Advances in high-field superconducting composites by addition of artificial pinning centres to niobium-titanium

Artificial pinning-centre (APC) niobium-titanium composites attain critical current density J(c) values higher than 4000 A mm(-2) at 5 T, 4.2 K, surpassing the barrier reached by the conventional Nb-Ti composite process. At 2 T APC composites achieve more than double the J(c) of conventional composites, making them particularly well suited for low-field applications. On the other hand, APC composites are inferior to conventional composites at 8 T, due to weak high-field pinning and reduced upper critical field. This review discusses fabrication techniques, microstructural development and superconducting and flux-pinning properties of APC composites. Key elements and underlying issues for achieving higher J(c) are identified and discussed in terms of the current state of the art.