Boundaries in B-free and B-doped Ni-rich (76at%) samples were studied by using spatially resolved electron energy loss spectroscopy, energy dispersive X-ray spectroscopy, annular dark-field imaging in an ultra-high vacuum scanning transmission electron microscope, and conventional electron microscopy. The Ni enrichment was seen as a 0.5 to 1.0nm-wide region at high-angle boundaries, in the absence or presence of B. By using electron energy loss spectroscopy, B segregation to the boundary was observed to vary along the interface. Electron energy loss spectroscopy of the Ni L2,3 edge showed that the B-rich regions had a bonding which was similar to that found in bulk Ni3Al, while the B-free regions exhibited a bonding which was similar to the more Ni-like nature of undoped boundaries. The results demonstrated that B segregation increased the cohesive strength of grain boundaries in the present material by making the bonding at the boundary similar to that in the bulk.

Structure, Chemistry and Bonding at Grain Boundaries in Ni3Al—I. The Role of Boron in Ductilizing Grain Boundaries. Muller, D.A., Subramanian, S., Batson, P.E., Silcox, J., Sass, S.L.: Acta Materialia, 1996, 44[4], 1637-45