Research On Preparation Of Nano Composite Cu-Cr Material By Mechanical Alloying And Spark Plasma Sintering

Recent years, there have been growing demands that the vacuum interrupters work inthe situation of high voltage, large capacity, and the device should be minimized. To meetthese requirements, intensive researches have focused on the improvement of vacuumcontact material properties. CuCr alloy, with good properties of low chopping current,large breaking capacity, high voltage withstanding and so on, is a promising materials tobe used. However, as little solid solubility of Cr in Cu, the CuCr alloys prepared byconventional methods have serious micro-structure, which leads to a limit performance.Thus, obtaining fine particles of Cr with a uniformly dispersion in Cu matrix is an efficientapproach to promote the performance of CuCr contact.In this thesis, the process of combination of Mechanical alloying with Spark PlasmaSintering was applied to prepare nano-crystalline CuCr composite materials. The phasestructures, morphology and element distribution were detected by XRD, SEM, OM, EDXand so on. The properties such as relative density, hardness and electrical conductivitywere also been studied. The influences of key parameters of MA and SPS on the structureand properties were also been investigated. The main research results are presented asfollowed.Higher MA efficiency is achieved when carbide balls with high density are used.With the Ball to Powder Ratio of30:1, MA time of50h, the average grain size is26nm,and the solid solubility of Cr in Cu is1.0065wt.%.Optimal usage of Process Control Agent leads to higher powder yield and betterdistribution. Optimum overall performance powder is prepared when the PCA content is5-15%: powder yield exceeds over90%, and the average grain size is26.1-35nm.Ball grading milling is an efficient method to refine the structure and improve the composition homogeneity. The fine, uniformly dispersed particles of Cr with an averagesize of3μm are obtained in the sintered specimens.Prolonged MA time can refine the micro-structures; extend the solid solubility of Crin Cu; and also obtain spherical powder particles. The powders were sintered after milledof70h. The uniformly dispersed particles of Cr are obtained in the sintered specimens.The average grain size of Cr is100nm.The warming rate and sintering temperature are key parameters for the properties.The combination of solid phase sintering and liquid phase sintering is achieved when thesintering temperature is900°C, with the warning rate of100°C/min. In this condition,The fine, uniformly dispersed particles of Cr are obtained in the sintered specimens. Thesuperior properties are also achieved: the relative density is97.35%; the hardness is282HV; the electrical conductivity is12.2MS/m.