Screw dislocations in BCC transition metals: from ab initio modeling to yield criterion

Abstract

We show here how density functional theory calculations can be used to predict the temperature- and orientation-dependence of the yield stress of body-centered cubic (BCC) metals in the thermally-activated regime where plasticity is governed by the glide of screw dislocations with a $1/2 \langle 111\rangle $ 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.

Keywords

• Dislocations
• Plasticity
• Density functional theory
• Body-centered cubic metals
• Tungsten