Microscopy of NbTi conductors

This paper reports on a high critical current density, Jc in the magnet conductor that is crucial to the success of the Superconducting Supercollider. Recent intensive quantification of the Nb-Ti microstructure as revealed by transmission electron microscopy has shown a direct relationship between the amount of a-Ti precipitate and the Jc. The amount of a-Ti precipitate produced by precipitation heat treatments has been shown to depend on the alloy composition, the temperature, the duration and frequency of heat treatment, and the amount of cold work drawing strain in the alloy. These conditions also affect the size and distribution of the precipitates which influences the magnetic field versus Jc behavior. In addition to these intrinsic properties of the Nb-Ti superconducting filaments extrinsically induced reduction in the composite Jc occurs, principally through filament non-uniformity in the final strand. The development of filament irregularity has been monitored throughout processing by scanning electron and light microscopy