Diffusion of 63Ni has been measured in pure and boron-doped polycrystalline Ni3Al intermetallic compounds as a function of temperature (692-1352°C), A1 concentration (24-26 at.% Al), and boron content (0-500 wt ppm). Volume and grain-boundary diffusion of 60Co and 68Ge have also been measured in pure Ni3, Al. Both conventional grinding and ion beam sputtering techniques have been used for the determination of the concentration profiles. The diffusivity of Ni, DNi*, is independent of Al content above 1000° C, indicating that antisite defects are prevailing on both sides of stoichiometry. However, DNi* shows a minimum at the stoichiometric composition below 1000°C, and this trend becomes clearer with decreasing temperature. The diffusivities of60Co and68Ge are also independent of Al concentration in the temperature range between 880 and 1200°C, but their grain-boundary diffusion depends on Al concentration. The addition of boron linearly increases DNi*, above 1000°C, but at lower temperatures,DNi*, in off-stoichiometric compositions decreases to the value for stoichiometric Ni3Al on the addition of 100 wt ppm boron, and then increases as above with the further additions of boron to ~500 wt ppm. The present diffusion data suggest that a small concentration of vacancies, independent of temperature, is present on both sides of, and at, stoichiometry at low temperature.
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