The Effect of a Light Impurity on the Electronic Structure of Dislocations in NiAl

2011 ◽  
Vol 318 ◽  
pp. 23-32 ◽  
Author(s):  
Li Qun Chen ◽  
Zheng Chen Qiu
Keyword(s):  
Electronic Structure ◽  
Single Crystals ◽  
Impurity Atom ◽  
Edge Dislocation ◽  
Density Functional ◽  
Dislocation Core ◽  
Interstitial Site ◽  
Dislocation Motion ◽  
Impurity Atoms ◽  
Discrete Variational Method

The effect of light impurities (C, N) upon the electronic structure of the [100](010) edge dislocation core in NiAl single crystals is investigated by using the Dmol and the discrete variational method within the framework of density functional theory. The impurity segregation energy, interatomic energy and charge distribution are calculated, and the effects of impurity atoms upon the dislocation motion are discussed. The energy analysis shows that both C and N atoms can stabilize the [100](010) edge dislocation core, and prefer to occupy the interstitial site in the Center-Ni dislocation core. Meanwhile, the impurity atoms can form strong bonding states with their neighboring host atoms via hybridization between the 2p orbitals of the impurity atom and the 3d4s4p orbitals of the host Ni atoms; as well as between the 2p orbitals of the impurity atom and the 3s3p orbitals of the host Al atoms. The strong interaction between impurity atom and host atoms in the dislocation core may improve the strength of NiAl single crystals.

Electronic structure and doping effect of Ni and Co in the kink on the edge dislocation of bcc iron

2007 ◽  
Vol 261-262 ◽  
pp. 37-46 ◽  
Author(s):  
Li Qun Chen ◽  
Zheng Chen Qiu
Keyword(s):  
Electronic Structure ◽  
Impurity Atom ◽  
Edge Dislocation ◽  
First Principles ◽  
Density Functional ◽  
Functional Theory ◽  
Discrete Variational Method ◽  
Solid Solution Softening ◽  
Bcc Iron ◽  
3D Impurities

Using the first-principles self-consistent discrete variational method based upon density functional theory, we investigated the energetics and the electronic structure of the 3d impurities Ni and Co in a kink on the [100](010) edge dislocation (ED) in bcc iron. The calculated results show that the interatomic energies between the impurity atom and the neighboring host atoms decrease. The bonding for the impurity atom (Ni, Co) and the neighboring host Fe atoms is weaker than that for an Fe atom at the X site and the corresponding atoms in the clean kink. These results indicate that sideways motion of the kink in the <100>{010} ED is accelerated by an impurity atom such as Ni or Co and that, consequently, the presence of impurities increases the dislocation mobility, thus leading to solid-solution softening.

CLUSTER-SIMULATED DISLOCATION CORE: MOTION AND TRAP FOR IMPURITY ATOMS

2005 ◽  
Vol 19 (15n17) ◽  
pp. 2353-2358
Author(s):  
YAN-QUAN FENG ◽  
FENG-LIANG SHI ◽  
CHONG-YU WANG
Keyword(s):  
Electronic Structures ◽  
Density Functional ◽  
Dislocation Core ◽  
Dislocation Motion ◽  
Functional Theory ◽  
Impurity Atoms ◽  
The Core ◽  
Discrete Variational Method ◽  
Bcc Iron ◽  
Method Of Density Functional

The electronic structures of a cluster-simulated edge dislocation core in bcc iron were computed using the discrete variational method of density functional theory Energy calculations show that the iron lattice and the impurity atoms trapped in the core have resistance to the dislocation motion. The ubiquitous P -embrittlement of iron can be explained electronically.

First-Principles Investigation of the Alloying Effect of Mn and Cr in the Kink on the Edge Dislocation in BCC Iron

2008 ◽  
Vol 272 ◽  
pp. 61-70
Author(s):  
Zheng Chen Qiu ◽  
Li Qun Chen
Keyword(s):  
Edge Dislocation ◽  
First Principles ◽  
Density Functional ◽  
Local Density ◽  
Interatomic Interaction ◽  
Dislocation Motion ◽  
Binding Energies ◽  
Pinning Effect ◽  
Discrete Variational Method ◽  
Bcc Iron

Using the first-principles self-consistent discrete variational method based on density functional theory, we investigated the energetics and the electronic structure of 3d impurity Mn and Cr in the kink on the [100](010) edge dislocation in bcc iron. The calculations of binding energies show that both Mn and Cr can stabilize the system containing kink. We also calculate the structural energy, the interatomic energy, the local density of states and the charge density difference. The results indicate that both Mn and Cr in the kink can enhance the interatomic interaction between the impurity atom and the neighboring Fe atoms due to the hybridization of impurity d-Fe d orbitals. The introduction of the Mn and Cr impurity leads to a strong pinning effect on the dislocation motion in bcc iron, which may explain the solid solute hardening of Mn and Cr.

