Abstract
We show here how density functional theory calculations can be used to predict the temperatureand orientation-dependence of the yield stress of body-centered cubic (BCC) metals in the thermallyactivated regime where plasticity is governed by the glide of screw dislocations with a 1/2 Burgers vector. Our numerical model incorporates non-Schmid effects, both the twinning/antitwinning asymmetry and non-glide effects, characterized through ab initio calculations on straight dislocations. The model uses the stress-dependence of the kink-pair nucleation enthalpy predicted by a line tension model also fully parameterized on ab initio calculations. The methodology is illustrated here on BCC tungsten but is applicable to all BCC metals. Comparison with experimental data allows to highlight both the successes and remaining limitations of our modeling approach.
Highlights
The plasticity of body-centered cubic (BCC) metals has attracted and will continue to attract a lot of attention for both technological and scientific reasons
Ab initio calculations have shown that screw dislocations in BCC transition metals induce a shortrange dilatation elastic field in addition to the elastic field given by the Volterra solution [39]
Ab initio calculations reveal that many specific features of BCC metals plasticity can be rationalized by core properties of the 1/2〈111〉 screw dislocation
Summary
The plasticity of body-centered cubic (BCC) metals has attracted and will continue to attract a lot of attention for both technological and scientific reasons. A still much debated observation is that the best prediction of the 0 K limit of the yield stress, the so-called Peierls stress, based on atomistic models is two to three times larger than experimental extrapolations [12,13,14] Another surprising feature of the screw dislocations is that they do not obey the classical Schmid law [15], which states that dislocation motion is driven only by the resolved shear stress, i.e. the part of the stress tensor, which produces a Peach–Koehler force in the glide plane of the dislocation. Dislocation glide involves kink pairs, which extend over several tens of Burgers vectors along the dislocations, requiring simulation cells too large for ab initio calculations In this case, classical molecular dynamics simulations with carefully tested interatomic potentials remain highly valuable [23,24,25,26]. We would like to show on the specific example of tungsten how data obtained from ab initio calculations can be used in a consistent way to develop a yield criterion including non-Schmid effects able to predict the plastic strength as a function of both the temperature and the direction and sign of the deformation axis
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