Effects of RE (La, Ce) on fcc-bcc martensitic transformation of iron via Bain transformation path

The fundamental understanding of the effects of rare earth (RE) on the phase transformation of Fe-based alloys is essential in the development of advanced RE-containing high strength steels. In this work, we investigated the effects of La and Ce on the martensitic phase transformation of Fe in terms of the driving force and minimum energy path (MEP) using the first-principles calculations. The calculations of for-mation energy show that the RE substitution increases the stabilization of fcc-Fe and decreases that of bcc-Fe, thus decreasing the driving force of phase transformation. Meanwhile, the analysis based on the generalized solid-state nudged elastic band (G-SSNEB) method indicates that in the RE-containing sys-tems, an additional energy barrier appears when the phase transformation proceeds along the Bain transition path to c/a ratio of 1.14 in the FM state, which is associated with a sudden decrease in magnetization due to the hybridization between the orbits of the RE atoms and those of the nearest neighbor Fe atoms. The results of potential-energy surfaces (PES) confirm that magnetic ordering and lattice volume change simultaneously with the Bain transition, and in comparison to pure Fe, the vari-ation between the onset and the end structural volumes of the phase transformation is slight for the RE -containing Fe systems. (c) 2021 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.