On the Factors Controlling the Structure of Dislocation Cores in B.C.C. Crystals

Vítek, V.; Lejček, L.; Bowen, D. K.

doi:10.1007/978-1-4684-1992-4_25

Cited by 74 publications

(78 citation statements)

References 15 publications

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“…61 The core structure of the 1 2 ͗111͘ screw dislocation found using the BOP for molybdenum is in full agreement with DFT calculations 58,62,63 but differs from that obtained in studies using central-force potentials. [64][65][66][67] Furthermore, studies of the motion of screw dislocations in molybdenum revealed the significance of stresses perpendicular to the slip direction on the onset of plastic deformation. 68,69 In iridium, unlike in any other fcc metal, two core structures for the screw dislocation have been found.…”

Section: Introductionmentioning

confidence: 99%

Bond-order potential for simulations of extended defects in tungsten

et al. 2007

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We present a bond-order potential (BOP) for the bcc transition metal tungsten. The bond-order potentials are a real-space semiempirical scheme for the description of interatomic interactions based on the tight-binding approximation. In the hierarchy of atomic-scale-modeling methods the BOPs thus provide a direct bridge between electronic-structure and atomistic techniques. Two variants of the BOP were constructed and extensively tested against accurate first-principles methods in order to assess the potentials' reliability and applicability. A comparison of the BOP with a central-force potential is used to demonstrate that a correct description of directional mixed covalent and metallic bonds is crucial for a successful and fully transferable model. The potentials are applied in studies of low-index surfaces, symmetrical tilt grain boundaries, and dislocations. We present a bond-order potential ͑BOP͒ for the bcc transition metal tungsten. The bond-order potentials are a real-space semiempirical scheme for the description of interatomic interactions based on the tight-binding approximation. In the hierarchy of atomic-scale-modeling methods the BOPs thus provide a direct bridge between electronic-structure and atomistic techniques. Two variants of the BOP were constructed and extensively tested against accurate first-principles methods in order to assess the potentials' reliability and applicability. A comparison of the BOP with a central-force potential is used to demonstrate that a correct description of directional mixed covalent and metallic bonds is crucial for a successful and fully transferable model. The potentials are applied in studies of low-index surfaces, symmetrical tilt grain boundaries, and dislocations.

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Section: Introductionmentioning

confidence: 99%

Bond-order potential for simulations of extended defects in tungsten

et al. 2007

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“…Later attempts to generalize the original treatment of Peierls and Nabarro assumed a more general core configuration from which they derived the interactions between the glide planes which satisfy the Peierls integral equation. The essence of these models was captured in a more comprehensive approach by Vitek,12,13 who introduced the concept of the generalized-stacking fault: Consider a perfect crystal cut across a single plane into two parts which are then subjected to a relative displacement through an arbitrary vector f and rejoined. The reconnected lattice has a surplus energy per unit area ␥(f).…”

Section: Introductionmentioning

confidence: 99%

Generalized-stacking-fault energy surface and dislocation properties of aluminum

et al. 2000

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We have employed the semidiscrete variational generalized Peierls-Nabarro model to study the dislocation properties of aluminum. The generalized-stacking-fault ͑GSF͒ energy surface entering the model is calculated by using first-principles density functional theory ͑DFT͒ and the embedded-atom method ͑EAM͒. Various core properties, including the core width, dissociation behavior, energetics, and Peierls stress for different dislocations have been investigated. The correlation between the core energetics and the Peierls stress with the dislocation character has been explored. Our results reveal a simple relationship between the Peierls stress and the ratio between the core width and the atomic spacing. The dependence of the core properties on the two methods for calculating the GSF energy ͑DFT vs EAM͒ has been examined. Although the EAM gives the general trend for various dislocation properties, it fails to predict the correct finer core structure, which in turn can affect the Peierls stress significantly ͑about one order of magnitude͒.

