Research On Synergistic Strengthening Effect And Deformation Mechanism Of Gradient Structural Materials—copper And Copper-zinc Alloys

The existence of gradient structure can significantly improve the strength and ductility of materials and improve the contradictory relationship between these two properties.At present,the research on the preparation of gradient structure materials and the mechanism of their plastic deformation is not perfect,and further investigation is needed.In this paper,the gradient structure materials of Cu,Cu-10 wt.%Zn and Cu-30 wt.%Zn were processed by surface mechanical attrition treatment(SMAT).Two types of gradient structures were prepared,i.e.single-layer gradient structure and dual-layer gradient structure,and the influence of the gradient structure of Cu materials on the synergetic strengthening behavior was investigated.Then,the influence of gradient structure of Cu?Cu-10 wt.%Zn and Cu-30 wt.%Zn materials with different stacking fault energy(SFE)on the strength-ductility of materials was analyzed,and the plastic strain mechanism of materials was explored by using digital image correlation(DIC)and in-situ EBSD analysis.The surface grains of the sample were refined effectively,and the surface hardness and yield strength were significantly increased,after SMAT treatment.Two kinds of Cu materials with single-layer gradient structure and dual-layer gradient structure were investigated,the yield strength of materials with dual-layer gradient structure is 20±5 MPa higher than that of single-layer gradient structure,and the uniform elongation is increased by 6%.This shows that materials with dual-layer gradient structure have higher synergetic strengthening effect,and the reason was that the presence of the gradient layer strengthens the heterogeneous deformation induction(HDI)effect.The strain of the dual-layer gradient structure was more uniform than that of the single-layer gradient structure,and the local strain concentration effect was effectively limited.In addition,the investigation of gradient structure of Cu?Cu-10 wt.%Zn and Cu-30 wt.%Zn materials,the material with lower SFE had improved strength and better ductility.Compared with annealed Cu-10 wt.%Zn,the uniform elongation of gradient structure Cu-10 wt.%Zn after SMAT processing for 2min only decreased by 6.63%,while Cu and Cu-30 wt.%Zn decreased by 17.45% and 17.58%respectively.The twin deformation mechanism and dislocation deformation mechanism will be carried out simultaneously in the plastic deformation process of the intermediate SFE material,so the intermediate SFE material has better strength and plastic combination.The DIC presents the evolution of the gradient structure material during plastic deformation,and the uniform distribution of surface slip bands proves that good ductility was provided by coarse matrix.Moreover,the higher local strain was concentrated at the intersection between the gradient layer and the matrix,which was also proved by the in-situ EBSD.The GNDs were aggregated in the gradient layer.With the increase of strain,GNDs move and accumulates in the interface of gradient layer and matrix.The material with gradient structure is forced to deform harmoniously during plastic deformation.