Electron Backscatter Diffraction Analysis on Nb3Sn and Nb3Al Multifilaments

Observations of fractured cross sections, which are frequently used to determine the grain size distribution in Nb3Sn, cannot be performed for Nb3Al since transgranular fracture is the dominant fracture mode. Instead, we have evaluated the grain size of Nb3Al using electron backscatter diffraction (EBSD). To check the validity of EBSD analysis for A15 grain structures, bronze-route Nb3Sn filaments were also examined by EBSD. The deformation-and-transformation of bcc supersaturated-solid solution Nb(Al)(ss) was found not only to homogenize and refine the grain size of the resultant Nb3Al but also to increase a ratio of high angle grain boundaries to low angle grain boundaries. The texture studies were made by pole figure works: the Nb(Al)(ss) retains a < 110 > fibrous texture as well as the filament barrier (Nb, Ta) does. The transformed Nb3Al also has the weak < 110 > fibrous texture, whereas Nb3Sn has almost never texture. A clear relationship between J(c)and the inverse of grain size was not observed.