Predicting Core Structure Variations and Spontaneous Partial Kink Formation for ½<111> Screw Dislocations in Three BCC NbTiZr Alloys

Abstract

Recent interest in chemically-complex solid-solution alloys has produced a number of new refractory BCC alloys with superior high-temperature properties. Preliminary atomistic studies show that, unlike simple BCC metals, these alloys produce equilibrium (screw) dislocations spread on varying glide planes along their length. This observation suggests that under load such defects produce kinks on different glide planes leading to a distribution of pinning points that significantly increases high-temperature strength. In order to validate this model a first-principle approach is developed to characterize these sub-nanoscale structures. We find significant spreading of the dislocation onto varying {110} planes (partial kinks) in NbTiZr and Nb17Ti33Zr50, while Nb50Ti33Zr17 produces a straight-compact dislocation as found in simple BCC metals. Chemical analysis around the dislocation indicate that the partial kinks form in response to increasing (decreasing) Ti and Zr (Nb) compositions. These results validate a growing body of work on understanding the hardening mechanisms in chemically-complex alloys.