The Experts below are selected from a list of 150 Experts worldwide ranked by ideXlab platform
Xiaoxu Huang - One of the best experts on this subject based on the ideXlab platform.
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Extended Dislocation boundaries in metals subjected to plane strain deformation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005Co-Authors: Xiaoxu HuangAbstract:Formation of Extended Dislocation boundaries is a characteristic feature in metals deformed monotonically. The Extended boundaries have preferred orientations both in the crystallographic coordinate system defined by the crystallographic lattice and in the sample system defined by the deformation sample axes. There is an argument in the literature about whether the preferred boundary orientations are dependent on the slip system determined by the grain orientation and deformation mode. In the present paper, this argument is investigated by detailed TEM examination of boundary orientations in grains of selected orientations that constitute a critical test for the argument. The results obtained confirm that the grain orientation plays a key role in determining the boundary plane orientation.
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Precise determination of Extended Dislocation boundary plane in transmission electron microscopy
Materials Science and Technology, 2005Co-Authors: Xiaoxu HuangAbstract:The crystallographic plane of Extended planar Dislocation boundaries can be determined from the boundary trace and electron diffraction when the boundaries are exactly parallel to the beam direction (edge on). It is proposed to combine observations of sample tilt induced change in both projected boundary thickness and boundary spacing for identification of the edge on condition and the boundary crystallographic plane. The boundary crystallographic and macroscopic planes have been determined for two selected grains with similar grain orientations in tensile deformed aluminium. The determined boundary crystallographic planes are similar for the two grains, and in both cases the boundaries are more closely aligned with the active slip plane than with the macroscopically most stressed plane. These results suggest that the boundary crystallographic plane is more important than the macroscopic plane and that grain orientation has a strong effect on the occurrence of the preferred boundary crystallographic plane.
John P. Hirth - One of the best experts on this subject based on the ideXlab platform.
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Some current topics in Dislocation theory
Acta Materialia, 2000Co-Authors: John P. HirthAbstract:Some topics of current interest in Dislocation theory are discussed. Included are considerations of the elastic fields of Dislocations with emphasis on nonlinear and anisotropic elastic effects and boundary conditions for computer simulations. Also discussed are core structures, Extended Dislocation arrays, boundaries and interfaces and Dislocations in thin films.
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Analysis of Extended Dislocation faults
Journal of Materials Research, 1992Co-Authors: Arun M. Kumar, John P. HirthAbstract:The relative stability of standard Extended Dislocation dipoles and some new stable defects with lozenge-shaped cross sections have been numerically estimated. An earlier study of these defects in an isotropic fee structure has been Extended to the anisotropic case to assess the effect of anisotropy on the calculations. The study is further Extended to the case of the L1_2 crystal structure of the ordered alloy Ni_3Al, where the Burgers vectors are large. Results indicate that the introduction of anisotropy has a small effect in determining the relative stability of Extended Dislocation faults. The results also show that the large values of the Burgers vectors stabilize the arrays in Ni_3Al and that the most stable defect favored is the screw lozenge array L _D.
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Extended Dislocation lozenges and dipoles in f.c.c. crystals
Philosophical Magazine A, 1992Co-Authors: Arun M. Kumar, John P. HirthAbstract:Abstract In addition to the standard Extended Dislocation dipoles, we show that there are four additional stable defects with lozenge-shaped cross-sections. The relative stability of these various types of Extended dipoles and faults in silver, a typical f.c.c. metal, is numerically evaluated. Isotropic linear elasticity is assumed in the analysis. The equilibrium configurations and the interaction energy of the unreacted, Extended Dislocation pairs gliding on parallel {111} planes are calculated. The change in energy is then computed after the Extended Dislocations near their equilibrium positions dissociate and react to form the faulted configurations. The results predict stable lozenge arrays for reactant screw Dislocations in addition to the traditional dipoles predicted for 60[ddot] reactant mixed Dislocations.
Ian P. Jones - One of the best experts on this subject based on the ideXlab platform.
