A MOLECULAR DYNAMICS STUDY OF AUSTENITE-FERRITE INTERFACE MOBILITY IN PURE IRON

Abstract

<p>Molecular dynamics (MD) simulations performed on two-phase simulation cells were used to compute the Austenite (FCC) / Ferrite (BCC) boundary mobility in pure iron (Fe) over the temperature range of 600K - 1400K. An embedded atom method interatomic potential was used to model Fe and the driving force for interface motion is the free energy difference between the two phases, which was computed as a function of temperature using a thermodynamic integration technique. For low index FCC/BCC crystallographic orientations, no interface motion was observed. But for slight misorientations steps were introduced at the interphase and sufficient mobility was observed over MD time scales. A new interphase mechanism was found that instead of the moving of structure disconnection by diffusion control, growing of misfit dislocations in each steps were observed (interphase control). The interphase velocity could reach 2 m/s and the mobility at 1000K was approximately 0.001 mol-m/J-s. In agreement with previous MD studies of grain boundary mobility, we found that the activation energy for the austenite-ferrite boundary mobility was much lower than the values found from previous experiments.</p>