極細多芯NbTiHf線の高磁界特性
1983 年 18 巻 5 号 p. 256-263
詳細
1983 年 18 巻 5 号 p. 256-263
A Nb-61.7at.%Ti-3at.%Hf alloy has been fabricated into multifilamentary wires and studied in terms of high field superconducting properties.
First, effects of precipitation heat treatment at temperatures between 325 and 500°C and cold working up to 99% area reduction ratio after the heat treatment on the superconducting properties at 4.2K were examined. The heat treatment enhances the critical current density, Jc, in low fields below 8T, but not that inhigh fields above 10T. The cold working after heat treatment is identified as critical to increasing Jc in high fields. Jc increases with reduction ratios up to 95%. Thus, to obtain high Jc in high fields a process emerges where the heat treatment producing a maximum upper critical field, Bc2, is followed by severe cold working. The concept underlying this may be applicable to alloy superconductors other than NbTiHf.
Second, the superconducting properties at 1.8K were investigated. The critical current density Jc vs. magnetic field B curves obtained for 4.2K are found to coincide with those for 1.8K when shifted along the B axis by 3.5T. The present NbTiHf superconductor has higher Jc and Bc2 at 1.8K than those of typical NbTi. For both 4.2 and 1.8K, maximum pinning forces in samples cold-worked after heat treatment appear at the same reduced field of about 0.5, indicating that the temperature scaling law may hold for this NbTiHf superconductor.
