| In the 21st century, high speed ,environmental protection and energy conservation are the themes of today's world, the transport high-speeding is a challenge to the existing friction material, and require it has more excellent performance. Friction material originally is asbestos friction material, but now it can be divided into three parts: metal-based, semi-metal-based, non-metallic and non-asbestos friction materials. And the properties of friction have been comprehensive enhanced. Metal-based friction material mainly includes copper and iron based material, but copper-based material has better properties than iron-based material. Copper has good plasticity, corrosion resistance, electrical conductivity, thermal conductivity. In the copper alloy, adding ceramic particles and reinforcing fibers can make the alloy have higher strength, wear resistance and temperature creep resistance. So as friction material, the copper alloy has a wide application prospect.In the study copper was used to be the base material preparing for high-speed train brake material. As is know to all, in recent years with the rapidly increasing of railway transport development, the train's speed and the load capacity, it demands for better performance friction material to fit this situation. The heat is the primary problem to be solved for high-speed train braking material because the train speed and braking power is proportional to the cube. Conventional resin-based material in heat transfer appeared to be inadequate, while the metal-based friction materials are able to overcome this problem. This study was designed to overcome the two problems: the first one is the strength problems of brake material, the strength of material increases with the amount of particles added decreased if adding the particles directly; the second one is the costs and content range of granule components. According to the traditional techniques, to ensure the strength of the material, it must increase the sintering pressure. And this will increase the cost and limit choice and increase particle content range. The research includes the following aspects:(1) TiC composite powder was prepared by equipment of planetary ball milling in order to study the formation mechanism of TiC and its influencing factors. The Ti, C mixed powders were milled for different time by different diameter ball. The Ti powder and C powder were mixed by the atomic ratio of 1:1, the diameters of ball were 8mm, 10mm and 12mm,the speed of ball mill was 500 r/min, the ball to weight ratio was 10:1, the milling time was 20h, 40h, 60h, 80h, 100h. The particle size and morphology of milled Ti, C composite powder were observed by SEM. The composition analysis of milled Ti, C composite powder was observed by X-ray. Results revealed that: During milling of TiC, in the early time the small diameter ball refined powder more easily than the big diameter. TiC could be produced by the small-diameter ball in the early of the milling, but the big diameter could not produce TiC. However, the completion of large-diameter ball used in the process of TiC reaction time shorter than the small-diameter balls, and eventually generate quantities of TiC. During the milling of TiC, when using the large-diameter ball milling, the process of TiC reaction was SHS mode. When the ball diameter is small, the process of TiC reaction was MRD mode.(2)Study TiC reinforced copper-matrix composites material. The Ti powder and C powder were mixed by the mass ratio of 4:1, the diameters of ball were 8mm, the speed of ball mill was 500 r/min, the ball to weight ratio was 10:1, and the milling time was 5h, 10h. The milled Ti, C powder and Cu powder were mixed by the mass ratio of 3:7, 1:9; the speed of ball mill was 200 r/min, the milling time was 1h. then Pressed the mixed powder and sintered it at the temperature 800℃,900℃,1000℃. The morphology of the sample was observed by Laser microscope, the hardness of the sample was measure by Micro Hardness Tester, the composition of composite powder and the sample was analysis by X-ray. Results revealed that: the material grain size of TiC particle reinforced copper-matrix composites decreased with the sintering temperature increased, the porosity content also decreased, the degree of densification increased gradually. The milling time of the Ti, C composite powder added was also affect the degree of densification, with the composite powder milling time increases, the degree of densification increases. During sintering of the TiC particle reinforced copper-matrix composites, mixed elements such as Ti, TiC, occurred solid solution with Cu.(3)Study copper-matrix brake materials prepared by cold-pressed and SPS sintered. Results revealed that: The friction properties of the cold sintering material tended to be stable with the load increasing, and this demonstrated good friction and wear properties. the maximum wear rate of the experimental material was between the 0.1-0.14cm3/MJ, and this is far below the international standard under the wear rate of 0.61cm3/MJ. But the friction coefficient ranged from 0.45 to 0.75 which is still significantly higher than under internationally accepted standards of 0.35. Materials sintered by SPS had high density and homogeneous organization, and the friction coefficientμdecreased with the load increasing. At the higher load the friction coefficient is only between 0.2 and 0.3. Contrasting these two method, we can see that materials sintered by SPS had lower friction coefficient, lower wear rate and higher density of third body which are in line with international standard requirements than the materials cold sintered. However, because of the high cost of SPS, in the actual generation of mass generation it still needed to be studied. |
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