Study On The Microstructure Evolutionand Thermal Properties Of Cu-Nb Composite Wires

Cu-Nb micro-composite wires are good candidate materials for pulsed magnet,due to its high strength and high electrical conductivity properties. However, there arelimited reports about the evolution of micro-structure and the thermal property andstability of wires. In present work, we chose the Cu-Nb composite wires with differentstrains which were fabricated by accumulative drawing and bundlingprocess (ADB).The micro-structure evolution during fabrication and the thermal property werecharacterized by means of SEM(scanning electron microscope),XRD(X-raydiffraction),EBSD(electron black-scattered diffraction),DSC(differential scanningcalorimeter) and Thermal dilatometer.The microstructure, mechanical behaviour andthermal stability were discussed. The internal stress at different temperature was alsoanalysized.The main results in this paper are as follows:①The Cu matrix of Cu-Nb micro-composite wires fabricated by ADB develops asharp <111> textureand shows multiscale character from micrometer to nanometer. Thethe Nb fibers develop <110>fiber texture parallel to drawing direction. However, theresidual tensile internal stress exists in Cu matrix and the residual compressivestressexists in Nb fibers of Cu-Nb wires.②The recrystallization temperature of Cu matrix in the Cu-Nb wires with thestrains9.6,14.4,17.7,24.8is in the region of150oC to190oC, and the recrystallizationtemperature of Nb fibers is about600oC. The recrystallization temperature doesn’tchange with the strains increasing. On the other hand, the wires show thermalcontraction in the drawing direction, and as the strain increases, the critical temperaturefor thermal contraction decreases while the contraction level increases.③The thermal contraction between185oC to250oCin the Cu–Nb wire withη=24.8during annelingis contributed to the recrystallization of Cu matrix which inducesthe release of residual internal stress, i.e., the annealing result in the release of thetensile internal stress in the Cu matrix and compressive stress in the Nb fibers. Inaddition, with the annealing temperature increaseing, the hardness of wire decreases.However，the hardness shows a slow decline at the temperatures between200oC to300oC due to the thermal contraction. When the temperature is above300oC, the hardnessdecreases rapidly.④With the annealing temperature increasing, the texture of Cu matrix in the wire withη=24.8changes from the <111>texture to <111> texture and <100> texture.However, there are appearing some <111> textures change to <100> textures at thetemperature region from200oC to330oC. on the other hand, With annealingtemperature increasing, the texture components of Nb fibers are mainly <110> textureand have not changed clearly.⑤When the annealing temperature is below400oC, the Nb fibers in the wire withη=24.8remains the fiber shape as that in the as-drawn wire. However, when theannealing temperature is higher than400oC, the Nb filaments become wavy in the edgeand grooves appear in some Nb filaments, and these grooves are favorable forspheroidization. After annealing at600oC or700oC, the Nb filaments break up, showingcylinderization and bamboo-like structure. When the temperature reaches970oC, thecoarsening is more obvious and new contact points join adjacent cylinders due to thecoarsening of Nb fibers...