Preparation Of Belt-fiber Reinforced Ag-Ni And Ag-Fe Electrical Contact Materials By Coating-sintering-plastic Deformation

Ag-Ni and Ag-Fe electrical contact materials were studied in this work.A belt-reinforced Ag-Ni and Ag-Fe electrical contacts by banded fibers are obtained by the method of coating-sintering-plastic deformation.The preparation method and the evolution law of microstructure and properties in plastic deformation are systematically studied.The main contents and results are as follows:The composite powders coated on the surface are obtained by powder meta llurgy mothod.The 3D networkis obtained by hot pressing.The thickness of the net becomes thinner with the decrease of the size of Ag particles.The Ag particles are coated by the networks of the second phase.Co-deformation is enhanced.In plastic deformation,the secondary phase net is torn,the cross section is evenly distributed in a strip,and the longitudinal section is along the axial belt-fiber.With the increase of true strain.the distribution of the second phase on the cross section tends to uni formly disperse.and the fiber shape tends to be slender on the longitudinal section.Under the same true strain,the thinner the second phase,the thinner the fiber.The fiber is up to 1275.69 m.In the plastic deformation,a large number of initiation of the twin boundary,the formation of dislocation with small angle orientation with sub structure.In plastic deformation,a large number of twin boundary were observed in the Ag matrix,the formation of dislocation with small angle orientation with sub structure.With the increase of true strain,some subgrain boundaries gradually change to the large angle grain boundary,and the Ag matrix occurs recrystallization and shows a weak<100>silk fabric.In the crystallization process,the Ag matrix tends to grow on the second phase with the lowest mismatch.Finally.Ag(111)//Ni(111)and Ag(111)//Fe(110)are formed in the Ag-Ni and Ag-Fe composite interface.The study shows that the formation of the second phase in the raw sintered billet is beneficial to the second phase co-deformation with Ag matrix.With the true strain incressing,the<100>fiber texture is formed in the Ni phase,and the<100>fiber texture is formed in the Fe phase.Under the same true strain,the thinner the secondary phase net is,the smaller the hydrostatic pressure is in the second phase,thus the stronger fiber texture is obtained.In addition,when the thickness of the Ni network is thinner,a belt-fiber is formed by the plastic deformation shows the {110} texture pointing to the radial direction.The effect of 3D continues networks on load transfer are confirmed.The relative density of the sample can be increased by hot extrusion.However,in the cold drawing process,due to the difference of the two phase elastic modulus,the accumulation of defects in the sample leads to the decrease of the relative density.The hardness and strength of the material are improved by the defect strengthening mechanism.Due to the formation of directional belt-fibers,the interface scattering of the current conduction path decreases,and the material conductivity increases with the increase of the true strain.True strain η=6.03,the conductivity of Ag-Ni and Ag-Fe electrical contact material are above 97%IACS(ASTM:conductive rate greater than 75%IACS),In the molten pool.one end of the a belt-fiber is pinned in the solid Ag matrix and the other in the molten pool,and the molten pool is stabilized by the capillary action.Therefore,the mass loss is low and stable,especially for the Ag-Ni material with Ag particle size of 180～250 μm,and the mass loss of material after 20 thousand contact is only 0.2 mg.