Electron Backscatter Diffraction Analysis on and 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 Jc and the inverse of grain size was not observed.