Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.605023
Title: Deformation mechanisms for the high temperature Bi-2223 superconductor
Author: James, M. P.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1996
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Abstract:
The future application of high temperature superconductors in high field magnets, energy storage, motors and generators, or power transmission depends on the production of long lengths of high quality material. This thesis describes the effect of different deformation mechanisms, during processing, for the high temperature Bi-2223 superconductor produced via the oxide power in tube method. The deformation behaviour of the tape is investigated during both longitudinal and cross rolling, pressing and lubricated pressing, and sequential pressing and lubricated sequential pressing. The emphasis of the study is the effect of deformation on the microstructure and critical current of the conductor. A critical thickness is found to exist during longitudinal rolling, at which point transverse cracks form in the ceramic powder core. Development of these cracks during further rolling is investigated. Cross rolling changes the orientation of the microcracks which inhibit the longitudinal Jc of the conductor. A similar result is found for pressing. Pressing beyond an optimum pressure causes silver penetration into the core. Sintering a tape prior to pressing is found to increase the resistance of silver penetration during deformation. When an industrial lubricant is applied to a tape the deformation path dramatically changes: the silver to superconductor interface area increases, thus increasing the Jc of the tape. A new pressing technique designated "sequential pressing" is developed. This is an efficient process that offers a valuable technique for producing long lengths of high quality Bi-2223 tape with the beneficial characteristics of pressed rather than rolled tape. Hot and cold pressing of Bi-2223 is modelled through the construction of densification mechanism maps. Data from two types of powder shows good correlation to the theoretical time contours on the maps. A temperature-density deformation map was also created for a Bi-2223 tape.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.605023  DOI: Not available
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