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.

D.A.Muller, S.Subramanian, P.E.Batson, J.Silcox, S.L.Sass: Acta Materialia, 1996, 44[4], 1637-45