| Pantograph plate,motor brush,conductive slip ring,relays,circuit breakers and other electrical contact components are widely used in aerospace,high-speed railway and nuclear energy industry.They play the role of bearing current,electric energy transmission and signal transmission.However,during the normal use of these electrical contact elements,they will be affected not only by electrical friction and wear,but also by arc corrosion happened between the electric contact,which will lead to contact materials phase change,material transfer,corrosion and other complex physical and chemical changes.So the ideal electrical contact materials need excellent electrical and thermal conductivity,mechanical strength,low friction coefficient and wear rate,excellent arc erosion resistance.With the rapid development of aerospace and nuclear industry and accelerated requirements of high-speed railway,traditional copper matrix composites such as Cu/G,the Cu/WS2 and Cu/Mo S2 cannot meet the performance requirement.Thus,it is necessary to develop new Cu matrix composites,which not only have excellent electrical performance,but also have good self-lubricating property and the arc erosion resistance.Ti3AlC2 powders were prepared by pressureless sintering from Ti,Al,and Ti C powders.The results show that the particle size of the prepared Ti3AlC2powders is uniformly distributed.The SEM image shows that Ti3AlC2 has a typical layered structure,and the laminates in the layered structure are evenly distributed,and the dividing line between the laminates is clearly visible.The Ti3AlC2 bulk was prepared by hot pressing sintering method.The XRD results show that there is no decomposition or oxidation of Ti3AlC2 during the sintering process,and the microstructure of Ti3AlC2 is banded or plate-like.Cu/Ti3AlC2 composites with Ti3AlC2 volume content of 25%,30%,35%,40%and45%were prepared by hot pressing sintering.The microstructure,physical and mechanical properties of the composites were studied.The results show that the reinforcing phase Ti3AlC2is uniformly distributed in the Cu matrix,and the number of holes in the composites increases with the increase of Ti3AlC2content.The XRD results show that Ti3AlC2 neither decomposes nor reacts with Cu in the sintering process.With the increase of Ti3AlC2 volume content,the relative density,Brinell hardness and bending strength of Cu/Ti3AlC2 composites decrease,while the electrical resistivity increases gradually.The effect of Ti3AlC2 content on the electrical sliding wear properties of Cu/Ti3AlC2composites was investigated by using a custom-designed block-on-ring electrical wear testing apparatus.The results show that with increasing Ti3AlC2content in the Cu/Ti3AlC2composites,the contact voltage drop increases,the friction coefficient decreases gradually,the wear rate decreases first and then increase.With the prolongation of electrical sliding wear experiment,a lubricating film gradually formed on the worn surface,which improves the wear resistance of Cu/Ti3AlC2composites.Raman spectroscopy and X-ray photoelectron spectroscopy show that the lubricating film is composed of Ti3AlC2,Ti O2,Al2O3 and Cu O,in which Ti O2 and Al2O3 are formed by decomposition of Ti3AlC2.The electrical sliding wear properties of Cu/30%Ti3AlC2 composites were investigated under the conditions of the electrical current density between 0-15 A/cm2along with an apparent contact pressure of 1.25-7.5 N/cm2 and sliding velocities ranging from 2.5 to 15 m/s.The results indicate that friction coefficient,wear rate,and contact voltage drop increase with an increase in the electrical current density.As the apparent contact pressure increases,the contact voltage drop of Cu/Ti3AlC2 composites increases gradually,while friction coefficient and wear rate first decrease and then increase.The wear will be aggravated if the apparent contact pressure is too low or too high.With an increase in the sliding velocity,the friction coefficient of the sliding pair decreases and the contact voltage drop increases gradually,while wear rate decreases first,then increases.Adhesion wear and arc erosion wear are the main wear mechanisms in the electrical sliding wear experiments of Cu/Ti3AlC2 composites.The arc erosion behavior of Ti3AlC2in oxygen,air,carbon dioxide,nitrogen,argon and sulfur hexafluoride was studied by using a custom-designed arc erosion equipment,and the effect of ambient atmospheres on the arc erosion performance of Ti3AlC2was discussed.The results show that the breakdown strength of Ti3AlC2 varies with the change of ambient atmospheres,and increases in the order of oxygen,air,carbon dioxide,nitrogen,argon and sulfur hexafluoride.On the contrary,the arc life is maximum in oxygen and minimum in sulfur hexafluoride.In oxygen,air and carbon dioxide,porous structures,large and wide cracks appear at the erosion area,which accompanied by a large number of crack propagation.In nitrogen,argon and sulfur hexafluoride,only small cracks appear on the erosion surface and no obvious crack propagation appear.In oxygen,air,carbon dioxide,nitrogen and sulfur hexafluoride,Ti3AlC2 is decomposed by arc erosion,the decomposition products are Al2O3 and Ti O2 in oxygen and air,Al2O3 in carbon dioxide,Al N in nitrogen,and Al F3 in sulfur hexafluoride.The erosion mechanism is called the"decompose-oxidation"process in oxygen,air and carbon dioxide,and the"decompose-rereaction"process in nitrogen and sulfur hexafloride.The arc erosion behavior of Cu/30%Ti3AlC2 composites in air,carbon dioxide,nitrogen and sulfur hexafluoride atmospheres was studied.The results show that the breakdown current of Cu/30%Ti3AlC2composites remains between 30.2 A and 31.2 A in each atmosphere.The arc energy and arc life are the highest in air,and decrease in the order of carbon dioxide,nitrogen and sulfur hexafluoride.Under the influence of arc structure,the erosion area in all atmospheres is approximately elliptical.Under the effect of high arc temperature and electromagnetic force,some bulges and pits are formed in the erosion area.The erosion damage is related to the arc energy and decreases in the order of air,carbon dioxide,nitrogen and sulfur hexafluoride.In air and carbon dioxide,the Cu/30%Ti3AlC2composites are seriously eroded and decompose.The erosion products are Cu O,Ti O2 and Al2O3 in air,and Cu O and Al2O3 in carbon dioxide.In nitrogen and sulfur hexafluoride,the Ti3AlC2 structure is maintained well. |
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