Powder metallurgical alternative for the processing of (Nb - Ta)3Sn multifilamentary wires, starting from elementary Nb and Ta powder

Ordinarily the Nb-Ta cores of alloyed Nb
3
Sn wires are prepared by electron beam melting followed by remelting for better homogenity. The present work describes the first attempt to replace the melting process by a more economical powder metallurgical technique, starting with Nb and Ta elementary powders. After the processing to fine wires, the ductile Ta particles are deformed to ribbon-like filaments, the average distance between two Ta "Walls'' being in the range of the A15 grain size. Thus an improvement of the pinning behavior of Nb
3
Sn multilfilamentary wires was expected. Nb/Ta powde mixtures (up tp 20 wt Z Ta) were extruded and deformed to rods. wich were inserted in a bronze matrix, the superconductor wires being produced by the conventional bronze route. It was found that during the reaction heat treatment Ta is partly dissolved in the A15 layer, the dissolved amount depending strongly on the reaction temperature. As a main result of the present investigation, the field dependence of J
c
for our wires after a reaction of 120 h at 675°C is similar to that of binary Nb
3
Sn wires, the absolute value of J
c
below 13 T being substantially higher than that of the latter. After 64 h at 700°c and 750°c, J
c
has the characteristics of alloyed Nb
3
Sn wires the absolute values of J
c
in the A15 phase being comparable to those of the best conventionally processed (Nb-Ta)
3
Sn wires. These high critical currents after the reaction at
T \leq 675\deg
C are discussed as a consequence of "artifical pinning" by the remaining Ta inclusions.