Method for manufacturing power-metallurgy processed Nb

1. A method for manufacturing a powder-metallurgy processed Nb 3 Sn superconducting wire, the method comprising the steps of:

filling a sheath made of Nb or a Nb alloy with a raw material powder containing Sn;

reducing a diameter of the sheath filled with the raw material powder to form a wire; and

heat-treating the wire to form a superconducting phase at an internal surface of the sheath,

wherein the raw material powder contains a Cu—Sn alloy powder or a Cu—Sn intermetallic compound powder and a Sn powder, and is compacted under isotropic pressure before the step of filling the sheath, and

wherein the Sn content in the Cu—Sn alloy powder or the Cu—Sn intermetallic compound powder is in a range of about 20 to 80 mass %, and the Sn powder is contained in the raw material powder at a mass ratio of about 0.2 to 2.0 relative to the Cu—Sn alloy powder or the Cu—Sn intermetallic compound powder.

2. The method according to claim 1 , wherein the Cu—Sn alloy powder or the Cu—Sn intermetallic compound powder has a maximum grain size of about 15 μm or less.

3. The method according to claim 1 , wherein the Sn powder contains 2,000 ppm or less of oxygen.

4. The method according to claim 3 , wherein the Sn powder is prepared by inert gas atomization.

5. The method according to claim 1 , wherein the sheath is surrounded by an intermediate barrier layer containing at least one metal element selected from the group consisting of Ta, Nb, V, Zr, Mo, Hf, and Ti.

6. A method for manufacturing a powder-metallurgy processed Nb 3 Sn superconducting wire, the method comprising the steps of:

filling a sheath made of Nb or a Nb alloy with a raw material powder containing Sn;

reducing a diameter of the sheath filled with the raw material powder to form a wire; and

heat-treating the wire to form a superconducting phase at an internal surface of the sheath,

wherein the raw material powder contains a Cu—Sn alloy powder or a Cu—Sn intermetallic compound powder and a Sn powder, and is compacted under isotropic pressure before the step of filling the sheath, and

wherein the raw material powder filling the sheath has a two-layer structure including an inner layer and an outer layer and the outer layer is formed of part of the Sn powder.

7. The method according to claim 6 , wherein the Cu—Sn alloy powder or the Cu—Sn intermetallic compound powder has a maximum grain size of about 15 μm or less.

8. The method according to claim 6 , wherein the Sn powder contains 2,000 ppm or less of oxygen.

9. The method according to claim 8 , wherein the Sn powder is prepared by inert gas atomization.

10. The method according to claim 6 , wherein the sheath is surrounded by an intermediate barrier layer containing at least one metal element selected from the group consisting of Ta, Nb, V, Zr, Mo, Hf, and Ti.

11. A precursor to a powder-metallurgy processed Nb 3 Sn superconducting wire, comprising:

a sheath made of Nb or a Nb alloy; and

a raw material powder filling the sheath, containing a Cu—Sn alloy powder or a Cu—Sn intermetallic compound powder and a Sn powder,

wherein the precursor is used in a process for manufacturing a powder-metallurgy processed Nb 3 Sn superconducting wire, including the steps of reducing the diameter of the precursor to form a wire, and heat-treating the wire to form a superconducting phase at the interface between the sheath and the raw material powder, and

wherein the Sn content in the Cu—Sn alloy powder or the Cu—Sn intermetallic compound powder is in the range of about 20 to 80 mass %, and the raw material powder contains the Sn powder in a mass ratio of about 0.2 to 2.0 relative to the Cu—Sn alloy powder or the Cu—Sn intermetallic compound powder.

12. The precursor according to claim 11 , wherein the Cu—Sn alloy powder or the Cu—Sn intermetallic compound powder has a maximum grain size of about 15 μm or less.

13. The precursor according to claim 11 , wherein the raw material powder has been compacted under isotropic pressure.