A Molecular Dynamics Study of Bidirectional Phase Transformation between bcc and fcc Iron

概要

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Bidirectional phase transformation between bcc and fcc iron is investigated by molecular dynamics simulation using the Finnis-Sinclair potential with a cutoff function in the atomic charge density. It is confirmed that the influence distance (i.e., cutoff distance) of the atomic charge density affects the relative stability between the bcc and fcc phases at high temperature: the bcc is stable at a long cutoff distance and the fcc is stable at a short cutoff distance. Hence, the bidirectional phase transformation across the A3 point comes true by changing the cutoff distance at the A3 point. The propagation of an fcc-bcc heterointerface with a Nishiyama-Wassermann orientation relationship is then examined by relaxation of an fcc-bcc biphasic system at various temperatures. The fcc-to-bcc phase transformation is observed below the A3 point, whereas the heterointerface does not move to any direction at the A3 point. On the other hand, the bcc-to-fcc phase transformation is observed above the A3 point, which has not been successful in previous studies using the original Finnis-Sinclair potential.