The Site Preference of Alloying Element Zr in NiAl Dislocation Core and its Effects on Bond Characters

2013 ◽  
Vol 344 ◽  
pp. 19-26
Author(s):  
Li Qun Chen ◽  
Zheng Chen Qiu
Keyword(s):  
Binding Energy ◽  
Edge Dislocation ◽  
Dislocation Core ◽  
Dislocation Motion ◽  
Partial Density ◽  
Site Preference ◽  
Alloying Element ◽  
Dislocation Interaction ◽  
High Temperature Alloys ◽  
Potential Applications

NiAl is one kind of high-temperature alloys with broad potential applications in aerospace industry. Its mechanical properties are believed to be largely related to the dislocation behavior and impurity-dislocation interaction. In the paper we report first principles study of the alloying effect of Zr in the [10(010) edge dislocation core of NiAl. The binding energy of doping system decreases 3.77 eV when a Zr atom substituted for an Al, only decreases 1.06 eV with substitution for a Ni atom. The result of the binding energy shows that a Zr atom prefers to occupy an Al site in the dislocation core of NiAl. The analyses of the charge distribution, the interatomic energy and the partial density of states suggest that Zr will greatly enhance the interaction between Zr atom and neighboring host atoms, as well as that between host atoms. These results show that the alloying element Zr induced pinning effect on the edge dislocation motion is predicted, and could be helpful for understanding microscopic mechanisms of alloying-induce hardening in NiAl alloy.

scholarly journals Electronic Structure Calculations of Oxygen Atom Transport Energetics in the Presence of Screw Dislocations in Tungsten

2019 ◽  
Author(s):  
Yue Zhao ◽  
Lucile Dezerald ◽  
Jaime Marian
Keyword(s):  
Electronic Structure ◽  
Screw Dislocation ◽  
Hard Core ◽  
Dislocation Core ◽  
Electronic Structure Calculations ◽  
Dislocation Motion ◽  
Solute Diffusion ◽  
Inelastic Interaction ◽  
Similar Time ◽  
Structure Calculations

Plastic flow in body-centered cubic (bcc) alloys is governed by the thermally-activated screw dislocation motion. In bcc interstitial solid solutions, solute diffusion can occur at very fast rates owing to low migration energies and solute concentrations. Under mechanical loading, solutes may move on the same or similar time scale as dislocations glide, even at low temperatures, potentially resulting in very rich co-evolution processes that may have important effects in the overall material response. It is therefore important to accurately quantify the coupling between interstitial impurities and dislocations, so that larger-scale models can correctly account for their (co)evolution. In this paper, we use electronic structure calculations to obtain the energetics of oxygen diffusion under stress and its interaction energy with screw dislocation cores in bcc tungsten. We find that oxygen atoms preferentially migrate from tetrahedral to tetrahedral sites with an energy of 0.2 eV. This energy couples only weakly to hydrostatic and deviatoric deformations, with activation volumes of less than $0.02$ and $0.2b^3$, respectively. The strongest effect is found for the inelastic interaction between O atoms and screw dislocation cores, which leads to attractive energies on the order of 1.5 eV and a structural transformation of the screw dislocation core from an `easy' to a `hard' core configuration

The First-Principles Study of Electronic Structure of Fe/MgO/Fe Magnetic Tunnel Junctions Interface

2005 ◽  
Vol 475-479 ◽  
pp. 2255-2258 ◽  
Author(s):  
Jia Xiang Shang ◽  
Fu He Wang ◽  
Xiao Fang Bi ◽  
Hui Bin Xu
Keyword(s):  
Electronic Structure ◽  
First Principles ◽  
Density Functional ◽  
Tunnel Junctions ◽  
Normal Component ◽  
Ferromagnetic Layer ◽  
Magnetic Tunnel Junctions ◽  
Discrete Variational Method ◽  
Ferromagnetic Layers ◽  
Component Interface

In this work series of models were constructed in order to investigate the relationship between atomic and electronic structure and TMR property. Models with normal component interface of Fe/MgO/Fe magnetic tunnel junctions were calculated by first-principles discrete variational method (DVM) within the framework of local spin density functional theory. The SP and TMR ratio of Fe at interface of ferromagnetic layer as well as density of states are analyzed. Our research shows that the thickness of ferromagnetic layers effect much on electronic structure. The interface and surface Fe layers have different feature from that of interior.

