| Cu and its alloys are widely used in electrical industry,instrument industry,shipbuilding industry and machinery manufacturing industry,et al.fields rely on their own excellent electrical and thermal conductivity properties.However,with the development of science and technology,the strength and conductivity of conventional Cu-based materials are too low to meet the actual requiements.In recent years,it has been found that Cu and its alloys can maintain ultra-high strength,excellent electrical and thermal conductivity simultaneously,which arosed many attentions from domestic and froeign.But the thermodynamic stability of nano-scale Cu grains are poor enough,which easy to lose stability and lead to grain growth even in room temprature.Grian boundary manipulation is a feasible way to improve the stability and mechanical properties of the grain boundary,which has a promising application prospects.In this paper,with the help of advanced concepts of grain boundary manipulation and firstprinciples calculations methods,the relationships between the structure and performance of pure copper grain boundaries are systematically discussed at the electronic and atomic levels,the segregation tendencies of alloying elements in some typical Cu grain boundaries are studied,and the mechanisms of alloying elements segregations influence the properties of grain boundaries are revealed,which have important theoretical guiding meaning and reference value for the improvement of grain boundary stability and mechanical properties and the design of alloys composition in nanocrystalline Cu.The main research contents and results are as follows:(1)The 12 common symmetric tilted grain boundaries in Cu were studied and the grain boundary energies and works of fracture of 12 STGBs were calculated by first-principles total energy calculations,the results show that works of fracture present a inverse relationship with GB energies,and fit a linear relationship of Y=-1.094X+3.170.Besides,the order of the thermodynamic stability of the 12 kinds of grain boundaries is ?3 [110](111)> ?11[110](113)>?9 [110](221)>?19 [110](331)>?5 [001](210)>?3 [110](112)>?43[110](335)>?27 [110](115)>?5 [001](310)>?17 [110](223)>?13 [001](320)>?17 [001](410).(2)The segregation tendency of 8 common alloying elements(Zr,Cr,Ag,Ca,Sn,Ni,Mg,Zn)in ?5 [001](210),?5 [001](310)and ?11 [110](113)STGBs were calculated by firstprinciples calculations.The results show among the eight alloying elements,besides the Ni element,other elements all can segregate to the three STGBs,thus reduce the GBs energies and stabilize GBs.In the Cu ?5 [001](210)and ?11 [110](113)STGBs,the segregation of Zr and Cr can strengthen the fracture strength of GBs.In the Cu ?5 [001](310)STGB,the segregation of Mg,Cr,Zr and Ag can strengthen the fracture strength of GBs.(3)With the help of COHP,we found that the increase number of low-energy bonded electrons and decrease number of high-energy anti-bonded electrons at GBs should repsonsible for the stabilization effect of alloying elements segregations.Through the calculation of differential charge density,we found that the covalent-like electron distribution states after electron redistribution between the alloying atoms and their surrounding neighboring atoms are the strengthen mechanisms of GB after the segregations of alloying elements.(4)In the ?5 [001](210)STGB,the GB stabilization effect of Zr and Cr elements cosegregation is better than Zr and Cr segregations individually,and its strengthening effects better than Zr segregation but weaker than Cr segregation.Zr and Cr elements cannot cosegregation in ?5 [001](310)STGB.In the ?11 [110](113)GB,both the GB stabilization and strengthening effects of Zr and Cr elements co-segregation are better than Zr and Cr segregations individually. |
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