| Silver matrix solid self-lubricating brush materials used for satellites were investigated in this paper, and the duration of this kind of materials in space application was increased. The physical and mechanical properties, along with friction and wear behaviors, of silver matrix brush materials were known after tests and analysis, so the mechanism and effect of the wear-resistance improvement of this material was investigated by two strength methods such as solid solution and carbon fiber reinforced. The improved materials were also compared with the application material, so as to find the mechanism of lifetime growth. The sliding electrical contact performance of AuNi9and AgCu10wire brushes were researched by friction and wear tests under electrical current. Comparing the silver matrix composite brushes with noble metal wire brushes, we clearly and completely know the properties and application characteristics of sliding electrical contact materials for space application. A model slip ring was made and its electrical properties were tested, the ring of this slip ring was made using solid solution strengthen silver matrix composite material. The application behavior of this slip ring was assessed, and this will be an important support for the development of new generation slip ring with high power and long duration in space.The main conclusions and results are summarized as follows:1) Ag-Cu composite powder was prepared by chemical adding copper method, and then it was used to prepare the Ag-2.5Cu-8MoS2composite by hot-pressing. The structure of the prepared composite is uniform and stable, and the interfaces of each function layer are clear and well combined. The relative density of prepared composite is above96.5%, and the bending strength of self-lubricating function layer is167.2MPa, and the hardness, friction coefficient, wear rate and static contact resistance are HB50,0.12-0.20,<2×10-13m3/N·m, and<0.54mΩ, respectively. The results of friction and wear test under3A current indicate that the stable friction coefficient of the material is about0.2and the stable operation life is above10km. The properties of the prepared Ag-2.5Cu-8MoS2composite satisfy the technology demand of some type of satellite.2) A new kind of Ag-2.5Cu-8MoS2composites was prepared with small size atomized AgCu alloy powder instead of Ag-Cu composite powder. The prepared material was strengthened by solid solution, and the wear rate of the composite was reduced from former50×10-14m3/N-m to5-8×10-14m3/N-m. The reduction degree of wear rate is almost a magnitude. The result turned out that the brush material prepared with atomized powder has high wear resistance, and the duration of the brush is increased.3) It was found that the influence of powder size and distribution to the mechanical properties and MoS2distribution of Ag-2.5Cu-8MoS2composite is significant. The hardness and bending strength of the composite increase with decreasing the size of alloy powder. As the size of alloy powder decreasing from-300+400mesh to-500mesh, the hardness and bending strength of composites increase from HB45.9,88.08MPa to HB56.8,179.08MPa. The distribution of MoS2particle in Ag-2.5Cu-8MoS2composites was improved when small size alloy powder was used, which caused the reduction of friction coefficient and its fluctuation. The operation stability of the material is significant improved.4) The Ag-2.5Cu-8MoS2composite was reinforced by graphitized carbon fiber, and Ag-2.5Cu-8MoS2-xCf composites with different volume fraction of carbon fiber were prepared. It is found that the friction coefficient of the composites increase slightly and the wear rate is improved a lot with increasing the amount of carbon fiber. The wear rate of the composite decreases from6.31×10-14m3/N-m to2.07×10-14m3/N·m when the volume fraction of carbon fiber increases from0%to15%. There is three times of increase with the wear rate the composite, and the strength effect to wear is remarkable.5) The friction and wear behaviors of Ag-2.5Cu-8MoS2-xCf composites were investigated under current. It is found that the influence of current on the wear rate of composites is insignificant. However, the influence of carbon fiber addition on contact voltage drop is apparent. The contact voltage drop values of all prepared composites are in the range of0.03-0.09V, but the value and fluctuation of contact voltage drop increase with the increase of carbon fiber content. Therefore, it is believed that the carbon fiber content in composite should be around6vol%, so that it has low contact voltage drop and good wear resistance (the wear rate of Ag-2.5Cu-8MoS2-6vol%Cf is3.02×10-14m3/N-m).6) The friction and wear behavior of AuNi9and AgCu10brush of one wire type and fiber type were investigated with or without current, and the match characteristic of this kind brush was found. AuNi9fiber brush matches well with gold plated Ni coating, and AgCu10fiber brush matches well with gold plated brass. The sliding electrical contact behavior of AuNi9brush sliding on the gold plated Ni coating is best among them. The friction coefficient of it is0.9, and the average contact voltage drop is0.5mV/A, which is three times lower than that of AgCu10.7) A new type of model slip ring was made using the silver matrix solid self-lubricating brush material as the ring material, and this is an innovation to the structure of slip ring. The test properties of the slip ring fit well with the design demand. The running test with one hundred thousand revolutions (1s/r) turned out that the static contact resistance increases at first, then decrease and finally maintain stable. The variation of contact resistance is about3-5mΩ during the running process, which shows that the contact between brush and ring is reliable. |
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