We know that in low SFE materials, dislocations may split into partials through energetically favourable reactions. But does the grain size or domain size also affect how the reaction from full dislocation to partials occur? Also if I deform a microcrystalline low SFE material, will partials still form and contribute to plasticity or only full dislocations contribute or is it a combination of both?
Sear Ahmad, unfortunately I couldn't enter WP of the first paper. Any how!! The splitting of the extended dislocation into two partial plus the formation of intrinsic stacking fault is completely a phenomena, which involves only the energetic considerations. Where it was assumed that in the calculation of the strain field energies of the dislocations taking part in the process, and one has to consider only the image forces associated with the bounding surfaces of the embedding single crystal. But it is funny enough I haven't seen in those calculations any parameter related to the size of the embedding matrix. Actually the main contribution to the energy comes from the dislocation core and the strain field itself. What people do for the energetic calculation here is to take the square of the Burgers vector and compared them!!! Then calculate the interaction forces between two partials using their respective strain fields, which is repulsive in the present case.
I have a published theory, which is naive but it works very well. But what happens to the model when the size of the grain becomes in the range few hundreds of Angstrom, it is not very clear.
Hello, Rohit,
The grain size influences the areas of grain boundaries. However, there seems no direct relationship between SFE and grain size, because the dissociation of a full dislocation takes place within the grain.
The grain size does affect another deformation mechanism-twinning, though. One needs to take care that fcc and hcp structures may have different properties assciated with SFE and twinning.
We need to know that the plasticity depends much more on generalized stacking-fault energy (GSFE) rather than stacking-fault energy. The maximum point of the generalized stacking-fault energy, or say unstable stacking-fault energy(USFE), dominates the width of a extended dislocation according to a modified P-N model. Well, if the width is too large, i.e. the USFE is too small, the cross-slip will be harder to be performed due to the pinning of dislocations. Therefore, the plasticity lies on the competition between the USFE and cross-slip probability which may have an equilibrium point to maximize the plasticity.
Best,
Yifeng Wu
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