The influence of transition metal solutes on the dislocation core structure and values of the Peierls stress and barrier in tungsten

Abstract

Several transition metals were examined to evaluate their potential for improving the ductility of tungsten. The dislocation core structure and Peierls stress and barrier of 1/2<111> screw dislocations in binary tungsten-transition metal alloys (W(1-x)TM(x)) were investigated using density functional theory calculations. The periodic quadrupole approach was applied to model the structure of the 1/2<111> dislocation. Alloying with transition metals was modeled using the virtual crystal approximation and the applicability of this approach was assessed by calculating the equilibrium lattice parameter and elastic constants of the tungsten alloys. Reasonable agreement was obtained with experimental data and with results obtained from the conventional supercell approach. Increasing the concentration of a transition metal from the VIIIA group, i.e. the elements in columns headed by Fe, Co and Ni, leads to reduction of the C' elastic constant and increase of the elastic anisotropy A = C(44)/C'. Alloying W with a group VIIIA transition metal changes the structure of the dislocation core from symmetric to asymmetric, similarly to results obtained for W(1-x)Re(x) alloys in the earlier work of Romaner et al (2010 Phys. Rev. Lett. 104 195503). In addition to a change in the core symmetry, the values of the Peierls stress and barrier are reduced. The latter effect could lead to increased ductility in a tungsten-based alloy. Our results demonstrate that alloying with any of the transition metals from the VIIIA group should have a similar effect to alloying with Re.

Ab initio investigation of the Peierls potential of screw dislocations in bcc Fe and W

“…10). The Peierls barrier amplitude amounts to about 90 meV/b (respectively 70 meV/b) using the PWSCF GGA (respectively SIESTA GGA), in good agreement with another estimate of the Peierls barrier from DFT calculations [36]. The effect of the exchange-correlation functional is less pronounced than in Fe: with SIESTA, the Peierls energy is about 10% larger with LDA than with GGA (Fig.…”

“…DFT calculations of the corresponding Peierls barrier in Fe have evidenced a single hump barrier, at variance with the Takeuchi rule mentioned above [28,30,34] (indeed, the Peierls barrier adopts a 'camel-hump' shape with a local minimum between Peierls valleys when the split core is metastable, see below for details). Other DFT calculations of the Peierls barrier that exhibit a single hump shape were reported in bcc W and W alloys [35,36]. We note that the Takeuchi rule holds for pair and embedded-atom method (EAM) potentials in most cases [28,37,30,34], but is not a consequence of the lack of angular dependence of interatomic potentials since it has recently been found possible to parameterize EAM potentials for Fe and W, which reproduce the expected single-hump Peierls barrier with a non-degenerate core structure [35,18].…”

On the binding of nanometric hydrogen–helium clusters in tungsten

“…At this point we also note that none of the potentials for pure W used in the above works reproduce the key features as good as 'EAM2' by Marinica et al [11]. In addition, a 1/2 < 1 1 1 > screw dislocation in bcc W relaxed by BOP provides a threefold degenerate core structure, which is contradictory to DFT results [35] and 'EAM2' by Marinica et al [11].…”

Interaction of hydrogen with dislocations in tungsten: An atomistic study

“…4 for a detailed explanation). Note that the BOP potential predicts the three-fold split structure for the dislocation core, which contradicts the ab initio result [13,[18][19][20][21]. Both versions of the EAM potential return the isotropic non-degenerate core structure, which complies with the ab initio data.…”