On the investigation of size effect in bcc α-iron under high strain rate and high temperature: Multiscale dislocations dynamics simulations

Size effect for BCC α-iron is investigated for micro-polycrystalline grains. MDDP simulations were performed to mimic impenetrable grain boundaries at sizes ranging between 0.5 μm and 2 μm at an applied rate of 105 s−1 at 300 K, 600 K and 900 K temperatures. For the three deformation temperatures, the Hall-Petch effect and the Orowan effect are reproduced. A comprehensive study of the microstructure evolution shows that screw dislocations control the plastic deformation of the polycrystalline materials via the activation of cross-slip mechanisms. Hardening is seen at low sizes for all temperatures at low strain range due to the dislocations pile up inside the grains prior to cross-slip activation. Once cross-slip is thermally activated, self-multiplication of dislocations is detected resulting in strain softening indicating that Orowan fit represented better the size effect in micro-polycrystalline BCC α-iron.