GRAIN-SIZE REDUCTION IN NB3SN WIRE USING COMPOSITE POWDER-METALLURGY FILAMENTS WITH CU(SN) ARTIFICIAL PINNING CENTERS

Cu(Sn) artificial pinning centers (APCs) were introduced into multifil amentary Nb3Sn wire using powder metallurgy Nb+Cu rods. In the composi te Nb+Cu filaments the Cu ribbons had a thickness of either 20 or 5 nm before reaction. During the 600-degrees-C anneal the APCs enhanced th e reaction rate and reduced the Nb3Sn grain size to <20 nm. The Cu con centration in the filaments decreased. In 20% Cu-20 nm APC wires the c ritical current density over the A15 area was 2250 A/mm2 at 12 T and 4 .2 K. Flux pinning increased strongly with decreasing field.