  Dislocation-solute interaction plays fundamental roles in mechanical
properties of alloys. Here, we disclose the essential features of
dislocation-carbon interaction in austenitic Fe at the atomistic scale. We show
that passage of a Shockley partial dislocation in face-centered cubic iron is
able to move carbon atoms on the slip plane forward by one Burgers vector,
revealing a novel dissociated dislocation-mediated transport mechanism. This
mechanism is induced by shear, which is distinct from the normal thermally
activated diffusion process. Furthermore, we show that there exists a fast
diffusion channel with significantly reduced diffusion energy barrier in the
partial dislocation core, which is highly localized and directional. These
inherent geometrical features are crucial for understanding the dependence of
the diffusivity of dislocation pipe diffusion on the character of dislocations;
most importantly, they can result in unbalanced pinning effect on the leading
and trailing partials in a mixed dislocation, consequently facilitating
stacking fault formation and deformation twinning. This explains the
controversial effects of carbon on deformation twinning observed in various
alloys. Our findings pave the road to tune mechanical properties of materials
by manipulating dislocation-interstitial interaction.
