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 multifilamentary Nb3Sn wire using powder metallurgy Nb+Cu rods. In the composite Nb+Cu filaments the Cu ribbons had a thickness of either 20 or 5 nm before reaction. During the 600 °C anneal the APCs enhanced the reaction rate and reduced the Nb3Sn grain size to <20 nm. The Cu concentration in the filaments decreased. In 20% Cu-20 nm APC wires the critical current density over the A15 area was 2250 A/mm2 at 12 T and 4.2 K. Flux pinning increased strongly with decreasing field.