| The Cu-Nb composite wires fabricated by the accumulative drawing and bundling process have high strength and high electrical conductivity,and are very attractive for applications in high pulsed magnetic field for achieving 100 T pulsed magnetic field strength.In this paper,the microstructure and texture evolution of Cu-Nb composite wires with different annealing tempertures have been characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）and nanoindentation mechanical test.The effects of annealing temperture on mechanical and electrical properties were analyzed.The microhardness of CuNb nanocomposite zone was analyzed and the strength of material was estimated by calculation.The relationship between microstructure and mechanical properties and electrical properties of the annealed materials was analyzed.The main conclusions are as follows:（1）The Nb filaments in the Cu-Nb composite wires fabricated by accumulative drawing and bundling process forms a curved ribbon-like morphology.The average width and thickness of a single Nb filament is about 320 nm and 20 nm,respectively,reaching the nanometer scale.The Nb filaments have a fiber structure in the longitudinal section.The thickness of the innermost copper matrix is about 76 nm.and there are a large number of dislocations and twins in Cu matrix,which is related to the high strain energy and lattice distortion of material after large plastic deformation.（2）After annealing at a temperature below 300 oC,the size and morphology of Nb filaments did not change significantly and still assumes a ribbon-like shape and maintain the fiber structure in deformed wire parallel to the drawing direction.After annealing at 400 oC,the Nb filaments remained ribbon-like,but discontinuous spherical bulges appeared on the surface of some filaments.When the annealing temperature is higher than 500 oC,the boundary splitting of Nb filaments becomes obvious and the splitting of Nb band occurs.With the increase of temperature,the cylindrization,spheroidization and coarsening of Nb filaments become more obvious.（3）For wires with different annealing tempertures,Cu matrix mainly exhibits a（111）orientation,and Nb mainly exhibits a（110）orientation.The diffraction peaks of Cu matrix and Nb filament are wider,and the intensity of diffraction peak is lower.As the annealing temperature increased,the intensity of diffraction peak gradually increases and the shape becomes sharper.The half-height widths of（111）Cu and（110）Nbb diffraction peaks show different trends.With the increase of annealing temperature,the half-height width of（111）Cu diffraction peak decreases slightly.The half-height width of the（110）Nb diffraction peak generally decreases first and then increases with increase of annealing temperature.（4）The Cu matrix in as-drawn Cu-Nb composite wires mainly formed<111>texture,and no obvious<200>texture is observed.The Nb filament mainly formed<110>texture parallel to the drawing direction.With the increase of temperature,the<111>texture of Cu matrix and<110>texture of Nb filaments show the trend of first strengthening and then weakening.（5）The Vickers hardness of Cu-Nb composite wire showed a monotonous decrease with increasing annealing temperature.The load-displacement curves all show a smooth curve shape and the displacement of CuNb region is always less than Cu matrix regions.With the increase of annealing temperature,the elastic modulus of different test areas showed a slight decline and the yield strength decreases with the increase of annealing temperature,the strength decreases and the plasticity increases.（6）As the annealing temperature increased,the electrical conductivity of wires increases.The conductivity of material is mainly determined by the continuity of conductive path of Cu matrix.The resistivity of wires is mainly affected by interface scattering and dislocation scattering.The recrystallization of Cu matrix and spheroidization,cylindricalization and coarsening of Nb filaments will reduce the CuNb interface,increase the continuity of conductive path of Cu matrix,and weaken the contribution of interface scattering to resistivity,resulting in a significant increase in conductivity. |
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