A calculation of the influence of isolated dislocations on self-diffusion measurements in F.C.C. metals at lower temperatures

Abstract

Calculations are made of the influence of dislocations on self‐diffusion measurements in f.c.c. metals at lower temperatures by a tracer sectioning technique, using a model of isolated dislocation pipes following Mimkes and Wuttig. It is found that under experimental circumstancesat lower temperatures the influence of a dislocation is restricted to a relatively small area around the pipe. If sectioning is performed until the activity of a stripped layer is 1/10 of the activity of the first layer, the influence on the penetration plot is scarcely perceptible for the case of a dislocation density of 106 to 107/cm2, these densities usually being found in well annealed f.c.c. single crystals. This outcome is not incompatible with experimental results.

Self‐diffusion in nickel at low temperatures

“…This approach gives an analytical solution to the problem of simultaneous diffusion in the bulk and along an isolated dislocation for an instantaneous source. Bakker and Backus [32] used this solution in their numerical calculations of the influence of dislocation on tracer measurements in DT to about f 10%.…”

The influence of the ferromagnetic transition on self-diffusion in B.C.C. FeSi

“…The influence of dislocations does not seem to be important a t low temperatures. The penetration plots according to equation (3) of In c versus x2 showed no significant departure from linearity for the lowest points as would have resulted from a sizeable contribution of diffusion through dislocations [18].…”

“…T cal/mol deg for 0 < x < 0.5; e) AH;, Ah';, and Y are temperature independent. Now we can split up €Im in the following way: (18) The first integral of the right-hand side of equation (18) can be considered as a constant enthalpy term, the value of which is calculated according to (dl), yielding -122r cal/mol. For the calculation of the second integral we use recent tables of the enthalpy of a-iron [36].…”

“…The values of the third integral follow from tables of C , [36] and (dl) to (d3). According to a) the right member of equation (18) has to be multiplied by 1008/1042, the ratio of Curie temperatures of Fe-7.64% Si and Fe, respectively. Using the foregoing assumptions and substitutions we performed a computer fit, by the least mean squares method, to the present data as given in Table 1.…”

A comparison between microsectioning studies of low-temperature self-diffusion in silver

“…A radioactive layer, about 100 nm thick, was electroplated onto the specimen, which is about ten times the section thickness removed. I n their analysis of the data they had to assume that the diffusivity in the deposited layer is the same as in the crystal which is doubtful, especially a t low temperatures [24].…”