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Journal ArticleDOI

A Peierls-Nabarro model for kink-pair generation in screw dislocations at low temperatures

Ahw Ngan1
01 Jan 1998-MRS Proceedings (Materials Research Society. The Journal's web site is located at http://www.mrs.org/publications/epubs/proceedings/spring2004/index.html)-Vol. 538, Iss: 1, pp 113-118

AbstractKink-pair generation in three-fold screw dislocations in the bcc lattice is investigated within the framework of the generalised Peierls-Nabarro model. Using a piece-wise plane strain approximation, the apparent activation energy is predicted to vary with stress in a parabolic manner which is in good agreement with experimental findings.

Topics: Plane stress (52%)

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Journal ArticleDOI
Abstract: The anisotropy of plasticity in b.c.c. metals is decomposed into two parts. The first, a variation of the Peierls stress with slip plane and sense of slip, is intrinsic to the b.c.c. structure and is reflected in the geometry of the screw dislocation core and of the generalized stacking fault energy ({gamma}) surface. The second part, a sensitivity of the Peierls stress to non-glide elements of the applied stress, is shown to be due to small edge fractional dislocation components in the screw dislocation core. These edge components and their change in response to non-glide applied stress can be explained by the characteristics of the {gamma}-surface. These concepts are illustrated by means of atomistic calculations, using Finnis-Sinclair interatomic force laws, for the b.c.c. transition elements of groups VB and VIB of the periodic table. Metals in the two groups are shown to fall into two classes of core structure and behavior; the contrasting properties can be explained in terms of the {gamma}-surfaces, and can be traced further to differences in the elastic constants.

404 citations


Book
01 Jan 1991

290 citations


Journal ArticleDOI
Abstract: The core structures and lattice friction stresses of single kinks on a screw dislocation in the b.c.c. lattice have been calculated by means of computer simulation. Interatomic binding potentials derived from first principles for potassium and by empirical methods for an iron-like material have been used. It is shown that a wide variety of kinks can exist on the dislocation, with core structures largely independent of the potential. The width of the kinks, i.e. the spatial extent of the kink displacement field parallel to the dislocation line, is found to vary strongly with potential, as does the kink Peierls stress. The calculated Peierls stresses, however, are found to be too small to explain the observed temperature dependence of the flow stress in real materials.

68 citations


Journal ArticleDOI
Abstract: Analysis of the temperature dependence of the flow stress of the b.c.c. metals α-Fe, Nb, Mo and Ta reveals their Peierls potentials. They are dam-like with a flat maximum or even have an intermediate minimum, but they are never sinusoidal. The elastic energy of the activated bulges in the dislocations is fully taken into account in a quasi-anisotropic calculation by making it trapezoidal. In the thermally activated configuration the amplitude of the bulge (the height of a kink pair) is the lattice periodicity a, double activation to 2a is excluded.

65 citations


Journal ArticleDOI
Ahw Ngan1
Abstract: The original Peierls-Nabarro model considers planar dissociation only and is therefore not valid for screw dislocations which have more than one slip plane In this work, a generalized Peierls-Nabarro model is developed to take into account the non-planar mode of dissociation for screw dislocations Solution to the governing integral equation can be obtained by a self-consistent numerical scheme The equilibrium configuration, strain and stress fields, and the energy of the dislocation core can be calculated from this model

48 citations