Effect of Final Cold Rolling on Flux Pinning in Multiply-Processed Bi:2223 Powder-in-Tube Tapes
Monofilamentary and multifilamentary B:2223 powder-in-silver-tube ribbons were prepared by deformation processing that concluded with the usual sequence of cold rolling and heat treatment (832 ~ 834°C) cycles. The primary purpose of the study was to investigate the effect on flux pinning of “final” cold rolling steps of 10% and 20% reduction in thickness. Vibrating sample magnetometery was employed to measure: the M-H loops, the irreversibility fields, HR, and flux creep (hence effective pinning potential, U0). Measurements were also performed after one further annealing step was taken. HRS and U0s were extracted and correlated with expected microstructural changes. Measurements made at 70 K and 90 K indicate that rolling degrades HR for both field- ┴ and field- ║ orientations. Subsequent annealing increases HR in some cases. Extrapolation of HR(T) to lower temperatures indicates that reduction may be beneficial to low-temperature pinning, at least for the field- ║ orientation. To some extent this correlates with the U0 results, which (while confined to the field- ┴ orientation) indicate that reductions of 10 and 20% progressively enhance pinning.
KeywordsCritical Current Density Subsequent Annealing Cold Deformation Flux Pinning Flux Creep
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