Impurity effects on atomic bonding inNi3Al

Abstract

First-principles electronic structure calculations based on the full-potential linear-muffin-tin-orbital method have been employed to study the contrasting effects of boron and hydrogen on the electronic structure of the I.lz ordered intermetallic Ni3Al. The total energy, the siteand I-projected densities of states, and the impurity-induced charge-density characteristics are calculated for various impurity configurations, to investigate the effects of local environment on the electronic structure. Total-energy calculations show that both boron and hydrogen impurities prefer to occupy octahedral interstitial sites that are entirely coordinated by six nickel atoms. Our results suggest that the underlying mechanism of the boron-induced strengthening in Ni3Al is the Ni-d and B-p hybridization between the nearestneighbor nickel and boron sites. This results in an enhancement of the intraplanar metallic bonding between the nickel atoms, an enhancement of interstitial bonding charge, and reduction of the bondingcharge directionality around the Ni atoms on the (001) NiAl planes. In contrast, hydrogen is found to enhance the bonding-charge directionality near some Ni atoms and to reduce the interstitial charge, suggesting that it promotes poor local cohesion. When both boron and hydrogen are present in Ni3Al, the dominant changes in the electronic structure are induced by boron and the charge distribution resembles that of Ni3Al+B. These results are broadly consistent with the notion of boron as a cohesion enhancer and hydrogen as an embrittler.

Biaxial strain effects on adatom surface diffusion on tungsten from first principles

“…Therefore ρ bond (r) represents the net charge redistribution of the system. 56,57 It is clear that these two oriented crowdions share several common characteristics: (1) the interplanar interaction is weak, (2) accumulating charge appears to be anisotropic; bonding has one-dimensional directionality, and (3) the crowdion pair shows a crowdion rather then a dumb-bell configuration. Therefore, both crowdion pairs have short migration distances and can glide within the surface layer.…”

First-Principles Study of the Electronic Properties of γ⁄γ′ Interface in Ni Based Superalloys

“…Nonequivalent atoms in the cell are denoted by numerical label, depending on their point-group symmetry. Based on the experiment 25) and theoretical calculation, 7) and also for the purpose to consider the effect of the local environment of the impurity on the electronic structure, the impurity atoms (labeled by X) are placed at two different octahedral interstitial sites: X1 at the center of the octahedral cell, where the impurity has the nearest neighbors of four Ni (6) and one Ni (7) and one Ni (5), and X2 at the center of the cube edge, where the impurity has the nearest neighbors of four Ni (6), one Ni (8) and one Al (17). We will refer to the X1 and X2 sites as the Ni-rich and Ni-deficient octahedral sites, respectively.…”

“…In spite of considerable theoretical efforts have been made to understand the effect of impurities on the mechanical behavior of bulk or grain boundary (GB) in Ni and Ni 3 Al on the basis of the electronic structure, [5][6][7][8][9][10][11][12] not many efforts have been made to investigate the fundamental mechanism of the = 0 interface. Up to now, only few first-principles calculations on the = 0 interface [13][14][15][16] have been carried out.…”

Systematic first-principles study of impurity hybridization in NiAl

“…[16] Further site and angular-momentum decomposition, i.e. the calculation of the weights w nil (k c ), is then performed only on the part of the LMTO wavefunction inside the MT spheres.…”

“…Sun et al have studied the effects of boron and hydrogen on Ni 3 Al using a full-potential linear muffin-tin orbital (FPLMTO) method. [16] They emphasized the increase of the inter- Site-projected 2s density of states at the impurity atom for the case where it is substituting an Al atom. Notice the strong resonance at the bottom of the band in the case of carbon.…”