size of the Cr phase is 6.9?m,which is 48.7% higher than the chromium phase size of 13.5?m in the CuCr25 alloy.This is because the Cr@Gr core-shell structure effectively suppresses the collision,condensation and abnormal growth of the Cr core due to diffusion and Brownian motion,and avoids the problems of Cr phase coarseness and segregation.Based on the Cr@Gr core-shell structure,Gr/CuCr25 composite material was prepared by vacuum hot pressing method.The average particle size of the Cr phase in the hot-pressed Gr/CuCr25 composite is 19.8?m,which is 23.7% higher than the CuCr25 refinement rate.This is because the Cr@Gr structure effectively reduces the agglomeration and cold welding of Cr particles in the initial powder mixing process,and hinders the growth of the sintering neck of the Cr particles during the sintering process,thereby refining the Cr phase.In addition,the Cr@Gr core-shell structure effectively improves the dispersion degree of graphene,avoids the agglomeration behavior of nano-graphene,reduces the density effect of Gr/CuCr25 composite materials,and improves the overall performance of Gr/CuCr25 composite materials.The Brinell hardness and electrical conductivity of the hot-pressed Gr/CuCr25 composites were 122.6 and 31.2Ms/m,which were 6.6% and 5.3% higher than CuCr25,respectively.Gr/CuCr25 composite was prepared by vacuum arc melting with different content of Gr.Compared with the microstructure and properties of CuCr25 without adding graphene,the Brinell hardness and conductivity of the contact material increased by 9.0% and 13.4% respectively when the content of graphene was 0.3wt%.When the amount of graphene is from 0.1wt.%-0.7wt.%,the particle size of Cr phase decreases.When the amount of graphene is 0.5wt.%,the average size of Cr phase reaches 25.9?m.Because graphene blocks the collision and coalescence of Cr nucleus,avoids the abnormal growth of Cr phase,refines the dendrite arm,reduces the secondary dendrite spacing,reduces the segregation of Cr,obtains the fine grain strengthening effect,and improves the strength of Gr/CuCr25 composite.Gr/CuCr10 composite was prepared by adding different content of Gr by vacuum hot pressing sintering.Compared with the microstructure and properties of CuCr10 without graphene,the Brinell hardness and conductivity of 0.5wt.% Gr/CuCr10 are 100.5 and 38.7 Ms/m respectively,which are 9.5% and 7.0% higher than those of CuCr10.The physical properties of 0.5wt.% Gr/CuCr10 electrical contact materials have met the requirements of CuCr25 national standard.With the addition of graphene from 0.1wt.%-0.5wt.%,the average particle size of chromium phase shows a decreasing trend.When the addition amount is 0.5wt.%,the average particle size reaches a minimum of 21.77?m,and the refining rate reaches 41.2%.The mechanism of Cr phase refinement was studied.It was found that the single or few layers of graphene played a certain interface blocking role in the agglomeration of Cr grains,avoided the continuous growth of Cr phase in the sintering process,played a role of fine grain strengthening,and improved the strength of Gr/CuCr10 composite.