Molecular dynamics simulations of the mechanisms controlling the propagation of bcc/fcc semi-coherent interfaces in iron

X Ou,J Sietsma,M J Santofimia

doi:10.1088/0965-0393/24/5/055019

Abstract

Molecular dynamics simulations have been used to study the effects of different orientation relationships between fcc and bcc phases on the bcc/fcc interfacial propagation in pure iron systems at 300 K. Three semi-coherent bcc/fcc interfaces have been investigated. In all the cases, results show that growth of the bcc phase starts in the areas of low potential energy and progresses into the areas of high potential energy at the original bcc/fcc interfaces. The phase transformation in areas of low potential energy is of a martensitic nature while that in the high potential energy areas involves occasional diffusional jumps of atoms.

Highlights

Martensite forms from austenite during the quenching process of steels, which has been the subject of intensive studies [1, 2]
The facetted growth of the original bcc phase is observed for the three systems, as shown by the configurations at 0.15 and 0.5 ps in figures 2(a)–(c)
The propagation of the bcc/fcc interface following a facetted style is observed in the molecular dynamics (MD) simulation of the bcc/fcc interface in the NW orientation relationships (ORs) in iron using the Ackland potential [22]

Summary

Introduction

Martensite forms from austenite during the quenching process of steels, which has been the subject of intensive studies [1, 2]. Other fcc-to-bcc transformation paths result in the Nishiyama–Wassermann (NW) [10] or Kurdjumov–Sachs (KS) [11] orientation relationships (ORs) They imply similar mechanisms of transformation with the Bain transformation but introduce a main shear in the 〈1 1 2 〉 direction of the {1 1 1} plane. The mobile interface did not migrate by a martensitic mechanism but by the rapid advance of the mobile defects forming on the primary disconnections Considering these contradictions from literature, three systems with different semi-coherent bcc/fcc interfaces are introduced in the present paper to investigate the mechanisms controlling the growth of the original bcc phase in iron by MD simulations. Mechanisms controlling the growth of the original bcc phase at the bcc/fcc interfaces for the three systems are studied in detail based on the atomic configuration during the transformation and the energy distribution of the atoms

Simulation conditions

Results and discussion

Conclusions