The self-diffusion of 63Ni along grain boundaries in the intermetallic alloys Ni-25.2Al, Ni-24.9Al-4.8W, Ni-24.2Al-4.7Cr, Ni-19.3Al-4.5Hf and Ni-27.6Al-4.9at%Co was investigated by using the radiotracer technique (figures 28 and 29). The diffusion penetration profiles were measured using the serial sectioning technique. Using the near-surface parts of the profiles which characterized lattice diffusion, the volume diffusion coefficients D were estimated. For pure Ni3Al, the agreement of the measured high temperature values of D with those of Bronfin et al. was good. By using the D-values and processing the tails of the measured profiles the grain-boundary diffusivity P (P = D′δ, where D′ was the grain-boundary diffusion coefficient and δ the grain-boundary width) was calculated. The P-values obtained exhibited an Arrhenius dependence:

Ni-Al, 1073-1273K:     D(m3/s) = 1.0 x 10-12exp[-195(kJ/mol)/RT]

Ni-Al-Co, 1073-1323K:     D(m3/s) = 1.1 x 10-11exp[-216(kJ/mol)/RT]

Ni-Al-Cr, 1073-1323K:     D(m3/s) = 7.7 x 10-10exp[-256(kJ/mol)/RT]

Ni-Al-Hf, 1073-1373K:     D(m3/s) = 6.9 x 10-12exp[-220(kJ/mol)/RT]

Ni-Al-W, 1073-1373K:     D(m3/s) = 3.4 x 10-12exp[-217(kJ/mol)/RT]

The main feature of grain-boundary self-diffusion in Ni3Al and its alloys was the relatively large activation energy (E′/E = 0.7) as compared with grain-boundary diffusion in face-centered cubic metals such as pure Ni. The Q-values in Ni3Al and its alloys were essentially the same as for pure Ni.

Nickel Self-Diffusion along Grain Boundaries in Ni3Al-Base Intermetallic Alloys. Zulina, N.P., Bolberova, E.V., Razumovskii, I.M.: Defect and Diffusion Forum, 1997, 143-147, 1453-6

Figure 28

Bulk diffusion of 63Ni in Ni3Al and alloys

Figure 29

Grain-boundary diffusion of 63Ni in Ni3Al and alloys