Mechanisms of self and impurity diffusion in Fe-Al intermetallic compounds
Final Report Abstract
The report provides the results of one part of the joint project “Mechanisms of self and impurity diffusion in Fe-Al intermetallic compounds”. The first-principles investigations in this partial project were performed using the concepts of density functional theory (DFT). Plane-wave based pseudopotentials and the projector-augmented waves (PAW) have been applied to describe Feand Al-containing alloys. Diffusion barriers have been obtained with in the Climbining Imange Nudged Elastic Band (CINEB) method. The calculations include the influence of the magnetic structure and the local magnetic configuration on the defect properties in Fe-Al intermetallic alloys. We discussed for B2-FeAl the relevant defect formation energies by separating the defect types into single and complex defects. Among the single defects the Fe antisites for Fe rich conditions, Fe vacancies in the intermediate region, i.e close to stoichiometry, and Al antisite under Al rich conditions appeared as the dominant defects. Including the possibility of complex formation, the double Fe antisites in Fe rich conditions, single Fe vacancies in the intermediate region and the double Al antisites close to Al rich conditions are the dominant defects. The obtained defect formation energies were used to calculate the defect concentrations at various temperatures and will be used to determine the stability range of the B2-FeAl phase in the binary Fe-Al phase diagram. Furthermore, the activation energies (derived from formation and migration energies) of several diffusion mechanism have been calculated. We studied the next-nearest neighbor jump of a Fe vacancy, the triple defect mechanism, the [110] six-jump cycle and the bent and straight [100] sixjump cycles. The triple defect mechanism has the highest diffusion activation energy due to its large formation energy and is therefore not a candidate for diffusion in B2-FeAl. The other mechanisms are lower in energy and therefore more likely to occur. Especially the Fe vacancy jump and the [110] six-jump cycle show the lowest activation energy, which is also in agreement with experiment near stoichiometry. The results for B2-FeAl are different from B2-NiAl. Therefore, the results obtained from one B2 compound cannot be immediately transfered to another one. Diffusion mechanisms are very material specific and can differ even for such closely related alloys as FeAl and NiAl. The obtained results have been exchanged with the Chinese partner to contribute to an evaluation and improvement of the empirical potentials obtained there.
Publications
- Thermodynamic and physical properties of FeAl and Fe3Al: an atomistic study by EAM simulation, Physica B 407, 4530-4536 (2012)
Y. Ouyang, X. Tong, C. Li, H. Chen, X. Tao, T. Hickel, Y. Du
(See online at https://doi.org/10.1016/j.physb.2012.08.025)
