THE EFFECTS OF BOTH DEVIATION FROM STOICHIOMETRY AND BORON ON GRAIN-BOUNDARIES IN NI3AL

X-ray spectra and Z-contrast images have been obtained from thin foils of off- stoichiometric Ni3Al both with and without boron. The results show that grain boundaries in nickel-rich Ni3Al are nickel-enriched and that the addition of boron increases this nickel enrichment. The nickel enrichment is present as a second phase along some boundaries in undoped material and along all boundaries in boron- doped material. The phase is shown, using convergent-beam electron diffraction, to be disordered and to have the same orientation as one of the adjacent grains. By comparison, grain boundaries in aluminium-rich Ni3, Al, either with or without boron, have compositions that are similar to the matrix. Correspondingly, a second phase was not found along the grain boundaries of this alloy. © 1990 Taylor & Francis Ltd.