A High-Resolution Aes Study of the Non-Uniform Distribution of Phosphorus on the Fractured Grain Boundaries of Doped Fe-Si Bicrystals

Symmetrical {013}, ⅀=5, bicrystals of Fe-3wt%Si doped with 270 ppm phosphorus, grown from seeds by floating-zone melting, were fractured in UHV, and the fracture surfaces were analyzed in a high-resolution scanning Auger microprobe. The phosphorus distribution was nonuniform over areas on the scale of 10 2 µm. The non-uniformities were sometimes fund to be associated with deformation bands, mainly twins, which formed in advance of the brittle crack as the specimens fractured. We have rationalized these observations in terms of fracture not along the central core of an extended phosphorus distribution at the grain boundary, but rather toward one side of the distribution. The deflection of the crack path at steps in the boundary would then produce the observed patterns of phosphorus distribution.