Effect of solute distribution on the screw dislocation motion in bcc Fe-based systems

Abstract

Screw dislocation motion in bcc Fe plays an important role in establishing the strong temperature and strain rate sensitivity of flow stress, which in turn promotes the ductile to brittle transition phenomenon in steel. Addition of solute atoms, possessing attractive interaction with screw dislocations, is believed to reduce the flow stress sensitivity of Fe. The present work intends to study the effect of Ni and Cu solute atom distribution on the screw dislocation motion in bcc Fe using molecular statics (MS) and molecular dynamics (MD) simulations. MS simulation results predict that the local distribution of Ni atoms around the screw dislocation greatly influences the Peierls stress of Fe at 0 K temperature, while Cu atom distribution has marginal effect. Moreover, the presence of Ni/Cu atoms ahead of the dislocation line helps to reduce the Peierls stress due to the dislocation-solute attractive interaction. MD simulation was performed on random Fe-Ni and Fe-Cu alloys to determine the effect of solute concentration on the temperature sensitivity of flow stress of Fe. The results showed that addition of Ni/Cu reduces the flow stress sensitivity of Fe by inducing solid solution softening effect at low temperature regime. Ni was found to be more effective than Cu in reducing the flow stress temperature sensitivity of Fe. The rationale behind the softening action of Ni and Cu is discussed in terms of changing the differential displacement plot and unstable stacking fault energy of Fe.