| Electrical contact materials are mainly used in electrical switches system. Its performances directly determine the reliability and service life of the electrical switches. With the development of contact materials preparation technology and the increase of material kinds, more attention are payed by scholars to the research of the copper based contact composites. Generally, the increasing relative density is the best way to improve the properties of PM products. There have heen some processes that can increase the relative density of PM products, such as double press/double sinter(DP/DS), melt infiltration, hot forging and hot-pressing process, and so on. Many studies show that, by hot-pressing process can prepare the high-performance products with the large relative density and homogeneity.In this paper, the high performance copper based electrical contact composites are prepared by the vacuum hot-pressing sintering process, a advanced powder metallurgy process, according to the requirements of the contact material. By powder metallurgy and smelting milling process, rare earth yttrium on the microstructure and mechanical properties of pure copper are studied. In turn, we prepared a new type of Cu-Re alloy powder and than studied the influences of the different quantity and different kinds of rare earth elements on the contact materials. Take the Cu-Y alloy powder as the matrix, the optimum hot pressing sintering process parameters are determined by the single factor experiment. And the densification mechanism analysis is also discussed; Under the optimal process parameters, the high performance of layer structural copper based electrical contact composites are prepared. Finally, the effects of the TiN and AlN on the microstructure and properties of copper based electric contact composites are discussed. The results show that:(1) The effect of rare earth yttrium on the microstructure and properties of pure copper are studied by hot-pressing and cold-pressing sintering process with orthogonal experimental method as so on. By the performance comparison of samples prepared the the two kinds of process, the optimum process parameters the hot-pressing and the cold-pressing sintering process are determined in the preparation of Cu-Y composites. Especially, the optimum compacting pressure of cold-pressing sintering process is 20 times than that in the hot-pressing process, and the sintering temperature of cold-pressing is higher. The overall performance of Cu-Y composites prepared by hot-pressing is significantly better than that by cold-pressing sinterng forming. With powder metallurgy method, both the hardness and the oxidation resistance of Cu is improved because of the addition of yttrium, which played a role in particle reinforcing. And it is also improved of copper matrix composites. However, the conductivity of copper decrease after Y is added to the samples. When the addition amount of Y is 0.5 wt.%, the composites have the optimum overall performance.(2) The Cu-Re alloy powders are prepared by atomization method. The influences of three kinds of rare earth elements(Y, Ce, La) on the copper based electrical contact material performance are explored. The research shows that the rare earth Y are mainly distributed on the surface of pure copper, so as to cut off some of the particles from air and refining the pure copper particles at the same time. It can also improve the interfacial properties, thus improve the combined properties of particles and matrix. With the increase of the content of rare earth in the copper alloy, the relative density and conductivity of samples are on the decline, but the hardness is on the rise and the upward trend is obvious. The relative density and oxidation resistance of samples from high to low order as: Y, Ce, La added sample. And relative density and conductivity of the samples added Y and Ce are no more differences. Adding different rare earth elements can improve its oxidation resistance. The effect is best when the rare earth content in copper alloy powders are 0.2 wt.%.(3) The effect of hot-pressing sintering process parameters(preloading pressure, holding pressure, sintering temperature, holding time) on the relative density and electrical conductivity is studied through the single factor experiment analysis. The optimum parameters of copper based electrical contact composites are determined: the preloading pressure of 5 MPa, the holding pressure of 50 MPa, the sintering temperature of 800 ?, the holding time of 2h. And it is concluded that sintering temperature and the holding pressure are the main influence factors of the sample performances. Under the optimal process parameters, the relative density and electrical conductivity are up to 99.56% and 57.60% IACS.(4) The copper based electrical contact layer-structural composites are successfully prepared under the optimal process parameters of vacuum hot-pressing sintering. The surface of samples have the excellent oxidation resistance and the material has remarkable electrical conductivity as a whole. The relative density of sample reaches 99.54% and the electrical conductivity reaches 72.56% IACS which increased by 46.62% than the single structural copper based electrical contact composite. The bending strength is 263.37 MPa and the hardness of the upper reaches 65.89 HB. With performances of preloading test specimen are obviously higher than that of without preloading test. Layer-structural materials combined with a good interface which belongs to the metallurgical bonding and no microstructural cracks appeared. So the interface between the upper and lower will not be the vulnerability of graded materials to weaken the overall performance of materials. Layer-structural composites compared with the commonly used contact material have more excellent physical properties.(5) The ceramic-reinforced phase of TiN and Al N are added into the matrix material. It is concluded that adding TiN can help to hinder the grew up of the copper matrix grain and evenly distributed in the matrix. The agglomerate phenomenon of AlN powder appeared in the matrix when the Al N added.The grain size uniform and the grain combined fine when adding TiN. The grain size tends to decrease with the increase of adding amount of adding TiN and AlN. With the addition of TiN and Al N, relative density of samples are presented reduce at vary degrees. Therefore, the electrical conductivity and oxidation resistance of the materials decrease. But the hardness of material increase and the performance of arc erosion resistance enhanced. When the adding amount of TiN was 1.5 wt.%, the properties such as density, conductivity, oxidation resistance and arc erosion resistance are reached the optimum. The comprehensive performance of TiN-added is superior to the AlN-added. |
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