Oxygen - Dislocation interaction in zirconium from first principles

Abstract

Plasticity in zirconium alloys is mainly controlled by the interaction of 1/3 1210 screw dislocations with oxygen atoms in interstitial octahedral sites of the hexagonal close-packed lattice. This process is studied here using ab initio calculations based on the density functional theory. The atomic simulations show that a strong repulsion exists only when the O atoms lie in the dislocation core and belong to the prismatic dislocation habit plane. This is a consequence of the destruction of the octahedral sites by the stacking fault arising from the dislocation dissociation. Because of the repulsion, the dislocation partially cross-slips to an adjacent prismatic plane, in agreement with experiments where the lattice friction on screw dislocations in Zr-O alloys has been attributed to the presence of jogs on the dislocations due to local cross-slip.

Oxygen-dislocation interaction in titanium from first principles

“…Comparing the present results with Ref. [26] on the interaction of screw dislocations with oxygen atoms in zirconium, we see that the same repulsive interaction resulting from the destruction of oxygen insertion sites by the stacking fault ribbon and leading to a change of dislocation core configuration is obtained in zirconium and titanium when the oxygen atom lies in its natural octahedral insertion sites. Therefore, in both metals, the screw dislocations gliding in prismatic planes undergo a stronger lattice friction because of the creation of jogs allowing to bypass the solute atoms.…”

“…1). These interstitial sites correspond to octahedral sites in the twined hcp crystal [26], since the pyramidal fault is a two-layer twin in the pyramidal stacking [28,29]. Both the pyramidal and mixed pyramidal-prismatic cores relax towards the same core shown in Figs.…”

First-Principles Calculations of Oxygen-Dislocation Interaction in Magnesium

“…This phenomenon indicates that a repulsive force exists between the O atom and the basal dislocation core. To verify this point, the interaction energy between oxygen and screw <a> dislocation core was computed in term of Equation (1) defined as [9,10,29]:…”

“…Furthermore, using ab initio calculations, Ventelon et al [8] found that carbon atoms would induce the reconstruction of screw dislocation core in Fe, and therefore be accountable for the solute-segregation related phenomena, such as yielding and strain aging in Fe-C alloy systems. Moreover, in the other two hexagonal close-packed (HCP) metals, Zr and Ti, researchers have discovered that interstitial oxygen atoms would increase the lattice friction against the glide of screw dislocation, thus significantly influencing the plasticity of Zr and Ti [9][10][11]. The aforementioned studies on interstitial nonmetallic alloying elements invoke us to speculate whether the mechanical properties of Mg can be tuned by the solutionization of nonmetallic elements.…”

“…Apparently, these studies are insufficient to clarify the underlying mechanism of the influence of interstitial nonmetallic atoms on the deformation behavior of Mg. In this work, we studied the interaction between O, a representative interstitial nonmetallic solute, and the screw <a> dislocation core in Mg in the scheme of first-principles and analyzed the implication of structural changes of dislocation cores to the mechanical properties of Mg, which would provide additional information on the role of interstitial nonmetallic atoms on the deformation behavior of Mg. Figure 1 shows the simulation cell consisting of a dislocation dipole with a period quadrupolar arrangement known as an S arrangement proposed by Clouet [16], which has been applied to model the dislocation core structure in Zr [10,17] and Mg [18] systems. Three vectors of the simulation box adopted periodic boundary conditions.…”