The effect of composition and temperature on grain boundary diffusion of 63Ni in Ni3Al alloys

The effect of stoichiometry on grain boundary self-diffusion of Ni in Ni3Al was investigated for compositions between 73 and 78 at.% Ni in pure Ni3Al alloys in the temperature range from 968 to 1190 K. Diffusion penetration profiles were obtained by a serial sectioning technique using the radiotracer 63Ni and sensitive liquid scintillation counting. A remarkable V-shaped concentration dependence of the grain boundary diffusion parameter P with a minimum near the stoichiometric composition was observed. The grain boundary diffusion activation enthalpy QgbNi decreases with increasing deviation of the Ni concentration from approximately stoichiometric Ni3Al. This behaviour can be understood and will be discussed with respect to computer simulation studies of the change in composition and state of order of grain boundaries in non-stoichiometric Ni3Al.