Effect of Final Cold Rolling on Flux Pinning in Multiply-Processed Bi:2223 Powder-in-Tube Tapes

Abstract

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. H_RS and U₀s were extracted and correlated with expected microstructural changes. Measurements made at 70 K and 90 K indicate that rolling degrades H_R for both field- ┴ and field- ║ orientations. Subsequent annealing increases H_R in some cases. Extrapolation of H_R(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.