HIGH FIELD PERFORMANCE OF CONVENTIONALLY PROCESSED NIOBIUM-TITANIUM CONDUCTORS CONTAINING ARTIFICIALLY-INTRODUCED NIOBIUM PINNING SITES

摘要

Artificial Pinning Center (APC) technology was developed as a means to improve the performance of NbTi conductors through control of the amount and distribution of the flux pinning phase. Unfortunately, the high field performance of APC conductors has almost invariably been inferior to that of conventionally processed conductors, at least in part due to depressed upper critical field. Supercon has investigated a method for improving high field performance in NbTi conductors through a combination of APC technology and conventional processing. A small volume percentage of Nb pinning material was artificially introduced into standard Nb47Ti* alloy. The percentage was chosen such that the average overall composition was Nb44Ti, an alloy which is known to have a higher upper critical field than Nb47Ti. The resulting composite was multiply restacked and processed to wire. Conventional precipitation heat treatments were applied during final processing. In addition to providing higher upper critical field, the added Nb was expected to contribute to pinning above and beyond that provided by the precipitated a-Ti. Improved high field critical current densities relative to a control were observed. The results of the investigation, including critical current density (J_c), upper critical field (H_(c2)), and critical temperature (T_c) data, are presented.