Direct Observation of the Growth of Voids in Multifilamentary Superconducting Materials Via Hot Stage Scanning Electron Microscopy

摘要

The need for large high field magnetic devices has focused attention on multifilamentary superconductors based on A15 compounds such as Nb sub 3 Sn. The commercial bronze process for fabricating multifilamentary superconducting Nb sub 3 Sn wires was developed. A major problem is strain sensitivity when long reaction times are employed. An improved hot stage for the scanning electron microscope was constructed to study the formation of the A15 phase by solid state diffusion. The nucleation and growth of voids near the interface of the A15 phase (Nb sub 3 Sn) and matrix were observed, monitored, and recorded on video tape. Successive layers of material heated in the hot stage were subsequently removed and the new surfaces were re-examined, using SEM-EDX and optical microscopy, to confirm the fact that the observed porosity was indeed a bulk rather than a surface phenomenon. These voids are considered to be a primary cause for degrading the mechanical, thermal and superconducting properties. (ERA citation 04:037085)