Application of titanium wire, titanium alloy wire and titanium nickel alloy wire in the fields of industrial and consumer goods

The Japan Institute of Atomic Energy (the original research) cooperated with the European Community, Russia, and the United States to establish the International Thermonuclear Experimental Reactor (ITER), and began engineering design activities (EDA) in 1992.

The EDA has carried out the technological development of various advanced devices, and the development of superconducting coils is one of them. The toroidal magnetic field coil (TF coil) is manufactured by the Efremov Institute of Electrical Physics and Engineering in Russia, and is designed and developed by the Japan Institute of Atomic Energy. The Nb3Sn superconducting wire is assembled with a titanium tube as a sheath. The following is a brief description of the advantages of using pure titanium tubes to assemble superconducting coils and their development results developed by the Japan Institute of Atomic Energy.

The superconducting coil for the test is composed of 1152 Nb3Sn superconducting wires (0.81mm in diameter) enclosed in a pure titanium tube (tube wall thickness 2mm, inner diameter 43mm), and a layer of 9 turns (height) is wound on the inner side of the support plate. 0.6m) composition (Figure 1). The overall outer diameter of the superconducting coil used in the test is 1.5m and the height is 2.8m. The stainless steel tube surrounding the support plate is used to cool the support plate. The superconducting coil is installed in the center of the prototype coil of the solenoid in the ITER. A current of 46kA flows through the prototype coil in a 13T magnetic field. Tests have verified that the superconducting coil meets the performance required by the IERTF coil. The critical current of the Nb3Sn superconducting wire will decrease under thermal or mechanical stress. In the past, the Nb3Sn superconducting wire was enclosed in a stainless steel tube. The difference in shrinkage (temperature change is 650C～-269C) will cause thermal stress, which will reduce the superconducting properties. For this reason, it is necessary to choose a material with the same thermal shrinkage rate as the Nb3Sn superconducting wire as the sealing tube. Such materials include Inconel 908 and titanium. Japan Harayan considered that pure titanium is superior to Inconel 908 in terms of non-magnetism, corrosion resistance, and processability, so it began experimental development work on titanium. According to the test results of the influence of the metal tube material on the critical current of the small Nb3Sn conductor; it can be seen that when a pure titanium tube is used when the magnetic field is 12T, the critical current value is twice that of a stainless steel tube. Based on this result, a pure titanium tube with a wall thickness of 2mm was used as the sealing tube of the superconducting coil for the test in Russia, and it was successfully energized in Japan Harayan, which increased the critical current of the conductor used in ITER by 30, making the same Cost has achieved higher operating performance.

Due to the very large electromagnetic force generated by the ITERTF coil, the metal tube is required to have sufficient strength. In addition, since the Nb3Sn superconducting material needs to be heat treated at 650C, 240h or more, the metal tube must also withstand this heat treatment. From the perspective of thermal shrinkage, pure titanium is a very ideal material, but it is necessary to study the effect of aging treatment on strength and toughness. Japan Haraken and Nippon Steel Corporation jointly studied the effect of the oxygen content of pure titanium after aging on the mechanical properties at liquid helium temperature (4K). The results show that the mechanical properties of pure titanium at 4K depend on the oxygen content in pure titanium. When the oxygen content is about 0.1, the necessary strength and toughness can be maintained after heat treatment (650C, 240h). Based on this result, the tube used for the superconducting coil used in the test is a pure titanium tube with an oxygen content of 0.106 produced in Russia.

This technology is also expected to be applied in fields such as power storage superconducting coils that require high magnetic fields and high current coils.
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