Towards the development of high strain tolerance superconductors for fusion magnet applications

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Through EBSD measurements for various kinds of Nb3Al samples, it was found that the grain size considerably changes with deformation degree prior to the phase transformation to Nb3Al phase. However correlation between the grain size and Jc was not clearly recognized. When TEM observation was performed to the Nb3Al phase, we could see high density crystal planer defects in the phase that could be the possible pinning centers. The crystal defects seem to be correlated to pinning mechanism. Atom probe tomography revealed clear Al segregation on the planer defects. Such Al segregations could not be observed in our measurements performed so far. Such a grain structure might be related to strong grain connectivity in the Nb3Al superconductors. As a result, the Nb3Al conductors might retain the high Jc performance under the strain.