The diffusion of Cr in [100]/[001] symmetrical bi-crystals with various tilt angles was investigated at temperatures ranging from 958 to 1197C (tables 134 and 135). It was found that, in low-angle boundaries, diffusion was dominated by a dislocation pipe mechanism whose activation energy was independent of the tilt angle, while the pre-exponential factor was a linear function of the sine of the tilt semi-angle. In the case of high-angle boundaries, the diffusion coefficients exhibited minima, and the activation energies exhibited maxima, for coincidence site lattice boundaries with = 13 (22.6, 67.4), = 17 (28.1, 61.9) and = 5 (36.9, 53.1). The pre-exponential factor also varied with the tilt angle, but the variation was random. The results confirmed that grain boundary diffusion was strongly affected by boundary structures and their associated energies.
X.M.Li, Y.T.Chou: Acta Materialia, 1996, 44[9], 3535-41
Table 134
Diffusion of Cr in [100]/[001] Nb Bicrystals as a Function of Tilt Angle
(°) | Temperature (C) | sD (m3/s) |
2.0 | 958 | 3.92 x 10-23 |
2.0 | 1197 | 5.28 x 10-22 |
8.0 | 958 | 5.64 x 10-23 |
8.0 | 1197 | 7.82 x 10-22 |
15.0 | 958 | 6.40 x 10-23 |
15.0 | 1197 | 8.02 x 10-22 |
20.0 | 958 | 8.73 x 10-23 |
20.0 | 1197 | 1.25 x 10-21 |
22.6 ( = 13) | 958 | 7.58 x 10-24 |
22.6 ( = 13) | 1197 | 1.16 x 10-22 |
26.0 | 958 | 7.47 x 10-23 |
26.0 | 1197 | 1.17 x 10-21 |
28.1 ( = 17) | 958 | 1.49 x 10-23 |
28.1 ( = 17) | 1197 | 2.96 x 10-22 |
continued
Table 134 (continued)
Diffusion of Cr in [100]/[001] Nb Bicrystals as a Function of Tilt Angle
(°) | Temperature (C) | sD (m3/s) |
31.0 | 958 | 6.66 x 10-23 |
31.0 | 1197 | 9.89 x 10-22 |
36.9 ( = 5) | 958 | 3.07 x 10-24 |
36.9 ( = 5) | 1197 | 9.22 x 10-23 |
43.0 | 958 | 1.57 x 10-22 |
43.0 | 1197 | 2.30 x 10-21 |
46.0 | 958 | 6.75 x 10-23 |
46.0 | 1197 | 1.02 x 10-21 |
53.1 ( = 5) | 958 | 3.94 x 10-24 |
53.1 ( = 5) | 1197 | 1.04 x 10-22 |
56.0 | 958 | 5.66 x 10-23 |
56.0 | 1197 | 8.69 x 10-22 |
61.9 ( = 17) | 958 | 4.61 x 10-24 |
61.9 ( = 17) | 1197 | 1.05 x 10-22 |
67.4 ( = 13) | 958 | 4.69 x 10-24 |
67.4 ( = 13) | 1197 | 1.01 x 10-22 |
69.0 | 958 | 4.50 x 10-23 |
69.0 | 1197 | 8.47 x 10-22 |
74.0 | 958 | 1.93 x 10-23 |
74.0 | 1197 | 4.15 x 10-22 |
78.0 | 958 | 1.27 x 10-23 |
78.0 | 1197 | 2.19 x 10-22 |
83.0 | 958 | 1.45 x 10-23 |
83.0 | 1197 | 2.34 x 10-22 |
Table 135
Arrhenius Parameters for Cr Grain Boundary Diffusion in
[100]/[001] Symmetrical Nb Bicrystals at 958 to 1197C
(°) | sD (m3/s) | Q (kJ/mol) |
2.0 | 2.86 x 10-16 | 162.0 |
8.0 | 4.15 x 10-16 | 162.1 |
continued
Table 135 (continued)
Arrhenius Parameters for Cr Grain Boundary Diffusion in
[100]/[001] Symmetrical Nb Bicrystals at 958 to 1197C
(°) | sD (m3/s) | Q (kJ/mol) |
15.0 | 4.91 x 10-16 | 162.8 |
20.0 | 1.35 x 10-16 | 170.1 |
22.6 ( = 13) | 6.17 x 10-16 | 187.4 |
26.0 | 1.29 x.10-15 | 171.7 |
28.1 ( = 17) | 9.02 x 10-16 | 183.7 |
31.0 | 1.23 x 10-15 | 171.7 |
36.9 ( = 5) | 6.28 x 10-15 | 220.6 |
43.0 | 1.92 x 10-15 | 167.4 |
46.0 | 1.00 x 10-15 | 169.0 |
53.1 ( = 5) | 1.66 x 10-15 | 204.0 |
56.0 | 9.18 x 10-16 | 171.8 |
61.9 ( = 17) | 5.43 x 10-16 | 190.8 |
67.4 ( = 13) | 9.62 x 10-16 | 196.7 |
69.0 | 1.79 x 10-15 | 178.5 |
74.0 | 4.55 x 10-16 | 174.6 |
78.0 | 3.74 x 10-16 | 177.8 |
83.0 | 3.40 x 10-16 | 175.0 |