Influence of Composition on Diffusion in Binary Nickel Aluminides

摘要

Original results on ~(67_Ga and ~(68)Ge diffusion in Ni and N13AI alloys are reported in this paper. The measurements are done in the temperature range from 773 to 1448 K using the residual activity method. The concentration dependence of the Ga volume and grain boundary (GB) diffusion was studied for three compositions between 22.4 and 24.8 at.% Alinpure(notboron alloyed) Ni_3Al alloys. In the case of ~(68)Ge diffusion, the volume diffusion in pure Ni and GB diffusion in Ni-24.8Al was studied. Similar to literature data on the ~(63)Ni GB diffusivity in Ni_3Al, ~(67)Ga GB diffusivity measured in nickel-rich Ni_3Al in the present paper is increasing with increasing Ni concentration. The observed values for activation energy Q_P were higher and GB diffusivities were lower for alloys with maximum Ni content compared to respective values for ~(67)Ga GB diffusion in nickel. GB diffusivities of ~(67)Ga in Ni_3Al are higher than those of ~(68)Ge and the activation enthalpy is about the same. The results are compared with the literature data on self-diffusion in nickel aluminides and are interpreted in terms of bulk and GB composition. It seems that - for the volume diffusion - the Ga, Ge and partially also In simulate reasonably the Al self-diffusion in Ni_3Al, but this is not the case of the GB diffusion in M3AI. It is argued that the reason may be significant differences in segregation behavior of these elements to GB's.