The effects of Mg doping on the microstructure and transport properties of internal tin-processed brass matrix Nb3Sn superconductors

摘要

The addition of Zn into Cu matrix has been proved to enhance the Sn activity and accelerate the formation of a Nb3Sn layer in internal tin-processed Nb3Sn wires. However, in our samples, Ti is doped in Sn cores, and during the reaction, Ti was observed to accumulate between the inner and outer sub-elements of the 1980-Nb-core multi-filamentary brass matrix wires. With the addition of Mg into the brass matrix, Ti accumulation between the sub-elements was significantly suppressed, which promoted Ti incorporation into the Nb3Sn layers. Meanwhile, the formed Nb3Sn layers exhibited smaller grain sizes. Compared to the brass (Cu-12wt%Zn) matrix wires, an improvement of critical current density (J(c)) was found in the Cu-12Zn-0.2Mg matrix wires due to the incorporation of Ti into the Nb3Sn layer and the refinement of the Nb3Sn grain size. The irreversibility field (B-irr) and maximum bulk pinning forces (F-p,F-max) were calculated from the Kramer plot by analyzing the J(c)(B) curves. A small amount of Mg (0.2 wt%) doping into the Cu-12Zn matrix wires can increase the B-irr value by about 0.5 T and the F-p,F-max value by about 3 similar to 4 GN m(-3) after the wires were heat treated between 670 degrees C and 730 degrees C. The non-Cu J(c) of the Cu-12Zn-0.2Mg matrix wires reaches the maximum value of 1533 A mm(-2) @12 T after heat treatment at 685 degrees C and decreases at higher temperatures.