Quantitative image analysis of filament coupling and grain size in ITER Nb(Ti)/sub 3/Sn strand manufactured by the internal Sn process

Excellent images of Nb/sub 3/Sn filaments and their grain structure can be obtained from high resolution scanning electron microscopy of filamentary Nb/sub 3/Sn strands. Our aim has been to explore the detailed macro- and micro-structural characterization that can been achieved using image analysis of such micrographs. We have quantitatively characterized the filament size, shape and separation by digital image analysis. We have also used fracture surfaces to quantify both grain boundary density and morphology. Grain size and morphology varies not only from filament to filament but within the same filament too. We quantify here, for the first time, clear trends in the variation of both grain size and morphology, as well as local grain boundary density with respect to position within the filaments.