Nonplanar core structure of 1/2<111> screw dislocations: An anisotropic Peierls-Nabarro model

The nonplanar core of the 1/2⟨111⟩ screw dislocation for body-centered cubic metals (groups VB, VIB metals and Fe) has been studied in the framework of the Peierls-Nabarro model, with special interest focused on the effect of crystal anisotropy. By the dislocation interaction model based on the anisotropic elasticity theory, the improved Peierls-Nabarro (P–N) model for nonplanar dislocation core structures is obtained from the variational principle. Full γ -surfaces of the {110} plane and elastic properties employed in this anisotropic P–N model are all achieved by density functional theory (DFT) calculations. The dislocation core structure and its associated dislocation deformation fields can be solved when taking the anisotropy of BCC crystals into account. It is found that with the anisotropic elasticity considered, the proposed nondegenerate nonplanar structure has the lowest energy state, compared to those for both planar and degenerate core structures. The effect of crystalline anisotropy on the nondegenerate core energy cannot be ignored in Cr, Fe, V and Nb. Furthermore, considering the crystal anisotropy, the Burgers vector distribution, the dislocation core energy state and the stress field are clearly distinguished from results predicted by the isotropic model. The crystal anisotropy plays an important role in long-range dislocations stress field especially in Nb and V. The effect of anisotropic elasticity on both long-range and short-range interactions between dislocations for above BCC materials cannot be ignored. The present results can help to build a deeper understanding on the combined effect of the anisotropic elasticity and nonplanar core structures on the dislocation properties.