Preparation Of Cu@Ag Composite Powder By Replacement-reduction Method And Its Densification At Low Temperature

Both copper and silver have the advantages of high thermal conductivity,high electrical conductivity,and good ductility.Their composite materials are widely used in defense industry,electronic printing,welding and other fields.In the preparation method of composite materials,powder metallurgy has been widely concerned because it can simply compound multiple elements to avoid the generation of uneven structures.The status of copper powder is essential to determine the performance of powder metallurgy products.However,copper powder as the most basic raw material is easy to oxidize,and during the mechanical mixing process,element aggregation will occur.These factors will affect the low-temperature sintering compaction and performance improvement of Cu-Ag composite materials.Therefore,in this paper,Cu@Ag coated powder is designed and prepared to cover the surface of copper with high oxidation resistance,which makes it difficult for copper to contact with air to oxidize.At the same time,silver is evenly dispersed in the copper surface to solve the problem of element aggregation in mechanical mixtures.The spark plasma sintering system(SPS)was used to sinter the Cu@Ag coated powder,in order to achieve the preparation of high-density,uniformly distributed Cu-Ag composite materials at a lower sintering temperature.In order to achieve the above research goals,this paper studied the microstructure,phase and oxidation resistance of Cu@Ag coated powder prepared by displacement-reduction method.Scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray diffractometry(XRD)and comprehensive thermal analyzers were used to characterize the microstructure and properties.After that,the SPS sintering of Cu@Ag coated powders was studied to prepare Cu-Ag composite materials and their low temperature densification and its mechanism,as well as its electrical and mechanical properties.The relationship between its performance and microstructure was analyzed.The results of the microstructure and properties of Cu@Ag coated powder show that without sensitization,the silver agglomeration is serious;using sensitized Cu powder as a raw material,Cu@Ag achieves excellent coating structure.The coating structure of the Cu@Ag powder prepared only by the displacement reaction method is poor,and the coating structure of the Cu@Ag powder prepared by the chemical reduction method is better;combining the above two methods,the Cu@Ag powder prepared by the displacement-reduction method is the best.The coating structure of Cu@Ag powder prepared by using glucose as a reducing agent is uniform.In the displacement-reduction method,0.25 g(6.25%wt)of Ag NO₃was used in the displacement reaction,and the Cu@Ag coated powder with the best structure could be prepared when reacted for 20 min.The best process obtained from the research is:at room temperature,using sensitized Cu powder,glucose as the reducing agent,taking the replacement-reduction method,and controlling the amount of Ag NO₃ in the replacement reaction to 0.25 g,the reaction time is 20 min.In the replacement-reduction method,the replacement reaction mainly occurs at the Sn active site on the Cu surface,and Ag forms a dotted distribution.The reduction reaction takes the newly generated Ag as the reaction center,grows nucleate,and gradually forms a complete coating layer.The Cu@Ag coated powder with dense coating structure is finally obtained.The results of the microstructure and phase evolution of Cu-Ag composites indicate that with the increase of sintering temperature,the density of Cu-Ag composites gradually increases,and the maximum density reaches 98.8%at 550?.According to analysis,the coating structure of Cu@Ag powder can achieve the necking of nano-silver on the surface of copper particles at low temperature,thereby promoting low-temperature sintering.The electrical and mechanical properties of Cu-Ag composite materials show that as the sintering temperature increases,the electrical conductivity of the Cu-Ag composite first increases and then decreases.At 500?,the electrical conductivity of the Cu-Ag composite reached a maximum of 75%IACS.As the temperature increases,the tensile strength of the Cu-Ag composite gradually increases.At 550?,the tensile strength of the Cu-Ag composite reaches a maximum value of 370 MPa.Combined with the relevant literature of Cu-Ag composite materials,the temperature increases,the solid solution between Cu and Ag increases,the electrical properties of the materials decrease,and the mechanical properties improve.