Systematic first-principles study of impurity hybridization in NiAl

Abstract

We have performed a systematic first-principles computational study of the effects of impurity atoms (boron, carbon, nitrogen, oxygen, silicon, phosporus, and sulfur) on the orbital hybridization and bonding properties in the intermetallic alloy NiAl using a full-potential linear muffin-tin orbital method. The matrix elements in momentum space were used to calculate real-space properties: onsite parameters, partial densities of states, and local charges. In impurity atoms that are empirically known to be embrittler (N and O) we found that the 2s orbital is bound to the impurity and therefore does not participate in the covalent bonding. In contrast, the corresponding 2s orbital is found to be delocalized in the cohesion enhancers (B and C). Each of these impurity atoms is found to acquire a net negative local charge in NiAl irrespective of whether they sit in the Ni or Al site. The embrittler therefore reduces the total number of electrons available for covalent bonding by removing some of the electrons from the neighboring Ni or Al atoms and localizing them at the impurity site. We show that these correlations also hold for silicon, phosporus, and sulfur.

First-principles investigation of the effects of B impurities on the mechanical properties of NiAl intermetallics

“…Many attempts have been made to improve the room temperature ductility of NiAl by investigating the effects of microalloying, macroalloying and reinforcing the ductile second phase [3][4][5][6][7][8][9]. Despite these attempts, room temperature brittleness is still a key problem for the applications of NiAl.…”

Tight‐binding parameters from the full‐potential linear muffin‐tin orbital method: A feasibility study on NiAl

“…We believe this is the first application of the direct extraction method to a real-space calculation of the electronic structure of an intermetallic alloy. The good agreement between the LDOS obtained using the TB extracted from the FPLMTO method and the accurate LDOS obtained directly from the FPLMTO method shows the feasibility of using this method to study more complicated cases, e.g., alloys with small concentration of impurity atoms [91]. One of the advantages of using TB parameters that are directly extracted from first-principles calculation, compared to parameters that are obtained by fitting some band structures and total energy, is that here the parameters are more than just fitting parameters and they possess a more reliable physical interpretation.…”

“…One of the advantages of using TB parameters that are directly extracted from first-principles calculation, compared to parameters that are obtained by fitting some band structures and total energy, is that here the parameters are more than just fitting parameters and they possess a more reliable physical interpretation. By directly extracting the TB parameters in a more complex case of a binary alloy with impurity we have been able recently to demonstrate a correlation between how well the parameters of an impurity atom match those of its host and its macroscopic effect as a cohesion enhancer or an embrittler in the host alloy [91].…”

Effects of C impurities on the elastic properties of NiAl intermetallics

“…However, NiAl's possible technological applications are limited by its poor ductility at low temperatures [1,2]. Different methods have been dedicated to manage the brittle behavior of NiAl, such as, micro-structural control through processing and second-phase reinforcement [3][4][5][6][7][8]. Up to now, the brittleness is still a major obstacle for the practical applications of NiAl.…”