Abstract
Molecular dynamics (MD) simulations are used to study the effect of different defect configurations and their arrangements in the parent fcc phase on atomistic mechanisms during the martensitic transformation mechanisms in pure Fe. The defect configurations considered are stacking faults (SF) and twin boundaries (TB) in single crystal fcc. Three arrangements of these defect structures are considered: parallel TB, intersecting SF, and intersecting SF and TB. Each of these defect configurations affect the transformation mechanisms and transformation temperatures. Parallel TB are the lowest-barrier sites for the atomic shear and thus accelerate the transformation process. The fcc phase with parallel TB follows the Nishiyama-Wasserman (NW) martensitic transformation mechanism. On the other hand, intersecting SF impede the atomic shear and thus retard the transformation. The atomistic transformation mechanism in this case first follows the hcp to bcc Burgers path and then the fcc to bcc Olson-Cohen model. The intersecting SF and TB result in a combined effect of both the previous cases. The simulation results show the occurrence of different atomistic mechanisms during martensitic transformation depending on the type of defects present in the parent fcc phase.
Highlights
The martensitic transformation mechanisms represent a diffusionless type of phase transformation in many material systems such as Zirconia, Titanium, and some Cu alloys
In particular we focus on the atomic shear that takes place in the parent fcc austenite phase in presence of defects and the role of austenite transforming to martensite
Molecular dynamics (MD) simulations were performed on a semi-empirical embedded atom method (EAM) potential to study the effect of pre-existing defects on the fcc-to-bcc martensitic transformation
Summary
The martensitic transformation mechanisms represent a diffusionless type of phase transformation in many material systems such as Zirconia, Titanium, and some Cu alloys. In Fe-C alloys the Preprint submitted to Elsevier martensitic transformation represents the change in crystal structure from facecentered-cubic (fcc) austenite to body-centered-cubic (bcc) or body-centeredtetragonal (bct) martensite. This mechanism mainly occurs by the displacive motion of atoms during rapid quenching and plays an important role in the mechanical properties of Fe-C alloys. The two-step theory considers the atomic displacements by introducing a new parameter called the angle of planar distortion. The details of these models can be found in the literature [1, 6, 7]
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