Study On Microstructure And Properties Of Rapidly Solidified CuCr25 Alloy

Cu-Cr alloy is the dominant material in the field of vacuum contact materials both in China and abroad.CuCr25 alloy has become the first choice of middle-high voltage circuits and medium-small vacuum switch contact materials for its excellent comprehensive performance.In the solid state,Cu and Cr are almost immiscible with each other,which makes Cu-Cr material maintain its advantages in the properties of the respective elements.However,it also causes serious segregation in Cu-Cr alloy as well,which increases the difficulty in preparation of the alloy.The properties of Cu-Cr alloy are mainly determined by its composition and microstructure,especially the size and distribution of Cr particles.Research shows that rapid solidification is beneficial to the refinement of Cr phase.Therefore,the study of Cu-Cr alloy contact material has been focused on rapid solidification method,which can optimize the process of the alloy and improve the properties of the material.In this paper,the vacuum melting-rapid solidification method was used to fabricate gradient CuCr25 alloy with fine Cr-rich phase structure by rapid solidification,using Q235 steel plate and T2 pure copper plate as cooling device.The microstructure of the alloy was analyzed by means of SEM,TEM,XRD,etc.The mechanical and electrical properties of the alloy were tested by means of micro-Vickers hardness tester,eddy conductivity tester and so on.By setting up the mathematical model,the cooling rate of the melt was simulated.Finally,the relationship between the solidification process,the microstructure formation mechanism and the properties of the alloy were analysed.The conclusions are as follows:(1)Due to the limited thermal conductivity and heat transfer capacity,the steel cooling CrCr25 alloy only obtains a 100?m-thick layer of micron-sized Cr-rich microstructure with uniform distribution in the thick part.The simulated cooling rate is 2.6×106K/s,which reaches the range of rapid solidification.The dissolution of Fe and other trace impurities into the alloy causes the lattice distortion of Cu-substrate.As a result,the hardness value of the material becomes larger,up to 190.88Hv,while the material conductivity is low,the maximum is only 37.8%IACS.(2)Due to the excellent thermal conductivity and heat transfer capacity,the copper cooling CuCr25 alloy obtains a 100?m-thick layer of micron-sized Cr-rich microstructure with uniform distribution in the thin part.Meanwhile,there forms a 400?m-thick layer of fine transitional Cr-rich phase which is about to transform from spherical equiaxed grain to dendritic.The simulated cooling rates of these two parts are 4.6×106K/s and 2.9×105K/s respectively,which both belong to the range of rapid solidification.Because of the refinement and precipitation of Cr particles in the alloy,the comprehensive properties of the material are optimized.The hardness value of the material is improved to a maximum value of 109.96 Hv.Simultaneously,the higher conductivity of the material remains,up to 54.9%IACS.(3)Besides,the copper cooling CuCr25 alloy obtains a 200?m-thick layer of sub-micron-sized Cr-rich microstructure with dense and uniform distribution in the thick part.Also,there forms a 800?m-thick layer of fine transitional Cr-rich phase which is about to transform from spherical equiaxed grain to dendritic.The simulated cooling rates of these two parts are 1.1×106K/s and 7.1×104K/s respectively,which both belong to the range of rapid solidification.For the same reason,the comprehensive properties of the material are excellent.The hardness value is 106.91Hv at most.The conductivity is up to 55.5%IACS.Based on the results above,we fabricate gradient CuCr25 alloy contact sample for industrial application.