Microstructural Features in Multicore Cu–Nb Composites

none5siThe study is devoted to heavily drawn multicore Cu–18Nb composites of cylindrical and rectangular shapes. The composites were fabricated by the melt-and-deform method, namely, 600 in situ rods of Cu–18%Nb alloy were assembled in a copper shell and cold-drawn to a diameter of 15.4 mm (e = 10.2) and then rolled into a rectangular shape the size of 3 × 5.8 mm (e = 12.5). The specimens were analyzed from the viewpoints of their microstructure, microhardness, and thermal stability. The methods of SEM, TEM, X-ray analysis, and microhardness measurements were applied. It is demonstrated that, at higher strain, the fiber texture ⟨110⟩Nb∥ ⟨111⟩Cu∥ DD (drawing direction), characteristic of this material, becomes sharper. The distortions of niobium lattice can be observed, namely, the {110} Nb interplanar distance is broadened in longitudinal direction of specimens and compacted in transverse sections. The copper matrix lattice is distorted as well, though its distortions are much less pronounced due to its recrystallization. Evolution of microstructure under annealing consists mainly in the coagulation of ribbon-like Nb filaments and in the vanishing of lattice distortions. The structural changes in Nb filaments start at 300–400 °C, then develop actively at 600 °C and cause considerable decrease of strength at 700–800 °C.openElena N. Popova, Irina L. Deryagina,Evgeniya G. Valova-Zaharevskaya, Ruello Maria Letizia, Vladimir V. PopovElena N., Popova; Irina L., Deryagina; Evgeniya G., Valova-Zaharevskaya; Ruello, Maria Letizia; Vladimir V., Popo

Structure and Properties of High-Strength Cu-7.7Nb Composite Wires under Various Steps of Strain and Annealing Modes

Microstructure and mechanical properties of in situ Cu-7.7Nb microcomposite (MC) wires manufactured by cold drawing with intermediate heat treatment (HT) have been studied. The evolution of Nb filaments morphology under various steps of deformation and modes of intermediate HT have been studied by the SEM and TEM methods. According to X-ray analysis, internal microstresses accumulate in the niobium filaments of the drawn MC, leading to a decrease in ductility. After heat treatment, the ductility of the wire increases significantly, since the microstresses in the niobium decrease even at the lowest HT temperature. The strength of the composite decreases under the HT because of negative changes in morphology and interface density of Nb filaments. The Nb texture is stable under the HT up to 800 °C. The Nb filaments morphology and semi-coherent boundaries at Cu/Nb interfaces are restored under the post-HT cold drawing, leading to a sharp increase in the strength of the MC wire. Reducing the niobium concentration to 7.7%Nb relative to the traditional MC with 16–20%Nb and the recovery of the wire ductility under the HT makes it possible to obtain long-scale high-strength microwires with an extremely small diameter of 0.05 mm and high ultimate tensile strength of 1227 MPa

Effect of Doping Mode and Composite Geometry on the Structure of Nanocrystalline Nb₃Sn Layers in Superconducting Nb/Cu-Sn Composites

Методами просвечивающей и сканирующей электронной микроскопии с привлечением количественного микроанализа изучены многоволоконные сверхпроводящие композиты Nb/Cu-Sn, изготовленные "бронзовым" методом и легированные титаном. Установлено влияние способа легирования ("искусственное" легирование Nb-волокон сплавом НТ50 или легирование титаном бронзовой матрицы) и внешнего диаметра композита на морфологию Nb-волокон и диффузионных слоев Nb3Sn и на средний размер зерен сверхпроводящей фазы. Выявлена корреляция между средним размером зерен фазы Nb3Sn и критической плотностью тока сверхпроводника.Multifilamentary superconducting bronze-processed Nb/Cu-Sn composites doped with Ti have been studied by transmission and scanning electron microscopy. The effect of doping mode (artificial doping of Nb filaments by inserts of NbTi alloy or Ti doping of the bronze matrix) and external wire diameter on the morphology of Nb filaments and Nb3Sn layers and on grain sizes of the superconducting phase has been revealed. Correlation between the average grain size of Nb3Sn phase and critical current density of a composite is demonstrated

Effect of Doping Mode and Composite Geometry on the Structure of Nanocrystalline Nb₃Sn Layers in Superconducting Nb/Cu-Sn Composites

Методами просвечивающей и сканирующей электронной микроскопии с привлечением количественного микроанализа изучены многоволоконные сверхпроводящие композиты Nb/Cu-Sn, изготовленные "бронзовым" методом и легированные титаном. Установлено влияние способа легирования ("искусственное" легирование Nb-волокон сплавом НТ50 или легирование титаном бронзовой матрицы) и внешнего диаметра композита на морфологию Nb-волокон и диффузионных слоев Nb3Sn и на средний размер зерен сверхпроводящей фазы. Выявлена корреляция между средним размером зерен фазы Nb3Sn и критической плотностью тока сверхпроводника.Multifilamentary superconducting bronze-processed Nb/Cu-Sn composites doped with Ti have been studied by transmission and scanning electron microscopy. The effect of doping mode (artificial doping of Nb filaments by inserts of NbTi alloy or Ti doping of the bronze matrix) and external wire diameter on the morphology of Nb filaments and Nb3Sn layers and on grain sizes of the superconducting phase has been revealed. Correlation between the average grain size of Nb3Sn phase and critical current density of a composite is demonstrated