22.08.2015   Comprehensive nuclear materials

From dilute to concentrated alloys: the case of Fe-Cr

Подпись: Figure 7 Structure of carbon-vacancy and carbon-self-interstitial complexes in iron, predicted from DFT calculations. Reproduced from Fu, C. C.; Meslin, E.; Barbu, A.; Willaime, F.; Oison, V. In Theory, Modeling and Numerical Simulation of Multi-Physics Materials Behavior, 2008; Vol. 139, pp 157-164, 168.
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In the approach described earlier, which considers low concentrations of solutes and defects, the number of independent configurations is rather small, and they can be easily taken into account in kinetics model. The situation is much more complex when considering Fe-Cr with Cr concentration in the range 10-20%. Nevertheless, first results have been obtained by considering the interaction of defects with one or two Cr atoms in the Fe matrix.81 These data could ideally be used to fit an improved empiri­cal potential, but the Fe-Cr system is rather difficult to model because of the strong interplay between magnetic and chemical interactions. This is also clearly one of the challenges in the field.

1.08.4.2.2 Подпись: Hf Ta W Re Os Ir Pt Au Figure 8 DFT-GGA solute-vacancy binding energies in iron for 3D, 4D, and 5D elements for 1-5 nn relative positions. Reprinted with permission from Olsson, P.; Klaver, T. P. C.; Domain, C. Phys. Rev. B 2010, 81, 054102. Copyright (2010) by the American Physical Society.
Point defects in hcp-Zr

Point defects in hcp-Zr have also been studied via DFT calculations. It was found in particular that the vacancy migration energy is lower by ~0.15 eV within the basal plane than out of the basal plane.82 The situation for the self-interstitial is quite complex, since among the known configurations, at least three configurations are found to have almost the same formation energy (within 0.1 eV): the octahedral (O), split dumbbell (S), and basal octahedral (BO) configurations.83,84