Fabrication And Properties Of Copper-based Pantograph Slider Materials

Urban rail transit and slow-speed heavy-load electric locomotive in mountainous areas are two very important fields in railway transportation at present,which demand large numbers of electrical locomotives.The copper-based pantograph sliders are critical parts in locomotives which play the role of electricity accepter.Interiorly,the consumption of the sliders is continuously growing,but importation is greatly dependent due to the domestic lack of related technology.In order to break the foreign monopoly of this product,it is very important to promote the localization of copper-based pantograph sliders in railway transportation.In this dissertation,the preparation process of copperbased pantograph sliders by P/M method,the effects of different kinds of lubricants for materials,and the cold pressing and the sintering behaviors were systematically studied.The phase composition,microstructure,mechanical property and friction-and-wear performance of the sintered materials had also been demonstrated.At the same time,the effects of aging temperature and aging time for microscopic structure,physical,mechanics,friction-and-wear performance of the copper alloy were explored.The results could provide technological and theoretical significance for the development of independent intellectual property rights of copper-based pantograph sliders.The main results are listed as follows:(1)Compacting behavior: In cold pressing process of the copper alloy mixed powder,the green density increased with pressing pressure improvement,but accordingly the increasing rate slowed down instead.The behavior of pressing of the copper alloy accorded with description of classical pressing equations,especially with Huang Peiyun's equation.Correlation coefficient(R)of least squares method was obtained as 0.997980,near the value 1,the hardening index(m)was 2.26313,and the suppression of modulus(M)was 6.05885 MPa for the P/M copper alloy.(2)Preparation process: In high temperature sintering process,the density of sintered body showed obvious tendency of initial increase and then decrease with the improvement of sintering temperature and the extension of sintering time.The optimized process with sintering temperature of 900 ? and sintering time of 2 h was obtained.Different contents of three kinds of lubricants such as graphite,Cu2 S and MoS2 were added in the copper-based P/M materials.After checking the properties,we found the graphite was most appropriate for copper-based P/M materials' properties.When the content of graphite was added as 2%,the comprehensive properties of copper-based pantograph sliders were the relatively optimal with the electrical resistivity of 0.22 ??·m,impact toughness of 34.2 J/cm~2,and hardness HB of 75.(3)Aging treatment: The P/M copper-based materials were taken a solution treatment at 830 ? for 2 hours and water hardening treatment,and then aged at 450 to 600 ? for 1 to 4 hours.The hardness,resistivity,impact toughness and tensile strength at different aging temperatures and time of the treated materials were systematically studied,and also,the microstructure and phase composition were analyzed.The results show that the hardness,impact toughness and tensile strength of P/M copper-based materials are initially increased then decreased,and resistivity are initially decreased then increased slightly with the increase of aging time.Various performances of P/M copper-based materials had been enhanced by the aging heat treatment.The fracture behaviors of the materials before and after aging treatment were identified as plastic fracture.Observed from the fracture,we found that the impact toughness was enlarged obviously.After the typical aging treatment at 500 ? for 3 h,the main phases were ?-copper and graphite,and the second phase of the hexagonal phase Cu10Sn3 precipitates was appeared also,which strengthened the matrix and accordingly improved the properties of the materials.The typical performances of the aging heat treatment materials were obtained with the electrical resistivity of 0.147 ???m,hardness HB of 89,tensile strength of 355.68 MPa,impact toughness of 47.1 J/cm~2,and friction coefficient of 0.189,which were sufficient for the requirements of national standards,and the comprehensive property could approach the level of foreign products.