Influence of simple metals on the stability of $\langle a\rangle$ basal screw dislocations in hexagonal titanium alloys

TL;DR

This study uses ab initio calculations to investigate how simple metal solutes like indium and tin affect the stability and slip behavior of basal screw dislocations in hexagonal titanium alloys, revealing they do not promote basal dissociation but increase lattice friction.

Contribution

It provides the first detailed atomic-level insight into how indium and tin influence dislocation behavior in titanium alloys, challenging previous hypotheses about their role in promoting basal slip.

Findings

Simple metals attract stacking faults but do not stabilize basal dissociation.

Solutes increase the energy barrier for basal slip, thus strengthening the material.

Dislocation spread remains in pyramidal and prismatic planes during slip, unaffected by solutes.

Abstract

Basal slip acts as a secondary deformation mode in hexagonal close-packed titanium and becomes one of the primary mechanisms in titanium alloyed with simple metals. As these solute elements also lead to a pronounced reduction of the energy of the basal stacking fault, one can hypothesize that they promote basal dissociation of dislocations which can then easily glide in the basal planes. Here, we verify the validity of this hypothesis using ab initio calculations to model the interaction of a screw dislocation with indium (In) and tin (Sn). These calculations confirm that these simple metals are attracted by the stacking fault existing in the dislocation core when it is dissociated in a basal plane, but this interaction is not strong enough to stabilize a planar configuration, even for a high solute concentration in the core. Energy barrier calculations reveal that basal slip, in the presence of In and Sn, proceeds without any planar dissociation, with the dislocation being spread in pyramidal and prismatic planes during basal slip like in pure Ti. The corresponding energy barrier is higher in presence of solute atoms, showing that In and Sn do not ease basal slip but increase the corresponding lattice friction. This strengthening of basal slip by solute atoms is discussed in view of available experimental data.