Screw dislocation-carbon interaction in BCC tungsten: an ab initio study

TL;DR

This study uses ab initio calculations to explore how carbon atoms interact with screw dislocations in tungsten, revealing strong binding, reconstruction effects, and high-temperature saturation of carbon at dislocation sites.

Contribution

It provides a detailed atomic-level understanding of carbon-dislocation interactions in tungsten, including reconstruction, binding, and thermodynamic saturation effects.

Findings

Carbon induces dislocation reconstruction and stable core configurations.

Strong carbon-dislocation attraction persists at large distances.

Dislocations remain saturated with carbon up to approximately 2500 K.

Abstract

The interaction between carbon and screw dislocations in tungsten is investigated using ab initio calculations. The presence of carbon atoms in the vicinity of the dislocation induces a reconstruction, with the dislocation relaxing to a configuration, the hard core structure, which is unstable in pure tungsten. The reconstruction corresponds to a strong binding of carbon in the prismatic sites created by the dislocation which is perfect for high concentrations of carbon segregated on the dislocation line. However, the reconstruction is only partial for lower atomic fractions, with the dislocation tending to fall back in its easy core ground state. This pinning by carbon atoms of the dislocation in an unstable position is well described by a simple line tension model. A strong carbon-dislocation attraction is also evidenced at larger separation distances, when the solute is in the fourth nearest neighbour octahedral sites of the reconstructed core. The equilibrium concentrations of carbon in these different segregation sites are modelled with an Ising model and using a mean-field approximation. This thermodynamic model evidences that screw dislocations remain fully saturated by carbon atoms and pinned in their hard core configuration up to about 2500 K.