Preparation, Microstructure And Properties Of Ag-Ni-TiB₂ Electrical Contact Materials

Ag-Ni electrical contact material has excellent electrical conductivity,strong thermal conductivity,and its contact resistance is small and very stable.In addition,the material also has good plastic processing properties and is easy to be processed into various parts.It is not necessary to use the additional silver layer when welding,thus saving the use of precious metals,so Ag-Ni contact materials are widely used in various kinds of micro switches,circuit breakers,relays and other products.Although the Ag-Ni electrical contact material has many advantages,the Ag-Ni electrical contact material has poor resistance to welding.The material transfer is easy to occur under the erosion of the arc,which greatly reduces the service life.Therefore,the application of Ag-Ni electrical contact materials is greatly limited.In order to overcome these drawbacks of Ag-Ni contacts,the enhancement phase is usually used to improve the performance of Ag-Ni contacts.In this experiment,Ag-Ni-TiB₂ powder was prepared by chemical reduction and liquid phase mechanical stirring method,and several conditions in the process were investigated,and the dispersive powder was obtained.Then the composite powder was pressed and sintered repeatedly,and the Ag-Ni-TiB₂ electrical contact material block with high compactness was obtained.Finally,the effects of the rolling properties,hardness,electrical conductivity,tensile strength,resistance to arc erosion and the addition of TiB₂?0.5%and 1%mass fraction?on the properties of Ag-Ni-TiB₂ contact materials are systematically studied,and the following results are obtained:?1?In the preparation of Ag powder,the concentration of AgNO₃ is 0.5mol/L,the concentration of ascorbic acid is 0.3mol/L,the reaction temperature is room temperature,the dispersant is 5%PVP,the pH of ascorbic acid is 4.The mixing mode is AgNO₃ fast into ascorbic acid,and the silver powder with a particle size of 1-2 um can be obtained at this time.In the preparation of Ag-Ni-TiB₂ composite powder,the Ni powder and TiB₂ powder are ultrasonic 1h,then the three powders are placed in the ethanol and mechanically stirred for 90min.Finally,a good dispersible Ag-Ni-TiB₂ composite powder is obtained.?2?After 200°C,2h annealing of the composite powder,using 250MPa pressure,the initial firing temperature of 900°C,sintering time of 2h can get a density of about80%of the primary firing compact;the second re-heating temperature is reduced to700°C,after the secondary recompression pressure is increased to 900MPa and sintered,samples with a density of 95%or more can be obtained.?3?The rolling process is used to plasticize Ag-Ni-TiB₂?0/0.5/1%?electrical contact materials with a density of over 95%and can be rolled into 0.3mm thick sheets.It shows that the material has good rolling plasticity.Rolling processing can effectively increase material density?greater than 99%?and hardness?118HV?.TiB₂ can play the role of dispersion strengthening in the matrix,the more the addition,the greater the hardness and tensile strength of the material.Compared with the AgNi10,the hardness of the 1%TiB₂ sample is increased by 23%and the tensile strength is increased by12.9%,but the added TiB₂ will reduce the plasticity and electrical conductivity of the material.?4?In the arc erosion experiment,the addition of TiB₂ can effectively improve the viscosity of the molten pool of the Ag-Ni contact material,reduce the spatter of the Ag-Ni contact material,and improve its ability to resist arc erosion.However,when the voltage is high,the addition of too much TiB₂ can not significantly improve the resistance to arc erosion of the material.