The Processing Techniques And Interface Research Of Precious Metal Layered Composite Materials

The rapid development of electrical industry need more and more requirements on electrical contactors; Composite electrical contacting materials, which are made from precious metals and alloys by multi-layer composite processing techniques, have attracted considerable research interest of material scientists due to their diversified functions, high properties and saving on precious metals. In this thesis, Ag/Cu layered composite materials are prepared by roll cladding, then diffusion annealing treated. The interface bonding lever of the composite materials has been tested, and the effects of rolling temperature, sintering temperature, sintering time on the microstructure, mechanical properties and solute distribution of the composite interfaces have been investigated. Moreover, the microstructure and solute distribution in the interfacial regions of the roll welding laminated Au/Ag/Cu alloy composite materials have also been studied in this thesis.Ag/Cu laminates prepared by roll bonding at different temperatures are studied. The results show that the interfacial properties of Ag/Cu laminates are decided by the interface bonding strength and the matrix mechanical properties. Higher interface bonding strength, lower matrix hardness and less disparity of the matrix hardness can do good to the bending level of the composites. The specimens bonded at 350癈 have better interface bonding level. Higher rolling temperature will bring about thicker oxide layer that will impair the interface bonding level.The as-rolled Ag/Cu specimens are diffusion annealing treated at different temperature, then the interface bonding level are tested. The results indicate that the Ag/Cu layered composite materials processed both by rolling at room temperature then diffusion annealing at 400癈 and rolling at 350癈 then diffusion annealing at 250 癈 have excellent bending properties . Rather high diffusion annealing temperature can make the grains excessively coarsened, and voids will form in theinterface region due to Kirkendall effect, which dramatically weaken the bond strength of the laminates. The bending lever can not be improved obviously, even though the diffusion annealing temperature are raised to 800癈 to conduct reaction diffusion treatment, .Ag/Cu bimetallic strips fabricated by room temperature are sintered at 750癈 for short periods. It is observed that voids have formed in the interfacial regions due to the atomic unbalanced diffusion. This results in the obvious reduction of the interface bond strength. Moreover, prolonging the sintering time can hardly improve the bond strength.Two kind of layered materials for the Au/Ag/Cu alloy composites are treated by diffusion annealing and the solute distribution in interfacial regions are tested. The results indicate that Au atoms diffuse rapidly under high sintering temperature for short periods, and sintering at high temperature can weaken the bond strength of composite strips. For this reason, it should be considered that the composites are sintered with a lower annealing temperature.