INCREASED CRITICAL-CURRENT DENSITY IN NB-TI WIRES HAVING NH ARTIFICIAL PINNING CENTERS

Artificial pinning center (APC) wires containing Nb 47 wt.% Ti with 24 vol.% of round Nb pins have produced very high critical current densi ties (J(c)) which are attributed to a sharply defined, nanometer-scale Nb-pin array. By reducing both the number of warm extrusion steps fro m four to three and the temperature of the third extrusion from 650 de grees C to 250 degrees C, the degree of pin-matrix interdiffusion has been reduced and J(c) values at all applied magnetic fields increased by 25-45% over those for a previous composite of almost identical desi gn. The best win achieved the very high J(c)(5 T, 4.2 K) value of 4600 A/mm(2). These results underscore the importance of the thermomechani cal treatment in determining the maximum flux pinning properties of AP C Nb-Ti wires. (C) 1997 American Institute of Physics.