[SY-B1] Properties of interstitials in concentrated Fe-Cr alloys from first principles
Point defects, for example self-interstitials and vacancies, play an important part in controlling properties of materials and their kinetic evolution. As a consequence, proper understanding and modelling of materials properties require precise knowledge of point defect behaviour and their characteristics, in particular their formation and migration energies. In magnetic alloys such as FeCr, the investigation of point defects is complicated, because their properties strongly depend on various parameters such as Cr composition, alloy short-range ordering and the defect local environment [1-3].
In this work, we have investigated properties of dumbbell-type defects in FeCr with a large dataset of density functional theory calculations, for Cr concentrations ranging from low to approx. 35%. Analysis shows that properties of self-interstitial and interstitial (IA) defects in concentrated bcc FeCr alloys fluctuate significantly as functions of the above parameters. These fluctuations are observed to a lesser or greater extent for the lattice parameter, chemical potentials, bulk moduli, relaxation volumes, magnetic moments, and migration energies of dumbbells. We conclude that the formation energy of dumbbells depends on the Cr content and also on the number of Cr atoms in the local environment of a defect. For each chemical composition the average migration energies of Cr IA defects (Cr-Cr, Cr-Fe dumbbells) moving to the first nearest-neighbour (1NN) position, are significantly smaller than those of Fe-Fe exchanging with the 1NN Fe atom. The relaxation volumes of dumbbells increase in the ordered structure and decrease in the disordered one with the increase of number of Cr atoms in the local environment of a defect. The trends exhibited by the mean values of the various properties have been observed and analysed, and the most stable directions of Fe-Fe, Fe-Cr and Cr-Cr dumbbells have been determined. Moreover, the energy of elastic interaction between such defects are quantitatively estimated using the suitably parametrized dipole tensors of the defects.
[1] D. Costa, G. Adjanor, C.S. Becquart, et al., J. Nucl. Mater. 452 (2014) 425-433
[2] D. Nguyen-Manh, M.Y. Lavrentiev, S.L. Dudarev, C. R. Physique 9 (2008) 379-388
[3] D. Nguyen-Manh, M.Y. Lavrentiev, M. Muzyk et al., J Mater Sci (2012) 47: 7385
In this work, we have investigated properties of dumbbell-type defects in FeCr with a large dataset of density functional theory calculations, for Cr concentrations ranging from low to approx. 35%. Analysis shows that properties of self-interstitial and interstitial (IA) defects in concentrated bcc FeCr alloys fluctuate significantly as functions of the above parameters. These fluctuations are observed to a lesser or greater extent for the lattice parameter, chemical potentials, bulk moduli, relaxation volumes, magnetic moments, and migration energies of dumbbells. We conclude that the formation energy of dumbbells depends on the Cr content and also on the number of Cr atoms in the local environment of a defect. For each chemical composition the average migration energies of Cr IA defects (Cr-Cr, Cr-Fe dumbbells) moving to the first nearest-neighbour (1NN) position, are significantly smaller than those of Fe-Fe exchanging with the 1NN Fe atom. The relaxation volumes of dumbbells increase in the ordered structure and decrease in the disordered one with the increase of number of Cr atoms in the local environment of a defect. The trends exhibited by the mean values of the various properties have been observed and analysed, and the most stable directions of Fe-Fe, Fe-Cr and Cr-Cr dumbbells have been determined. Moreover, the energy of elastic interaction between such defects are quantitatively estimated using the suitably parametrized dipole tensors of the defects.
[1] D. Costa, G. Adjanor, C.S. Becquart, et al., J. Nucl. Mater. 452 (2014) 425-433
[2] D. Nguyen-Manh, M.Y. Lavrentiev, S.L. Dudarev, C. R. Physique 9 (2008) 379-388
[3] D. Nguyen-Manh, M.Y. Lavrentiev, M. Muzyk et al., J Mater Sci (2012) 47: 7385