Preparation And Properties Of The Silver-nickel Contact Material Addition With Metal Oxides

The silver-based contact materials are widely used in the low-voltage apparatus attributed to its good comprehensive performance. And the latest research for the silver-based contact materials without cadmium is mainly concentrated in the research and application of Ag-Ni and Ag-Sn O2. Though the improvement of process and application of additives are conducive to improving these materials’ comprehensive performance, it does still need to further study to improve, such as the poor anti-welding characteristic of Ag-Ni, and the poor wettability and processability of Ag-Sn O2. Previous research indicated that the Ag-Ni and Ag-Sn O2 were complementary in the electrical and physical properties. However, the report of the preparation and performance of the silver-nickel contact material addition with metal oxides was comparatively rare. Hence this thesis is intended to provide a preparation process planning for the silver-based contact material, and to explore the feasibility of the idea that the electrical and physical properties of Ag-Ni and Ag-Sn O2 are complementary to each other in a certain extent. Which also provides theoretical basis and technical support for further research on the silver-based contact material without cadmium.Firstly, the composite powders of the nickel and metal oxides were prepared by the high energy ball milling technology, and which were used to prepare the Ag-Ni-Sn O2-Cu O-La2O3(Ag-Ni-Me O) composite powders with adding an appropriate amount of silver powder by the milling technology. Then the Ag-Ni-Me O composite powders were used to fabricate the Ag-Ni-Me O contact materials by the powder metallurgy. The effect of the parameters of the processes on the performance and microstructure of these materials was investigated by using the X-ray diffraction(XRD), the scanning electron microscope(SEM), the energy dispersive spectrometer(EDS), the electrical conductivity, the Vickers hardness, and the Archimedes method. And the parameters of the processes included the milling medium, the milling times, the way of adding silver powder, the protection gas in heat treatment process and the initial pressure value. Finally, the Ag-Ni-Me O contact materials were fabricated by the optimized preparation process, the physical properties and the arc erosion behaviors of these materials were tested and analysed, and the surface morphology before and after the discharge test were observed and analysed by using SEM, EDS, and the metallographic microscope. And the effects of the preparation process and the content of the metal oxides on the performance and microstructure of these materials were explored. The main conclusions of this thesis are as follows.(1)The effects of the technological parameters on the properties and microstructure of the Ag-Ni-Me O contact materials were investigated, and these parameters were determined. The experimental results showed that the anhydrous ethanol was chosen as the milling medium, all the silver powder were divided into two equal parts during the ball milling process of Ag-Ni-Me O composite powder, the milling time of nickel mixed with metal oxides was 1h, and the milling time of the first adding silver powder was also 1h. Moreover, the protection gas in heat treatment process and the initial pressure value were nitrogen and 300 MPa, respectively.(2)The Ag-Ni-Me O contact materials with different content of metal oxides were prepared by the optimized preparation process. Meanwhile, the metallurgical structure of these materials were observed and analysed. And the effects of the preparation process and the content of the metal oxides on the performance and microstructure of these materials were investigated. The results indicated that the physical properties of the Ag-Ni-Me O contact material were obvious improved by the re-pressing and annealing process and the re-pressing and re-sintering process, especially the re-pressing and annealing process. With the decrease of the content of metal oxides, the electrical conductivity and hardness of the material were gradually declining, and the main reasons were the pores in the materials by the extent of the nickel particles’ refinement gradually declining and the dispersion strengthening effect of metal oxides particles on silver matrix obviously weakening. But the relative density had no significant change, which varied from 91 percent to 96 percent. The physical properties of the Ag-Ni-Me O contact material reached optimal when the content of metal oxides was 10 percent. Moreover, in terms of the metallurgical structure of the Ag-Ni-Me O contact material, which not only related to the preparation process but also was influenced by the content of metal oxides of the material. And the preparation process could markedly affect both the densification of the material and the distribution uniformity and dispersion of nickel and metal oxides particles in Ag matrix.(3)The arc erosion behaviors of the Ag-Ni-Me O contact materials fabricated by the optimized preparation process were analysed by testing the materials’ discharge performance and observing the surface morphology, and the effects of the preparation process and the content of the metal oxides on the performance and microstructure of these materials were studied.(a)The results showed that the breakdown field of the Ag-Ni-Me O contact materials was, on the whole, floating around a certain value, which was independent of the content of metal oxides in the materials. And the arc erosion of the surface of these materials were small due to the limited times of discharge.(b)Furthermore, the surface morphology of these materials after the arc erosion test were mainly paste structure, pores, and microcracks. And the arc erosion behaviors of these materials’ central area were more obvious, while the surface near the edge of the materials was mainly shallower arc erosion pits.(c)In addition, the average breakdown field and the extent of the arc erosion in the materials’ surface were influenced by the content of the metal oxides in these materials. Especially, there were higher average breakdown field and slight more obvious arc erosion of the surface in the higher content of the metal oxides. However, the effect of the content of the metal oxides on the area of the arc erosion in these materials was not obvious.(d)The Ag-Ni-Me O contact materials with higher content of metal oxides had better arc erosion resistance in consideration of the average breakdown field and the arc erosion behaviors of the materials’ surface. And the arc erosion resistance of the Ag80Ni10 Me O10 was preferable to the Ag80Ni13 Me O7. Consequently, it is conducive to improve the arc erosion resistance of the Ag-Ni-Me O contact materials by appropriately increasing the content of the metal oxides.Moreover, the optimal proportion of components and the optimal preparation process of the Ag-Ni-Me O contact materials are determined by taking into account the physical properties and the arc erosion behaviors of these materials with different content of metal oxides. The optimal proportion of components of the Ag-Ni-Me O contact materials is 80%(mass percent) Ag, 10% Ni, 9% Sn O2, 0.5% Cu O and 0.5% La2O3. And the optimal preparation process of these materials is, in order, ball milling, annealing, pressing, sintering, re-pressing, annealing, re-pressing and re-sintering process. The optimal process parameters include the initial pressure value(300MPa), the sintering temperature(820℃), the re-pressing value(600MPa), the re-pressing value(700MPa) and the re-sintering temperature(800℃), and so on.