A molecular dynamics simulation study of the velocities, mobility and activation energy of an austenite–ferrite interface in pure Fe

• Published in: Acta materialia 2012-06, Vol.60 (10), p.4328-4335
• Main Authors: Song, H., Hoyt, J.J.
• Format: Article
• Language: English
• Subjects: Activation energy; Applied sciences; Boundaries; Exact sciences and technology; Iron; Massive; Mathematical models; Metals. Metallurgy; Mobility; Molecular dynamics; Orientation; Phase transformations; Simulation; Transformations
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2012.04.023

Molecular dynamics simulations have been used to obtain the mobility, in pure Fe, of a face-centered cubic (fcc)–body-centered cubic (bcc) interphase boundary with an orientation given by (110)bcc//(776)fcc and [001]bcc//[−110]fcc. The interface is best described by a 4.04° rotation, about an axis lying in the boundary plane, from the Nishiyama–Wasserman orientation and the boundary consists of a parallel array of steps (disconnections). An embedded atom method interatomic potential was employed to model Fe, and the free energy difference as a function of temperature between the fcc and bcc phases, which provided the driving force for boundary motion, was determined by a thermodynamic integration procedure. Although the boundary was found to be very mobile, the transformation did not proceed by a martensite mechanism. The boundary mobility was obtained for several temperatures in the range 600–1400K and Arrhenius behavior was found with an activation energy of 16.5±2.7kJmol−1 and a pre-exponential factor equal to 7.8(±0.9)×10−3mmolJ−1s−1. The activation energy is much lower than that extracted from experiments on the massive transformation in Fe alloys and possible reasons for the discrepancy are discussed.