  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.
