A study was made of the grain boundary diffusivity of the 181W radioisotope in ferritic steels (table 72). The diffusivity in binary Fe-Cr alloys (8 to 12wt%Cr), in a ternary (Fe-8Cr-0.17C) alloy and in 2 commercial modifications of 8%Cr ferritic steel, was measured by using the serial sectioning method at temperatures ranging from 773 to 1123K. It was found that varying the Cr concentration from 8 to 12wt% did not affect the value of sD. The addition of C, and perhaps also of P, decreased sD in a similar manner to that previously observed in a study of Fe diffusion in Fe-Ni-Cr-C and Fe-Ni-Cr-P austenitic alloys. It was concluded that the binary alloys could be considered pure (C-free) at temperatures above 883K whereas, at lower temperatures (due probably to residual C segregation at grain boundaries), a considerable decrease in sD was observed; as compared with values which were extrapolated from high temperatures. It was noted that the grain boundary diffusivity of W was insensitive to small changes in the concentration of other alloying or impurity elements.
J.Čermák, J.Ruzicková, A.Pokorná: Scripta Metallurgica et Materialia, 1995, 33[2], 289-94
Table 72
Grain-Boundary Diffusivity of 181W in Fe-Cr Alloys
Cr (wt%) | Temperature (K) | sD (m3/s) |
8.07 | 1123 | 3.80 x 10-20 |
10.18 | 1123 | 3.54 x 10-20 |
12.25 | 1123 | 2.44 x 10-20 |
8.07 | 1063 | 5.40 x 10-21 |
continued
Table 72 (continued)
Grain-Boundary Diffusivity of 181W in Fe-Cr Alloys
Cr (wt%) | Temperature (K) | sD (m3/s) |
10.18 | 1063 | 4.39 x 10-21 |
12.25 | 1063 | 3.27 x 10-21 |
8.07 | 1003 | 6.37 x 10-22 |
10.18 | 1003 | 6.53 x 10-22 |
12.25 | 1003 | 1.14 x 10-21 |
8.03 | 983 | 7.64 x 10-23 |
8.36 | 983 | 1.94 x 10-23 |
8.50 | 983 | 1.95 x 10-23 |
8.07 | 943 | 5.67 x 10-22 |
10.18 | 943 | 3.58 x 10-22 |
12.25 | 943 | 4.10 x 10-22 |
8.03 | 943 | 2.47 x 10-23 |
8.36 | 943 | 8.96 x 10-24 |
8.50 | 943 | 1.21 x 10-23 |
8.03 | 903 | 8.23 x 10-24 |
8.36 | 903 | 1.35 x 10-24 |
8.50 | 903 | 2.46 x 10-24 |
8.07 | 883 | 4.80 x 10-23 |
10.18 | 883 | 4.92 x 10-23 |
12.25 | 883 | 5.81 x 10-23 |
8.03 | 863 | 1.86 x 10-24 |
8.36 | 863 | 9.30 x 10-26 |
8.50 | 863 | 5.05 x 10-25 |
8.07 | 823 | 5.60 x 10-25 |
10.18 | 823 | 3.74 x 10-25 |
12.25 | 823 | 2.52 x 10-25 |
8.03 | 823 | 4.07 x 10-25 |
8.36 | 823 | 5.17 x 10-26 |
8.50 | 823 | 6.27 x 10-26 |
8.07 | 773 | 9.01 x 10-26 |
Table 72 (continued)
Grain-Boundary Diffusivity of 181W in Fe-Cr Alloys
Cr (wt%) | Temperature (K) | sD (m3/s) |
10.18 | 773 | 2.34 x 10-26 |
12.25 | 773 | 5.95 x 10-26 |
8.03 | 773 | 1.59 x 10-26 |
8.36 | 773 | 6.13 x 10-27 |
8.50 | 773 | 6.47 x 10-27 |