  Molecular dynamics simulations have been performed to understand the
influence of temperature on the tensile deformation and fracture behavior of
$<$111$>$ BCC Fe nanowires. The simulations have been carried out at different
temperatures in the range 10-1000 K employing a constant strain rate of
$1\times$ $10^8$ $s^{-1}$. The results indicate that at low temperatures
(10-375 K), the nanowires yield through the nucleation of a sharp crack and
fails in brittle manner. On the other hand, nucleation of multiple 1/2$<$111$>$
dislocations at yielding followed by significant plastic deformation leading to
ductile failure has been observed at high temperatures in the range 450-1000 K.
At the intermediate temperature of 400 K, the nanowire yields through
nucleation of crack associated with many mobile 1/2$<$111$>$ and immobile
$<$100$>$ dislocations at the crack tip and fails in ductile manner. The
ductile-brittle transition observed in $<$111$>$ BCC Fe nanowires is
appropriately reflected in the stress-strain behavior and plastic strain at
failure. The ductile-brittle transition increases with increasing nanowire
size. The change in fracture behavior has been discussed in terms of the
relative variations in yield and fracture stresses and change in slip behavior
with respect to temperature. Further, the dislocation multiplication mechanism
assisted by the kink nucleation from the nanowire surface observed at high
temperatures has been presented.
