The grain-boundary diffusion of 63Ni in polycrystalline Ni3Al intermetallic was studied by using the residual activity method at 773 to 1173K (tables 23 and 24). Samples whose compositions spanned stoichiometry (24.0 to 26.8at%Al), were prepared either without boron or with two different boron concentrations (0.106 and 0.268at%). Differences were observed between the nickel grain-boundary diffusivity in a pure stoichiometric alloy on the one hand and in off-stoichiometric and boronized alloys on the other hand. The interpretation of the results was based (i) upon the influence of boron additions and deviations from stoichiometry upon the degree of order in grain boundaries (ii) upon the accelerating effect of extended defects (columnar cavities) in grain boundaries upon grain-boundary diffusion, and (iii) upon a strong interaction between nickel and boron atoms that probably caused an increase in the activation energy for grain-boundary diffusion.

Influence of Boron Doping and Stoichiometry upon the Ni Grain Boundary Diffusion in Ni3Al Intermetallic. Čermák, J., Rův̌zicková, J., Stloukal, I., Pokorná, A.: Scripta Materialia, 1997, 37[1], 31-5

Table 24

Arrhenius parameters for grain-boundary diffusion of 63Ni in Ni3Al