Atomistic simulations on ductile-brittle transition in <111> BCC Fe nanowires

TL;DR

This study uses molecular dynamics simulations to explore how temperature influences the transition from brittle to ductile failure in <111> BCC Fe nanowires, revealing size-dependent behavior and dislocation mechanisms.

Contribution

It provides detailed atomistic insights into the temperature-dependent ductile-brittle transition and size effects in <111> BCC Fe nanowires through molecular dynamics simulations.

Findings

Brittle failure at low temperatures (10-375 K) with crack nucleation.

Ductile failure at high temperatures (450-1000 K) with dislocation activity.

Size increases the temperature range for ductile behavior.

Abstract

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.