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

Solutes such as carbon can strongly impact plasticity in BCC tungsten and tungsten alloys. Therefore, we investigated on the interaction between carbon atoms and screw dislocations, which motion controls plasticity of tungsten at low temperature. Since dislocation mobility depends on the defect core region, ab initio calculations have been performed to model the dislocation-carbon interaction in tungsten where interatomic bonding is described at the electronic level.

In BCC transition metals, carbon induces a core reconstruction [1] with the dislocations moving from its stable configuration known as the easy core to a hard core configuration which is unstable in the solute-free metal. Our calculations confirm this core reconstruction for large concentration of carbon segregated on the dislocation line in tungsten, corresponding to a strong binding of carbon to the dislocation core. However, this reconstruction is not complete all along the line when the carbon concentration is reduced, contrary to what is obtained in iron-carbon systems [2]. This different behaviour arises from the Peierls potentials of both metals. The hard core configuration’ is an energy maximum in the case of tungsten whereas it is a saddle point for iron, thus corresponding to a flat region of the dislocation energy landscape [3]. Finally, calculations have been performed on other interstitial sites in the vicinity of the dislocation, evidencing other possible segregation sites for carbon.

[1] B. Lüthi et al.; Modelling and Simulation in Materials Science and Engineering 25; 2017

[2] B. Lüthi et al.; Computational Materials Science 148; 2018

[3] L. Dezerald et al.; Physical Review B 89; 2014