The self-diffusion of 63Ni along boundaries in 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 radiotracer and serial sectioning techniques. By using the near-surface parts of the profiles, which reflected lattice diffusion, the volume diffusion coefficients were estimated (table 25). In the case of pure Ni3Al, the agreement of the high-temperature results with published data was good. By using the bulk diffusion results, and by analyzing the tails of the measured profiles, grain-boundary diffusivities were calculated. These (table 26) could be described by:

Ni-Al (1273-1073K):     D (m3/s) = 1 x 10-12 exp[-195(kJ/mol)/RT]

Ni-Al-Hf (1373-1023K):     D (m3/s) = 6.4 x 10-12 exp[-219(kJ/mol)/RT]

Ni-Al-W (1373-1023K):     D (m3/s) = 3.3 x 10-12 exp[-217(kJ/mol)/RT]

Ni-Al-Co (1273-1023K):     D (m3/s) = 6.8 x 10-13 exp[-189(kJ/mol)/RT]

Ni-Al-Cr (1323-1023K):     D (m3/s) = 1.8 x 10-9 exp[-265(kJ/mol)/RT]

By using the bulk and grain-boundary diffusion data, the boundary energies were estimated by using the Borisov semi-empirical relationship. It was noted that the calculated energies exhibited a marked positive temperature dependence.

Nickel Self-Diffusion along Grain Boundaries in Ni3Al-Base Intermetallic Alloys. Zulina, N.P., Bolberova, E.V., Razumovskii, I.M.: Acta Materialia, 1996, 44[9], 3625-31

Table 25

Bulk diffusion of Ni in Ni3Al-based alloys

continued

Table 25 (continued)

Bulk diffusion of Ni in Ni3Al-based alloys