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The interaction between Extended Dislocations and antiphase domain boundaries — I: superpartial separation and the yield stress
Intermetallics, 2001Co-Authors: T.s. Rong, Mark Aindow, Ian P. JonesAbstract:Abstract The interaction between an Extended superDislocation in an ordered structure and an antiphase domain boundary (APB) has been analysed. In contrast to previous treatments (Cottrell AH. Relation of properties to microstructure. ASM Monograph 1954. p. 131; Ardley GW. Acta Metall 1955;3:525) we include the effects of (i) the small strip of perfect crystal within an Extended Dislocation straddling an APDB and (ii) the ledge in an APDB which has been cut by a Dislocation. We also revisit the concept of ‘APDB thickness’. The new analysis leads to a more marked variation of superpartial separation with domain size than previously calculated and also predicts a variation of yield stress with domain size which is in better agreement with experiment than are previous calculations.
C. Lane Rohrer - One of the best experts on this subject based on the ideXlab platform.
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Cluster/Dislocation interactions in dilute aluminum-based solid solutions
Journal of Materials Research, 1995Co-Authors: C. Lane RohrerAbstract:The influence of single solute atoms and solute clusters on an Extended edge Dislocation dipole in Al was studied by atomistic simulation. Single Cu and Ag solute/Dislocation interaction energy calculations showed that Cu interacts strongly with an Al Extended Dislocation and prefers sites in the compressive region, in agreement with elasticity theory predictions. Single Ag atoms, however, are strongly repelled by an Al Extended Dislocation, in contrast with elasticity theory predictions. Monte Carlo simulations of Al: 1% Cu, Al: 2% Cu, Al: 1% Ag, Al: 0.5% Cu, 0.5% Ag, and Al: 0.75% Cu, 0.25% Ag were carried out in the presence of an Extended Dislocation dipole at 600 K allowing for solute segregation. Cu atoms in the binary alloys were observed to segregate to the compressive regions of the Extended Dislocation dipole, forming widespread “atmospheres” over the width of both Extended Dislocations which did not affect the partial Dislocation spacing. Ag in the binary alloy formed small Ag zones which also had little influence on the spacing between the partials. The ternary systems, however, exhibited highly localized solute clusters that had a large impact on the Extended Dislocation dipole structure, increasing the separation between the partial Dislocations. The resulting cluster structures are discussed along with their influence on the apparent stacking fault energy of the alloy systems.
R. G. Hoagland - One of the best experts on this subject based on the ideXlab platform.
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Extended Dislocation barriers in tilt boundaries in fcc crystals
Material Research Innovations, 1998Co-Authors: J. P. Hirth, R. G. HoaglandAbstract:Extended Dislocation barriers at tilt boundaries in fcc crystals are considered. For boundaries with a high degree of lattice coincidence, stable Extended Dislocation barriers, analogous to those occurring within a single crystal, are shown to exist. Other boundaries can have components equivalent to the high coincidence boundaries. The boundary barriers are shown to be possible nucleation sources for mechanical twins or martensite phase transformations.
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An atomistic study of the strength of an Extended-Dislocation barrier
Modelling and Simulation in Materials Science and Engineering, 1998Co-Authors: Michael I. Baskes, R. G. Hoagland, Tomoaki TsujiAbstract:The stress dependence of a lock consisting of a stair rod symmetrically located between two Shockley partials in face-centred cubic nickel was examined by atomistic simulation. The applied stress forced the partials into the stair rod. As the partials move into the lock with increasing strain, the separation distances are reasonably consistent with a linear elastic calculation of equilibrium separation except at the closest approach where the elastic calculation overestimates the separation. The overestimation is attributable to core overlap. The lock underwent several unstable transitions before becoming an inverted arrangement of its initial configuration. The sequence of transitions involves an asymmetric configuration at 2.3% strain containing an extrinsic fault, a transition at 4.8% strain that changes the stair rod to , and a transition that inverts the lock at 6% strain with the stair rod becoming . The evolution of the lock is not reversible.
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A computer simulation of an Extended Dislocation barrier in a FCC crystal
1995Co-Authors: R. J. Kurtz, R. G. Hoagland, J. P. HirthAbstract:A computer simulation has been performed to examine the formation and breakdown of various Extended Dislocation barriers in a crystal of atomistically simulated aluminum. Under an appropriate stress tensor an Extended mixed Dislocation was found to decompose by one of its partial Dislocations dissociating into a 1/6[110] type stairrod Dislocation and a glissile partial on an intersecting glide plane. The mechanism is shown to provide an efficient way to generate stacking faults, can be relevant to twin formation, and provides a stable barrier to Dislocation motion.
