Preparation Of Nano-grained Cu-Cr-TiB₂Composite Materials By MA-SPS Method

CuCr alloy is widely used as electronical conductivity material in the electrical industry and has been well known as the best electrical contact materials in high-current vacuum interrupters. In recent years, there have been growing demands that the vacuum interrupters work in the situation of high voltage, large capacity and mechanical property are also demanded. Studies show that nano-sized CuCr alloy could significantly enhance the material's electrical property. What's more, with the ultrafine TiB2particles distributed in Cu, the mechanical properties of the alloy can be significantly enhancedIn the thesis, mechanical alloying and spark plasma sintering were applied to prepare nano-grained Cu-Cr-TiB2composite materials. The phase structures, morphology and element distribution were detected by XRD, SEM, EDS, TEM, and so on. The properties such as relative density, hardness, electrical conductivity and abrasive resistance were also been studied. The effects of the TiB2content and the key parameters of MA and SPS about the structure and properties were also been investigated. The effection mechanism of TiB2in the composite was also discussed. The main research results are presented as followed.The optimum parameters of MA process are as follows:PCA is5wt%ethyl alcohol, ball to powder ratio is30:1and milling time is80h. The powder gaining rate is more than95%, the average grain size of the composite powder are all about20nm and the lattice strain rate of Cu is0.417%. No visible evidence of impurity be detected. With the TiB2content increases from0wt%to10wt%, the grain size of alloy decreases and the lattice strain rate increases. The phenomenon can be explained as the ultrafine TiB2"micro milling balls" effecting with the alloy and preventing the dislocation motion.The optimum parameters of SPS process are as follows:sintering temperature is920℃, holding time is5min and axial pressure is50MPa. The relative density approaches to99%, the average grain size of the composite material is about100nm and each phase are evenly distributed. No obvious peak of impurity was detected. With the TiB2content increases, the relative density and electrical conductivity decrease gradually, the HV hardness and wear resistance first increase quickly and then relaxedly. Ultrafine TiB2particles will cause dislocation strengthening so that the mechanical property increases but the electrical conductivity reduces.After synthesizing all characterization information, the nano-grained composite materials containing2-4wt%TiB2are considered to display optimal comprehensive performance. The properties of CuCr25-2wt%TiB2and CuCr25-4wt%TiB2composite materials are respectively presented as follows:the relative density are98.3%and96.4%, electrical conductivity are27.9IACS%and24.9IACS%, hardness are both about3.9GPa. Compared with pure CuCr25, the hardness of those two materials both increaed more than30%, the electrical conductivity are reduced by3.4%and16.4%respectively, the wear resistance are enhanced by100%and700%respectively under the experimental condition.