The diffusion of 63Ni and 114mIn in the intermetallic L12 phase Ni3Al was measured at 900 to 1200C for compositions between 73.5 and 77at%Ni, in steps of 0.5at%. The In isotope served as a substitute for 26Al. The usual serial sectioning method was applied using a precision parallel grinder. There was only a weak concentration dependence of the diffusion coefficient at temperatures >950C but it gets stronger with decreasing temperature. There was a minimum of the diffusion coefficient at 76 and not at 75at%Ni as may be expected. The diffusion of 63Ni in Ni3Al and in pure Ni was comparable. The same was true for the diffusion of 114mIn in Ni3Al. Very likely the diffusion of 63Ni was by a normal vacancy mechanism and the diffusion of 114mIn by In antisite atoms in the Ni sublattice. The D0*-values were for In (and probably for Al as well) considerably higher than for Ni. This could be due to a higher entropy term. As a consequence of the considerably larger D0*-values of In an intersection of the two linear Arrhenius plots for Ni and Al was observed at about 950C for all concentrations except Ni76Al24. This fits well to interdiffusion investigations where at higher temperatures Al was found to be the faster component, and Ni at lower temperatures.

Diffusion of 63Ni and 114mIn in the γ′-Phase Ni3Al. Shi, Y., Frohberg, G., Wever, H.: Physica Status Solidi A, 1995, 152[2], 361-75

Figure 18

Hydrogen permeation flux in Ni74.7Al19.4Fe5.8B0.1

White circles, 140µm; black squares, 70µm; white squares, 60µm

Figure 19

Hydrogen permeation flux in Ni77.8Al21.3Zr0.8B0.1

White circles, 140µm; black squares, 210µm;

white squares, 305µm; black circles, 255µm