Study On The Preparation Process And Mechanical Properties Of Copper-based Multilayer Structure Composite Materials

With the increasing demand of engineering materials,metal materials with high strength and good ductility have attracted more and more attention.By the technology of severe plastic deformation,the strength of the material is increased more,but most of the ductility is lost.In order to avoid strength-ductility trade off,the creation of heterostructures is particularly beneficial,and the strain gradient in the heterogeneous structure can promote the coordination of strength-ductility.The heterogeneous multilayered structure utilizes the excellent properties of the constituent materials and significantly improves the mechanical properties of the material by adjusting the constituent layers and interfaces.Copper has an excellent ductility,but its strength and wear resistance are poor,the traditional performance of copper and copper alloys limits its further application in various fields.At present,there are few systematic studies on the mechanical behavior of heterogeneous multilayer material.In this paper,copper and copper alloys with multi-layer structure materials were prepared by electroplating process,and the mechanical properties were studied.The multilayered gradient structure copper was successfully prepared by electroplating and SMAT methods.By controlling the pre-treatment process and improving the bath formulation,a uniform and dense coating is obtained,which better solves the problem of interlayer bonding.Through multi-layer bonding and coordinated deformation between grains of different sizes,a multi-layer gradient copper material with good overall performance was obtained.Through comparison,it was found that the multilayer structure can indeed increase the strength of the material on the basis of a single layer gradient structure,breaking through the limitations of the single layer.Due to a certain structural change between the coating and the matrix,the abrupt change of their properties and the bonding force between different layers have a great influence on the plasticity of multilayer structure materials.Pure copper was used as the substrate and Ni plating was prepared by electroplating process.Cu/Ni layered composites with different thickness ratios were obtained.The influence of different thickness ratios on the mechanical behavior of multilayer materials was studied and discussed.The results show that the appropriate combination of coating thickness and matrix thickness may result in better coordination of the strength and plasticity of the composite.The yield strength of the composite depends mainly on the intrinsic strength of the Ni and Cu layers.After electroplating Ni,SMAT technology is used to make the grain of the coating more fine,the yield strength is obviously improved,and the combination of the coating and the matrix is more dense.It is not easy to separate during the stretching process,and better coordinate deformation and retain part of its plasticity.Electroplating was performed on the pure copper substrate to prepare alternately Ni plating and Cu plating to obtain a Cu/Ni multilayer structure material.The strain rate dependence of the strength and ductility of the Cu/Ni multilayer material and its mechanism were analyzed.It was found that the multilayer material has obvious strain rate sensitivity(larger m value)caused by the stress gradient at the interface in the layered structure.The strength of a Cu/Ni multilayer material is not entirely provided by the Ni coating,and part of it originates from the back stress generated by the accumulation of a large number of dislocations at the interface.The layered structure material has obvious Bauschinger effect,when the strain rate increases,the strain gradient increases,resulting in more geometrically necessary dislocations to hinder dislocation movement and contribute to higher back stress,and the greater the back stress,the greater its contribution to strength.The mechanical properties and microstructure of copper-based multilayered composites were analyzed by different test methods.The results show that the mechanical properties of the three-layered gradient copper are better than those of the double-layered gradient copper.The thicker the single-layer coating and the more gradient layers,the better the obtained sample performance.When the thickness ratio of Cu matrix to Ni plating layer is between 12 and 8,the Cu/Ni layered composite material achieves a good coordinated deformation of the soft phase and the hard phase,so that the strength-plasticity has a good match.In the Cu/Ni multi-layer structure material,the interface of 10 min sample is more,the back stress is higher,the strength is higher,and its mechanical performance is better than 30 min sample.