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The role of interstitial carbon impurities on the dislocation glide in bcc iron is investigated by means of molecular dynamics simulations. The local stress induced by carbon atoms, interaction energy map for the a 0 /2〈1 1 1〉{1 1 0} and a 0 /2〈1 1 1〉{1 1 2} edge dislocations and the dynamics of dislocation–carbon interaction is assessed. The local stress exerted on the dislocation due to the carbon atoms and computed by atomistic simulations is used to describe the interaction strength on the continuum level. The derived here analysis of the atomistic data enabled the determination of the activation enthalpy and volume as a function of stress. Having that information, a comparative study demonstrates that at finite temperature, the resistance to the dislocation glide induced by the carbon atoms is lower in {1 1 2} than in {1 1 0} slip systems. [ABSTRACT FROM AUTHOR]

Disconnection motion along () and () twins in Zr is investigated using atomic-scale simulation. In particular, the high mobility of glissile disconnections is studied in terms of the atomic shears and shuffles involved. Using a quasi-static simulation procedure, the displacements of individual atoms are followed as they transit from matrix sites, through interfacial sites, and hence to twin sites by repeated passages of disconnections along the interface. It is found that the overall displacements for the cases studied are those predicted by the Bilby and Crocker (1965) theory which invokes homogeneous shear deformation. However, the present work enables atomic tracks to be followed through the cores of moving disconnections. The combinations of shears and shuffles in the two twinning systems are found to be quite distinct. In addition to tracking their coordinates, the variation of hydrostatic pressure experienced by the atoms is also quantified. [ABSTRACT FROM PUBLISHER]

Abstract: The mechanism of coupled migration and shear is studied in a range of [0001] tilt boundaries in hexagonal close-packed metal using atomic-scale computer simulation. Symmetrical tilt boundaries spanning the low- and high-angle regimes and comprising regular arrays of grain boundary dislocations are simulated. For each misorientation, θ, the perfect boundary (pristine) is investigated as well as one containing a disconnection. Both types of structures are subjected to incremental applied strains to determine the stress that produces coupled migration and shear. The stress for motion in the pristine case, entailing nucleation, is higher than the Peierls stress for motion when disconnections are present. We conclude that the applied stresses in our simulations exert a Peach–Koehler force on pre-existing disconnections, thereby providing a feasible mechanism with a well-defined driving force that produces coupled migration and shear. This mechanism is feasible for the lower-angle boundaries studied, and facile for the high-angle cases. [Copyright &y& Elsevier]

Abstract: Properties of basal and first order prism plane dislocations with Burgers vector 1/3 〈〉 in α-Zr have been investigated by computer simulation. Results for a recent interatomic potential (MA07) are assessed and compared with an older one (AWB95). The elastic constants have been calculated with the inner relaxations allowed for and the energy and vector of metastable stacking faults have been determined and compared with published ab initio estimates. The core of the screw dislocation spreads principally in the prism plane in the MA07 model, in contrast to basal plane dissociation in the AWB95 model, and the prism-to-basal ratio of the Peierls stress for the screw is 0.28 with the MA07 model, compared with 3.31 with the AWB95 model. Simulation of the dynamics of dislocation motion under applied stress reveal how the drag coefficient varies with slip system and temperature. The results for the MA07 model are consistent with the known slip geometry of Zr, suggesting that it offers significant advantages for large-scale atomic simulation of dislocation behaviour. [Copyright &y& Elsevier]

Abstract: Impact of reject brine chemical composition on soils in Riyadh Saudi Arabia, was evaluated. Soil samples at three depths along transect on both sides of the pond were taken, in addition to, water samples from feed, product, reject and pond. Results showed that, the salinity of the brine reached up to, 5500mgl−1. The concentrations of soluble ions were exceeding the allowable limits in most water samples. The ratio of major ions and concentration factor was higher. The concentrations of heavy metals were in the allowable limits for drinking water standards especially, in the feed, and product waters. Results pertaining soil properties indicated that the soil pH, ECe values and, the concentrations of soluble ions were higher in soils closed to the pond. Also, the concentrations of heavy metals were negatively correlated with CaCO3 content and soil pH (expect for Pb; Zn; Cd and Cr), while it was highly correlated with clay content of the soil. Generally, higher ESP and ECe values in the studied soils can lead to lower permeability, poor aeration and consequently soil deterioration. [Copyright &y& Elsevier]