Free energies of austenite and martensite Fe–C alloys: an atomistic study

Abstract

We investigate the influence of C interstitials on the phase stability of Fe–C crystals. We employ the Meyer–Entel interatomic interaction potential which is able to reproduce the austenite-martensite phase transition for pure Fe, and supplement it by a simple pairwise Fe–C interaction potential. Using two different thermodynamic methods, we calculate the free energies of the martensite and austenite phases. We find that C destabilizes the ground-state bcc phase. The decrease in the equilibrium transformation temperature with increasing C content parallels the one found in the experiment. This destabilization is found even if C is added for a potential in which only the bcc phase is stable until the melting point; here, for sufficiently high C addition, a stable fcc phase is established in the phase diagram.

Keywords:

• free energy
• solid–solid phase transitions
• molecular dynamics simulation
• martensite
• Fe–C alloy
• martensitic phase transformation

Acknowledgments

We acknowledge the support by the Deutsche Forschungsgemeinschaft via the Sonderforschungsbereich 926. Discussions with Cemal Engin, Luis Sandoval and Nina Gunkelmann are gratefully acknowledged.