Titanium for conductor conduit in superconducting coil

Details Titanium for conductor conduit in superconducting coil Titanium for conductor conduit in superconducting coil

1994-05-16

1996-05-07

Kastler, Scott

Alloys or metallic compositions

Titanium base

148421, C22C 1400

Patent

active

055143326

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to large-current superconducting wire material for use in nuclear fusion reactors, energy storage apparatuses and other such devices.
2. Description of the Prior Art
In the prior art there is used forced cooled type multi-filament superconducting wire formed of stabilizer and several hundred superconductor filaments twisted together, with each filament being about one millimeter in diameter, arranged inside stainless steel conduit pipe.
When the superconductor is Nb.sub.3 Sn or an alloy of Nb.sub.3 Sn, a problem is that the critical current density of the superconductor is degraded to some 20 to 40 percent below that of the multi-filament superconducting wire of Nb.sub.3 Sn or Nb.sub.3 Sn alloy. It is considered that this may be the result of compressive strain on the Nb.sub.3 Sn arising from the difference between the thermal shrinkage factors of the Nb.sub.3 Sn and the stainless steel.
One possible solution is to use, as the conduit material, a nickel alloy such as Incoloy 908 that has substantially the same thermal shrinkage factor as Nb.sub.3 Sn, and a high tensile strength at the temperature of liquid helium (hereinafter referred to as "4K"). However, because such alloys are ferromagnetic and also have problems with respect to corrosion-resistance, they have not yet been applied as a conduit material.
Titanium (pure titanium and titanium alloy) is a non-magnetic, highly corrosion-resistant material with a thermal shrinkage factor which is close to that of Nb.sub.3 Sn, and its excellent balance of strength and toughness at very low temperatures makes it an excellent prospect as a material for conductor conduit in superconducting coil.


SUMMARY OF THE INVENTION

The object of this invention is to provide a superconductor that resolves the problem of the degradation in the critical current density of superconductors that use Nb.sub.3 Sn or Nb.sub.3 Sn alloy, and possesses good mechanical properties as well as good fracture toughness.


BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become more apparent from a consideration of the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a graph showing the relationship between the oxygen content of titanium at 4K, and its tensile properties;
FIG. 2 is a graph showing the relationship between the oxygen content of titanium at 4K, Charpy energy absorption value and K.sub.10 value;
FIGS. 3a and 3b are graphs showing the relationship between content amounts of impurities other than oxygen, and fracture toughness (K.sub.10 value and Charpy energy absorption value);
FIG. 4 is a graph showing the degree of change in the tensile properties and fracture toughness at 4K of titanium subjected to aging treatment; and
FIG. 5 is a graph showing the mechanical properties, at 4K, of base metal portions compared with welded portions of titanium.


DETAILED DESCRIPTION OF THE INVENTION

The titanium for conductor conduit in superconducting coil produced in accordance with this invention comprises, in mass % 0.07 to 0.13 percent O, up to 0.10 percent Fe, up to 0.10 percent C+N, and up to 0.005 percent H, with the remainder being Ti and unavoidable impurities, said titanium exhibiting good mechanical properties, corrosion-resistance and thermal shrinkage properties of base metal and welded portions at 4K.
Conduit pipe material for superconducting wire used in nuclear fusion reactors and other such large-current applications is generally required to have the following properties: (1) the same thermal shrinkage factor as that of Nb.sub.3 Sn, (2) non-magnetic, (3) corrosion-resistance, (4) high strength, high toughness and reliability at 4K, (5) weldability (defect-free welded portions, welded portions that have the same mechanical qualities as those of the base metal), and (6) bendability (low strength at room temperature).
After establishing what the problems were with the prior art technology and what n

REFERENCES:
The Nikkankogyo Shimbunsha Ltd., "Titanium Metal and Its Application", pp. 42-45 and 160-161, Dec. 15, 1983.

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