Constitutional and thermal point defects inB2NiAl

Abstract

The formation energies of point defects and the interaction energies of various defect pairs in NiAl are calculated from first principles within an order N, locally self-consistent Green's-function method in conjunction with multipole electrostatic corrections to the atomic sphere approximation. The theory correctly reproduces the ground state for the off-stoichiometric NiAl alloys. The constitutional defects ͑antisite Ni atoms and Ni vacancies in Ni-rich and Al-rich NiAl, respectively͒ are shown to form ordered structures in the ground state, in which they tend to avoid each other at the shortest distance on their sublattice. The dominant thermal defects in Ni-rich and stoichiometric NiAl are calculated to be triple defects. In Al-rich alloys another type of thermal defect dominates, where two Ni vacancies are replaced by one antisite Al atom. As a result, the vacancy concentration decreases with temperature in this region. The effective defect formation enthalpies for different concentration regions of NiAl are also obtained.

Site preference and effect of alloying on elastic properties of ternaryB2 NiAl-based alloys

“…However, as shown in Ref. 40, this configuration is energetically unfavorable because 2E(V Al ) > E(Ni Al ). In the case of E X > 0 there are two possibilities.…”

“…If E X < 0, then there is a strong Ni site preference, because atoms X prefer to go to the Ni sublattice despite the Ni antisite formation on the Al sublattice. 40 Besides, an atom X can occupy the Ni sublattice with the formation of two Al vacancies (2V Al ) to keep the Ni concentration constant. However, as shown in Ref.…”

Theoretical modeling of molar volume and thermal expansion

“…One of the frequently studied compounds is B2 NiAl which contains high concentrations of constitutional point defects and shows large deviations from stoichiometric composition. Korzhavyi et al (2000) calculated the formation energies of point defects in NiAl using an order N, locally self-consistent Green's function method. The calculated formation energies and lattice parameters agree reasonably with the measurements on the non-stoichiometric NiAl.…”

Ab initioprediction of vacancy properties in concentrated alloys: The case of fcc Cu-Ni

“…In so far alloys have been considered, it is usually in the low-point defect concentration limit so that point defects can be assumed to be noninteracting. Within these limitations, point defect properties in ordered structures such as B2-AlNi [12][13][14][15][16], B2-FeAl [12,17,18], and L1 2 -Ni 3 Al [19] have been theoretically studied. As described in Refs.…”