The temperature dependence of 95Zr diffusion and of the isotope effect of 88Zr and 95Zr were measured in alloys containing 6.7 or 13.6at%Sc (table 375). The Arrhenius plots were more strongly curved than those for self-diffusion in pure β-Zr. This was contrary to previous findings for Zr-Nb alloys. The data on the isotope effect were consistent with a predominant monovacancy mechanism over the entire stability range of the body-centered cubic structure. The diffusion anomaly was attributed to phonon-assisted diffusion jumps which were induced by a softening of the LA(2/3)[111]-type phonon mode. This resulted in a continuous decrease in the free enthalpy of migration with decreasing temperature. Under this assumption, values were calculated for the frequency factor and the activation enthalpy which represented the normal diffusion behavior of these alloys. A systematic variation in the electronic structure upon alloying group-Vb or IIIb metals with group-IVb metals was suggested to be responsible for the observed continuous change in the diffusion anomaly of β-Zr-Nb alloys, pure β-Zr, and β-Zr-Sc alloys.
C.Herzig, U.Köhler: Acta Metallurgica, 1987, 35[7], 1831-7
Table 375
Diffusion of Zr in Zr-Sc Alloys
Sc (at%) | Temperature (K) | D (m2/s) |
6.7 | 1906 | 1.35 x 10-11 |
6.7 | 1796 | 7.50 x 10-12 |
6.7 | 1680 | 3.40 x 10-12 |
6.7 | 1566 | 1.91 x 10-12 |
6.7 | 1484 | 1.05 x 10-12 |
6.7 | 1453 | 9.27 x 10-13 |
6.7 | 1389 | 5.98 x 10-13 |
6.7 | 1380 | 5.20 x 10-13 |
6.7 | 1349 | 4.75 x 10-13 |
6.7 | 1308 | 3.56 x 10-13 |
6.7 | 1300 | 3.40 x 10-13 |
13.6 | 1873 | 1.40 x 10-11 |
13.6 | 1826 | 1.07 x 10-11 |
13.6 | 1745 | 6.72 x 10-12 |
13.6 | 1673 | 4.81 x 10-12 |
13.6 | 1668 | 4.30 x 10-12 |
13.6 | 1589 | 2.70 x 10-12 |
13.6 | 1540 | 2.08 x 10-12 |
13.6 | 1519 | 1.78 x 10-12 |
13.6 | 1470 | 1.29 x 10-12 |
13.6 | 1430 | 1.06 x 10-12 |
13.6 | 1416 | 9.90 x 10-13 |