QUANTITATIVE IMAGE-ANALYSIS OF FILAMENT COUPLING AND GRAIN-SIZE IN ITER NB(TI)(3)SN STRAND MANUFACTURED BY THE INTERNAL SN PROCESS

Excellent images of Nb3Sn filaments and their grain structure can be o btained from high resolution scanning electron microscopy of filamenta ry Nb3Sn strands. Our aim has been to explore the detailed macro- and micro structural characterization that can been achieved using image a nalysis 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 a nd morphology. Grain size and morphology varies not only from filament to filament but within the same filament too. We quantify here, for t he first time, clear trends in the variation of both grain size and mo rphology, as well as local grain boundary density with respect to posi tion within the filaments.