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“…It is generally believed that the core structure of these dislocations is a controlling factor of their mobility. 3 Theoretical studies on these dislocations have led to two types of core structures: asymmetric 3-5 core and symmetric core. [5][6][7][8] In differential displacement ͑DD͒ maps, 3 the asymmetric core ͓Fig.…”

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“…In bcc metals, the Peierls stress depends strongly on the orientation of the shearing. 3,5 In this paper, we study in detail the twinning ( ϭϪ30°) and antitwinning ( ϭ30°) shearing on ͑112͒ planes, where is the angle between the plane with the maximum shear stress and the neighboring ͑110͒ plane. Two recent atomistic calculations 8,10 of the Peierls stress for Ta show good agreement when the applied stress is in the twinning direction: ab initio density-functional theory ͑DFT͒ calculations lead to 675 MPa and calculations using the model generalized pseudopotential theory ͑MGPT͒ potential lead to 600 MPa.…”

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Role of core polarization curvature of screw dislocations in determining the Peierls stress in bcc Ta: A criterion for designing high-performance materials

et al. 2003

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We use a family of embedded atom model potentials all based on accurate quantum-mechanical calculations to study the relation between Peierls stress and core properties of the 1/2a͗111͘ screw dislocation in bcc tantalum ͑Ta͒. We find that the Peierls stress ( P ) is a function of the core-polarization curvature ͑⌸͒ near the equilibrium core configuration. Our results suggest that the computationally available quantity ⌸ is a useful criterion for designing high-performance materials. DOI: 10.1103/PhysRevB.67.140101 PACS number͑s͒: 62.20.Fe, 61.72.Lk Determining the fundamental atomistic mechanisms that underlie plastic deformations of macroscopic materials is a key, enabling step toward designing materials with improved and tailored properties. This is particularly important for bcc metals, which are the basis of some of the highestperforming alloys, but whose behavior is more complex than fcc and hcp materials. 1 Computer simulations could be used to investigate the individual and collective dislocation motions in these materials and guide the development of highperformance materials. 2 At low temperatures, plasticity in bcc metals is governed by low mobility screw dislocations with Burgers vector b ϭ1/2a͗111͘. It is generally believed that the core structure of these dislocations is a controlling factor of their mobility. 3 Theoretical studies on these dislocations have led to two types of core structures: asymmetric 3-5 core and symmetric core. [5][6][7][8] In differential displacement ͑DD͒ maps, 3 the asymmetric core ͓Fig. 1͑a͔͒ spreads in three ͗112͘ directions on ͕110͖ planes, while the symmetric core ͓Fig. 1͑b͔͒ is compact. The main differences between these two types of cores are the relative displacements in the ͗111͘ direction of the two sets of three atoms in the core ͓atoms ͕A, C, E͖ and ͕B, D, F͖ in Fig. 1͑c͔͒. The ''polarization'' 9 of the dislocation core can be used to distinguish different core configurations and is defined by Eq. ͑1͒,or F͒ is the relative displacement between two neighboring atoms in the two columns denoted as X and Y in Fig. 1͑c͒, and b is the magnitude of the dislocation Burgers vector. Thus a symmetric core leads to pϭ0, while pϭ1 corresponds to a fully asymmetric core. The Peierls stress is the minimal shear stress required to move a dislocation in an otherwise perfect crystal. In bcc metals, the Peierls stress depends strongly on the orientation of the shearing. 3,5 In this paper, we study in detail the twinning ( ϭϪ30°) and antitwinning ( ϭ30°) shearing on ͑112͒ planes, where is the angle between the plane with the maximum shear stress and the neighboring ͑110͒ plane. Two recent atomistic calculations 8,10 of the Peierls stress for Ta show good agreement when the applied stress is in the twinning direction: ab initio density-functional theory ͑DFT͒ calculations lead to 675 MPa and calculations using the model generalized pseudopotential theory ͑MGPT͒ potential lead to 600 MPa. However, for the antitwinning direction the calculated Peierls stresses differ by a factor of...

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On the Factors Controlling the Structure of Dislocation Cores in B.C.C. Crystals

Cited by 74 publications

References 15 publications

Bond-order potential for simulations of extended defects in tungsten

Bond-order potential for simulations of extended defects in tungsten

Generalized-stacking-fault energy surface and dislocation properties of aluminum

Role of core polarization curvature of screw dislocations in determining the Peierls stress in bcc Ta: A criterion for designing high-performance materials

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