Internal Friction in Plastically Deformed High-Purity NiAl Single Crystals

1998 ◽  
Vol 552 ◽  
Author(s):  
M. Hirscher ◽  
D. Schaible
Keyword(s):  
Internal Friction ◽  
Single Crystals ◽  
High Purity ◽  
Formation Enthalpy ◽  
Dislocation Motion ◽  
Zone Melting ◽  
Interstitial Impurity ◽  
Impurity Atoms ◽  
Kink Pair ◽  
Friction Measurements

ABSTRACTHigh-purity stoichiometric NiAl single crystals have been prepared by crucible-free inductive zone melting and afterwards well annealed at temperatures below 1200 K. Internal friction measurements of torsionally deformed single crystals show two relaxation maxima at 500 and 800 K which anneal during the measurement. The first maximum can be assigned to the dislocation motion by kinkpair formation and the annealing to pinning of these dislocations by interstitial impurity atoms. The second maximum is attributed to the Snoek-Köster relaxation of dislocations in the presence of mobile interstitial impurity atoms and the annealing to the pinning of dislocations by vacancies. The kink-pair formation enthalpy in NiAl was estimated.

Interactions of Point and Extended Defects in Structural Intermetallics: Real-Space Lmto-Recursion Calculations

1997 ◽  
Vol 491 ◽  
Author(s):  
O. Yu. Kontsevoi ◽  
O. N. Mryasov ◽  
Yu. N. Gornostyrev ◽  
A. J. Freeman
Keyword(s):  
Electronic Structure ◽  
Dislocation Core ◽  
Real Space ◽  
Dislocation Motion ◽  
Localized States ◽  
Extended Defects ◽  
Recursion Method ◽  
Extended Defect ◽  
Structure Changes ◽  
Ternary Additions

ABSTRACTA real-space TB-LMTO-recursion method for electronic structure calculations is applied to the study of interacting extended and point defects in NiAl. Results of calculations for the pure intermetallic and with ternary additions (within a supercell model) show good agreement with band structure results. Further, electronic structure and total energy calculations of point (single impurity, M=Ti, V, Cr, Mn, Fe and Co) and planar defects such as anti-phase boundaries (APB) were carried out and the interaction between them was determined. We found that for the ½〈111〉{110} APB in NiAl, ternary additions occupy exclusively the 3d-metal sublattice and decrease the APB energy (except for Co). Finally, we employ TB-LMTO-REC to study the electronic structure of the most complex extended defect, a dislocation. We demonstrate for the 〈100〉{010} edge dislocation in NiAl that: (i) quasi-localized states may exist as a result of specific lattice distortions in the dislocation core with a type of “broken” bonds; (ii) the electronic structure changes appreciably in the process of dislocation motion; (iii) van-Hove singularities present in the ideal crystal may be shifted to E;r as a result of the dipolar character of the deformations in the dislocation core.

Density Functional Theory Study of Kink with P in BCC Iron

2010 ◽  
Vol 305-306 ◽  
pp. 39-47
Author(s):  
Li Qun Chen ◽  
Tao Yu ◽  
Zheng Chen Qiu
Keyword(s):  
Density Functional Theory ◽  
Electronic Structure ◽  
Edge Dislocation ◽  
Density Functional ◽  
Density Functional Theory Study ◽  
Functional Theory ◽  
The Core ◽  
Impurity Segregation ◽  
Pinning Effect ◽  
Bcc Iron

The optimal geometries and mechanical properties of a kink with P are studied by applying density functional theory to the ½[111](1¯10) edge dislocation in bcc iron. The calculated impurity segregation energy shows that the P atom can be potentially trapped by the kink, and the doping P preferably segregates to the core region of the ½[111](1¯10) edge dislocation rather than to the <100>(010) edge dislocation. The analysis of the electronic structure indicates that the sideward motion of the kink is impeded owing to strong a interaction between P and neighboring Fe atoms. That is, the P induces a pinning effect on the ½[111](1¯10) edge dislocation. The hybridizations between P and Fe come from P 3p and Fe 3d4s4p. The p and d states have an obvious orientation, which may not be favorable to the toughness of iron. The localized effect of the P-kink complex distinctly affects the electronic structure as well as the energy of the system.

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