Study On The Preparation And Mechanical Behavior Of Heterostructure Copper

Pure copper is a soft metal,reddish-orange with metallic luster,good ductility,high thermal conductivity and high electrical conductivity,so it is widely used in various fields.However,pure copper has low strength and poor wear resistance,which makes it increasingly unable to meet the high-performance requirements of materials in various fields.Traditional materials strengthening methods can increase the strength of materials and reduce the ductility sharply,which makes the improvement of comprehensive mechanical properties not obvious and the practicability is very low.Therefore,how to increase the strength of pure copper without causing a large ductility reduction is the focus of research.In recent years,the introduction of heterogeneous structure has provided a new research direction for materials with excellent strength and ductility.In a heterogeneous structure,the soft regions and hard regions(e.g.,small and large grains)were mixed together.The soft regions undergo more plastic deformation than the hard regions,so the gradient of plastic deformation increases.This adjustment of the plastic gradient requires the storage of geometrically necessary dislocations,which can contribute to work hardening,thereby increasing the overall strength and ductility of the material.This paper says the preparation of copper heterostructure by surface mechanical attrition,and 5mm-Cu-Dual,1.5mm-Cu-Single,2mm-Cu-Single and 2.5mm-Cu-Single samples were prepared by controlling the thickness of the sample and the single and doublesided SMAT process.A series of samples were used to study the difference in mechanical properties of heterogeneous structure copper in different proportions of heterostructure and the effect of single-sided and double-sided SMAT process on mechanical properties of materials under the same proportion of heterostructure layer.The results of microhardness test,quasi-static tensile test and Bauschinger effect test show that the heterogeneous structure can greatly improve the mechanical properties of pure copper and retain the good ductility of the materials.The yield strength of all samples increases by maximum 207.8% and minimum 141% coMPared with pure copper.And the ductility of all samples is maximum 75.01% of pure copper and minimum 44% of pure copper,respectively,By means of metallographic analysis,scanning electron microscopic(SEM)analysis,EBSD test and analysis,the microstructure and thickness of the heterostructure layer and its fracture mode during tension were obtained.The mechanical behavior and stress-strain distribution of heterogeneous copper during tension were analyzed by macro-and micro-digital image correlation tests.The experimental results show that the main reasons for the increase of the strength of the heterostructure copper are grain refinement strength,small angle grain boundary strengthening(dislocation strengthening)and coordinated deformation caused by back stress.As the proportion of the heterostructure copper decreases with the proportion of the heterostructure layer,the yield strength and tensile strength also decrease and the uniform elongation increases accordingly.When the proportion of the heterostructure layer is lower than a certain value,its contribution to the material strength will become weaker and not completely linear.The yield strength,tensile strength and uniform elongation of the 3mmCu-Dual,4mm-Cu-Dual and 5mm-Cu-Dual samples treated with double-sided SMAT were better than those 1.5mm-Cu-Single,2mm-Cu-Single and 2.5mm-Cu-Single samples treated with single-sided SMAT at the same proportion of heterostructure layers.Double-sided SMAT samples have double-layer heterostructure layer,which leads to higher back stress,resulting in higher back stress strengthening and back stress work hardening to coordinate deformation,affecting the overall yield strength and uniform elongation of the materials.The digital image correlation test shows that stress and strain preferentially concentrate at the junction of heterostructure layer and coarse-grained layer,where a large number of stress concentrates to produce coordinated deformation of heterostructure,thus improving the mechanical properties of materials.The strengthening mechanism of coordinated deformation of heterogeneous structures is confirmed at the micro level.