The effect of stoichiometry upon the grain boundary self-diffusion of Ni in Ni3Al was investigated for compositions between 73 and 78at%Ni in pure Ni3Al alloys at 968 to 1190K. Diffusion penetration profiles were obtained by using a serial sectioning technique, radiotracer 63Ni and sensitive liquid scintillation counting. A marked V-shaped concentration dependence of the grain boundary diffusion parameter P, with a minimum near to the stoichiometric composition, was observed (table 27, figures 25 and 26). The grain boundary diffusion activation enthalpy QgbNi decreased with increasing deviation of the Ni concentration from approximately stoichiometric Ni3Al (table 28). This behaviour was attributed to changes in composition and in the state of order of grain boundaries in non-stoichiometric Ni3Al.
The Effect of Composition and Temperature on Grain Boundary Diffusion of 63Ni in Ni3Al Alloys. Frank, S., Herzig, C.: Materials Science and Engineering A, 1997, 239-240[1-2], 882-8
Table 26
Grain boundary diffusion of Ni in Ni3Al-based alloys
Alloy | Temperature (K) | D (m3/s) |
Ni-Al | 1273 | 1.2 x 10-20 |
Ni-Al | 1173 | 1.7 x 10-21 |
Ni-Al | 1073 | 3.8 x 10-22 |
Ni-Al | 973 | 1.0 x 10-22 |
Ni-Al-Hf | 1373 | 3.3 x 10-20 |
Ni-Al-Hf | 1323 | 1.6 x 10-20 |
Ni-Al-Hf | 1273 | 7.0 x 10-21 |
Ni-Al-Hf | 1223 | 2.2 x 10-21 |
Ni-Al-Hf | 1173 | 9.9 x 10-22 |
Ni-Al-Hf | 1123 | 4.0 x 10-22 |
Ni-Al-Hf | 1073 | 1.7 x 10-22 |
Ni-Al-Hf | 1023 | 4.3 x 10-23 |
Ni-Al-W | 1373 | 1.9 x 10-20 |
Ni-Al-W | 1323 | 1.1 x 10-20 |
Ni-Al-W | 1273 | 3.7 x 10-21 |
Ni-Al-W | 1223 | 1.8 x 10-21 |
Ni-Al-W | 1173 | 7.5 x 10-22 |
Ni-Al-W | 1123 | 2.3 x 10-22 |
Ni-Al-W | 1073 | 1.1 x 10-22 |
Ni-Al-W | 1023 | 2.9 x 10-23 |
Ni-Al-Co | 1273 | 1.2 x 10-20 |
Ni-Al-Co | 1223 | 5.5 x 10-21 |
Ni-Al-Co | 1173 | 2.6 x 10-21 |
Ni-Al-Co | 1123 | 1.2 x 10-21 |
continued
Table 26 (continued)
Grain boundary diffusion of Ni in Ni3Al-based alloys
Alloy | Temperature (K) | D (m3/s) |
Ni-Al-Co | 1073 | 2.9 x 10-22 |
Ni-Al-Co | 1023 | 1.8 x 10-22 |
Ni-Al-Cr | 1323 | 6.1 x 10-20 |
Ni-Al-Cr | 1273 | 2.6 x 10-20 |
Ni-Al-Cr | 1223 | 7.8 x 10-21 |
Ni-Al-Cr | 1173 | 3.1 x 10-21 |
Ni-Al-Cr | 1123 | 9.1 x 10-22 |
Ni-Al-Cr | 1073 | 1.6 x 10-22 |
Ni-Al-Cr | 1023 | 6.5 x 10-23 |
Figure 25
Concentration dependence of Ni grain-boundary diffusion in Ni3Al
Curves, from top to bottom, 1190K, 1066K, 1012K, 968K
Figure 26
Temperature dependence of Ni grain-boundary diffusion in Ni3Al
Curves, from top to bottom, 77.6, 73.4, 75.2(at%)Ni