Study On The Radiation And Arc Erosion Behavior Of Cu-Ti₃AlC₂ Composite

A large number of relays,conductive slip rings,brushes,potentiometers,and other electrical contact components are widely used in the automatic control systems and electrical equipments of aviation industry,aerospace technology and high-speed train.These components play an important role in the transmission of electric energy,electrical signals,or the connecting/cutting off the circuit.Their performance will directly affect the stability,accuracy,reliability and service life of electrical apparatuses,instruments and the circuits.On the basis of electrifying,the electrical contact materials for fabrication of these components can bear certain loads,withstand friction and wear,suffer from electirc arc and radiation damage by neurons,charged particles,?rays and so on in the nuclear energy environment.Therefore,the ideal electrical contact materials should have high conductivity,high thermal conductivity,high mechanical strength,low friction coefficient,low wear rate,good arc erosion resistance and radiation resistance.Copper based graphite reinforcing materials were widely used in electrical contact materials because of their excellent mechanical strength,good conductivity,thermal conductivity and good lubricity.However,with the rapid development of aerospace and high-speed rail industry,the traditional copper graphite composite materials were difficult to meet its requirements.Therefore,it is urgent to develop a new type of copper matrix composite,which has good lubricity,arc erosion resistance and resistance to particle irradiation while maintaining high electrical conductivity.With TiC,Ti,Al,Sn and Si as raw materials,Ti₃AlC₂ powder material was prepared by pressureless sintering method in argon atmosphere.From the HRTEM image of TEM,the lattice parameter of c axis was 1.87 nm,which was close to the theoretical value 18.578?.The crystal planes on the selected area electron diffraction pattern proved to be the Ti₃AlC₂ material.After calculating the peak intensity from the XRD pattern,the purity of the fabricated Ti₃AlC₂ could reach to 98%.The effects of different irradiated energy and time on the morphology,composition and structure of Ti₃AlC₂ were investigated by electron irradiation in situ.The reasons of its composition and structure changes were discussed from two directions of[0001]and[11 2 0].It was found that there were no changes neither on the morphology of the material nor the selected diffraction pattern under the action of 100 keV energy.The minmum theoretical incident energy to make the Ti,Al and C atoms isolated was429.7 keV,168.3-195.7 keV and 135.0-147.9 keV,respectively.The electron energy of 100 keV was not high enough to provide the minimum energy required for the atom to break away from the original crystal structure,therefore there was no changes on the morphology.By increasing the irradiated energy to 200 keV,the morphologies of"wave"and"holes"were formed and the ratio of Al to Ti atoms decreased gradually with the extension of time.Some diffraction spots gradually weakened or even disappeared on the selected diffraction pattern,but there was no amorphous ring observed.From the established theoretical model,it could be inferred that the weak diffraction points were caused by the displacement of Al atoms,C interstitial atoms and anti-site defects of Ti-Al.By using a self-made arc ablation device,the influences of breakdown voltages on arc erosion of a Ti₃AlC₂ cathode were investigated and the mechanism of arc ablation was studied.It was found that pits,cracks and ejected particles were formed on the eroded cathode,which were induced by the combination of Marangoni effect,electromagnetic force,buoyancy and arc plasma force.With the increased breakdown voltages,the breakdown current and the ablation area increased,the breakdown strength decreased gradually.Al₂O₃ and TiO₂ were formed on the surface.In addition,the mixtures of anatase and rutile TiO₂ occured from 3 kV to 8 kV.At higher voltages of 9 and 10 kV,only rutile TiO₂ would be founded in the eroded surface.Cu-Ti₃AlC₂ composites with reinforced phase of 10%,15%,20%,25%,30%and35%were prepared by hot pressing sintering method.The influence of Ti₃AlC₂content on its physical and mechanical properties was studied.It was shown that with the increase of Ti₃AlC₂ content,the relative density and the bending strength decreased gradually.At the same time,the electrical resistivity increased and the Brinell hardness increased first and then decreased.By using a self-made arc ablation device,the effects of Ti₃AlC₂ content on arc ablation properties of Cu-Ti₃AlC₂ composites were investigated.After eroded by 8 kV DC voltage,the breakdown voltage of Cu-Ti₃AlC₂ composites fluctuated between 45A and 50 A,and the arc life maintained 25 ms.When the volume fraction of Ti₃AlC₂was 10%and 15%,there was no crack on the eroded surfaces,but the cracks ocurred at 25%,30%and 35%.The pits and ejected particles were formed on the six eroded samples with various Ti₃AlC₂ content,which were decomposed and oxidized to CuO,TiO₂ and Al₂O₃.With the increase of Ti₃AlC₂ content,only part of Cu matrix was oxidized.Cu-20 vol.%Ti₃AlC₂ composite was chosen as the cathode material to study the effects of breakdown voltages on its arc ablation propety.It was shown that under the action of 3,4,5,6,7,8,9,10 kV DC voltage,the eroded surfaces of Cu-20 vol.%Ti₃AlC₂ cathodes were covered with protrusions and craters.With the increase of breakdown voltage,the breakdown current increased,and the radius of the arc erosion area increased gradually.At the same time,the current density decreased,which caused the depth of the"crater"to be shallow.No cracks were formed during the arc erosion process.Under the same experimental condition,the arc erosion property of Cu-20 vol.%Ti₃AlC₂ composite was better than that of pure Ti₃AlC₂ bulk.