Study On Preparation Microstructure And Properties Of CuCr Vacuum Contact Materials

With the progress of electric power technology of China recently,the vacuum switch has developed greatly,which requires higher standards for the core components of contact materials.CuCr contact materials are the preferred materials of vacuum switches for worldwide.But,in order to meet the requirements for using at more stringent environment,a novel CuCr contact material must to be developed.It has been found that the microstructure of CuCr alloy has significant influence on its macro performance.Nowadays,the approaches to improve the properties of CuCr contact materials follow as:1.add new components to optimize the compositions;2.improve or adopt new processes;3.subsequent processing and heat-treatment.In this paper,Cr powders were pre-milled by high-energy mechanical milling,and the CuCr alloys were prepared by advanced hot isostatic pressing(HIP)technique.The new components Zr and TiC were added and followed by solid solution aging heat-treatment.The effects of Cr particle size,additive compositions and heat-treatment on the microstructure,vickers hardness,electrical conductivity,mechanical properties and vacuum breakdown performance of CuCr contact materials were researched.Microstructure and properties of CuCr contact materials were studied.It was found that fully densified CuCr contact materials could be successfully prepared by HIP at 1000℃*120MPa*2h.Its microstructures are uniform,and the phases are pure.Additional Zr particles were presented in the Cu matrix and enriched at the Cu/Cr interface to improve the sintering properties of Cu and Cr.Additional TiC particles exist in the Cu matrix and fill the gap between Cu and Cr.The results showed that adjunction of TiC particles could improve the mechanical properties of alloys while its electrical conductivity decreased slightly.With the decrease of particle size of Cr,the mechanical properties of the contact materials were improved and the conductivity reduced a little relatively.The mechanical properties were improved obviously and the conductivity were increased to a certain extent by using solid solution at 960℃ for 1h,then aging treated at 500℃ for 4h.Investigation on the properties of electric breakdown ablation of CuCr alloys showed that the breakdown took place on the Cr-rich phase and the boundaries of Cr-rich phases and Cu-rich phases.With the decrease of Cr particle size,the breakdown voltage improved,chopping current decreased and the arc life extended slightly.By adding TiC particles,the electric breakdown took place in TiC phase with lower electron work function and the interphase boundaries of copper and TiC.Meanwhile,the electric arc was effectively dispersed.The breakdown voltage improved,chopping current decreased and the arc life extended.After solid solution aging treatment,the electric ablation area was dispersed more effectively,the breakdown strength improved,chopping current decreased and the arc life extended.The relative electrical conductivity of CuCr29Zr1(Cr76μm),CuCr28Zr1TiC1(Cr76μm)and CuCr28Zr1TiC1(Cr10-15μm)contact materials was 44.76%IACS,40.17%IACS and 33.60%IACS,respectively.The tensile strength was 357.0MPa,374.3MPa and 400.7MPa.The breakdown voltage of them was 5.38×107V/m,7.69×107V/m and 1.26×108V/m.And the chopping current was 4.04A,3.8A and 3.14A,respectively.