Spiral superconducting NbTi filaments: electric field and critical current

As a first step to a better understanding of the voltage—current characteristics of fine filament multifilamentary composite superconductors, the electric field and critical current along a single spiral-shaped filament were studied. When the spiral superconducting filament was carrying constant current and placed in a magnetic field, the local critical current and electric field vary due to the change of the angle between the magnetic field and filament axis. A theory is presented which enables us to calculate the mean and local values of the electric field and critical current of spiral samples for arbitrary orientation between the magnetic field and spiral axis. The presented experimental results are in good agreement with this theory.     

Further improvements in current density by reduction of filament spacing in multifilamentary NbTi superconductors

Current densities, J_cs, approaching those required in the dipole magnets of the Superconducting Super Collider have been achieved in conventional multifilamentary NbTi superconductors of the type used in the Colliding Beam Accelerator and the Tevatron magnet designs. These high J_cs have resulted from a simple reduction in the spacing-to-diameter ratio, S/D, from 0.35 to 0.13, keeping other factors the same.     

Influence of CuNi matrix on a.c. losses and voltage-current characteristics of fine filament NbTi superconductors

The results of a.c. loss measurements at 4.2 K in two types of fine filament NbTi superconductors with a CuNi matrix are presented. The conductors were manufactured by Alsthom Atlantique (France) and Showa Electric Wire & Cable (SEWC, Japan). A.c. losses per cycle were determined from magnetization measurements on samples without transport current, subjected to the external magnetic field perpendicular to the conductor axis. Measurements were carried out at two frequencies: 0.1 and 50 Hz. The range of magnetic field amplitudes for Alsthom Atlantique and SEWC samples was 2.5 × 10⁻³ − 3T and 5 × 10⁻² − 2 T, respectively. By measurements at T ≈ T_c, 77 and t~300 K, we proved the existence of hysteretic loss in the CuNi matrix of these conductors. Current-voltage characteristics were also measured. Critical current densities determined from magnetization and current-voltage characteristics were compared. The observed difference is discussed.     

Emergence of NbTi as supermagnet material

The discovery and emergence of NbTi as a high field superconductor is reviewed. The prehistory and setting for its discovery are described, and an anecdotal history follows its development up to the first successful large scale applications.     

Inter-dependence of grain growth,Nb segregation,and chemical ordering in FeSiNb nanocrystals

It is known that small Nb additions help stabilize Fe₃Si against grain growth. We studied the microstructural stability of (Fe₃Si)_.95Nb_0.5 during annealing by Mössbauer spectrometry, x-ray diffractometry, and transmission electron microscpy. We measured the development of grain growth, chemical ordering, and the segregation of Nb atoms. We identified inter-relationships between these processes. Chemical ordering was found to be linked to Nb segregation; after the segregation of Nb atoms, DO₃ chemical order developed in the Fe₃Si crystallites. Grain growth was found to be impeded when Nb segregation occurred, although the development of DO₃ order could be involved.     

Pinning force in superconducting NbAlGe systems

Results of direct mechanical measurements of the pinning force in NbAlGe superconducting bulk samples are given. The dependence of average measured pinning force on the external magnetic field up to 5 T at 4.2 K was determined experimentally. The results obtained are compared with those determined by critical current density measurements previously performed electrically on the same samples.     

Application of pulsed electric current in immiscible liquid and droplet processing

Electromagnetic, chemical and thermo-mechanical processing can be applied to the fabrication of polymeric materials which react to external fields such as stress, temperature, moisture, pH, electric or magnetic fields to optimise properties. In this article, the application of the pulsed electromagnetic field in an immiscible liquid phase is reviewed. The droplet behaviour of polymer emulsion's liquid phases is enriched with significant complex phenomena. In emulsion, droplet break-up, size evolution, coalescence, coarsening, flocculation and interfacial interaction among droplets are assessed as a function of processing.

This review was submitted as part of the 2018 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.     

Microstructure characterization of nanometer carbides heterogeneous precipitation in Ti–Nb and Ti–Nb–Mo steel

The influences of micro-alloying elements and hot deformation on the precipitation morphology of Ti–Nb and Ti–Nb–Mo steels were investigated. The nanometer sized carbide particles randomly dispersed in the ferrite matrix are attributed mainly to severe deformation at high temperature and low isothermal holding temperature. Of the two steels with different combinations of the micro-alloying elements, Ti–Nb and Ti–Nb–Mo, the steel with Ti–Nb–Mo was more effective in precipitating hardening due to its slower carbide coarsening rate. Based on observations of micrographs, the nano-sized TiMoC and TiNbC precipitated in polygonal ferrite grains when the Ti–Nb–Mo and Ti–Nb steels were isothermally treated at 650 °C for 3 min and 180 min. The smaller of the two carbides, TiMoC, precipitated in the ferrite grain, and the hardness of Ti–Nb–Mo steel was higher than that of Ti–Nb steel. Moreover, the tiny ferrite grains and high dislocation density in the Ti–Nb–Mo steel were found to provide an attractive combination of strength and toughness.