Small angle [001] twist boundaries and [001](110) tilt boundaries in B-free and B-doped Ni-rich Ni{sub 3}Al (76 at. pct. Ni) were examined using conventional electron microscopy techniques as well as annular dark field (ADF) imaging, X-ray Fluorescence (XRF) and spatially resolved electron energy loss spectroscopy (EELS) in an UHV scanning transmission electron microscope. The interface Structure consists of periodically spaced pairs of a/2{l_angle}110{r_angle} partial dislocations, linked by an antiphase boundary (APB). An analysis of the separation of the partials gives APB energies which are lower than in bulk Ni{sub 3}Al and which decrease with increasing misorientation angle. EELS, XRF and ADF imaging demonstrate that the APBs are Ni-rich. The observations on the APB chemistry and energy taken together lead to the conclusion that Ni-enrichment occurs to lower boundary energy by decreasing the number of high energy Al-Al bonds across the APB. These results on small angle boundaries lead to the suggestion that Ni-enrichment also occurs at large angle boundaries to decrease the number of high energy bonds across the interface.
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