銅安定化Nb-Ti超電導線の引張性質の温度依存性

抄録

Two types of copper-stabilized Nb-Ti superconducting wires No. 1 and 2, were tensile-tested at various temperatures from 7 to 293K. Samples No. 1 and 2 have copper ratios of 3.92 and 7.72, cross sections of 0.86mm×1.7mm and 0.5mm diameter, 740 and 24 filaments of which diameter are 22 and 38μm, and were twisted and none-twisted, respectively, Temperature and strain rate dependences of yield stress, 0.2% proof stress, the stress corresponding to yielding in superconducting filaments, tensile-strength, elongation to fracture and serrated deformation were investigated in detail. The main results obtained are as follows: (1) Yield stress and proof stress increase slightly with decreasing temperature and the stress corresponding to yielding in the filaments and tensile strength increase with decreasing temperatures to about 15K and then decrease at temperatures below 15K in both the samples. (2) Elongation increases with decreasing temperature to about 15K, and then decrease in both the samples. Values of elongation at 7K of sample No. 1 show considerable scatter (0.7-18%) and values of elongation at temperatures above 15K show no scatter. Very low values of elongation seems to be due to remarkable discontinuous slip in thin regions of the filaments. (3) Yield stress, proof stress, the stress corresponding to the yielding in the filaments and tensile strength increase with increasing strain rate at 293K and show independence of strain rates at 7K in both the samples. (4) Elongation of sample No. 2 at 7 and 293K increase with increasing strain rate, On the other hand, elongation of sample No. 1 is independent of strain rates at 293K and values of elongation show considerable scatter at 7K regardless of strain rates.