We succeeded in the fabrication of high-J c MgB 2 /Fe wires applying the internal Mg diffusion (IMD) process with pure Mg core and SiC addition. A pure Mg rod with 2 mm diameter was placed at the center of a Fe tube, and the space between Mg and Fe tube was filled with B powder or the powder mixture of B-(5mol%)SiC. The composite was cold worked into 1.2mm diameter wire and finally heat treated at temperatures above the melting point of Mg(~650 o C). During the heat treatment liquid Mg infiltrated into B layer and reacted with B to form MgB 2 . X-ray diffraction analysis indicated that the major phase in the reacted layer is MgB 2 . SEM analysis shows that the density of MgB 2 layer is higher than that of usual powder-in-tube(PIT) processed wires. The wires with 5mol% SiC addition heat treated at 670 o C showed J c values higher than 10 5 A/cm 2 in 8T and 41,000A/cm 2 in 10T at 4.2K. These values are much higher than those of usual PIT processed wires even compared to the ones with SiC addition. Higher density of MgB 2 layer obtained by the diffusion reaction is the major cause of this excellent J c values.
A modeling study was carried out to provide a description of the critical current distribution of bent multifilamentary Bi2223/Ag/Ag alloy superconducting composite tape samples. In the modeling, the difference between the tensile fracture strain of the Bi2223 filaments along the sample length under no residual strain and residual strain was used as a unifying parameter for the description of the damage evolution. The unifying parameter was treated to be different from sample to sample and also from position to position in each sample. The statistics of the unifying parameter were combined with the shape of the core and exerted tensile strain of the Bi2223 filaments, from which the relation of the heterogeneous damage evolution to the distribution of the critical current was formulated. The proposed model was applied to the reported data of 33 samples of the round robin test of VAMAS (Versailles project on advanced materials and standard)/TWA16 (Technical working area 16, superconducting materials) in 2000-2001. The reported distributions of the critical current of the bent-damaged samples were described well by the present model.
A wire-conductor fabrication method has been developed for Cu–Ag alloys containing 2–60 at. % Ag where high strength and high conductivity conductors are obtained by cold working combined with intermediate heat treatment. The intermediate heat treatment is repeated 3–4 times at 350–450 °C for 1–2 h at appropriate stages of reduction of area. The optimized Cu-16 at. % Ag alloy wire with 99% reduction of area showed a tensile strength of 1000 MPa and an electrical conductivity of 80% IACS at room temperature. This suggests that the wires fabricated may be very promising for high-field pulsed magnet use.
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