THE EFFECT OF COMPOSITION AND TEMPERATURE ON GRAIN-BOUNDARY DIFFUSIONOF NI-63 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 p ure Ni3Al alloys in the temperature range from 968 to 1190 K. Diffusio n penetration profiles were obtained by a serial sectioning technique using the radiotracer Ni-63 and sensitive liquid scintillation countin g. A remarkable V-shaped concentration dependence of the grain boundar y diffusion parameter P with a minimum near the stoichiometric composi tion was observed. The grain boundary diffusion activation enthalpy Q( gb)(Ni) decreases with increasing deviation of the Ni concentration fr om eb approximately stoichiometric Ni3Al. This behaviour can be unders tood and will be discussed with respect to computer simulation studies of the change in composition and state of order of grain boundaries i n non-stoichiometric Ni3Al. (C) 1997 Elsevier Science S.A.