Metallurgical Characterization of Niobium/Tin Superconducting Multifilamentary Wires.

摘要

The origin of a high incidence of discontinuous Nb filaments in Niobium/bronze multifilamentary drawn wires is discussed. It is suggested their occurrence is most likely an intrinsic part of the manufacturing process. Studies on the application of the limiting grain size concept in the bronze by the Nb filaments, suggests this effect only sets an upper bound on the attainable grain size and in reality, the actually observed grain size and sub-grain size is lower than this upper bound. This leads to extensive hardening of the bronze phase as the Nb/bronze multifilamentary wires are progressively reduced to ultra-fine dimensions. Preliminary ageing studies of a 13 wt % Sn bronze alloy, suggest the alpha bronze may exhibit some age hardening decomposition phenomena in the 300 to 400 degree C temperature range for unprestrained solution heat treated and quenched material. An even stronger hardening phenomena in this temperature range occurs if the material is prestrained 65% in compression after solution heat treatment but prior to ageing. Contemplated further studies in the area are presented. (Author)