Low Temperature Mechanical Properties Of Micro Scale NbTi Superconducting Filaments

The ITER program is currently China’s largest participation in international research cooperation project, the main function is to verify the possibility of peaceful use of nuclear fusion. Principle of the device is through the tokmak(tokmak) magnets have a huge magnetic field with constraint of high temperature plasma, so as to realize controllable nuclear fusion. The use of 4.5K helium cooling NbTi or Nb3 Sn winding cable superconductor magnet TokMark(CICC conductor). The micron scale NbTi filament is constitute the main part of the NbTi / Cu superconducting composite wire, the mechanical properties of the superconducting wire research has become one of the foundations of CICC and Tokamak magnet structural safety, functional design. MEMS and micro devices, on the other hand, a large number of use scale in micron or submicron scale of microscale materials such as copper wire, metal film, the material mechanical properties at low temperature research will provide guarantee for the device application at low temperature, so study the low temperature performance of micron scale materials both from face to the needs of the country, or academic frontiers have important scientific significance.Considering micro scale mechanical properties of material at low temperature test, Huazhong University of science and technology in development of fiber tensile machine based on the developed precise temperature control device, the micro scale materials under low temperature mechanical properties test. Using the device for the experimental study of different diameters and different strain rates and different temperatures of micron copper wire. Test results show that the low temperatures of different diameters of micron copper wire has scale effect. However, at room temperature, there is no obvious scale effect. Effect of tensile rate range of 5-30mm/min at room temperature and low temperature of micron copper is not obvious. Different temperatures of 35 and 50 wire Young’s modulus and tensile strength the temperature dependence, tensile strength and Young’s modulus were with the change of temperature into a linear relationship, but the yield strength along with the temperature change is not obvious.To study the mechanical properties of liquid nitrogen environment NbTi superconducting filament, we also design a set of microscale at room temperature and liquid nitrogen environment material tensile experiment equipment, USES the device of micron scale NbTi filaments of different diameter, two wire stranded wire, three wire winding has carried on the experimental study. Test results show that micron scale NbTi filaments under normal temperature and liquid nitrogen environment without scale effect, from the tensile curve of the initial segment and unloading period of little change on the numerical calculated results. Through 7 nbti filaments for repeated ten times add after unloading experiment found that compared with the tensile curve has obvious degradation phenomenon. Finally, by comparing the filament winding structure often, the results showed that under low temperature, the tensile strength of the winding structure under normal temperature does not change significantly compared with monofilament, and low temperature trends to increase significantly, and the main reason is friction between wire under the low temperature effect should not be neglected.