Effects of ternary additions on the twin energy and site preference in γ-TiAl

1994 ◽  
Vol 9 (7) ◽  
pp. 1755-1760 ◽  
Author(s):  
Jian-hua Xu ◽  
A.J. Freeman
Keyword(s):  
Total Energy ◽  
Local Density Approximation ◽  
Relative Stability ◽  
Local Density ◽  
Site Preference ◽  
Density Approximation ◽  
Self Consistent ◽  
Ternary Additions

Site preference and the effects of ternary additions (Mn, V, etc.) on the twin energy in γ-TiAl were studied by means of all-electron total energy self-consistent calculations based on the local density approximation. The results show that when Mn, Ti, or V substitute on the Al-sites in γ-TiAl, the twin energy is about 20–25% lower than that of stoichiometric γ-TiAl; this may explain observations of increased twinning activity in 48% Al TiAl. By contrast, when ternary additions of V (or Al) occupy Ti-sites, the twin energy has nearly the same value as that of pure γ-TiAl, which is consistent with the observation of only a few twins for Al-rich compositions. By comparing the total energy of Ti6(XAl5) and (Ti5X)Al6 supercells, it is found that the relative stability of Ti6(XAl5) over (Ti5X)Al6 (i.e., the preference for occupying Al-sites) is increased in going from Nb, V, Cr, and Ti to Mn, in agreement with observation that excess Ti occupies Al-sites, and Nb preferentially substitutes on the Ti-sites. The results indicate that Mn preferentially substitutes on the Al-sites, and V (or Cr) may occupy both Ti- and Al-sites.

Site Preference of Ternary Additions in Ni3Si

1994 ◽  
Vol 364 ◽  
Author(s):  
M. Sluiter ◽  
Y. Kawazoe
Keyword(s):  
Electronic Structure ◽  
Local Density Approximation ◽  
Local Density ◽  
Electronic Structure Calculations ◽  
Site Preference ◽  
Density Approximation ◽  
Magnetic Effects ◽  
Spin Polarized ◽  
Ternary Additions ◽  
Structure Calculations

AbstractThe site preference of Al and elements in the 3rd row of the periodic table in Ni3Si was studied in a systematic way by using electronic structure calculations based on the local density approximation. Alloying elements in this intermetallic may occupy exclusively the Ni or Si sublattices, or may exhibit no particular site preference. By performing the calculations both for spin-polarized and non-spin-polarized cases, it was found that magnetism affects the computed site substitution behavior of Mn, Fe, and Co in Ni3Si. In the case of Fe, e.g., a preference for the Ni sublattice is computed when magnetic effects are ignored, but when magnetic effects are accounted for it is found that Fe has no significant site preference Specific trends regarding the site preference across the transition metal series are shown and discussed.

Self-consistent-field calculations of atoms and ions using a modified local-density approximation

1994 ◽  
Vol 50 (1) ◽  
pp. 171-176 ◽  
Author(s):  
David A. Liberman ◽  
James R. Albritton ◽  
Brian G. Wilson ◽  
William E. Alley
Keyword(s):  
Local Density Approximation ◽  
Local Density ◽  
Density Approximation ◽  
Consistent Field ◽  
Self Consistent ◽  
Self Consistent Field

CHEMISORPTION OF O2 AND CO ON COPPER CLUSTERS

1996 ◽  
Vol 03 (01) ◽  
pp. 687-693 ◽  
Author(s):  
HENRIK GRÖNBECK ◽  
ARNE ROSÉN
Keyword(s):  
Charge Transfer ◽  
Local Density Approximation ◽  
Size Dependence ◽  
Local Density ◽  
Wave Functions ◽  
Density Approximation ◽  
Copper Clusters ◽  
Self Consistent ◽  
Stable Product ◽  
Transfer Mechanisms

The initial chemisorption of O 2 and CO on small copper clusters in the range from six to nine atoms has been investigated using a self-consistent jellium description of the clusters. The calculations were performed within the local-density approximation expanding the wave functions in a linear combination of atomic and spherical jellium orbitals. The results indicate a strong size dependence in the chemisorption energies. O 2 was found to be most strongly bound to the Cu 9 cluster while COCu 6 was the most stable product in the case of CO chemisorption. The observations are consistent with experiments and the underlying reasons were traced to differences in cluster-adsorbate hybridization and charge-transfer mechanisms.

Site Preference of Ternary Additions in Ni3A1

1994 ◽  
Vol 364 ◽  
Author(s):  
M. Sluiter ◽  
M. Takahashi ◽  
Y. Kawazoe
Keyword(s):  
Electronic Structure ◽  
Local Density ◽  
Electronic Structure Calculations ◽  
Alloying Elements ◽  
Site Preference ◽  
Density Approximation ◽  
Magnetic Effects ◽  
Spin Polarized ◽  
Ternary Additions ◽  
Structure Calculations

AbstractThe site preference of a large number of alloying elements in Ni3AI (γ′) was studied in a systematic way by using electronic structure calculations based on the local density approximation. Alloying elements in this intermetallic may occupy exclusively the Ni or Al sublattices, or may exhibit no particular site preference. By performing the calculations both for spin-polarized and non-spin-polarized cases, it was found that magnetism strongly affects the computed site substitution behavior of Mn, Fe, and Co in Ni3Al. In the case of Fe, for example, a preference for the Ni sublattice is computed when magnetic effects are ignored, but when magnetic effects are accounted for it is found that Fe has no significant site preference, in much better agreement with a large number of experimental determinations. Some trends regarding the site preference across the periodic table are shown and discussed.

Sign in / Sign up

Export Citation Format

Share Document